Low Cost, Precision Analog Front End and Controller for Battery Test/Formation Systems AD8451 Data Sheet FEATURES GENERAL DESCRIPTION Integrated constant current and voltage modes with automatic switchover Charge and discharge modes Precision voltage and current measurement Integrated precision control feedback blocks Precision interface to PWM or linear power converters Fixed gain settings Current sense gain: 26 V/V (typ) Voltage sense gain: 0.8 V/V (typ) Excellent ac and dc performance Maximum offset voltage drift: 0.9 V/C Maximum gain drift: 3 ppm/C Low current sense amplifier input voltage noise: 9 nV/Hz typ Current sense CMRR: 108 dB min TTL compliant logic The AD8451 is a precision analog front end and controller for testing and monitoring battery cells. A precision fixed gain instrumentation amplifier (IA) measures the battery charge/ discharge current, and a fixed gain difference amplifier (DA) measures the battery voltage (see Figure 1). Internal laser trimmed resistor networks set the gains for the IA and the DA, optimizing the performance of the AD8451 over the rated temperature range. The IA gain is 26 V/V and the DA gain is 0.8 V/V. Voltages at the ISET and VSET inputs set the desired constant current (CC) and constant voltage (CV) values. CC to CV switching is automatic and transparent to the system. A TTL logic level input, MODE, selects the charge or discharge mode (high for charge, and low for discharge). An analog output, VCTRL, interfaces directly with the Analog Devices, Inc., ADP1972 pulse-width modulation (PWM) controller. APPLICATIONS The AD8451 simplifies designs by providing excellent accuracy, performance over temperature, flexibility with functionality, and overall reliability in a space-saving package. The AD8451 is available in an 80-lead, 14 mm x 14 mm x 1.40 mm LQFP and is rated for an operating temperature of -40C to +85C. Battery cell formation and testing Battery module testing FUNCTIONAL BLOCK DIAGRAM ISREFH/ ISREFL ISMEA ISET IVE0/IVE1 VINT AD8451 ISVP MUX CONSTANT CURRENT LOOP FILTER 26 ISVN VCLP x1 CURRENT SENSE IA VCTRL VCLN (CHARGE/ DISCHARGE) SWITCHING VOLTAGE SENSE DA BVP 0.8 CONSTANT VOLTAGE LOOP FILTER BVN BVREFH/ BVREFL BVMEA VSET VVE0/ VVE1 VVP0 VSETBF VINT VOLTAGE REFERENCE VREF 12137-001 MODE Figure 1. Rev. 0 Document Feedback Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 (c)2014 Analog Devices, Inc. All rights reserved. Technical Support www.analog.com AD8451 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 MODE Pin, Charge and Discharge Control ........................... 21 Applications ....................................................................................... 1 Applications Information .............................................................. 22 General Description ......................................................................... 1 Functional Description .............................................................. 22 Functional Block Diagram .............................................................. 1 Power Supply Connections ....................................................... 23 Revision History ............................................................................... 2 Current Sense IA Connections ................................................. 23 Specifications..................................................................................... 3 Voltage Sense DA Connections ................................................ 23 Absolute Maximum Ratings ............................................................ 6 Thermal Resistance ...................................................................... 6 Battery Current and Voltage Control Inputs (ISET and VSET) ....................................................................................................... 23 ESD Caution .................................................................................. 6 Loop Filter Amplifiers ............................................................... 24 Pin Configuration and Function Descriptions ............................. 7 Connecting to a PWM Controller (VCTRL Pin) ...................... 24 Typical Performance Characteristics ............................................. 9 Step-by-Step Design Example................................................... 24 IA Characteristics ......................................................................... 9 Evaluation Board ............................................................................ 26 DA Characteristics ..................................................................... 11 Introduction ................................................................................ 26 CC and CV Loop Filter Amplifiers, and VSET Buffer .......... 13 Features and Tests....................................................................... 26 VINT Buffer ................................................................................ 15 Evaluating the AD8451.............................................................. 27 Reference Characteristics .......................................................... 16 Schematic and Artwork ............................................................. 28 Theory of Operation ...................................................................... 17 Outline Dimensions ....................................................................... 32 Overview...................................................................................... 17 Ordering Guide .......................................................................... 32 Instrumentation Amplifier (IA) ............................................... 18 Difference Amplifier (DA) ........................................................ 19 CC and CV Loop Filter Amplifiers .......................................... 19 REVISION HISTORY 3/14--Revision 0: Initial Version Rev. 0 | Page 2 of 32 Data Sheet AD8451 SPECIFICATIONS AVCC = +15 V, AVEE = -15 V; DVCC = +5 V; TA = 25C, unless otherwise noted. Table 1. Parameter CURRENT SENSE INSTRUMENTATION AMPLIFIER Internal Fixed Gain Gain Error Gain Drift Gain Nonlinearity Offset Voltage (RTI) Offset Voltage Drift Input Bias Current Temperature Coefficient Input Offset Current Temperature Coefficient Input Common-Mode Voltage Range Over Temperature Overvoltage Input Range Differential Input Impedance Input Common-Mode Impedance Output Voltage Swing Over Temperature Capacitive Load Drive Short-Circuit Current Reference Input Voltage Range Reference Input Bias Current Output Voltage Level Shift Maximum Scale Factor Common-Mode Rejection Ratio (CMRR) Temperature Coefficient Power Supply Rejection Ratio (PSRR) Voltage Noise Voltage Noise, Peak to Peak Current Noise Current Noise, Peak to Peak Small Signal -3 dB Bandwidth Slew Rate VOLTAGE SENSE DIFFERENCE AMPLIFER Internal Fixed Gains Gain Error Gain Drift Gain Nonlinearity Offset Voltage (RTO) Offset Voltage Drift Differential Input Voltage Range Input Common-Mode Voltage Range Differential Input Impedance Input Common-Mode Impedance Output Voltage Swing Over Temperature Capacitive Load Drive Short-Circuit Current Test Conditions/Comments Min Typ Max 26 VISMEA = 10 V TA = TMIN to TMAX VISMEA = 10 V, RL = 2 k ISREFH and ISREFL pins grounded TA = TMIN to TMAX -110 15 TA = TMIN to TMAX TA = TMIN to TMAX VISVP - VISVN = 0 V TA = TMIN to TMAX AVEE + 2.3 AVEE + 2.6 AVCC - 55 0.1 3 3 +110 0.9 30 150 2 10 AVCC - 2.4 AVCC - 2.6 AVEE + 55 150 150 TA = TMIN to TMAX AVEE + 1.5 AVEE + 1.7 AVCC - 1.2 AVCC - 1.4 1000 40 ISREFH and ISREFL pins tied together VISVP = VISVN = 0 V ISREFL pin grounded ISREFH pin connected to VREF pin VISMEA/VISREFH VCM = 20 V TA = TMIN to TMAX VS = 20 V f = 1 kHz f = 0.1 Hz to 10 Hz f = 1 kHz f = 0.1 Hz to 10 Hz AVEE AVCC 5 17 6.8 108 20 8 108 122 9 0.2 80 5 1.5 5 23 9.2 0.01 VISMEA = 10 V 0.8 VIN = 10 V TA = TMIN to TMAX VBVMEA = 10 V, RL = 2 k BVREFH and BVREFL pins grounded TA = TMIN to TMAX VBVN = 0 V, VBVREFL = 0 V VBVMEA = 0 V 0.1 3 3 500 4 +16 +27 -16 -27 200 90 TA = TMIN to TMAX AVEE + 1.5 AVEE + 1.7 AVCC - 1.5 AVCC - 1.7 1000 30 Rev. 0 | Page 3 of 32 Unit V/V % ppm/C ppm V V/C nA pA/C nA pA/C V V V G G V V pF mA V A mV mV/V dB V/V/C dB nV/Hz V p-p fA/Hz pA p-p MHz V/s V/V % ppm/C ppm V V/C V V k k V V pF mA AD8451 Parameter Reference Input Voltage Range Output Voltage Level Shift Maximum Scale Factor CMRR Temperature Coefficient PSRR Output Voltage Noise Voltage Noise, Peak to Peak Small Signal -3 dB Bandwidth Slew Rate CONSTANT CURRENT AND CONSTANT VOLTAGE LOOP FILTER AMPLIFIERS Offset Voltage Offset Voltage Drift Input Bias Current Over Temperature Input Common-Mode Voltage Range Output Voltage Swing Over Temperature Closed-Loop Output Impedance Capacitive Load Drive Source Short-Circuit Current Sink Short-Circuit Current Open-Loop Gain CMRR PSRR Voltage Noise Voltage Noise, Peak to Peak Current Noise Current Noise, Peak to Peak Small Signal Gain Bandwidth Product Slew Rate CC to CV Transition Time VINT AND CONSTANT VOLTAGE BUFFER Nominal Gain Offset Voltage Offset Voltage Drift Input Bias Current Over Temperature Input Voltage Range Output Voltage Swing Current Sharing and Constant Voltage Buffers Over Temperature VINT Buffer Over Temperature Output Clamps Voltage Range VCLP Pin VCLN Pin Closed-Loop Output Impedance Capacitive Load Drive Short-Circuit Current PSRR Data Sheet Test Conditions/Comments BVREFH and BVREFL pins tied together BVREFL pin grounded BVREFH pin connected to VREF pin VBVMEA/VBVREFH VCM = 10 V, RTO TA = TMIN to TMAX VS = 20 V, RTO f = 1 kHz, RTI f = 0.1 Hz to 10 Hz, RTI Min AVEE Typ Max AVCC Unit V 4.5 1.8 80 5 2 5.5 2.2 mV mV/V dB V/V/C dB nV/Hz V p-p MHz V/s 0.05 100 105 2 1 0.8 150 0.6 +5 +5 AVCC - 1.8 AVCC - 1 AVCC - 1 TA = TMIN to TMAX TA = TMIN to TMAX VVCLN = AVEE + 1 V, VVCLP = AVCC - 1 V TA = TMIN to TMAX -5 -5 AVEE + 1.5 AVEE + 1.5 AVEE + 1.7 0.01 1000 1 40 140 VCM = 10 V VS = 20 V f = 1 kHz f = 0.1 Hz to 10 Hz f = 1 kHz f = 0.1 Hz to 10 Hz 100 100 10 0.3 80 5 3 1 1.5 VVINT = 10 V 1 TA = TMIN to TMAX CV buffer only TA = TMIN to TMAX TA = TMIN to TMAX TA = TMIN to TMAX VINT buffer only -5 -5 AVEE + 1.5 150 0.6 +5 +5 AVCC - 1.8 V/V V V/C nA nA V AVEE + 1.5 AVEE + 1.7 VVCLN - 0.6 VVCLN - 0.6 AVCC - 1.5 AVCC - 1.5 VVCLP + 0.6 VVCLP + 0.6 V V V V VVCLN AVEE + 1 AVCC - 1 VVCLP V V pF mA dB 1 1000 40 VS = 20 V Rev. 0 | Page 4 of 32 V V/C nA nA V V V pF mA mA dB dB dB nV/Hz V p-p fA/Hz pA p-p MHz V/s s 100 Data Sheet Parameter Voltage Noise Voltage Noise, Peak to Peak Current Noise Current Noise, Peak to Peak Small Signal -3 dB Bandwidth Slew Rate VOLTAGE REFERENCE Nominal Output Voltage Output Voltage Error Temperature Drift Line Regulation Load Regulation Output Current, Sourcing Voltage Noise Voltage Noise, Peak to Peak DIGITAL INTERFACE, MODE INPUT Input Voltage High, VIH Input Voltage Low, VIL Mode Switching Time POWER SUPPLY Operating Voltage Range AVCC AVEE Analog Supply Range DVCC Quiescent Current AVCC AVEE DVCC TEMPERATURE RANGE For Specified Performance Operational AD8451 Test Conditions/Comments f = 1 kHz f = 0.1 Hz to 10 Hz f = 1 kHz, CV buffer only f = 0.1 Hz to 10 Hz Min VOUT = 10 V Typ 10 0.3 80 5 3 1 With respect to AGND 2.5 1 10 40 400 10 TA = TMIN to TMAX VS = 10 V IVREF = 1 mA (source only) f = 1 kHz f = 0.1 Hz to 10 Hz MODE pin (Pin 39) With respect to DGND With respect to DGND Max 100 5 2.0 DGND AVCC - AVEE 7 6.5 40 -40 -55 Rev. 0 | Page 5 of 32 V % ppm/C ppm/V ppm/mA mA nV/Hz V p-p DVCC 0.8 V V ns 36 0 36 5 V V V V 10 10 70 mA mA A +85 +125 C C 500 5 -31 5 3 Unit nV/Hz V p-p fA/Hz pA p-p MHz V/s AD8451 Data Sheet ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 2. Parameter Analog Supply Voltage (AVCC - AVEE) Digital Supply Voltage (DVCC - DGND) Maximum Voltage at Any Input Pin Minimum Voltage at Any Input Pin Operating Temperature Range Storage Temperature Range The JA value assumes a 4-layer JEDEC standard board with zero airflow. Rating 36 V 36 V AVCC AVEE -40C to +85C -65C to +150C Table 3. Thermal Resistance Package Type 80-Lead LQFP Stresses at or above those listed under Absolute Maximum Ratings may cause permanent damage to the product. This is a stress rating only; functional operation of the product at these or any other conditions above those indicated in the operational section of this specification is not implied. Operation beyond the maximum operating conditions for extended periods may affect product reliability. ESD CAUTION Rev. 0 | Page 6 of 32 JA 54.7 Unit C/W Data Sheet AD8451 ISVP 1 VINT AVEE 69 NC 70 IVE1 71 IVE0 72 NC 73 ISREFB NC 74 ISET AVCC 75 ISMEA 76 AVEE 77 ISREFH AGND 78 VREF ISREFL 79 NC 80 ISREFLS NC NC PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 68 67 66 65 64 63 62 61 PIN 1 INDENTFIER 60 VCLP 59 VCTRL RGP 2 NC 3 58 VCLN NC 4 57 AVCC NC 5 56 VINT NC 6 55 NC NC 7 54 VVE1 NC 8 53 VVE0 52 NC NC 9 AD8451 NC 10 51 VVP0 50 VSETBF NC 12 49 VSET NC 13 48 NC NC 14 47 DVCC NC 15 46 NC NC 16 45 DGND NC 17 44 NC NC 18 43 NC 29 30 31 32 33 34 35 36 37 38 39 40 NC BVN NC NC BVNS AVEE BVMEA AVCC MODE NC 28 BVREFL 27 BVREFLS 26 AGND 25 BVREFH 24 NC 23 VREF 22 NC 21 BVP 41 NC NC 42 VREF ISVN 20 BVPS RGN 19 NC = NO CONNECT. DO NOT CONNECT TO THIS PIN. 12137-002 TOP VIEW NC 11 Figure 2. Pin Configuration Table 4. Pin Function Descriptions Pin No. 1, 20 Mnemonic ISVP, ISVN Input/Output 1 Input 2, 19 RGP, RGN N/A 3 to 18, 21, 23, 25, 31, 33, 34, 40, 41, 43, 44, 46, 48, 52, 55, 63, 66, 69, 78 to 80 22, 35 24, 32 26, 42, 73 27 NC N/A BVPS, BVNS BVP, BVN VREF BVREFH Input Input Output Input 28, 75 29 AGND BVREFL N/A Input 30 BVREFLS Input Description Current Sense Instrumentation Amplifier Positive (Noninverting) and Negative (Inverting) Inputs. Connect these pins across the current sense shunt resistor. Negative Input of the Preamplifiers of the Current Sense Instrumentation Amplifier. No Connect. Do not connect to this pin. Kelvin Sense Pins for the BVP and BVN Voltage Sense Difference Amplifier Inputs. Voltage Sense Difference Amplifier Inputs. Voltage Reference Output Pins. VREF = 2.5 V. Reference Input for the Voltage Sense Difference Amplifier. To level shift the voltage sense difference amplifier output by approximately 5 mV, connect this pin to the VREF pin. Otherwise, connect this pin to the BVREFL pin. Analog Ground Pins. Reference Input for the Voltage Sense Difference Amplifier. The default connection is to ground. Kelvin Sense Pin for the BVREFL Pin. Rev. 0 | Page 7 of 32 AD8451 Data Sheet Pin No. 36, 61, 72 37 38, 57, 70 39 Mnemonic AVEE BVMEA AVCC MODE Input/Output 1 N/A Output N/A Input 45 47 49 50 51 53 54 56, 62 58 59 DGND DVCC VSET VSETBF VVP0 VVE0 VVE1 VINT VCLN VCTRL N/A N/A Input Output Input Input Input Output Input Output 60 64 65 67 68 71 74 VCLP IVE1 IVE0 ISET ISREFB ISMEA ISREFH Input Input Input Input Output Output Input 76 ISREFL Input 77 ISREFLS Input 1 Description Analog Negative Supply Pins. The default voltage is -15 V. Voltage Sense Difference Amplifier Output. Analog Positive Supply Pins. The default voltage is 15 V. TTL Compliant Logic Input Selects Charge or Discharge Mode. Low = discharge, high = charge. Digital Ground Pin. Digital Supply. The default voltage is 5 V. Target Voltage for the Voltage Sense Control Loop. Buffered Voltage VSET. Noninverting Input of the Voltage Sense Integrator for Discharge Mode. Inverting Input Voltage for the Voltage Sense Integrator for Discharge Mode. Inverting Input of the Voltage Sense Integrator for Charge Mode. Minimum Output of the Voltage Sense and Current Sense Integrator Amplifiers. Low Clamp Voltage for VCTRL. Controller Output Voltage. Connect this pin to the input of the PWM controller (for example, the COMP pin of the ADP1972). High Clamp Voltage for VCTRL. Inverting Input of the Current Sense Integrator for Charge Mode. Inverting Input of the Current Sense Integrator for Discharge Mode. Target Voltage for the Current Sense Control Loop. Buffered Voltage ISREFL. Current Sense Instrumentation Amplifier Output. Reference Input for the Current Sense Amplifier. To level shift the current sense instrumentation amplifier output by approximately 20 mV, connect this pin to the VREF pin. Otherwise, connect this pin to the ISREFL pin. Reference Input for the Current Sense Amplifier. The default connection is to ground. Kelvin Sense Pin for the ISREFL Pin. N/A means not applicable. Rev. 0 | Page 8 of 32 Data Sheet AD8451 TYPICAL PERFORMANCE CHARACTERISTICS AVCC = +15 V, AVEE = -15 V, TA = 25C, and RL = , unless otherwise noted. 30 20 25 15 20 15 10 5 0 -5 -10 -10 -5 0 15 10 5 OUTPUT VOLTAGE (V) 20 30 25 0 -5 -10 -15 0 -5 5 10 15 20 OUTPUT VOLTAGE (V) Figure 3. Input Common-Mode Voltage vs. Output Voltage for AVCC = +25 V and AVEE = -5 V Figure 6. Input Common-Mode Voltage vs. Output Voltage for AVCC = +15 V and AVEE = -15 V 15 15 10 AVCC = +15V AVEE = -15V 10 INPUT CURRENT (mA) INPUT CURRENT (mA) 5 AVCC = +15V AVEE = -15V -20 -20 -15 -10 12137-003 AVCC = +25V AVEE = -5V 10 12137-006 INPUT COMMON-MODE VOLTAGE (V) INPUT COMMON-MODE VOLTAGE (V) IA CHARACTERISTICS 5 0 -5 -10 5 0 -5 -10 0 5 10 15 20 25 30 35 40 45 INPUT VOLTAGE (V) -15 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 12137-004 -15 -35 -30 -25 -20 -15 -10 -5 5 10 15 20 25 30 35 40 45 INPUT VOLTAGE (V) Figure 4. Input Overvoltage Performance for AVCC = +25 V and AVEE = -5 V 12137-007 AVCC = +25V AVEE = -5V Figure 7. Input Overvoltage Performance for AVCC = +15 V and AVEE = -15 V 17.0 20 16.8 19 INPUT BIAS CURRENT (nA) 16.4 AVCC = +15V AVEE = -15V 16.2 16.0 AVCC = +25V AVEE = -5V 15.8 15.6 18 17 +IB 16 -IB 15 14 15.4 15.0 -15 -10 -5 0 5 10 15 20 25 INPUT COMMON-MODE VOLTAGE (V) 12 -40 -30 -20 -10 0 10 20 30 40 50 60 70 TEMPERATURE (C) Figure 5. Input Bias Current vs. Input Common-Mode Voltage Figure 8. Input Bias Current vs. Temperature Rev. 0 | Page 9 of 32 80 90 12137-008 13 15.2 12137-005 INPUT BIAS CURRENT (nA) 16.6 AD8451 Data Sheet 160 20 150 0 140 GAIN ERROR (V/V) 130 CMRR (dB) -20 -40 120 110 100 90 -60 80 70 -80 0 10 20 30 40 50 60 70 90 80 TEMPERATURE (C) 50 0.1 12137-009 -100 -40 -30 -20 -10 1 10 100 1k 10k 100k FREQUENCY (Hz) Figure 9. Gain Error vs. Temperature 12137-012 60 Figure 12. CMRR vs. Frequency 0.3 160 AVCC = +25V AVEE = -5V 140 0.2 120 AVCC PSRR (dB) CMRR (V/V) 0.1 0 100 80 AVEE 60 -0.1 40 -0.2 0 10 20 30 40 50 60 70 80 90 TEMPERATURE (C) 0 12137-010 -0.3 -40 -30 -20 -10 1 10 10k 100k 1M 10k 100k Figure 13. PSRR vs. Frequency 50 30 20 10 0 10k 100 k FREQUENCY (Hz) 1M 10M 12137-011 -10 Figure 11. Gain vs. Frequency RTI 10 1 0.1 1 10 100 1k FREQUENCY (Hz) Figure 14. Spectral Density Voltage Noise, RTI vs. Frequency Rev. 0 | Page 10 of 32 12137-014 SPECTRAL DENSITY VOLTAGE NOISE (nV/Hz) 100 40 GAIN (dB) 1k FREQUENCY (Hz) Figure 10. Normalized CMRR vs. Temperature AVCC = +15V AVEE = -15V -20 1k 100 100 12137-013 20 Data Sheet AD8451 50 50 40 40 30 20 10 0 -10 -20 -30 -40 -10 0 5 10 15 20 25 30 OUTPUT VOLTAGE (V) 10 0 -10 -20 -30 -50 -20 -15 -10 0 -5 5 15 10 20 Figure 15. Input Common-Mode Voltage vs. Output Voltage for AVCC = +25 V and AVEE = -5 V Figure 18. Input Common-Mode Voltage vs. Output Voltage for AVCC = +15 V and AVEE = -15 V 0 50 -10 0 -20 -30 -50 -100 10k 100k 1M FREQUENCY (Hz) -200 -40 -30 -20 -10 12137-016 30 40 50 60 70 80 90 3 2 -40 1 CMRR (V/V) -20 -60 0 -1 -100 -2 10k 100k FREQUENCY (Hz) 1M 12137-017 -80 1k 20 Figure 19. Gain Error vs. Temperature VALID FOR ALL RATED SUPPLY VOLTAGES -120 100 10 TEMPERATURE (C) Figure 16. Gain vs. Frequency 0 0 Figure 17. CMRR vs. Frequency -3 -40 -30 -20 -10 0 10 20 30 40 50 60 70 TEMPERATURE (C) Figure 20. Normalized CMRR vs. Temperature Rev. 0 | Page 11 of 32 80 90 12137-020 VALID FOR ALL RATED SUPPLY VOLTAGES -50 100 1k 12137-019 -150 -40 CMRR (dB) AVCC = +15V AVEE = -15V OUTPUT VOLTAGE (V) GAIN ERROR (ppm) GAIN (dB) 20 -40 AVCC = +25V AVEE = -5V -5 30 12137-018 INPUT COMMON-MODE VOLTAGE (V) 60 12137-015 INPUT COMMON-MODE VOLTAGE (V) DA CHARACTERISTICS AD8451 Data Sheet 0 SPECTRAL DENSITY VOLTAGE NOISE (nV/Hz) 1k -20 AVEE -60 RTI 100 -80 AVCC -100 -120 10 100 1k 10k FREQUENCY (Hz) 100k 12137-021 VALID FOR ALL RATED SUPPLY VOLTAGES -140 Figure 21. PSRR vs. Frequency 10 0.1 1 10 100 1k 10k 100k FREQUENCY (Hz) Figure 22. Spectral Density Voltage Noise, RTI vs. Frequency Rev. 0 | Page 12 of 32 12137-022 PSRR (dB) -40 Data Sheet AD8451 500 2.0 400 1.8 OUTPUT SOURCE CURRENT (mA) 300 AVCC = +25V AVEE = -5V 100 0 -100 -200 -300 1.6 1.4 1.0 AVCC = +15V AVEE = -15V 0.8 0.6 0.4 -400 0.2 -10 -5 0 5 10 15 20 25 INPUT COMMON-MODE VOLTAGE (V) 0 -40 -30 -20 -10 12137-023 -500 -15 AVCC = +25V AVEE = -5V 1.2 0 10 Figure 23. Input Offset Voltage vs. Input Common-Mode Voltage for Two Supply Voltage Combinations 90 AVCC = +25V AVEE = -5V OPEN-LOOP GAIN (dB) INPUT BIAS CURRENT (pA) 40 50 60 70 80 90 120 -45.0 100 -67.5 80 60 50 40 30 Figure 26. Output Source Current vs. Temperature for Two Supply Voltage Combinations 100 70 20 TEMPERATURE (C) 12137-026 200 AVCC = +15V AVEE = -15V CONSTANT CURRENT LOOP AND CONSTANT VOLTAGE LOOP AMPLIFIERS AVCC = +15V AVEE = -15V 30 PHASE 80 -90.0 -112.5 60 -135.0 40 GAIN 20 -157.5 0 -180.0 -20 -202.5 PHASE (Degrees) INPUT OFFSET VOLTAGE (V) CC AND CV LOOP FILTER AMPLIFIERS, AND VSET BUFFER 20 -5 0 5 10 15 20 25 INPUT COMMON-MODE VOLTAGE (V) -40 10 100 10k 100k 1M -225.0 10M FREQUENCY (Hz) Figure 24. Input Bias Current vs. Input Common-Mode Voltage for Two Supply Voltage Combinations Figure 27. Open-Loop Gain and Phase vs. Frequency 100 160 80 140 120 CMRR (dB) 60 40 20 0 100 80 60 40 -20 -40 -40 -30 -20 -10 0 10 20 30 40 50 60 70 TEMPERATURE (C) 80 CONSTANT CURRENT LOOP AND CONSTANT VOLTAGE LOOP FILTER AMPLIFIERS 20 -IB +IB 90 12137-025 INPUT BIAS CURRENT (nA) 1k 12137-027 -10 Figure 25. Input Bias Current vs. Temperature 0 10 100 1k 10k FREQUENCY (Hz) Figure 28. CMRR vs. Frequency Rev. 0 | Page 13 of 32 100k 1M 12137-028 0 -15 12137-024 10 AD8451 Data Sheet 1.5 140 120 1.0 OUTPUT VOLTAGE (V) +PSRR PSRR (dB) 100 80 60 -PSRR 40 AVCC = +15V AVEE = -15V 0.5 TRANSITION 0 -0.5 -1.0 20 ISET 1k 10k 100k 1M FREQUENCY (Hz) 12137-029 100 -1.5 -15 10 100 1k 10k 100k FREQUENCY (Hz) 12137-030 SPECTRAL DENSITY VOLTAGE NOISE (nV/Hz) 100 10 0 5 10 15 20 Figure 31. CC to CV Transition 1k 1 -5 TIME (s) Figure 29. PSRR vs. Frequency 1 0.1 -10 Figure 30. Range of Spectral Density Voltage Noise vs. Frequency for the Op Amps and Buffers Rev. 0 | Page 14 of 32 25 30 35 12137-031 VCTRL 0 10 Data Sheet AD8451 VINT BUFFER 0.5 6 CL = 100pF RL = 2k VCTRL OUTPUT WITH RESPECT TO VCLP 0.4 0.3 0.2 0.1 VCLP AND VCLN REFERENCE 0 VALID FOR ALL RATED SUPPLY VOLTAGES -0.1 4 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE SWING (V) 5 -0.2 3 2 1 -0.3 VCTRL OUTPUT WITH RESPECT TO VCLN 0 -0.4 10 20 30 40 50 60 70 80 90 TEMPERATURE (C) -1 0 15 20 25 30 35 40 Figure 35. Large Signal Transient Response, RL = 2 k, CL = 100 pF 15 0.20 CL = 10pF CL = 100pF CL = 510pF CL = 680pF CL = 1000pF 0.15 OUTPUT VOLTAGE (V) VCLP 10 5 TEMP = -40C TEMP = +25C TEMP = +85C 0 -5 0.10 0.05 0 -0.05 -0.10 VCLN -15 100 1k -0.15 10k 100k 1M LOAD RESISTANCE () -0.20 0 1 2 3 4 5 6 7 8 9 10 TIME (s) 12137-036 -10 12137-033 Figure 36. Small Signal Transient Response vs. Capacitive Load Figure 33. Output Voltage Swing vs. Load Resistance at Three Temperatures 100 6 5 OUTPUT IMPEDANCE () VCLP 4 3 TEMP = -40C TEMP = 0C TEMP = +25C TEMP = +85C VIN = +6V/-1V 2 1 10 1 VCLN 0 15 20 25 30 35 OUTPUT CURRENT (mA) 40 0.1 10 12137-034 -1 10 100 1k 10k 100k FREQUENCY (Hz) Figure 34. Clamped Output Voltage vs. Output Current at Four Temperatures Figure 37. Output Impedance vs. Frequency Rev. 0 | Page 15 of 32 1M 12137-037 OUTPUT VOLTAGE SWING (V) 10 TIME (s) Figure 32. Output Voltage Swing with Respect to VCLP and VCLN vs. Temperature CLAMPED OUTPUT VOLTAGE (V) 5 12137-035 0 12137-032 -0.5 -40 -30 -20 -10 AD8451 Data Sheet REFERENCE CHARACTERISTICS 2.51 AVCC = +25V AVEE = -5V 1100 LOAD REGULATION (ppm/mA) 2.50 OUTPUT VOLTAGE (V) 1200 TA = +85C TA = +25C TA = 0C TA = -20C TA = -40C 2.49 2.48 2.47 1000 900 800 700 1 2 3 4 5 6 7 8 9 10 OUTPUT CURRENT--SOURCING (mA) 600 -40 -30 -20 -10 2.7 2.6 2.5 2.4 -10 TA = +85C TA = +25C TA = 0C TA = -20C TA = -40C -9 -8 -7 -6 -5 -4 -3 -2 OUTPUT CURRENT--SINKING (mA) -1 0 12137-039 OUTPUT VOLTAGE (V) 2.8 30 50 40 60 70 80 90 Figure 40. Source and Sink Load Regulation vs. Temperature SPECTRAL DENSITY VOLTAGE NOISE (nV/Hz) AVCC = +25V AVEE = -5V 20 TEMPERATURE (C) Figure 38. Output Voltage vs. Output Current (Sourcing) over Temperature 2.9 10 0 Figure 39. Output Voltage vs. Output Current (Sinking) over Temperature Rev. 0 | Page 16 of 32 1k 100 10 0.1 1 10 100 1k 10k FREQUENCY (Hz) Figure 41. Spectral Density Voltage Noise vs. Frequency 100k 12137-041 0 12137-038 2.46 12137-040 AVCC = +25V AVEE = -5V Data Sheet AD8451 THEORY OF OPERATION OVERVIEW The AD8451 provides two control loops--CC loop and a CV loop--that transition automatically after the battery reaches the user defined target voltage. These loops are implemented via two precision specialty amplifiers with external feedback networks that set the transfer function of the CC and CV loops. Moreover, in the AD8451, these loops reconfigure themselves to charge or discharge the battery by toggling the MODE pin. To form and test a battery, the battery must undergo charge and discharge cycles. During these cycles, the battery terminal current and voltage must be precisely controlled to prevent battery failure or a reduction in the capacity of the battery. Therefore, battery formation and test systems require a high precision analog front end to monitor the battery current and terminal voltage. The analog front end of the AD8451 includes a precision current sense fixed gain instrumentation amplifier (IA) to measure the battery current and a precision voltage sense fixed gain difference amplifier (DA) to measure the battery voltage. Figure 42 is a block diagram of the AD8451 that illustrates the distinct sections of the AD8451, including the IA and DA measurement blocks, and the loop filter amplifiers. Figure 43 is a block diagram of a battery formation and test system. 80 69 AVEE VINT 53 19.2k - 9 AVEE BATTERY CURRENT SENSING IA 52 VSET BUFFER 10k 10 51 + 11 1667 10k - 1x CONSTANT CURRENT AND VOLTAGE LOOP FILTER AMPLIFIERS 20k 50 49 13 48 14 47 VCLP VCTRL VCLN AVCC VINT NC VVE1 VVE0 NC VVP0 VSETBF VSET NC AD8451 46 15 10k 100k 18 - +/- 19 + + - BATTERY VOLTAGE SENSING DA 17 45 44 80k 43 100k 16 100 31 32 33 34 35 Figure 42. Detailed Block Diagram Rev. 0 | Page 17 of 32 36 37 38 39 DGND NC NC NC 40 NC 30 MODE 29 AVCC 28 NC 27 BVN 26 NC 25 BVREFLS 24 BVREFL 23 41 AGND 22 BVREFH 21 NC VREF MODE 20 DVCC 42 50k ISVN 54 + 8 NC RGN NC CV LOOP FILTER AMPLIFIER BVP NC 56 AVCC NC NC 57 55 BVPS NC 59 AVEE 6 NC NC IVE1 + 1.1mA NC NC 60 58 CC LOOP FILTER AMPLIFIER 10k 12 NC IVE0 1x 4 79.9k NC 61 62 - + - VREF NC 63 64 1x +/- 5 65 VINT BUFFER NC NC 66 67 7 NC NC ISET ISREFB 68 ISREFL BUFFER MODE 3 NC AVCC ISMEA 70 71 2.5V VREF 12137-042 2 AVEE ISREFH AGND ISREFL ISREFLS NC VREF 72 73 BVMEA NC 74 AVEE NC 75 76 BVNS NC 77 NC NC 78 100k RGP 79 1 806 ISVP NC NC Battery formation and test systems charge and discharge batteries using a constant current/constant voltage (CC/CV) algorithm. In other words, the system first forces a set constant current into or out of the battery until the battery voltage reaches a target value. At this point, a set constant voltage is forced across the battery terminals. AD8451 SET BATTERY CURRENT Data Sheet CONSTANT VOLTAGE LOOP FILTER AMPLIFIER ISET V1 VINT BUFFER + - 1x CONSTANT CURRENT LOOP FILTER AMPLIFIER MODE SWITCHES (3) D D C IVE0 DC VVE0 VSETBF 1x CV BUFFER IVE1 C VVE1 V2 POWER CONVERTER SWITCHED OR LINEAR + - VSET VVP0 SET BATTERY VOLTAGE VCTRL AVEE C = CHARGE D = DISCHARGE BATTERY CURRENT AD8451 CONTROLLER VINT ISVP + SENSE RESISTOR IA ISVN - ISMEA SYSTEM LOOP COMPENSATION BVP + BVMEA BATTERY DA - BVN 12137-043 EXTERNAL PASSIVE COMPENSATION NETWORK Figure 43. Signal Path of an Li-Ion Battery Formation and Test System Using the AD8451 INSTRUMENTATION AMPLIFIER (IA) Reversing Polarity When Charging and Discharging Figure 43 shows that during the charge cycle, the power converter feeds current into the battery, generating a positive voltage across the current sense resistor. During the discharge cycle, the power converter draws current from the battery, generating a negative voltage across the sense resistor. In other words, the battery current polarity reverses when the battery discharges. In the CC control loop, this change in polarity can be problematic if the polarity of the target current is not reversed. To solve this problem, the AD8451 IA includes a multiplexer preceding its inputs that inverts the polarity of the IA gain. This multiplexer is controlled via the MODE pin. When the MODE pin is logic high (charge mode), the IA gain is noninverting, and when the MODE pin is logic low (discharge mode), the IA gain is inverting. +CURRENT SHUNT ISVP RGP 100k ISREFH IA 10k + 19.2k 806 ISREFL - 10k G = 2 SUBTRACTOR + 1667 ISMEA - 10k RGN -CURRENT SHUNT - ISVN 10k 20k + POLARITY INVERTER MODE Figure 44. IA Simplified Block Diagram IA Offset Option As shown in Figure 44, the IA reference node is connected to the ISREFL and ISREFH pins via an internal resistor divider. This resistor divider can be used to introduce a temperature insensitive offset to the output of the IA such that it always reads a voltage higher than zero for a zero differential input. Because the output voltage of the IA is always positive, a unipolar analog-to-digital converter (ADC) can digitize it. Rev. 0 | Page 18 of 32 12137-044 Figure 44 is a block diagram of the IA, which is used to monitor the battery current. The architecture of the IA is the classic 3-op-amp topology, similar to the Analog Devices industry-standard AD8221 and AD620, with a fixed gain of 26. This architecture provides the highest achievable CMRR at a given gain, enabling high-side battery current sensing without the introduction of significant errors in the measurement. For more information about instrumentation amplifiers, see A Designer's Guide to Instrumentation Amplifiers. VREF POLARITY INVERTER Data Sheet AD8451 When the ISREFH pin is tied to the VREF pin with the ISREFL pin grounded, the voltage at the ISMEA pin is increased by 20 mV, guaranteeing that the output of the IA is always positive for zero differential inputs. Other voltage shifts can be realized by tying the ISREFH pin to an external voltage source. The gain from the ISREFH pin to the ISMEA pin is 8 mV/V. For zero offset, tie the ISREFL and ISREFH pins to ground. The resistors that form the DA gain network are laser trimmed to a matching level better than 0.1%. This level of matching minimizes the gain error and gain error drift of the DA while maximizing the CMRR of the DA. This matching also allows the controller to set a stable target voltage for the battery over temperature while rejecting the ground bounce in the battery negative terminal. Battery Reversal and Overvoltage Protection Like the IA, the DA can also level shift its output voltage via an internal resistor divider that is tied to the DA reference node. This resistor divider is connected to the BVREFH and BVREFL pins. The AD8451 IA can be configured for high-side or low-side current sensing. If the IA is configured for high-side current sensing (see Figure 43) and the battery is connected backward, the IA inputs may be held at a voltage that is below the negative power rail (AVEE), depending on the battery voltage. To prevent damage to the IA under these conditions, the IA inputs include overvoltage protection circuitry that allows them to be held at voltages of up to 55 V from the opposite power rail. In other words, the safe voltage span for the IA inputs extends from AVCC - 55 V to AVEE + 55 V. DIFFERENCE AMPLIFIER (DA) Figure 45 is a block diagram of the DA, which is used to monitor the battery voltage. The architecture of the DA is a subtractor amplifier with a fixed gain of 0.8. This gain value allows the DA to funnel the voltage of a 5 V battery to a level that can be read by a 5 V ADC with a 4.096 V reference. BVP 100k DA 79.9k VREF BVMEA Figure 45. DA Simplified Block Diagram 12137-045 80k The CC and CV loop filter amplifiers are high precision, low noise specialty amplifiers with very low offset voltage and very low input bias current. These amplifiers serve two purposes: * * - BVN 100k CC AND CV LOOP FILTER AMPLIFIERS 100k BVREFL 50k BVREFH + When the BVREFH pin is tied to the VREF pin with the BVREFL pin grounded, the voltage at the BVMEA pin is increased by 5 mV, guaranteeing that the output of the DA is always positive for zero differential inputs. Other voltage shifts can be realized by tying the BVREFH pin to an external voltage source. The gain from the BVREFH pin to the BVMEA pin is 2 mV/V. For zero offset, tie the BVREFL and BVREFH pins to ground. Using external components, the amplifiers implement active loop filters that set the dynamics (transfer function) of the CC and CV loops. The amplifiers perform a seamless transition from CC to CV mode after the battery reaches its target voltage. Figure 46 is the functional block diagram of the AD8451 CC and CV feedback loops for charge mode (MODE logic pin is high). For illustration purposes, the external networks connected to the loop amplifiers are simple RC networks configured to form single-pole inverting integrators. The outputs of the CC and CV loop filter amplifiers are coupled to the VINT pins via an analog NOR circuit (minimum output selector circuit), such that they can only pull the VINT node down. In other words, the loop amplifier that requires the lowest voltage at the VINT pins is in control of the node. Thus, only one loop amplifier, CC or CV, can be in control of the system charging control loop at any given time. Rev. 0 | Page 19 of 32 AD8451 Data Sheet CURRENT POWER VCTRL BUS IOUT IBAT ISVP SENSE RESISTOR R1 V1 RS ISVN IA + GIA ISMEAS ISET IVE1 C1 - POWER CONVERTER CC LOOP AMPLIFIER VINT VINT BUFFER VCLP - + ANALOG `NOR' + MINIMUM OUTPUT SELECTOR 1x BVP BVN DA + GDA - MODE 5V - BVMEA VSET VVE1 CV LOOP AMPLIFIER VCLN V3 V4 VINT V3 < VCTRL < V4 V2 12137-046 + VBAT - VCTRL C2 R2 Figure 46. Functional Block Diagram of the CC and CV Loops in Charge Mode (MODE Pin High) 1.00 where: IBAT_SS = is the steady state charging current. GIA is the IA gain. RS is the value of the shunt resistor. 3 0.50 2 1 CC CHARGE ENDS 0 0 0 1 2 3 TIME (Hours) 4 5 Figure 47. Representative Constant Current to Constant Voltage Transition near the End of a Battery Charging Cycle VVSET G DA 2. where: VBAT_SS = steady state battery voltage. GDA is the DA gain. Because the offset voltage of the loop amplifiers is in series with the target voltage sources, VISET and VVSET, the high precision of these amplifiers minimizes this source of error. Figure 47 shows a typical CC/CV charging profile for a Li-Ion battery. In the first stage of the charging process, the battery is charged with a CC of 1 A. When the battery voltage reaches a target voltage of 4.2 V, the charging process transitions such that the battery is charged with a CV of 4.2 V. The following steps describe how the AD8451 implements the CC/CV charging profile (see Figure 46). In this scenario, the battery begins in the fully discharged state, and the system has just been turned on such that IBAT = 0 A at Time 0. 1. 0.75 0.25 The target voltage is set at VBAT_SS = 4 VOLTAGE (V) VISET G IA x RS 5 TRANSITION FROM CC TO CV CC CHARGE BEGINS 12137-047 IBAT_SS = 1.25 CURRENT (A) The unity-gain amplifier (VINT buffer) buffers the VINT pins and drives the VCTRL pin. The VCTRL pin is the control output of the AD8451 and the control input of the power converter. The VISET and VVSET voltage sources set the target constant current and the target constant voltage, respectively. When the CC and CV feedback loops are in a steady state, the charging current is set at 3. 4. 5. Because the voltages at the ISMEA and BVMEA pins are less than the target voltages (VISET and VVSET) at Time 0, both integrators begin to ramp, increasing the voltage at the VINT node. Rev. 0 | Page 20 of 32 As the voltage at the VINT node increases, the voltage at the VCRTL node rises, and the output current of the power converter, IBAT, increases (assuming that an increasing voltage at the VCRTL node increases the output current of the power converter). When the IBAT current reaches the CC steady state value, IBAT_SS, the battery voltage is still less than the target steady state value, VBAT_SS. Therefore, the CV loop tries to keep pulling the VINT node up while the CC loop tries to keep it at its current voltage. At this point, the voltage at the ISMEA pin equals VISET; therefore, the CC loop stops integrating. Because the loop amplifiers can only pull the VINT node down due to the analog NOR circuit, the CC loop takes control of the charging feedback loop, and the CV loop is disabled. As the charging process continues, the battery voltage increases until it reaches the steady state value, VBAT_SS, and the voltage at the BVMEA pin reaches the target voltage, VVSET. Data Sheet 6. 7. AD8451 the internal switches in the CC and CV amplifiers, the frequency response of the loops in charge mode does not affect the frequency response of the loops in discharge mode. The CV loop tries to pull the VINT node down to reduce the charging current (IBAT) and prevent the battery voltage from rising any further. At the same time, the CC loop tries to keep the VINT node at its current voltage to keep the battery current at IBAT_SS. Because the loop amplifiers can only pull the VINT node down due to the analog NOR circuit, the CV loop takes control of the charging feedback loop, and the CC loop is disabled. Unlike simpler controllers that use passive networks to ground for frequency compensation, the AD8451 allows the use of feedback networks for its CC and CV loop filter amplifiers. These networks enable the implementation of both proportional differentiator (PD) Type II and proportional integrator differentiator (PID) Type III compensators. Note that in charge mode, both the CC and CV loops implement inverting compensators, whereas in discharge mode, the CC loop implements an inverting compensator, and the CV loop implements a noninverting compensator. As a result, the CV loop in discharge mode includes an additional amplifier, VSET buffer, to buffer the VSET node from the feedback network (see Figure 48). The analog NOR (minimum output selector) circuit that couples the outputs of the loop amplifiers is optimized to minimize the transition time from CC to CV control. Any delay in the transition causes the CC loop to remain in control of the charge feedback loop after the battery voltage reaches its target value. Therefore, the battery voltage continues to rise beyond VBAT_SS until the control loop transitions; that is, the battery voltage overshoots its target voltage. When the CV loop takes control of the charge feedback loop, it reduces the battery voltage to the target voltage. A large overshoot in the battery voltage due to transition delays can damage the battery; thus, it is crucial to minimize delays by implementing a fast CC to CV transition. VINT Buffer The unity-gain amplifier (VINT buffer) is a clamp amplifier that drives the VCTRL pin. The VCTRL pin is the control output of the AD8451 and the control input of the power converter (see Figure 46 and Figure 48). The output voltage range of this amplifier is bounded by the clamp voltages at the VCLP and VCLN pins such that Figure 48 is the functional block diagram of the AD8451 CC and CV feedback loops for discharge mode (MODE logic pin is low). In discharge mode, the feedback loops operate in a similar manner as in charge mode. The only difference is in the CV loop amplifier, which operates as a noninverting integrator in discharge mode. For illustration purposes, the external networks connected to the loop amplifiers are simple RC networks configured to form single-pole integrators (see Figure 48). The reduction in the output voltage range of the amplifier is a safety feature that allows the AD8451 to drive devices such as the ADP1972 PWM controller, whose input voltage range must not exceed 5.5 V (that is, the voltage at the COMP pin of the ADP1972 must be below 5.5 V). Compensation MODE PIN, CHARGE AND DISCHARGE CONTROL In battery formation and test systems, the CC and CV feedback loops have significantly different open-loop gain and crossover frequencies; therefore, each loop requires its own frequency compensation. The active filter architecture of the AD8451 CC and CV loops allows the frequency response of each loop to be set independently via external components. Moreover, due to The MODE pin is a TTL logic input that configures the AD8451 for either charge or discharge mode. A logic low (VMODE < 0.8 V) corresponds to discharge mode, and a logic high (VMODE > 2 V) corresponds to charge mode. Internal to the AD8451, the MODE pin toggles all single-pole, double throw (SPDT) switches in the CC and CV loop amplifiers and inverts the gain polarity of the IA. VVCLN - 0.5 V < VVCTRL < VVCLP + 0.5 V CURRENT POWER VCTRL BUS IOUT ISVP + VBAT - RS ISVN BVP BVN MODE IA ISMEAS + GIA ISET IVE0 CC LOOP AMPLIFIER VINT VINT BUFFER ANALOG `NOR' + MINIMUM OUTPUT SELECTOR - 1x VSET + 1x VSET BUFFER - BVMEA - POWER CONVERTER VCLP - DA + GDA C1 VSETBF VVP0 VVE0 CV LOOP AMPLIFIER VCTRL VCLN V3 V4 VINT V3 < VCTRL < V4 V2 R2 R2 C2 C2 Figure 48. Functional Block Diagram of the CC and CV Loops in Discharge Mode (MODE Pin Low) Rev. 0 | Page 21 of 32 12137-048 SENSE RESISTOR R1 V1 IBAT AD8451 Data Sheet APPLICATIONS INFORMATION This section describes how to use the AD8451 in the context of a battery formation and test system. This section includes a design example of a small scale model of an actual system. * FUNCTIONAL DESCRIPTION * The AD8451 is a precision analog front end and controller for battery formation and test systems. These systems use precision controllers and power stages to put batteries through charge and discharge cycles. Figure 49 shows the signal path of a simplified switching battery formation and test system using the AD8451 controller and the ADP1972 PWM controller. For more information on the ADP1972, see the ADP1972 data sheet. The AD8451 is suitable for systems that form and test NiCad, NiMH, and Li-Ion batteries and is designed to operate in conjunction with both linear and switching power stages. A logic input pin (MODE) that changes the configuration of the controller from charge to discharge mode. A logic high at the MODE pin configures charge mode; a logic low configures discharge mode. A fixed gain IA that senses low-side or high-side battery current. A fixed gain DA that measures the terminal voltage of the battery. SET BATTERY CURRENT ISET CONSTANT VOLTAGE LOOP FILTER AMPLIFIER 1x IVE0 IVE1 ADP1972 PWM LEVEL SHIFTER OUTPUT FILTER OUTPUT DRIVERS DC-TO-DC POWER CONVERTER MODE SWITCHES (3) D DC VVE0 DC VVE1 C 1x CV BUFFER VCTRL + - VSET VVP0 AVEE C = CHARGE D = DISCHARGE BATTERY CURRENT AD8451 CONTROLLER VINT ISVP + IA - ISVN SENSE RESISTOR ISMEA BVMEA + DA EXTERNAL PASSIVE COMPENSATION NETWORK - BVP BATTERY BVN 12137-049 SET BATTERY VOLTAGE AVCC VINT BUFFER + - CONSTANT CURRENT LOOP FILTER AMPLIFIER VSETBF * * * The AD8451 includes the following blocks (see Figure 42 and the Theory of Operation section for more information). * Two loop filter error amplifiers that receive the battery target current and voltage and establish the dynamics of the CC and CV feedback loops. A minimum output selector circuit that combines the outputs of the loop filter error amplifiers to perform automatic CC to CV switching. An output clamp amplifier that drives the VCTRL pin. The voltage range of this amplifier is limited by the voltage at the VCLP and VCLN pins such that it cannot overrange the subsequent stage. The output clamp amplifier can drive switching and linear power converters. Note that an increasing voltage at the VCTRL pin must translate to a larger output current in the power converter. A 2.5 V reference whose output node is the VREF pin. Figure 49. Complete Signal Path of a Battery Test or Formation System Suitable for Li-Ion Batteries Rev. 0 | Page 22 of 32 Data Sheet AD8451 POWER SUPPLY CONNECTIONS Optional Low-Pass Filter The AD8451 requires two analog power supplies (AVCC and AVEE), one digital power supply (DVCC), one analog ground (AGND), and one digital ground (DGND). AVCC and AVEE power all the analog blocks, including the IA, DA, and op amps, and DVCC powers the MODE input logic. AGND provides a reference and return path for the 2.5 V reference, and DGND provides a reference and return path for the digital circuitry. The AD8451 is designed to control both linear regulators and switching power converters. Linear regulators are generally noise free, whereas switch mode power converters generate switching noise. Connecting an external differential low-pass filter between the current sensor and the IA inputs reduces the injection of switching noise into the IA (see Figure 50). ISVP Connect decoupling capacitors to all the supply pins. A 1 F capacitor in parallel with a 0.1 F capacitor is recommended. CURRENT SENSE IA CONNECTIONS For a description of the IA, see the Theory of Operation section, Figure 42, and Figure 44. The IA fixed gain is 26. Current Sensors Two common options for current sensors are isolated current sensing transducers and shunt resistors. Isolated current sensing transducers are galvanically isolated from the power converter and are affected less by the high frequency noise generated by switch mode power supplies. Shunt resistors are less expensive and easier to deploy. If a shunt resistor sensor is used, a 4-terminal, low resistance shunt resistor is recommended. Two of the four terminals conduct the battery current, whereas the other two terminals conduct virtually no current. The terminals that conduct no current are sense terminals that are used to measure the voltage drop across the resistor (and, therefore, the current flowing through it) using an amplifier such as the IA of the AD8451. To interface the IA with the current sensor, connect the sense terminals of the sensor to the ISVP and ISVN pins of the AD8451 (see Figure 50). RGP IBAT - 4 TERMINAL SHUNT DUT 10k 20k + 1667 LPF 10k RGN - ISVN - 10k 20k + 12137-050 A commonly used power supply combination is +15 V for AVCC, -15 V for AVEE, and +5 V for DVCC. The +15 V rail for AVCC provides enough headroom to the IA such that it can be connected in a high-side current sensing configuration. The -15 V rail for AVEE allows the DA to sense accidental reverse battery conditions (see the Reverse Battery Conditions section). 10k + The rated absolute maximum value for AVCC - AVEE is 36 V, and the minimum operating AVCC and AVEE voltages are +5 V and -5 V, respectively. Due to the high PSRR of the AD8451 analog blocks, AVCC can be connected directly to the high current power bus (the input voltage of the power converter) without risking the injection of supply noise to the controller outputs. Figure 50. 4-Terminal Shunt Resistor Connected to the Current Sense IA VOLTAGE SENSE DA CONNECTIONS For a description of the DA, see the Theory of Operation section, Figure 42, and Figure 45. The DA fixed gain is 0.8. Reverse Battery Conditions The output voltage of the AD8451 DA can be used to detect a reverse battery connection. A -15 V rail for AVEE allows the output of the DA to go below ground when the battery is connected backward. Therefore, the condition can be detected by monitoring the BVMEA pin for a negative voltage. BATTERY CURRENT AND VOLTAGE CONTROL INPUTS (ISET AND VSET) The voltages at the ISET and VSET input pins set the target battery current and voltage for the CC and CV loops. These inputs must be driven by a precision voltage source (or a digitalto-analog converter [DAC] connected to a precision reference) whose output voltage is referenced to the same voltage as the IA and DA reference pins (ISREFH/ISREFL and BVREFH/BVREFL, respectively). For example, if the IA reference pins are connected to AGND, the voltage source connected to ISET must also be referenced to AGND. In the same way, if the DA reference pins are connected to AGND, the voltage source connected to VSET must also be referenced to AGND. In constant current mode, when the CC feedback loop is in a steady state, the ISET input sets the battery current as follows: IBAT_SS = VISET V = ISET G IA x RS 26 x RS where: GIA is the IA gain. RS is the value of the shunt resistor. Rev. 0 | Page 23 of 32 AD8451 Data Sheet In constant voltage mode, when the CV feedback loop is in steady state, the VSET input sets the battery voltage as follows: VBAT_SS = VVSET V = VSET 0. 8 G DA where GDA is the DA gain. Therefore, the accuracy and temperature stability of the formation and test system are not only dependent on the precision of the AD8451, but also on the accuracy of the ISET and VSET inputs. LOOP FILTER AMPLIFIERS The AD8451 has two loop filter amplifiers, also known as error amplifiers (see Figure 49). One amplifier is for constant current control (CC loop filter amplifier), and the other amplifier is for constant voltage control (CV loop filter amplifier). The outputs of these amplifiers are combined using a minimum output selector circuit to perform automatic CC to CV switching. Table 5 lists the inputs of the loop filter amplifiers for charge mode and discharge mode. Table 5. Integrator Input Connections Feedback Loop Function Control the Current While Discharging a Battery Control the Current While Charging a Battery Control the Voltage While Discharging a Battery Control the Voltage While Charging a Battery Reference Input ISET Feedback Terminal IVE0 ISET IVE1 VSET VVE0 VSET VVE1 The CC and CV amplifiers in charge mode and the CC amplifier in discharge mode are inverting integrators, whereas the CV amplifier in discharge mode is a noninverting integrator. Therefore, the CV amplifier in discharge mode uses an extra amplifier, the VSET buffer, to buffer the VSET input pin (see Figure 42). In addition, the CV amplifier in discharge mode uses the VVP0 pin to couple the signal from the BVMEA pin to the integrator. Given the architecture of the AD8451, the controller requires that an increasing voltage at the VCTRL pin translates to a larger output current in the power converter. If this is not the case, a unity-gain inverting amplifier can be added in series with the AD8451 output to add an extra inversion. STEP-BY-STEP DESIGN EXAMPLE This section describes the systematic design of a 1 A battery charger/discharger using the AD8451 controller and the ADP1972 PWM controller. The power converter used in this design is a nonisolated buck boost dc-to-dc converter. The target battery is a 4.2 V fully charged, 2.7 V fully discharged Li-Ion battery. Step 1: Design the Switching Power Converter Select the switches and passive components of the buck boost power converter to support the 1 A maximum battery current. The design of the power converter is beyond the scope of this data sheet; however, there are many application notes and other helpful documents available from manufacturers of integrated driver circuits and power MOSFET output devices that can be used for reference. Step 2: Identify the Control Voltage Range of the ADP1972 The control voltage range of the ADP1972 (voltage range of the COMP input pin) is 0.5 V to 4.5 V. An input voltage of 4.5 V results in the highest duty cycle and output current, whereas an input voltage of 0.5 V results in the lowest duty cycle and output current. Because the COMP pin connects directly to the VCTRL output pin of the AD8451, the battery current is proportional to the voltage at the VCTRL pin. For information about how to interface the ADP1972 to the power converter switches, see the ADP1972 data sheet. Step 3: Determine the Control Voltage for the CV Loop The relationship between the control voltage for the CV loop (the voltage at the VSET pin), the target battery voltage, and the DA gain is as follows: CONNECTING TO A PWM CONTROLLER (VCTRL PIN) The VCTRL output pin of the AD8451 is designed to interface with linear power converters and with PWM controllers such as the ADP1972. The voltage range of the VCTRL output pin is bound by the voltages at the VCLP and VCLN pins, as follows: VVCLN - 0.5 V < VVCTRL < VVCLP + 0.5 V CV Battery Target Voltage = VVSET VVSET = G DA 0. 8 In charge mode, for a CV battery target voltage of 4.2 V, select a CV control voltage of 3.36 V. In discharge mode, for a CV battery target voltage of 2.7 V, select a CV control voltage of 2.16 V. Because the maximum rated input voltage at the COMP pin of the ADP1972 is 5.5 V, connect the clamp voltages of the output amplifier to 5 V (VCLP) and ground (VCLN) to prevent overranging of the COMP input. As an additional precaution, install an external 5.1 V Zener diode from the COMP pin to ground with a series 1 k resistor connected between the VCTRL and COMP pins. Consult the ADP1972 data sheet for additional applications information. Rev. 0 | Page 24 of 32 Data Sheet AD8451 Step 4: Determine the Control Voltage for the CC Loop and the Shunt Resistor The relationship between the control voltage for the CC loop (the voltage at the ISET pin), the target battery current, and the IA gain is as follows: CC Battery Target Current = V VISET = ISET G IA x RS 26 x RS The voltage across the shunt resistor is as follows: Step 5: Choose the Control Voltage Sources The input control voltages (the voltages at the ISET and VSET pins) can be generated by an analog voltage source such as a voltage reference or by a DAC. In both cases, select a device that provides a stable, low noise output voltage. If a DAC is preferred, Analog Devices offers a wide range of precision converters. For example, the AD5668 16-bit DAC provides up to eight 0 V to 4 V sources when connected to an external 2 V reference. To maximize accuracy, the control voltage sources must be referenced to the same potential as the outputs of the IA and DA. For example, if the IA and DA reference pins are connected to AGND, connect the reference pins of the control voltage sources to AGND. V V Shunt Resistor Voltage = ISET = ISET G IA 26 For target current of 1 A, choosing a 20 m shunt resistor results in a control voltage of 4 V. When selecting a shunt resistor, consider the resistor style and construction. For low power dissipation applications, many temperature stable SMD styles can be soldered to a heat sink pad on a printed circuit board (PCB). For optimum accuracy, choose a shunt resistor that provides force and sense terminals. In these resistors, the battery current flows through the force terminals and the voltage drop in the resistor is read at the sense terminals. Step 6: Select the Compensation Devices Feedback controlled switching power converters require frequency compensation to guarantee loop stability. There are many references available about how to design the compensation for such power converters. The AD8451 provides active loop filter error amplifiers for the CC and CV control loops that can implement proportional integrator (PI), PD, and PID compensators using external passive components. Rev. 0 | Page 25 of 32 AD8451 Data Sheet EVALUATION BOARD INTRODUCTION FEATURES AND TESTS The AD8451-EVALZ evaluation board is a convenient standalone platform for evaluating the major elements of the AD8451, either as a standalone component or connected to a battery test/formation system. SMA connectors provide access for input voltages to the sensitive instrumentation (IA) and difference (DA) amplifiers. ISVP and ISVN connectors are the IA inputs, and BVP and BVN are the DA inputs. These inputs accept the dc voltages from battery current and voltage measurement sources, or from a precision dc voltage source. SMA connectors ISET and VSET are available for precision dc control voltages for CC or CV battery charging voltages. SMA ISREFLO is available for applying a nonzero reference voltage to the IA. SMA VCTRL connects to the input of a dc-to-dc power converter as seen in Figure 52. Convenient test loops are provided connecting scope probes or instruments for the remainder of the input/output. In the latter configuration, the AD8451-EVALZ operates just as it would within a system including the PWM and dc-to-dc power converter. Simply connect the current and voltage sense voltages from the system directly to the board terminus. This feature is used when setting or evaluating loop compensation using a field of passive compensation components. Figure 51 is a photograph of the AD8451-EVALZ. 12137-051 The MODE switch selects between the charge and discharge option. Figure 52 is a schematic of the AD8451-EVALZ. Table 6 lists and describes the various switches and functions. Figure 51. Photograph of the AD8451-EVALZ Rev. 0 | Page 26 of 32 Data Sheet AD8451 Table 6. AD8451-EVALZ Test Switches and Functions Switch MODE RUN_TEST1 RUN_TEST2 ISREF_HI ISREF_LO Function Selects the charge or the discharge mode. Selects between the user inputs and the 2.5 V AD8451 reference voltage. Tests the CC or CV loop filter amplifiers. The ISREF_HI switch connects Pin 74 (ISREFH) to the internal 2.5 V reference (2.5 position) or to the SMA connector EXT (the external input for a user defined VREF input). Connects Pin 76 (ISREFL) to ground (NORM) or to the ISREFL SMA input connector. Operation The MODE switch selects CHG (logic high) or DISCH (logic low). The AD8451 operates normally when the RUN_TEST1 switch is in the RUN position. When in the TEST position, 2.5 V is applied to the ISET and VSET inputs. The voltage at the VCTRL output (TPVCTRL) for all positions is 0 V when RUN_TEST1 is in RUN position and 2.5 V when RUN_TEST1 in TEST position. When in the 2.5V position, the ISREF_HI switch connects Pin 74 (ISREFH, an internal 100 k resistor) to Pin 73 (VREF, the 2.5 V reference). When the ISREF_LO switch is in the NORM position, the output at Pin 71 (ISMEA) shifts positive by 20 mV. When in the NORM position and the ISREF_HI switch is in the EXT position, there is no offset applied to the ISMEA output. When in the EXT position, the ISREFLO SMA is selected. EVALUATING THE AD8451 Test the Instrumentation Amplifier Connect the TPISVN jumper to ground, and then apply 100 mV dc to TPISVP. Measure 2.6 V at the TPISMEA output. Subtract any offset voltages from the output reading before calculating the gain. 20 mV Offset at IMEAS Output Connect a jumper from TPISVP to TPISVN to ground by using another jumper and any one of the convenient black test loops. Measure 0 V 2.86 mV at the TPISMEA output (that is, the IA residual offset voltage multiplied by gain). Move the ISREFLO switch to the EXT position, and the ISREFHI switch to the 20 mV (EXT) position. The output will then increase by 20 mV. Test the Difference Amplifier Insert a shorting jumper at Header GND_BVN. With 1 V dc applied to TPBVP, measure 0.8 V at TPBVMEA. For the most accurate gain measurement, subtract the offset voltage from the output voltage before calculating gain. 5 mV Offset at BVMEAS Output Insert jumpers in the GND_BVP and GND_BVN headers. Measure 0 V 0.4mV at the TPBVMEA output (that is, the DA residual offset voltage multiplied by gain). Connect a jumper between TPBREFH and TP2.5V. The output will then increase by 5 mV. Default Position CHG RUN RUN EXT NORM Note the four compensation networks, CC-CHARGE, CCDISCHARGE, CV-CHARGE, and CV-DISCHARGE, located on the right-hand side of the schematic shown in Figure 52. To make it easier to locate these components, the configuration of these networks on the AD8451-EVALZ PCB approximates that shown in the schematic (see Figure 52). Each of the components locations accommodates both standard, 1206 size, surface-mount chip resistors and capacitors or leaded components inserted into the pairs of TP thru holes spanning the SM footprints. The TP holes accept the popular 0.025" test pins if leaded devices are preferred for multiple loop tests. As shipped, CC and CV loop amplifier filters are configured as voltage followers by replacing feedback capacitors to the inverting inputs with resistors, and removing the dc coupling resistors from the IA and DA outputs. The feedback loops must be reconfigured to close the loops to operate as precision feedback loops. Loop compensation requires knowledge of the output dc-to-dc power converter. It is assumed that the AD8451 is most often used with a switching converter. The scope and breadth of this switching converter design architecture is quite broad, and a thorough discussion of all the types and variants of this type of converter is well beyond the scope of this data. CC and CV Integrator Tests When the circuit and component details of the power converter are known, proceed with a calculation of the loop parameters and components, and the values necessary to achieve loop compensation. Switches RUN_TEST1 and RUN_TEST2 set up the required circuit conditions to test the integrators. RUN_TEST1 disconnects the external inputs ISET and VSET and applies 2.5 V dc from the reference, simultaneously, to both of the CC and CV. Because the loop is of the type proportional/integrating (PI), a direct dc path is required from the IA and DA amplifiers to the error inputs of the CC and CV loop amplifiers. Install these resistors at the R1, R6, R7, R11, and R12 locations. RUN_TEST2 has three positions: RUN, TEST_CC, and TEST_CV. Likewise, the CC and CV amplifiers must be reconfigured from voltage followers to integrators by replacing the 0 capacitors at C6, C10, C11, C19, and C24 with appropriate capacitors. Loop Compensation The AD8451-EVALZ is suitable for use as a test platform for system loop compensation experiments. However, before installing the platform in a system, component changes are necessary. Rev. 0 | Page 27 of 32 + ISVN 5V C4 10F 35V TPISVN RGN +5V + C8 10F 35V DVCC 25 V C7 10F + 35V AVCC -5V RGP TPISVP AVEE ISVP 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 NC 22 79 78 23 TPBVP GND_BVP 21 ISVN RGN NC NC NC NC NC NC NC NC NC NC NC NC NC NC NC NC RGP ISVP NC 80 NC BVPS 77 24 76 TPISREFLS NC NC GND6 GND7 GND8 GND9 GND10 ISREFLS BVP BVP C18 10F 10V 25 75 2.5 26 74 TPISREFH 27 1 72 29 71 2.5 70 69 30 31 X1 TPBVN 32 68 34 67 2 35 66 6 VSET 5 C21 1F 50V -5V 36 65 37 64 TPISET 1 RUN GND_BVN TP_BVP 33 3 R19 1k TEST TPISREFB CR3 5.1V 25 V TPISMEA AD8451 TPBVREFH 28 73 -5V C5 C20 10F 1F 10V 50V ISREFH BREFH TPISREFL AGND VREF 2.5V VREF AGND GND1 GND2 GND3 GND4 GND5 ISREFL NC 2 ISMEA 3 NC 1 AVCC 3 2 ISET NC EXT NORM EXT IVE0 AVEE ISREFL NC BVNS 63 4 VSET IVE1 BVMEA ISET 25V 38 NC AVCC RUN_ TEST1 62 39 61 C9 0.1F 50V 40 VVP0 51 NC 52 VVE0 53 VVE1 54 NC 55 VINT 56 45 46 42 JP 1 VVE1 R17 0 JP 1 5 7 DISCH 1 8 VVP0 TP8 TP5 TP25 TP3 TP6 R6 TBD1206 TP12 TP36 TP10 TP37 TP24 TP27 TP39 TP35 R13 10k 1206 TP32 TP38 TP34 C22 TBD1206 TP17 R10 10k 1206 TP31 C12 TBD1206 TP23 R14 10k 1206 TP33 C23 TBD1206 TP30 TP16 R8 10k 1% 1206 TP29 C1 TBD1206 TP15 VVP0 TP44 TPBVMEA AVCCRET DVCCRET AVEERET TP62 TP63 TP59 C19* 0 1206 TP52 TP60 R9 10k 1206 TP47 C13 TBD1206 TP51 TP58 R5 10k 1206 TP19 TP57 C11* 0 1206 C15 TBD1206 TP46 TP1 TP61 TP18 C24* 0 1206 TP50 TP56 R15 10k 1206 TP42 TP43 VVE0 TVVE 1 C17 TBD1206 TP49 TP55 TP54 C10* 0 1206 C14 TBD1206 TP45 VINT TP13 C6* TBD1206 1206 TP48 TP53 TP14 R4 10k 1206 TP41 TVVE1 IVE 0 TP40 R3 10k 1206 TIVE1 R2 10k 1% 1206 C3 TBD1206 TP11 TP9 *0 1206 RESISTORS ARE TEMPORARILY INSTALLED IN LOCATIONS C6, C14, C17, C15, AND C19. SEE TEXT FOR FURTHER EXPLANATION. TP4 C2 TBD1206 TP28 CV -DISCHARGE TP26 R12 TBD1206 CV -CHARGE TP2 R1 TBD1206 CC -DISCHARGE TP7 R7 TBD1206 CC -CHARGE R11 BVMEA TBD1206 BVMEA VSETBF CR 1 5 .1 V ISMEA VCTRL TPVCTRL 6 VVE1 MODE CHG 3 5 V 2 C19 10F 10V 5V CR2 5.1V R19 1k VSET TPVSETBF TPMODE NC 41 VREF NC 43 NC NC 44 NC DGND NC DVCC 47 NC 48 VSET 49 VINT 25V AVCC 57 VCLN 58 VCTRL 59 R18 1k R16 0 5V TVVE1 TPVCLN TPVCLP VCLP 60 -5V VSETBF 50 -5V T_CC RUN_ 3 T_CV TEST2 1 RUN 4 2 VINT VINT MODE ISREFHI AVEE BREFL TPBREFL BREFLS TPBVREFLS ISREFB NC NC NC NC BVN BVN Rev. 0 | Page 28 of 32 NC Figure 52. AD8451-EVALZ Schematic TPBVNS AVEE NC ISREFLO AD8451 Data Sheet SCHEMATIC AND ARTWORK 12137-052 AD8451 12137-053 Data Sheet 12137-054 Figure 53. AD8451-EVALZ Top Silkscreen Figure 54. AD8451-EVALZ Primary Side Copper Rev. 0 | Page 29 of 32 Data Sheet 12137-055 AD8451 12137-056 Figure 55. AD8451-EVALZ Secondary Side Copper Figure 56. AD8451-EVALZ Power Plane Rev. 0 | Page 30 of 32 AD8451 12137-057 Data Sheet Figure 57. AD8451-EVALZ Ground Plane Rev. 0 | Page 31 of 32 AD8451 Data Sheet OUTLINE DIMENSIONS 0.75 0.60 0.45 16.20 16.00 SQ 15.80 1.60 MAX 61 80 60 1 PIN 1 14.20 14.00 SQ 13.80 TOP VIEW (PINS DOWN) 0.15 0.05 SEATING PLANE 0.20 0.09 7 3.5 0 0.10 COPLANARITY VIEW A 20 41 40 21 VIEW A 0.65 BSC LEAD PITCH ROTATED 90 CCW 0.38 0.32 0.22 051706-A 1.45 1.40 1.35 COMPLIANT TO JEDEC STANDARDS MS-026-BEC Figure 58. 80-Lead Low Profile Quad Flat Package [LQFP] (ST-80-2) Dimensions shown in millimeters ORDERING GUIDE Model 1 AD8451ASTZ AD8451ASTZ-RL AD8451-EVALZ 1 Temperature Range -40C to +85C -40C to +85C Package Description 80-Lead LQFP 80-Lead LQFP Evaluation Board Z = RoHS Compliant Part. (c)2014 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D12137-0-3/14(0) Rev. 0 | Page 32 of 32 Package Option ST-80-2 ST-80-2