AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Features The AAT1152 SwitchRegTM is a member of AnalogicTech's Total Power Management ICTM product family. The Step-down switching converter is ideal for applications where high efficiency, small size, and low ripple are critical. Able to deliver 1A with internal Power MOSFETs, the current-mode controlled IC provides high efficiency using synchronous rectification. Fully internally compensated, the AAT1152 simplifies system design and lowers external part count. * * * * * * * * * * * * * * * * The AAT1152 features a Power Good (POK) function which monitors the output, alerting the system if the output voltage falls out of regulation. The AAT1152 is available in MSOP-8 package, rated over -40 to 85C. SwitchRegTM 5.5V max supply input Fixed output voltage: 1.1V-4.2V with 100 mV increment 1A output current Integrated low on resistance power switches Synchronous rectification Up to 95% efficiency Power Good signal Internally compensated current mode control High initial accuracy: 1% 850kHz switching frequency Constant PWM mode Low output ripple with light load Internal softstart Current limit protection Over-Temperature protection MSOP-8 package Applications * * * * * Computer Peripherals Set Top Boxes Network Cards Cable/DSL Modems High efficiency conversion from 5V or 3.3V supply Typical Application INPUT 100k VP 10F AAT1152 FB POK 4.1H LX ENABLE 100 VCC OUTPUT SGND PGND 47F 0.1F 1152.2003.01.0.9 1 Preliminary Information General Description AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Pin Descriptions Pin # Symbol Function 1 FB 2 SGND 3 EN Converter enable pin 4 VCC Small Signal Filtered Bias Supply 5 VP Input supply for converter power stage 6 LX Inductor connection pin 7 POK 8 PGND Feedback input pin Signal Ground Power Good indicator. Open-drain output is low when VOUT falls out of regulation. Power ground return for output stage Pin Configuration MSOP-8 2 8 7 2 2 1 1 FB SGND EN VCC 3 6 4 5 PGND POK LX VP 1152.2003.01.0.9 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Absolute Maximum Ratings (TA=25C unless otherwise noted) Symbol Description VCC, VP VLX VFB VEN, VPOK TJ TLEAD VESD VCC, VP to GND LX to GND FB to GND POK, EN to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) ESD Rating 1 - HBM Value Units 6 -0.3 to VP+0.3 -0.3 to VCC+0.3 -0.3 to 6 -40 to 150 300 3000 V V V V C C V Note: Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum rating should be applied at any one time. Note 1: Human body model is a 100pF capacitor discharged through a 1.5K resistor into each pin. Thermal Characteristics Symbol JA PD Description Maximum Thermal Resistance (MSOP-8) Maximum Power Dissipation (MSOP-8) 2 2 Value Units 150 833 C/W mW Rating Units -40 to +85 C Note 2: Mounted on a demo board. Recommended Operating Conditions Symbol T 1152.2003.01.0.9 Description Ambient Temperature Range 3 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Electrical Characteristics (VIN = VCC = VP = 5V, TA= -40 to 85C unless otherwise noted. Typical values are at TA = 25C) Symbol VIN VOUT ILIM IQ VOUT (VOUT*VIN) VOUT/VOUT FOSC RDSON(H) RDSON(L) VEN(H) VEN(L) IEN VUVLO VUVLO(hys) TSD THYS ISHDN 4 Description Conditions Min Operation Voltage TA = 25C Full temp DC Output Voltage Tolerance IOUT = 500mA Current Limit Quiescent Supply Current Load Regulation Line Regulation Oscillator frequency High-side Switch On-resistance Low-side Switch On-resistance Enable input high voltage Enable input low voltage Enable Pin Leakage Current TA = 25C No load, VFB = 0 VIN = 4.2V, ILOAD = 0 to 1A VIN = 2.7 to 5.5V TA = 25C TA = 25C TA = 25C VIN = 2.7 to 5.5V VIN = 2.7 to 5.5V VEN = 5.5V VIN rising VIN falling Undervoltage Lockout Undervoltage Lockout Hysteresis Over Temp Shutdown Threshold Over Temp Shutdown Hysteresis Shutdown current VTH(POK) Power Good Threshold RPOK Power Good Pull-Down On-Resistance Typ 2.7 -1.0 -2.0 1.2 700 160 3 0.2 850 110 100 Max Units 5.5 +1.0 +2.0 V 300 1000 150 150 1.4 0.6 1 2.5 1.2 250 140 15 VEN = 0, VIN = 5.5V VFB Ramping Up VFB Ramping Down 1 90 88 4 % A A % %/V kHz m m V V A V mV C C A % of VFB 1152.2003.01.0.9 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Typical Characteristics High Side RDS(ON) vs. Temperature Low Side RDS(ON) vs. Temperature 170 170 3.6V 150 150 RDS(ON) (m) RDS(ON) (m) 2.7V 130 110 70 -20 5.5V 4.2V 90 0 20 40 130 3.6V 2.7V 110 5.5V 90 60 80 100 4.2V 70 -20 120 0 20 40 60 80 100 120 Temperature (C) Temperature (C) Enable Threshold vs. Input Voltage RDS(ON) vs. Input Voltage 130 1.2 120 Enable Threshold (V) RDS(ON) (m) High Side 110 100 Low Side 90 80 2.5 3 3.5 4 4.5 5 5.5 1.1 VEN(H) 1 0.9 VEN(L) 0.8 0.7 2.5 Input Voltage (V) 3 3.5 4 4.5 5 5.5 Input Voltage (V) Oscillator Frequency Variation vs. Temperature VIN=3.6V 3.5 10 2.5 6 Variation (%) Variation (%) Oscillator Frequency Variation vs. Supply Voltage 1.5 0.5 -0.5 2 -2 -6 -1.5 2.5 3 3.5 4 4.5 Supply Voltage (V) 1152.2003.01.0.9 5 5.5 -10 -20 0 20 40 60 80 100 Temperature (C) 5 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Typical Characteristics Line Regulation VOUT=1.5V 1.0 0.25 0.6 0.15 VIN = 2.7V 0.2 -0.2 IOUT = 1.0A Accuracy (%) Output Voltage Error (%) Output Voltage vs. Temperature IOUT=900mA, VOUT=1.5V VIN = 3.6V 0.05 -0.15 -0.6 -1.0 -20 IOUT = 0.4A -0.05 -0.25 0 20 40 60 80 2.5 100 3 3.5 4.5 5 5.5 Input Voltage (V) Temperature (C) Load Regulation VOUT=3.3V, VIN=5.0V Load Regulation VOUT= 1.5V, VIN=3.6V 0 0 -1 -1 VOUT Error (%) Error (%) 4 -2 -3 -2 -3 -4 -4 -5 -5 0 0 150 300 450 600 750 900 Efficiency vs. Input Voltage VOUT=1.5V 450 600 IO = 1A Gain (dB) 70 225 32 180 16 100F 8 Phase 47F 0 47F -16 Gain 69F 100F -32 -40 50 3.5 4 Input Voltage (V) 4.5 5 5.5 10 100 135 90 45 69F -8 -24 60 3 1050 0 -45 -90 -135 Phase (degrees) IO = 0.4A 2.5 900 40 24 90 80 750 Loop Gain and Phase vs. Output Capacitor VIN = 3.6V IOUT = 0.3A 100 Efficiency (%) 300 Output Current (A) IOUT (mA) 6 150 -180 -225 1000 Frequency (kHz) 1152.2003.01.0.9 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Typical Characteristics No Load Input Current vs. Temperature VCC = VP VCC = 5.5V VCC = 5.0V Operating Current (A) Input Current (mA) 12 Non-Switching IQ vs. Temperature FB = 0V, VP = VCC 10 8 6 VCC = 4.2V 4 VCC = 3.6V VCC = 2.7V 2 0 -20 -5 10 25 40 55 70 85 200 190 180 VCC = 5.5V VCC = 5.0V 170 160 150 140 130 VCC = 4.2V VCC = 2.7V 120 110 100 -20 -5 10 25 VCC = 3.6V 40 55 70 85 Temperature (C) Temperature (C) Switching Waveform Transient Response VOUT 50mV/div V(LX) 2V/div Inductor Current 500mA/div IL 500mA/div VIN=3.6V VOUT=1.5V IOUT=1.2A VIN=3.6V VOUT=1.5V ILOAD=0.25 to 1.2A 500nsec/div 20s/div Output Ripple 1.5V, No Load Output Ripple 1.5V, 1A Load VOUT 5mV/div BW=20MHz VOUT 5mV/div BW=20MHz VIN=3.6V VOUT=1.5V IOUT=0A VIN=3.6V VOUT=1.5V IOUT=1A LX 2V/div LX 2V/div 500nsec/div 1152.2003.01.0.9 500nsec/div 7 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Typical Characteristics Output Ripple 3.3V, No Load VOUT 5mV/div BW=20MHz VOUT 5mV/div BW=20MHz VIN=5.0V VOUT=3.3V IOUT=0A VIN=5.0V VOUT=3.3V IOUT=1A LX 2V/div LX 2V/div 500nsec/div 8 Output Ripple 3.3V, 1A Load 500nsec/div 1152.2003.01.0.9 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Functional Block Diagram VCC VP= 2.7V- 5.5V 1.0V REF FB OP. AMP CMP DH LOGIC LX OSC DL Temp. Sensing Power Good SGND POK Applications Information 850 kHz 1 Amp DC-DC Synchronous Buck Converter Control Loop The AAT1152 is a peak current mode buck converter. The inner, wide bandwidth loop controls the peak current of the output inductor. The output inductor current is sensed through the P-Channel MOSFET (high side) and is also used for short circuit and overload protection. A fixed slope compensation signal is added to the sensed current to maintain stability. The loop appears as a voltage programmed current source in parallel with the output capacitor. The voltage error amplifier output programs the current loop for the necessary inductor current to 1152.2003.01.0.9 EN PGND force a constant output voltage for all load and line conditions. The feedback resistive divider is internal, dividing the output voltage to the error amplifier reference voltage of 1.0V. The error amplifier does not have a large DC gain typical of most error amplifiers. This eliminates the need for external compensation components while still providing sufficient DC loop gain for load regulation. The crossover frequency and phase margin are set by the output capacitor value only. Soft-Start/Enable Soft start increases the inductor current limit point in discrete steps when the input voltage or enable input is applied. It limits the current surge seen at the input and eliminates output voltage overshoot. The enable input, when pulled low, forces the AAT1152 into a low power non-switching state. The total input current during shutdown is less that 1A. 9 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Enable 2V/div VOUT 1V/div IL 0.5A/div VIN=3.6V VOUT=1.5V IL=1A 200sec/div Figure 1: Inrush Limit Power and Signal Source Current Limit and Over-temperature protection Separate small signal ground and power supply pins isolate the internal control circuitry from the noise associated with the output MOSFET switching. The low pass filter R1 and C3 in schematic figures 3 and 4 filters the noise associated with the power switching. For overload conditions the peak input current is limited. Figure 2 displays the VI current limit characteristics. As load impedance decreases and the output voltage falls closer to zero, more power is dissipated internally, raising the device temperature. Thermal protection completely disables switching when internal dissipation becomes excessive, protecting the device from damage. The junction over-temperature threshold is 140C with 15C of hysteresis. Current Limit Characteristic 3.5 VCC =VP = 5.0V VO = 3.3V Figure 4 schematic 3 VOUT (V) 2.5 2 1.5 VCC =VP =3.6V VO = 1.5V Figure 3 schematic 1 0.5 0 0 0.5 1 1.5 2 2.5 IOUT (A) Figure 2. 10 1152.2003.01.0.9 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Power Good The AAT 1152 features an integrated Power Good (POK) comparator and open-drain output signal. The POK pin goes low when the converter's output is 12% or more below its nominal regulation voltage or when the device is in shutdown. Connect a pull-up resistor from POK to the converter's input or output. Typical resistor pull-up values range from 100k to 10k. Inductor The output inductor is selected to limit the ripple current to some predetermined value, typically 2040% of the full load current at the maximum input voltage. Manufacturer's specifications list both the inductor DC current rating, which is a thermal limitation, and the peak current rating, which is determined by the saturation characteristics. The inductor should not show any appreciable saturation under all normal load conditions. During over load and short circuit conditions, the average current in the inductor can meet or exceed the ILIMIT point of the AAT1152 without effecting the converter performance. Some inductors may have sufficient peak and average current ratings yet result in excessive losses due to a high DCR. Always consider the losses associated with the DCR and its effect on the total converter efficiency when selecting an inductor. For a 1 Amp load and the ripple set to 30% at the maximum input voltage, the maximum peak to peak ripple current is 300 mA. The inductance value required is 3.9H. L= V VOUT 1 - OUT IO k F VIN L= 1.5V 1.5V 11.0A 0.3 830kHz 4.2V L = 3.9H 1152.2003.01.0.9 The factor "k" is the fraction of full load selected for the ripple current at the maximum input voltage. The corresponding inductor rms current is: IRMS = 2 I2 Io = 1.0A I + o 12 I is the peak to peak ripple current which is fixed by the inductor selection above. For a peak to peak current of 30% of the full load current the peak current at full load will be 115% of the full load. The 4.1H inductor selected from the Sumida CDRH5D18 series has a 57 m DCR and a 1.95 Amp DC current rating. At full load the inductor DC loss is 57mW which amounts to a 3.8% loss in efficiency. Input Capacitor The primary function of the input capacitor is to provide a low impedance loop for the edges of pulsed current drawn by the AAT1152. A low ESR/ESL ceramic capacitor is ideal for this function. To minimize the stray inductance the capacitor should be placed as close as possible to the IC. This keeps the high frequency content of the input current localized, minimizing radiated and conducted EMI while facilitating optimum performance of the AAT1152. Ceramic X5R or X7R capacitors are ideal for this function. The size required will vary depending on the load, output voltage and input voltage source impedance characteristics. A typical value is around 10F. The input capacitor RMS current varies with the input voltage and the output voltage. The equation for the maximum RMS current in the input capacitor is: IRMS = IO VO VO 1VIN VIN The input capacitor RMS ripple current reaches a maximum when VIN is two times the output voltage where it is approximately one half of the load current. Losses associated with the input ceramic capacitor are typically minimal and not an issue. The proper placement of the input capacitor can be seen in the reference design layout in figures 5 and 6. 11 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter R5 100k U1 AAT1152-1.0 Vin+ 3.3V R1 100 R2 C1 10F Pok 100k C3 0.1F EN Vp FB Vcc Pok EN LX Sgnd Pgnd R3 2.55k 1% Vo+ 1.25V1A R4 10k 1% LX L1 2.7H C2 100F VC1 Murata 10F 6.3V X5R GRM42-6X 5R106K6.3 C2 MuRata 100F 6.3V GRM43-2 X5R 107M 100F 6.3V L1 Sumida CDRH4D28-2R 7H Figure 3: 3.3V to 1.25V converter Output Capacitor Since there are no external compensation components, the output capacitor has a strong effect on loop stability. Larger output capacitance will reduce the crossover frequency with greater phase margin. For the 1.5V 1A design using the 4.1 H inductor, a 47F capacitor provides a stable loop with 35 degrees of phase margin at a crossover frequency of 100 kHz. Doubling the capacitance to 100F reduces the crossover frequency to half while increasing the phase margin to 60 degrees. In addition to assisting stability, the output capacitor limits the output ripple and provides holdup during large load transitions. A 100F X5R or X7R ceramic capacitor provides sufficient bulk capacitance to 12 stabilize the output during large load transitions and has ESR and ESL characteristics necessary for low output ripple. The output capacitor rms ripple current is given by: IRMS = 1 2 3 (VOUT + VFWD) (VIN - VOUT) L F VIN For a ceramic capacitor the dissipation due to the RMS current of the capacitor is not a concern. Tantalum capacitors, with sufficiently low ESR to meet output voltage ripple requirements, also have an RMS current rating much greater than that actually seen in this application. 1152.2003.01.0.9 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter R5 100k U1 AAT1152-1.5 Vin+ 2.7V-5.5V R1 100 EN R2 100k C1 10F Pok Vp FB Vcc Pok EN LX L1 4.1H LX Sgnd Pgnd C3 0.1F Vo+ 1.5V 1A C2 100F VC1 Murata 10F 6.3V X5R GRM42-6X5R106K6.3 C2 MuRata 100F 6.3V GRM43-2 X5R 107M 100F 6.3V L1 Sumida CDRH5D 18-4R 1H 1.5V Efficiency vs. IOUT 100 2.7V Efficiency (%) 80 60 4.2V 40 3.6V 20 0 10 100 1000 Iout (mA) Figure 4: Lithium-Ion to 1.5V Output Converter Figure 5: AAT1152 Layout Top Layer 1152.2003.01.0.9 Figure 6: AAT1152 Layout Bottom Layer 13 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Adjustable Output Layout Considerations For applications requiring an output other than the fixed outputs available, the 1V version can be programmed externally. Resistors R3 and R4 of figure 3 force the output to regulate higher than 1 Volt. R4 should be 100 times less than the internal 1 MegOhm resistance of the FB pin. Once R4 is selected R3 can be calculated. For a 1.25V output with R4 set to 10.0k, R3 is 2.55k. Figures 5 and 6 display the suggested PCB layout for the AAT1152. The most critical aspect of the layout is the placement of the input capacitor C1. For proper operation C1 must be placed as close as possible to the AAT1152. R3 = (VO - 1) R4 = 0.25 10.0k = 2.55k PLOSS = Thermal Calculations There are two types of losses associated with the AAT1152 output switching MOSFET, switching losses and conduction losses. The conduction losses are associated with the Rds(on) characteristics of the output switching device. At full load, assuming continuous conduction mode (CCM), a simplified form of the total losses is: IO2 (RDSON(H) VO + RDSON(L) (VIN - VO)) + tsw F IO VIN + IQ VIN VIN Once the total losses have been determined the junction temperature can be derived from the JA for the MSOP-8 package. Design Example Specifications IOUT = 1.0A IRIPPLE = 30% of full load at max VIN VOUT = 1.5V VIN = 2.7 - 4.2 V (3.6V nominal) Fs = 830 kHz Maximum Input Capacitor Ripple: IRMS = IO VO VO IO 1= = 0.5ARMS VINMAX VINMAX 2 P = ESRCOUT IRMS2 = 5m 0.52 A = 1.25mW 14 1152.2003.01.0.9 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Inductor Selection: L= V VOUT 1.5V 1.5V 1 - OUT = 1= 3.9H IO k F VIN 1.0A 0.3 830kHz 4.2V Select Sumida inductor CDRH5D18 4.1H 57m 2.0 mm height. I = 1.5V VO V 1.5V 1- O = 1= 280mA L F VIN 4.1H 830kHz 4.2V IPK = IOUT + I = 1.0A + 0.14A = 1.14A 2 P = IO2 DCR =57mW Output Capacitor Dissipation: IRMS = VOUT (VIN - VOUT) 1.5V (4.2V - 1.5V) 1 1 = =82mARMS L F VIN 2 3 2 3 4.1H 830kHz 4.2V PESR = ESRCOUT IRMS2 = 5m .0822 A = 33W AAT1152 Dissipation: P= = IO2 * (RDSON(H) * VO + RDSON(L) * (VIN -VO)) VIN (0.14 * 1.5V + 0.145 * (3.6V - 1.5V)) 3.6V + (tsw * F * IO + IQ) * VIN + (20nsec * 830kHz * 1.0A + 0.3mA) * 3.6V = 0.203W TJ(MAX) = TAMB + JA * PLOSS = 85C + 150C/W * 0.203W = 115C 1152.2003.01.0.9 15 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Table 1: Surface Mount Inductors Manufacturer Part Number Value Max DC Current DCR TaiyoYuden Toko Sumida Sumida MuRata MuRata NPO5DB4R7M A914BYW-3R5M-D52LC CDRH5D28-4R2 CDRH5D18-4R1 LQH55DN4R7M03 LQH66SN4R7M03 4.7H 3.5H 4.2H 4.1H 4.7H 4.7H 1.4A 1.34A 2.2A 1.95A 2.7A 2.2A .038 .073 .031 .057 .041 .025 Size (mm) LxWxH 5.9 x 6.1 x 2.8 5.0 x 5.0 x 2.0 5.7 x 5.7 x 3.0 5.7 x 5.7 x 2.0 5.0 x 5.0 x 4.7 6.3 x 6.3 x 4.7 Type Shielded Shielded Shielded Shielded Non-shielded Shielded Table 2: Surface Mount Capacitors 16 Manufacturer Part Number Value Voltage Temp. Co. Case TDK MuRata MuRata MuRata MuRata C4532X5ROJ107M GRM43-2 X5R 107M 6.3 GRM43-2 X5R 476K 6.3 GRM40 X5R 106K 6.3 GRM42-6 X5R 106K 6.3 100F 100F 47F 10F 10F 6.3V 6.3V 6.3V 6.3V 6.3V X5R X5R X5R X5R X5R 1812 1812 1812 0805 1206 1152.2003.01.0.9 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter Ordering Information Output Voltage Package Marking Part Number (Tape and Reel) 1.0V MSOP-8 AAT1152IKS-1.0-T1 1.1V MSOP-8 AAT1152IKS-1.1-T1 1.2V MSOP-8 AAT1152IKS-1.2-T1 1.5V MSOP-8 AAT1152IKS-1.5-T1 1.8V MSOP-8 AAT1152IKS-1.8-T1 2.0V MSOP-8 AAT1152IKS-2.0-T1 2.5V MSOP-8 AAT1152IKS-2.5-T1 3.0V MSOP-8 AAT1152IKS-3.0-T1 3.3V MSOP-8 AAT1152IKS-3.3-T1 Package Information MSOP-8 4 4 4.90 0.10 3.00 0.10 1.95 BSC 0.95 REF 0.60 0.20 PIN 1 3.00 0.10 0.85 0.10 0.95 0.15 10 5 GAUGE PLANE 0.254 BSC 0.155 0.075 0.075 0.075 0.65 BSC 0.30 0.08 All dimensions in millimeters. 1152.2003.01.0.9 17 AAT1152 850kHz 1A Synchronous Buck DC/DC Converter AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech's standard warranty. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. Advanced Analogic Technologies, Inc. 830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 18 1152.2003.01.0.9