LTC6655 0.25ppm Noise, Low Drift Precision Buffered Reference Family Features n n n n n n n n n n n n Description Low Noise: 0.25ppmP-P (0.1Hz to 10Hz) 625nVP-P for the LTC6655-2.5 Low Drift: 2ppm/C Max High Accuracy: 0.025% Max Fully Specified from -40C to 125C 100% Tested at -40C, 25C and 125C Load Regulation: <10ppm/mA Sinks and Sources Current: 5mA Low Dropout: 500mV Maximum Supply Voltage: 13.2V Low Power Shutdown: <20A Max Available Output Voltages: 1.25V, 2.048V, 2.5V, 3V, 3.3V, 4.096V, 5V Available in an 8-Lead MSOP Package Applications n n n n n n n n Instrumentation and Test Equipment High Resolution Data Acquisition Systems Weigh Scales Precision Battery Monitors High Temperature Applications Precision Regulators Medical Equipment High Output Current Precision Reference The LTC(R)6655 is a complete family of precision bandgap voltage references, offering exceptional noise and drift performance. This low noise and drift is ideally suited for the high resolution measurements required by instrumentation and test equipment. In addition, the LTC6655 is fully specified over the temperature range of -40C to 125C, ensuring its suitability for demanding automotive and industrial applications. Advanced curvature compensation allows this bandgap reference to achieve a drift of less than 2ppm/C with a predictable temperature characteristic and an output voltage accurate to 0.025%, reducing or eliminating the need for calibration. The LTC6655 can be powered from as little as 500mV above the output voltage to as much as 13.2V. Superior load regulation with source and sink capability, coupled with exceptional line rejection, ensures consistent performance over a wide range of operating conditions. A shutdown mode is provided for low power applications. Available in a small MSOP package, the LTC6655 family of references is an excellent choice for demanding precision applications. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical Application Low Frequency 0.1Hz to 10Hz Noise (LTC6655-2.5) Basic Connection LTC6655-2.5 3V < VIN 13.2V CIN 0.1F VIN VOUT_F SHDN VOUT_S GND VOUT COUT 10F 500nV/DIV 6655 TA01a 1s/DIV 6655 TA01b 6655fa LTC6655 Absolute Maximum Ratings (Note 1) Pin Configuration Input Voltage VIN to GND........................................... -0.3V to 13.2V SHDN to GND............................ -0.3V to (VIN + 0.3V) Output Voltage: VOUT_F....................................... -0.3V to (VIN + 0.3V) VOUT_S...................................................... -0.3V to 6V Output Short-Circuit Duration....................... Indefinite Operating Temperature Range (Note 2).. -40C to 125C Storage Temperature Range (Note 2)...... -65C to 150C Lead Temperature Range (Soldering, 10 sec) (Note 3).................................................................. 300C TOP VIEW SHDN VIN GND* GND 1 2 3 4 8 7 6 5 GND* VOUT_F VOUT_S GND* MS8 PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 150C, JA = 300C/W *CONNECT PINS TO DEVICE GND (PIN 4) Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LTC6655BHMS8-1.25#PBF LTC6655BHMS8-1.25#TRPBF LTFDG 8-Lead Plastic MSOP -40C to 125C LTC6655CHMS8-1.25#PBF LTC6655CHMS8-1.25#TRPBF LTFDG 8-Lead Plastic MSOP -40C to 125C LTC6655BHMS8-2.048#PBF LTC6655BHMS8-2.048#TRPBF LTFDH 8-Lead Plastic MSOP -40C to 125C LTC6655CHMS8-2.048#PBF LTC6655CHMS8-2.048#TRPBF LTFDH 8-Lead Plastic MSOP -40C to 125C LTC6655BHMS8-2.5#PBF LTC6655BHMS8-2.5#TRPBF LTFCY 8-Lead Plastic MSOP -40C to 125C LTC6655CHMS8-2.5#PBF LTC6655CHMS8-2.5#TRPBF LTFCY 8-Lead Plastic MSOP -40C to 125C LTC6655BHMS8-3#PBF LTC6655BHMS8-3#TRPBF LTFDJ 8-Lead Plastic MSOP -40C to 125C LTC6655CHMS8-3#PBF LTC6655CHMS8-3#TRPBF LTFDJ 8-Lead Plastic MSOP -40C to 125C LTC6655BHMS8-3.3#PBF LTC6655BHMS8-3.3#TRPBF LTFDK 8-Lead Plastic MSOP -40C to 125C LTC6655CHMS8-3.3#PBF LTC6655CHMS8-3.3#TRPBF LTFDK 8-Lead Plastic MSOP -40C to 125C LTC6655BHMS8-4.096#PBF LTC6655BHMS8-4.096#TRPBF LTFDM 8-Lead Plastic MSOP -40C to 125C LTC6655CHMS8-4.096#PBF LTC6655CHMS8-4.096#TRPBF LTFDM 8-Lead Plastic MSOP -40C to 125C LTC6655BHMS8-5#PBF LTC6655BHMS8-5#TRPBF LTFDN 8-Lead Plastic MSOP -40C to 125C LTC6655CHMS8-5#PBF LTC6655CHMS8-5#TRPBF LTFDN 8-Lead Plastic MSOP -40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 6655fa LTC6655 AVAILABLE OPTIONS OUTPUT VOLTAGE INITIAL ACCURACY TEMPERATURE COEFFICIENT PART NUMBER 1.250 0.025% 0.05% 2ppm/C 5ppm/C LTC6655BHMS8-1.25 LTC6655CHMS8-1.25 2.048 0.025% 0.05% 2ppm/C 5ppm/C LTC6655BHMS8-2.048 LTC6655CHMS8-2.048 2.500 0.025% 0.05% 2ppm/C 5ppm/C LTC6655BHMS8-2.5 LTC6655CHMS8-2.5 3.000 0.025% 0.05% 2ppm/C 5ppm/C LTC6655BHMS8-3.0 LTC6655CHMS8-3.0 3.300 0.025% 0.05% 2ppm/C 5ppm/C LTC6655BHMS8-3.3 LTC6655CHMS8-3.3 4.096 0.025% 0.05% 2ppm/C 5ppm/C LTC6655BHMS8-4.096 LTC6655CHMS8-4.096 5.000 0.025% 0.05% 2ppm/C 5ppm/C LTC6655BHMS8-5 LTC6655CHMS8-5 See Order Information section for complete part number listing. Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VOUT + 0.5V, VOUT_S connected to VOUT_F, unless otherwise noted. PARAMETER CONDITIONS Output Voltage LTC6655B LTC6655C Output Voltage Temperature Coefficient (Note 4) LTC6655B LTC6655C Line Regulation VOUT + 0.5V VIN 13.2V, SHDN = VIN MIN TYP -0.025 -0.05 l l ISOURCE = 5mA 5 25 40 ppm/V ppm/V 15 ppm/mA ppm/mA 30 ppm/mA ppm/mA 3 10 LTC6655-1.25, LTC6655-2.048, LTC6655-2.5 ISOURCE = 5mA, VOUT Error 0.1% l LTC6655-3, LTC6655-3.3, LTC6655-4.096, LTC6655-5 ISOURCE = 5mA, VOUT Error 0.1% IOUT = 0mA, VOUT Error 0.1% l VOUT + 0.5 l VOUT + 0.2 Output Short-Circuit Current Short VOUT to GND Short VOUT to VIN Shutdown Pin (SHDN) Logic High Input Voltage Logic High Input Current, SHDN = 2V l l Logic Low Input Voltage Logic Low Input Current, SHDN = 0.8V l l Supply Current Shutdown Current 3 13.2 V 13.2 13.2 V V 20 20 2.0 mA mA 12 V A 0.8 15 V A l 7 7.5 mA mA l 20 A 5 No Load SHDN Tied to GND % % ppm/C ppm/C l Operating Voltage (Note 6) 0.025 0.05 2 5 l ISINK = 5mA UNITS 1 2.5 l Load Regulation (Note 5) MAX 6655fa LTC6655 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VOUT + 0.5V, VOUT_S connected to VOUT_F, unless otherwise noted. PARAMETER CONDITIONS Output Voltage Noise (Note 7) 0.1Hz f 10Hz 10Hz f 1kHz 0.25 0.67 ppmP-P ppmRMS Turn-On Time 0.1% Settling, COUT = 2.7F 400 s 60 ppm/kHr 30 35 60 ppm ppm ppm Long-Term Drift of Output Voltage (Note 8) Hysteresis (Note 9) T = -0C to 70C T = -40C to 85C T = -40C to 125C Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: Precision may be affected if the parts are stored outside of the specified temperature range. Large temperature changes may cause changes in device performance due to thermal hysteresis. For best performance, extreme temperatures should be avoided whenever possible. Note 3: The stated temperature is typical for soldering of the leads during manual rework. For detailed IR reflow recommendations, refer to the Applications Information section. Note 4: Temperature coefficient is measured by dividing the maximum change in output voltage by the specified temperature range. Note 5: Load regulation is measured on a pulse basis from no load to the specified load current. Load current does not include the 2mA sense current. Output changes due to die temperature change must be taken into account separately. Note 6: Excludes load regulation errors. Minimum supply for the LTC66551.25, LTC6655-2.048 and LTC6655-2.5 is set by internal circuitry supply requirements, regardless of load condition. Minimum supply for the LTC6655-3, LTC6655-3.3, LTC6655-4.096 and LTC6655-5 is specified by load current. Note 7: Peak-to-peak noise is measured with a 2-pole highpass filter at 0.1Hz and 3-pole lowpass filter at 10Hz. The unit is enclosed in a still-air environment to eliminate thermocouple effects on the leads, and the test time is 10 seconds. Due to the statistical nature of noise, repeating MIN TYP MAX UNITS noise measurements will yield larger and smaller peak values in a given measurement interval. By repeating the measurement for 1000 intervals, each 10 seconds long, it is shown that there are time intervals during which the noise is higher than in a typical single interval, as predicted by statistical theory. In general, typical values are considered to be those for which at least 50% of the units may be expected to perform similarly or better. For the 1000 interval test, a typical unit will exhibit noise that is less than the typical value listed in the Electrical Characteristics table in more than 50% of its measurement intervals. See Application Note 124 for noise testing details. RMS noise is measured with a spectrum analyzer in a shielded environment. Note 8: Long-term stability typically has a logarithmic characteristic and therefore, changes after 1000 hours tend to be much smaller than before that time. Total drift in the second thousand hours is normally less than one-third that of the first thousand hours with a continuing trend toward reduced drift with time. Long-term stability is also affected by differential stresses between the IC and the board material created during board assembly. Note 9: Hysteresis in output voltage is created by mechanical stress that differs depending on whether the IC was previously at a higher or lower temperature. Output voltage is always measured at 25C, but the IC is cycled to the hot or cold temperature limit before successive measurements. Hysteresis is roughly proportional to the square of the temperature change. For instruments that are stored at well controlled temperatures (within 20 or 30 degrees of operational temperature), hysteresis is usually not a significant error source. 6655fa LTC6655 Typical Performance Characteristics Characteristic curves are similar for most voltage options of the LTC6655. Curves from the LTC6655-1.25, LTC6655-2.5 and the LTC6655-5 represent the range of performance across the entire family of references. Characteristic curves for other output voltages fall between these curves and can be estimated based on their voltage output. 1.25V Low Frequency 0.1Hz to 10Hz Noise 1.25V Output Voltage Temperature Drift 200nV/ DIV 1s/DIV 6655 G01 1.25V Load Regulation (Sourcing) 20 3 TYPICAL UNITS OUTPUT VOLTAGE CHANGE (ppm) OUTPUT VOLTAGE (V) 1.2504 1.2502 1.2500 1.2498 1.2496 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125C 25C -40C 10 0 -10 -20 -30 -40 0.001 125 0.01 0.1 1 OUTPUT CURRENT (mA) 6655 G03 6655 G02 1.25V Output Voltage Noise Spectrum 1.25V Load Regulation (Sinking) 160 35 120 80 40 IOUT 30 0.01 0.1 1 OUTPUT CURRENT (mA) 20 10 2.7F 10F 100F 0.1 COUT = 3.3F 1 10 FREQUENCY (kHz) 6655 G04 6655 G07 10 8 6 4 40 30 20 10 2 0 TA = 25C 50 NUMBER OF PARTS SUPPLY CURRENT (A) VOUT 10mV/DIV 1.25V VOUT Distribution 60 125C 25C -40C 12 0mA IOUT -5mA 6655 G06 1000 1.25V Shutdown Supply Current vs Input Voltage 14 200s/DIV 100 200s/DIV 6655 G05 1.25V Sourcing Current with a 3.3F Output Capacitor COUT = 3.3F 0mA VOUT 10mV/DIV 15 0 0.01 10 5mA 25 5 0 0.001 1.25V Sinking Current with a 3.3F Output Capacitor 40 125C 25C -40C NOISE VOLTAGE (nV/Hz) OUTPUT VOLTAGE CHANGE (ppm) 200 10 0 2 8 6 10 4 INPUT VOLTAGE (V) 12 14 6655 G08 0 1.2495 1.2498 1.2500 VOUT (V) 1.2503 1.2505 6655 G09 6655fa LTC6655 Typical Performance Characteristics Characteristic curves are similar for most voltage options of the LTC6655. Curves from the LTC6655-1.25, LTC6655-2.5 and the LTC6655-5 represent the range of performance across the entire family of references. Characteristic curves for other output voltages fall between these curves and can be estimated based on their voltage output. 2.5V Low Frequency 0.1Hz to 10Hz Noise 2.5V Output Voltage Temperature Drift 500nV/ DIV 6655 G10 1s/DIV 2.5V Load Regulation (Sourcing) 10 3 TYPICAL UNITS OUTPUT VOLTAGE CHANGE (ppm) OUTPUT VOLTAGE (V) 2.5010 2.5005 2.5000 2.4995 2.4990 -50 0 50 100 TEMPERATURE (C) 0 -10 -20 -30 -40 125C 25C -40C -50 0.001 150 0.01 0.1 1 OUTPUT CURRENT (mA) 10 6655 G12 6655 G11 2.5V Supply Current vs Input Voltage 2.5V Load Regulation (Sinking) 140 120 100 80 60 40 20 8 14 7 12 6 SUPPLY CURRENT (A) 125C 25C -40C SUPPLY CURRENT (mA) OUTPUT VOLTAGE CHANGE (ppm) 160 5 4 3 2 125C 25C -40C 1 0 -20 0.001 0.01 0.1 1 OUTPUT CURRENT (mA) 0 10 2.5V Shutdown Supply Current vs Input Voltage 0 6655 G13 2.5V Minimum VIN - VOUT Differential (Sourcing) 2 4 6 8 10 INPUT VOLTAGE (V) 12 10 8 6 4 0 14 0 2 4 6 8 10 INPUT VOLTAGE (V) 6655 G14 2.5V Minimum VIN - VOUT Differential (Sinking) 10 125C 25C -40C 2 120 COUT = 2.7F 0.01 0.01 125C 25C -40C 0.1 INPUT - OUTPUT VOLTAGE (V) 1 6655 G16 NOISE VOLTAGE (nVHz) OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) 100 0.1 1 0.1 0.01 -0.15 14 6655 G15 2.5V Output Voltage Noise Spectrum 10 1 12 125C 25C -40C -0.05 0.05 INPUT - OUTPUT VOLTAGE (V) 80 60 COUT = 10F COUT = 100F 40 20 0.15 6655 G17 0 0.01 0.1 1 10 FREQUENCY (kHz) 100 1000 6655 F01 6655fa LTC6655 Typical Performance Characteristics Characteristic curves are similar for most voltage options of the LTC6655. Curves from the LTC6655-1.25, LTC6655-2.5 and the LTC6655-5 represent the range of performance across the entire family of references. Characteristic curves for other output voltages fall between these curves and can be estimated based on their voltage output. 2.5V Temperature Drift Distribution 2.5V VOUT Distribution 90 14 TA = 25C 12 80 70 NUMBER OF PARTS NUMBER OF PARTS 2.5 -40C TO 125C 60 50 40 30 20 2.0 10 VTH_UP VTRIP (V) 100 8 6 0 2.4992 2.4996 2.5000 VOUT (V) 2.5004 0 2.5008 0 0.4 0.8 1.2 1.6 2 2.5V Output Impedance vs Frequency 2 4 80 60 40 COUT = 2.7F COUT = 10F COUT = 100F 10 100 6655 G22 6 8 VIN (V) 10 12 14 6655 G21 2.5V Line Regulation 2.502 COUT = 2.7F COUT = 10F COUT = 100F OUTPUT VOLTAGE (V) 100 OUTPUT IMPEDENCE () POWER SUPPLY REJECTION RATIO (dB) 10 0.1 1 FREQUENCY (kHz) 0.0 2.8 6655 G20 120 0.01 2.4 DRIFT (ppm/C) 2.5V Power Supply Rejection Ratio vs Frequency 0 0.001 VTH_DN 1.0 0.5 6655 G19 20 1.5 4 2 10 2.5V SHDN Input Voltage Thresholds vs VIN 1 0.1 0.01 0.001 0.01 0.1 1 10 FREQUENCY (kHz) 100 1000 6655 G23 2.501 2.500 2.499 2.498 125C 25C -40C 0 2 10 4 6 8 INPUT VOLTAGE (V) 12 14 6655 G24 6655fa LTC6655 Typical Performance Characteristics Characteristic curves are similar for most voltage options of the LTC6655. Curves from the LTC6655-1.25, LTC6655-2.5 and the LTC6655-5 represent the range of performance across the entire family of references. Characteristic curves for other output voltages fall between these curves and can be estimated based on their voltage output. 5V Low Frequency 0.1Hz to 10Hz Noise 5V Output Voltage Temperature Drift 5.0010 5V Load Regulation (Sourcing) 10 OUTPUT VOLTAGE CHANGE (ppm) 3 TYPICAL UNITS OUTPUT VOLTAGE (V) 5.0005 500nV/ DIV 5.0000 4.9995 4.9990 6655 G25 1s/DIV 4.9985 -50 -25 0 25 50 75 TEMPERATURE (C) 100 0 -10 -20 -30 -40 -50 0.01 125 125C 25C -40C 0.1 1 OUTPUT CURRENT (mA) 6655 G26 200 180 5 60 40 20 NOISE VOLTAGE (nV/Hz) 80 4 3 2 125C 25C -40C 1 0 -20 0.01 0.1 1 OUTPUT CURRENT (mA) 0 10 0 2 8 6 10 4 INPUT VOLTAGE (V) 6655 G28 14 140 120 100 80 60 40 20 0 0.01 2.7F 10F 100F 0.1 1 10 FREQUENCY (kHz) 100 1000 6655 G30 5V Minimum VIN-VOUT Differential (Sinking) 10 5V Start-Up Response with a 3.3F Output Capacitor 10 OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) 12 160 6655 G29 5V Minimum VIN-VOUT Differential (Sourcing) 1 0.1 0.01 0.01 5V Output Voltage Noise Spectrum 6 125C 25C -40C SUPPLY CURRENT (mA) OUTPUT VOLTAGE CHANGE (ppm) 100 6655 G27 5V Supply Current vs Input Voltage 5V Load Regulation (Sinking) 10 125C 25C -40C 0.1 INPUT-OUTPUT VOLTAGE (V) 1 6655 G31 VIN 2V/DIV 1 VOUT 2V/DIV 0.1 0.01 -0.3 125C 25C -40C -0.2 -0.1 0 INPUT-OUTPUT VOLTAGE (V) COUT = 3.3F 400s/DIV 6655 G33 0.1 6655 G32 6655fa LTC6655 Pin Functions SHDN (Pin 1): Shutdown Input. This active low input powers down the device to <20A. If left open, an internal pull-up resistor puts the part in normal operation. It is recommended to tie this pin high externally for best performance during normal operation. VOUT_S (Pin 6): VOUT Sense Pin. Connect this pin at the load and route with a wide metal trace to minimize load regulation errors. This pin sinks 2mA. Output error is RTRACE * 2mA, regardless of load current. For load currents <100A, tie directly to VOUT_F pin. VIN (Pin 2): Power Supply. Bypass VIN with a 0.1F, or larger, capacitor to GND. VOUT_F (Pin 7): VOUT Force Pin. This pin sources and sinks current to the load. An output capacitor of 2.7F to 100F is required. GND (Pin 4): Device Ground. This pin is the main ground and must be connected to a noise-free ground plane. GND (Pins 3, 5, 8): Internal Function. Ground these pins. BLOCK DIAGRAM 2 1 VIN SHDN + BANDGAP VOUT_F 7 - VOUT_S 4 GND 6 6655 BD GND 3,5,8 6655fa LTC6655 Applications Information Bypass and Load Capacitors The LTC6655 voltage references require a 0.1F or larger input capacitor located close to the part to improve power supply rejection. An output capacitor with a value between 2.7F and 100F is also required. The output capacitor has a direct effect on the stability, turn-on time and settling behavior. Choose a capacitor with low ESR to insure stability. Resistance in series with the output capacitor (ESR) introduces a zero in the output buffer transfer function and could cause instability. The 2.7F to 100F range includes several types of capacitors that are readily available as through-hole and surface mount components. It is recommended to keep ESR less than or equal to 0.1. Capacitance and ESR are both frequency dependent. At higher frequencies capacitance drops and ESR increases. To insure stable operation the output capacitor should have the required values at 100kHz. In order to achieve the best performance, caution should be used when choosing a capacitor. X7R ceramic capacitors are small, come in appropriate values and are relatively stable over a wide temperature range. However, for a low noise application X7R capacitors may not be suitable since they may exhibit a piezoelectric effect. The mechanical vibrations cause a charge displacement in the ceramic dielectric and the resulting perturbation can look like noise. If X7R capacitors are necessary, a thorough bench evaluation should be completed to verify proper performance. For very low noise applications where every nanovolt counts, film capacitors should be considered for their low noise and lack of piezoelectric effects. Film capacitors such as polyester, polystyrene, polycarbonate, and polypropylene have good temperature stability. Additional care must be taken as polystyrene and polypropylene have an upper temperature limit of 85C to 105C. Above these temperatures, the working voltages need to be derated according to manufacturer's specifications. Another type of film capacitor is polyphenylene sulfide (PPS). These devices work over a wide temperature range, are stable, and have large capacitance values beyond 1F. In general, film capacitors are found in surface mount and leaded packages. Table 1 is a partial list of capacitor companies and some of their available products. In voltage reference applications, film capacitor lifetime is affected by temperature and applied voltage. When polyester capacitors are operated beyond their rated temperatures (some capacitors are not rated for operation above 85C) they need to be derated. Voltage derating is usually accomplished as a ratio of applied voltage to rated voltage limit. Contact specific film capacitor manufacturers to determine exact lifetime and derating information. The lifetime of X7R capacitors is long, especially for reference applications. Capacitor lifetime is degraded by operating near or exceeding the rated voltage, at high temperature, with AC ripple or some combination of these. Most reference applications have AC ripple only during transient events. Table 1. Film Capacitor Companies COMPANY DIELECTRIC AVAILABLE CAPACITANCE TEMPERATURE RANGE TYPE Cornell Dublier Polyester 0.5F to 10F -55C to 125C DME Dearborn Electronics Polyester 0.1F to 12F -55C to 125C 218P, 430P, 431P, 442P, and 410P Tecate Polyester 0.01F to 18F -40C to 105C 901, 914, and 914D Wima Polyester 10F to 22F -55C to 100C MKS 4, MKS 2-XL Vishay Polyester 1000pF to 15F -55C to 125C MKT1820 Vishay Polycarbonate 0.01F to 10F -55C to 100C MKC1862, 632P Dearborn Electronics Polyphenylene Sulfide (PPS) 0.01F to 15F -55C to 125C 820P, 832P, 842P, 860P, and 880P Wima Polyphenylene Sulfide (PPS) 0.01F to 6.8F -55C to 140C SMD-PPS 6655fa 10 LTC6655 Applications Information The choice of output capacitor also affects the bandwidth of the reference circuitry and resultant noise peaking. As shown in Figure 1, the bandwidth is inversely proportional to the value of the output capacitor. 120 NOISE VOLTAGE (nVHz) Noise peaking is related to the phase margin of the output buffer. Higher peaking generally indicates lower phase margin. Other factors affecting noise peaking are temperature, input voltage, and output load current. 80 40 0 0.01 2.5V * -6 3.3 * 10 F = 412s 0.02A The resulting turn-on time is shown in Figure 3. Here the output capacitor is 3.3F and the input capacitor is 0.1F. 1,2 VIN 3V CIN 0.1F 1 10 FREQUENCY (kHz) 100 1000 6655 F01 7 LTC6655-2.5 6 VOUT 100 COUT 3.3F 3,4,5,8 VGEN 0.5V 6655 F02 Figure 2. Transient Load Test Circuit VIN 2V/DIV VOUT 1V/DIV COUT = 3.3F Figure 4 shows the output response to a 500mV step on VIN. The output response to a current step sourcing and sinking is shown in Figures 5 and 6, respectively. Figure 7 shows the output response as the current goes from sourcing to sinking. 0.1 Figure 1. Output Voltage Noise Spectrum COUT ISC For example, the LTC6655-2.5V, with a 3.3F output capacitor and a typical short-circuit current of 20mA, the start-up time would be approximately: COUT = 100F 20 Results for the transient response plots (Figures 3 to 8) were produced with the test circuit shown in Figure 2 unless otherwise indicated. tON = VOUT * COUT = 10F 60 Start-Up and Load Transient Response The turn-on time is slew limited and determined by the short-circuit current, the output capacitor, and output voltage as shown in the equation: COUT = 2.7F 100 200s/DIV 6655 F03 Figure 3. Start-Up Response VIN 3.5V 3V Shutdown Mode The LTC6655 family of references can be shut down by tying the SHDN pin to ground. There is an internal pull-up resistor tied to this pin. If left unconnected this pin rises to VIN and the part is enabled. Due to the low internal pull-up current, it is recommended that the SHDN pin be pulled high externally for normal operation to prevent accidental VOUT 50mV/DIV COUT = 3.3F 400s/DIV 6655 F04 Figure 4. Output Response with a 500mV Step On VIN 6655fa 11 LTC6655 Applications Information shutdown due to system noise or leakage currents. The turn-on/turn-off response due to shutdown is shown in Figure 8. 0mA IOUT -5mA VOUT 10mV/DIV COUT = 3.3F 200s/DIV 6655 F05 Figure 5. Output Response with a 5mA Load Step Sourcing To control shutdown from a low voltage source, a MOSFET can be used as a pull-down device as shown in Figure 9. Note that an external resistor is unnecessary. A MOSFET with a low drain-to-source leakage over the operating temperature range should be chosen to avoid inadvertently pulling down the SHDN pin. A resistor may be added from SHDN to VIN to overcome excessive MOSFET leakage. The SHDN thresholds have some dependency on VIN and temperature as shown in the Typical Performance Characteristics section. Avoid leaving SHDN at a voltage between the thresholds as this will cause an increase in supply current due to shoot-through current. 5mA IOUT 0mA VOUT 10mV/DIV 3V VIN 13.2V COUT = 3.3F 200s/DIV 6655 F06 C1 1F VIN VOUT_F LTC6655-2.5 Figure 6. Output Response with 5mA Load Step Sinking SHDN TO C GND VOUT_S VOUT C2 10F 2N7002 6655 F09 2mA IOUT -2mA Figure 9. Open-Drain Shutdown Circuit Long-Term Drift VOUT 10mV/DIV COUT = 3.3F 200s/DIV 6655 F07 Figure 7. Output Response Showing a Sinking to Sourcing Transition SHDN 2V/DIV Long-term drift cannot be extrapolated from accelerated high temperature testing. This erroneous technique gives drift numbers that are wildly optimistic. The only way long-term drift can be determined is to measure it over the time interval of interest. The LTC6655 long-term drift data was collected on 80 parts that were soldered into printed circuit boards similar to a real world application. The boards were then placed into a constant temperature oven with a TA = 35C, their outputs were scanned regularly and measured with an 8.5 digit DVM. Typical long-term drift is illustrated in Figure 10. VOUT 1V/DIV COUT = 3.3F 1ms/DIV 6655 F08 Figure 8. Shutdown Response with 5mA Source Load 6655fa 12 LTC6655 Applications Information 30 4 TYPICAL UNITS LTC6655-2.5 25 80 NUMBER OF UNITS LONG-TERM DRIFT (ppm) 120 40 0 20 15 10 -40 -80 5 0 500 1500 1000 HOURS 2000 0 -90 -70 -50 -30 -10 10 30 50 70 90 110 DISTRIBUTION (ppm) 2500 6655 F11 6655 F10 Figure 11. Hysteresis Plot -40C to 125C Figure 10. Long-Term Drift 0.14 Hysteresis 0.12 NO LOAD 0.06 0.02 0 0 10 5 15 VIN (V) 6655 F12 Figure 12. LTC6655-2.5 Power Consumption 125 MAXIMUM AMBIENT OPERATING TEMPERATURE (C) The MSOP8 package has a thermal resistance (JA) equal to 300C/W. Under the maximum loaded condition, the increase in die temperature is over 35C. If operated at these conditions with an ambient temperature of 125C, the absolute maximum junction temperature rating of the device would be exceeded. Although the maximum junction temperature is 150C, for best performance it is recommended to not exceed a junction temperature of 125C. The plot in Figure 13 shows the recommended maximum ambient temperature limits for differing VIN and load conditions using a maximum junction temperature of 125C. 0.08 0.04 Power Dissipation Power dissipation for the LTC6655 depends on VIN and load current. Figure 12 illustrates the power consumption versus VIN under a no-load and 5mA load condition at room temperature for the LTC6655-2.5. Other voltage options display similar behavior. 5mA LOAD 0.10 POWER (W) Thermal hysteresis is a measure of change of output voltage as a result of temperature cycling. Figure 11 illustrates the typical hysteresis based on data taken from the LTC6655-2.5. A proprietary design technique minimizes thermal hysteresis. 115 NO LOAD 105 5mA LOAD 95 85 75 65 55 0 3 6 9 VIN (V) 15 12 6655 F13 Figure 13. LTC6655-2.5 Maximum Ambient Operating Temperature 6655fa 13 LTC6655 Applications Information PC Board Layout 7 The LTC6655 reference is a precision device that is factory trimmed to an initial accuracy of 0.025%, as shown in the Typical Performance Characteristic section. The mechanical stress caused by soldering parts to a printed circuit board may cause the output voltage to shift and the temperature coefficient to change. To reduce the effects of stress-related shifts, mount the reference near the short edge of a printed circuit board or in a corner. In addition, slots can be cut into the board on two sides of the device to reduce mechanical stress. A thicker and smaller board is stiffer and less prone to bend. Finally, use stress relief, such as flexible standoffs, when mounting the board. Additional precautions include making sure the solder joints are clean and the board is flux free to avoid leakage paths. A sample PCB layout is shown in Figure 14. + 2 LTC6655-2.5 6 2mA 4 LOAD STAR 6655 F15 MINIMIZE RESISTANCE OF METAL Figure 15. Kelvin Connection for Good Load Regulation output current <100A), VOUT_S should be tied to VOUT_F by the shortest possible path to reduce errors caused by resistance in the sense trace. Careful attention to grounding is also important, especially when sourcing current. The return load current can produce an I * R drop causing poor load regulation. Use a "star" ground connection and minimize the ground to load metal resistance. Although there are several pins that are required to be connected to ground, Pin 4 is the actual ground for return current. Optimal Noise Performance VIN GND The LTC6655 offers extraordinarily low noise for a bandgap reference--only 0.25ppm in 0.1Hz to 10Hz. As a result, system noise performance may be dominated by system design and physical layout. VOUT 6655 F14 Figure 14. Sample PCB Layout Load Regulation To take advantage of the VOUT Kelvin force/sense pins, the VOUT_S pin should be connected separately from the VOUT_F pin as shown in Figure 15. The VOUT_S pin sinks 2mA, which is unusual for a Kelvin connection. However, this is required to achieve the exceptional low noise performance. The I * R drop on the VOUT_S line directly affects load regulation. The VOUT_S trace should be as short and wide as practical to minimize series resistance The VOUT_S trace adds error as RTRACE * 2mA, so a 0.1 trace adds 200V error. The VOUT_F pin is not as important as the VOUT_S pin in this regard. An I * R drop on the VOUT_F pin increases the minimum supply voltage when sourcing current, but does not directly affect load regulation. For light loading of the output (maximum Some care is required to achieve the best possible noise performance. The use of dissimilar metals in component leads and PC board traces creates thermocouples. Variations in thermal resistance, caused by uneven air flow, create differential lead temperatures, thereby causing thermoelectric voltage noise at the output of the reference. Minimizing the number of thermocouples, as well as limiting airflow, can substantially reduce these errors. Additional information can be found in Linear Technology Application Note 82. Position the input and load capacitors close to the part. Although the LTC6655 has a DC PSRR of over 100dB, the power supply should be as stable as possible to guarantee optimal performance. A plot of the 0.1Hz to 10Hz low frequency noise is shown in the Typical Performance Characteristic section. Noise performance can be further improved by wiring several LTC6655s in parallel as shown in the Typical Applications section. With this technique the noise is reduced by N, where N is the number of LTC6655s in parallel. 6655fa 14 LTC6655 Applications Information Noise Specification Noise in any frequency band is a random function based on physical properties such as thermal noise, shot noise, and flicker noise. The most precise way to specify a random error such as noise is in terms of its statistics, for example as an RMS value. This allows for relatively simple maximum error estimation, generally involving assumptions about noise bandwidth and crest factor. Unlike wideband noise, low frequency noise, typically specified in a 0.1Hz to 10Hz band, has traditionally been specified in terms of expected error, illustrated as peak-to-peak error. Low frequency noise is generally measured with an oscilloscope over a 10 second time frame. This is a pragmatic approach, given that it can be difficult to measure noise accurately at low frequencies, and that it can also be difficult to agree on the statistical characteristics of the noise, since flicker noise dominates the spectral density. While practical, a random sampling of 10 second intervals is an inadequate method for representation of low frequency noise, especially for systems where this noise is a dominant limit of system performance. Given the random nature of noise, the output voltage may be observed over many time intervals, each giving different results. Noise specifications that were determined using this method are prone to subjectivity, and will tend toward a mean statistical value, rather than the maximum noise that is likely to be produced by the device in question. Because the majority of voltage reference data sheets express low frequency noise as a typical number, and as it tends to be illustrated with a repeatable plot near the mean of a distribution of peak-to-peak values, the LTC6655 data sheet provides a similarly defined typical specification in order to allow a reasonable direct comparison against similar products. Data produced with this method generally suggests that in a series of 10 second output voltage measurements, at least half the observations should have a peak-to-peak value that is below this number. For example, the LTC6655-2.5 measures less than 0.25ppmP-P in at least 50% of the 10 second observations. As mentioned above, the statistical distribution of noise is such that if observed for long periods of time, the peak error in output voltage due to noise may be much larger than that observed in a smaller interval. The likely maximum error due to noise is often estimated using the RMS value, multiplied by an estimated crest factor, assumed to be in the range of 6 to 8.4. This maximum possible value will only be observed if the output voltage is measured for very long periods of time. Therefore, in addition to the common method, a more thorough approach to measuring noise has been used for the LTC6655 (described in detail in Linear Technology's AN124) that allows more information to be obtained from the result. In particular, this method characterizes the noise over a significantly greater length of time, resulting in a more complete description of low frequency noise. The peak-to-peak voltage is measured for 10 second intervals over hundreds of intervals. In addition, an electronic peak-detect circuit stores an objective value for each interval. The results are then summarized in terms of the fraction of measurement intervals for which observed noise is below a specified level. For example, the LTC6655-2.5 measures less than 0.27ppmP-P in 80% of the measurement intervals, and less than 0.295ppmP-P in 95% of observation intervals. This statistical variation in noise is illustrated in Table 2 and Figure 17. The test circuit is shown in Figure 16. Table 2 50% 60% 70% 80% 90% Low Frequency Noise (ppmP-P) 0.246 0.252 0.260 0.268 0.292 This method of testing low frequency noise is superior to more common methods. The results yield a comprehensive statistical description, rather than a single observation. In addition, the direct measurement of output voltage over time gives an actual representation of peak noise, rather than an estimate based on statistical assumptions such as crest factor. Additional information can be derived from a measurement of low frequency noise spectral density, as shown in Figure 18. It should be noted from Figure 18 that the LTC6655 has not only a low wideband noise, but an exceptionally low flicker noise corner of 1Hz! This substantially reduces low frequency noise, as well as long-term variation in peak noise. 6655fa 15 15 RST -15 RST LTC6655 2.5V 10k 10k 1F P P 1F F S 1F REFERENCE UNDER TEST SD IN 9V 1300F 1F 4 **1.2k T 100k 0.005F + -15V 4.7k 4.7k A1 LT1012 100k - + 0.005F A6 1/4 LT1058 - + A5 1/4 LT1058 - SHIELD 100k A = 10 LOW NOISE PRE-AMP 100k + 16 0.1F - A8 1/4 LT1058 + - A7 1/4 LT1058 -15V Q2 1k - DVM + 1k 5 A2 LT1097 0.022F SEE APPENDIX C FOR POWER, SHIELDING AND GROUNDING SCHEME = 1/4 LTC202 = 2N4393 = 1N4148 RST = Q2 + 10k* 1M* RC2 +V 10k B2 +15 BAT-85 BAT-85 RESET PULSE GENERATOR +15 = POLYPROPELENE P 10k 330F 16V 330F 16V + 6655 F16 A4 330F OUTPUT CAPACITORS = <200nA LEAKAGE AT 1VDC AT 25C = TANTALUM,WET SLUG ILEAK < 5nA SEE TEXT/APPENDIX B FROM OSCILLOSCOPE SWEEP GATE OUTPUT VIA ISOLATION PULSE TRANSFORMER 10k + A4 LT1012 - ROOT-SUM-SQUARE CORRECTION SEE TEXT T A2 0.1F 124k* 0.1F 0.1F 100* OUT 124k* 74C221 C2 CLR2 +15 0.22F 330F 16V 330F 16V IN 330* +15 - A3 LT1012 + A = 100 AND 0.1Hz TO 10Hz FILTER Q1, Q2 = THERMALLY MATED 2SK369 (MATCH VGS 10%) OR LSK389 DUAL THERMALLY LAG SEE TEXT TO OSCILLOSCOPE INPUT VIA ISOLATED PROBE, 1V/DIV = 1V/DIV, REFERRED TO INPUT, SWEEP = 1s/DIV 10* 100k* * = 1% METAL FILM ** = 1% WIREWOUND, ULTRONIX105A O TO 1V = O TO 1V SHIELDED CAN - INPUT + - 1F 2k Figure 16. Detailed Noise Test Circuitry. See Application Note 124. - PEAK + PEAK + Q1 900* 15V 200* 750* 450* 1k* PEAK TO PEAK NOISE DETECTOR AC LINE GROUND 1F -15V Q3 2N2907 10k 1N4697 10V + 0.15F + 15V LTC6655 Applications Information 6655fa LTC6655 Applications Information shown in Figure 19, the output voltage shifts. After the device expands, due to the heat, and then contracts, the stresses on the die have changed position. This shift is similar, but more extreme than thermal hysteresis. 35 NUMBER OF OBSERVATIONS 30 25 20 Experimental results of IR reflow shift are shown below in Figure 20. These results show only shift due to reflow and not mechanical stress. 15 10 5 300 750 850 650 550 PEAK-TO-PEAK NOISE (nV) 380s 950 6655 F17 Figure 17. Low Frequency Noise Histogram of the LTC6655-2.5 200 TP = 260C TL = 217C TS(MAX) = 200C TS = 190C 225 TEMPERATURE (C) 0 450 150 tP 30s T = 150C tL 130s RAMP TO 150C 75 40s 160 120s 0 120 0 2 6 4 MINUTES 8 10 6655 F19 80 Figure 19. Lead-Free Reflow Profile 40 0 8 0.1 1 10 FREQUENCY (Hz) 100 6655 F18 Figure 18. LTC6655-2.5 Low Frequency Noise Spectrum IR Reflow Shift The mechanical stress of soldering a part to a board can cause the output voltage to shift. Moreover, the heat of an IR reflow or convection soldering oven can also cause the output voltage to shift. The materials that make up a semiconductor device and its package have different rates of expansion and contraction. After a part undergoes the extreme heat of a lead-free IR reflow profile, like the one 7 6 NUMBER OF UNITS NOISE VOLTAGE (nV/Hz) RAMP DOWN 5 4 3 2 1 0 -0.029 -0.023 -0.017 -0.011 -0.005 OUTPUT VOLTAGE SHIFT DUE TO IR REFLOW (%) 6655 F20 Figure 20. Output Voltage Shift Due to IR Reflow 6655fa 17 LTC6655 Typical Applications Extended Supply Range Reference Extended Supply Range Reference 4V TO 30V R1 BZX84C12 C1 0.1F 6V TO 80V R1 R2 100k 4.7k LTC6655-2.5 VIN VOUT_F SHDN VOUT_S VOUT C1 0.1F BZX84C12 C2 10F GND ON SEMI MMBT5551 0.1F VIN SHDN VOUT_F LTC6655-2.5 VOUT_S GND 6655 TA02 VOUT C2 10F 6655 TA03 Boosted Output Current 4V TO 13.2V Boosted Output Current LTC6655-2.5 SHDN VOUT_F VIN C1 0.1F GND Q1 2N2222 VOUT + 1.8V TO 13.2V VOUT VOUT_S C1 1F C2 4.7F 6655 TA05 C3 0.1F IMAX SET BY NPN R1 220 R2 1k C4 1F 2N2905 35mA MAX VIN SHDN VOUT_F LTC6655-2.5 VOUT_S GND VOUT C2 10F 6655 TA04 Output Voltage Boost VIN VOUT + 0.5V TO 13.2V VIN C1 1F VOUT_F LTC6655-2.5 SHDN VOUT_S GND VOUT = VOLTAGE OPTION + 0.002 * R THIS EXAMPLE USES 2.5V AS THE VOLTAGE OPTION C2 10F R VOUT 2.5V TO 4.5V R = 0k to 1k 6655 TA07 FOR R USE A POTENTIOMETER THAT CAN HANDLE 2mA, IS LOW NOISE AND HAS A LOW TEMPERATURE COEFFICIENT Low Noise Precision Voltage Boost Circuit VIN VOUT + 0.5V TO 13.2V C1 1F VIN VOUT_F LTC6655-2.5 SHDN VOUT_S VIN LT1677 + + -- GND R3 5k VOUT = VOLTAGE OPTION * (1 + R1/R2) THIS EXAMPLE USES 2.5V AS THE VOLTAGE OPTION R1 10k C2 10F VOUT 5V RLOAD R2 10k 6655 TA08 FOR R1 AND R2 USE VISHAY TRIMMED RESISTOR ARRAY (VSR144 OR MPM). WITH A PRECISION ARRAY THE MATCHING AND LOW TC WILL HELP PRESERVE LOW DRIFT. R3 = R1||R2 6655fa 18 LTC6655 Typical Applications Low Noise Statistical Averaging Reference eN = eN/N; Where N is the Number of LTC6655s in Parallel LTC6655-2.5 SHDN VOUT_F 3V TO 13.2V VIN C1 0.1F GND R1 32.4 VOUT_S VOUT C2 2.7F C9 4.7F LTC6655-2.5 SHDN VOUT_F VIN C3 0.1F GND R2 32.4 VOUT_S C4 2.7F LTC6655-2.5 SHDN VOUT_F VIN C5 0.1F GND R3 32.4 VOUT_S C6 2.7F LTC6655-2.5 SHDN VOUT_F VIN 6655 TA06a C7 0.1F GND VOUT_S R4 32.4 C8 2.7F Low Frequency Noise (0.1Hz to 10Hz) with Four LTC6655-2.5 in Parallel 200nV/ DIV 320nVP-P 0.1Hz to 10Hz 1s/DIV 6655 TA06b 6655fa 19 LTC6655 Package Description MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660 Rev F) 0.889 p 0.127 (.035 p .005) 5.23 (.206) MIN 3.20 - 3.45 (.126 - .136) 3.00 p 0.102 (.118 p .004) (NOTE 3) 0.65 (.0256) BSC 0.42 p 0.038 (.0165 p .0015) TYP 8 7 6 5 0.52 (.0205) REF RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 p 0.102 (.118 p .004) (NOTE 4) 4.90 p 0.152 (.193 p .006) DETAIL "A" 0o - 6o TYP GAUGE PLANE 0.53 p 0.152 (.021 p .006) DETAIL "A" 1 2 3 4 1.10 (.043) MAX 0.86 (.034) REF 0.18 (.007) SEATING PLANE 0.22 - 0.38 (.009 - .015) TYP 0.65 (.0256) BSC 0.1016 p 0.0508 (.004 p .002) MSOP (MS8) 0307 REV F NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6655fa 20 LTC6655 Revision History REV DATE DESCRIPTION A 02/10 Voltage Options Added (1.250, 2.048, 3.000, 3.300, 4.096, 5.000), Reflected Throughout the Data Sheet PAGE NUMBER 1 to 22 6655fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 21 LTC6655 Typical Application Low Noise Precision 24-Bit Analog-to-Digital Converter Application 2.5k 5V VREF 0.01F LTC2449 10F 0.01F 1nF 50 SDI SCK SDO CS SPI INTERFACE - 1/2 LTC6241 + BUSY EXT fO REF+ REF- 4 2.5k ADCINP GND GND -2.5V MUXOUTP GND GND 3,5,8 - 1/2 LTC6241 + GND 0.1F VREF GND LTC6655 7 VOUT_F 1 6 SHDN VOUT_S VIN 50 ADCINN GND THERMOCOUPLE 1nF MUXOUTN GND RTD 2 VCC CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8 CH9 CH10 CH11 CH12 CH13 CH14 CH15 COM GND 5k 7.5V RREF 400 6655 TA09 Related Parts PART NUMBER DESCRIPTION COMMENTS LT(R)1236 Precision Low Drift Low Noise Reference 0.05% Max, 5ppm/C Max, 1ppm (Peak-to-Peak) Noise LT1460 Micropower Series References 0.075% Max, 10ppm/C Max, 20mA Output Current LT1461 Micropower Series Low Dropout 0.04% Max, 3ppm/C Max, 50mA Output Current LT1790 Micropower Precision Series References 0.05% Max, 10ppm/C Max, 60mA Supply, SOT23 Package LT6650 Micropower Reference with Buffer Amplifier 0.5% Max, 5.6A Supply, SOT23 Package LTC6652 Precision Low Drift Low Noise Reference 0.05% Max, 5ppm/C Max, -40C to 125C, MSOP8 LT6660 Tiny Micropower Series Reference 0.2% Max, 20ppm/C Max, 20mA Output Current, 2mm x 2mm DFN 6655fa 22 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com LT 0210 REV A * PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2009