LT6656 1µA Precision Series Voltage Reference Features Description Low Drift A Grade: 10 ppm/°C Max B Grade: 20 ppm/°C Max n High Accuracy A Grade: 0.05% Max B Grade: 0.1% Max n Ultralow Supply Current: 850nA n High Output Drive Current: 5mA Min n Low Dropout Voltage: 10mV Max n Fully Specified from –40°C to 85°C n Operational from –55°C to 125°C n Wide Supply Range to 18V n Reverse Input/Output Protection n Available Output Voltage Options: 1.25V, 2.048V, 2.5V, 3V, 3.3V, 4.096V and 5V n Thermal Hysteresis: 25ppm n Low Profile (1mm) ThinSOT™ Package The LT®6656 is a small precision voltage reference that draws less than 1µA of supply current and can operate with a supply voltage within 10mV of the output voltage. The LT6656 offers an initial accuracy of 0.05% and temperature drift of 10ppm/°C. The combined low power and precision characteristics are ideal for portable and battery powered instrumentation. n Applications Precision A/D and D/A Converters Portable Gas Monitors n Battery- or Solar-Powered Systems n Precision Regulators n Low Voltage Signal Processing n Micropower Remote Sensing n n The LT6656 can supply up to 5mA of output drive with 65ppm/mA of load regulation, allowing it to be used as the supply voltage and the reference input to a low power ADC. The LT6656 can accept a supply voltage up to 18V and withstand the reversal of the input connections. The LT6656 output is stable with 1µF or larger output capacitance and operates with a wide range of output capacitor ESR. This reference is fully specified for operation from –40°C to 85°C, and is functional over the extreme temperature range of –55°C to 125°C. Low hysteresis and a consistent temperature drift are obtained through advanced design, processing and packaging techniques. The LT6656 is offered in the 6-lead SOT-23 package. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical Application Output Voltage Temperature Drift LT6656-2.5 2.503 Basic Connection 0.1µF 2.502 VOUT 2.5V 1µF 6656 TA01a VOUT (V) 2.51V ≤ VIN ≤ 18V LT6656-2.5 VIN VOUT GND 38 TYPICAL UNITS 2.501 2.500 2.499 2.498 –40 –20 0 20 40 TEMPERATURE (°C) 60 80 6652 TA01b 6656fa LT6656 Absolute Maximum Ratings Pin Configuration (Note 1) Input Voltage............................................................±20V Output Voltage............................................ –0.3V to 20V Output Voltage Above Input Voltage..........................20V Specified Temperature Range Commercial.............................................. 0°C to 70°C Industrial..............................................–40°C to 85°C Operating Temperature Range................ –55°C to 125°C Output Short Circuit Duration .......................... Indefinite Junction Temperature ........................................... 150°C Storage Temperature Range (Note 2)...... –65°C to 150°C Lead Temperature (Soldering, 10 sec.) (Note 3).................................................................. 300°C TOP VIEW GND* 1 6 VOUT GND 2 5 NC NC 3 4 VIN S6 PACKAGE 6-LEAD PLASTIC TSOT-23 TJMAX = 150°C, θJA = 230°C/W *CONNECT PIN TO DEVICE GND (PIN 2) Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LT6656ACS6-1.25#PBF LT6656ACS6-1.25#TRPBF LTFNK 6-Lead Plastic TSOT-23 0°C to 70°C LT6656BCS6-1.25#PBF LT6656BCS6-1.25#TRPBF LTFNK 6-Lead Plastic TSOT-23 0°C to 70°C LT6656AIS6-1.25#PBF LT6656AIS6-1.25#TRPBF LTFNK 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656BIS6-1.25#PBF LT6656BIS6-1.25#TRPBF LTFNK 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656ACS6-2.048#PBF LT6656ACS6-2.048#TRPBF LTFNN 6-Lead Plastic TSOT-23 0°C to 70°C LT6656BCS6-2.048#PBF LT6656BCS6-2.048#TRPBF LTFNN 6-Lead Plastic TSOT-23 0°C to 70°C LT6656AIS6-2.048#PBF LT6656AIS6-2.048#TRPBF LTFNN 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656BIS6-2.048#PBF LT6656BIS6-2.048#TRPBF LTFNN 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656ACS6-2.5#PBF LT6656ACS6-2.5#TRPBF LTFGW 6-Lead Plastic TSOT-23 0°C to 70°C LT6656BCS6-2.5#PBF LT6656BCS6-2.5#TRPBF LTFGW 6-Lead Plastic TSOT-23 0°C to 70°C LT6656AIS6-2.5#PBF LT6656AIS6-2.5#TRPBF LTFGW 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656BIS6-2.5#PBF LT6656BIS6-2.5#TRPBF LTFGW 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656ACS6-3#PBF LT6656ACS6-3#TRPBF LTFNQ 6-Lead Plastic TSOT-23 0°C to 70°C LT6656BCS6-3#PBF LT6656BCS6-3#TRPBF LTFNQ 6-Lead Plastic TSOT-23 0°C to 70°C LT6656AIS6-3#PBF LT6656AIS6-3#TRPBF LTFNQ 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656BIS6-3#PBF LT6656BIS6-3#TRPBF LTFNQ 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656ACS6-3.3#PBF LT6656ACS6-3.3#TRPBF LTFNS 6-Lead Plastic TSOT-23 0°C to 70°C LT6656BCS6-3.3#PBF LT6656BCS6-3.3#TRPBF LTFNS 6-Lead Plastic TSOT-23 0°C to 70°C LT6656AIS6-3.3#PBF LT6656AIS6-3.3#TRPBF LTFNS 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656BIS6-3.3#PBF LT6656BIS6-3.3#TRPBF LTFNS 6-Lead Plastic TSOT-23 –40°C to 85°C 6656fa LT6656 Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LT6656ACS6-4.096#PBF LT6656ACS6-4.096#TRPBF LTFNV 6-Lead Plastic TSOT-23 0°C to 70°C LT6656BCS6-4.096#PBF LT6656BCS6-4.096#TRPBF LTFNV 6-Lead Plastic TSOT-23 0°C to 70°C LT6656AIS6-4.096#PBF LT6656AIS6-4.096#TRPBF LTFNV 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656BIS6-4.096#PBF LT6656BIS6-4.096#TRPBF LTFNV 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656ACS6-5#PBF LT6656ACS6-5#TRPBF LTFNX 6-Lead Plastic TSOT-23 0°C to 70°C LT6656BCS6-5#PBF LT6656BCS6-5#TRPBF LTFNX 6-Lead Plastic TSOT-23 0°C to 70°C LT6656AIS6-5#PBF LT6656AIS6-5#TRPBF LTFNX 6-Lead Plastic TSOT-23 –40°C to 85°C LT6656BIS6-5#PBF LT6656BIS6-5#TRPBF LTFNX 6-Lead Plastic TSOT-23 –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature and performance grades are identified by a label on the shipping container. 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/ Available Options SPECIFIED TEMPERATURE RANGE 0°C to 70°C –40°C to 85°C OUTPUT VOLTAGE INITIAL ACCURACY TEMPERATURE COEFFICIENT ORDER PART NUMBER** ORDER PART NUMBER** 1.250V 0.05% 0.1% 10ppm/°C 20ppm/°C LT6656ACS6-1.25 LT6656BCS6-1.25 LT6656AIS6-1.25 LT6656BIS6-1.25 2.048V 0.05% 0.1% 10ppm/°C 20ppm/°C LT6656ACS6-2.048 LT6656BCS6-2.048 LT6656AIS6-2.048 LT6656BIS6-2.048 2.500V 0.05% 0.1% 10ppm/°C 20ppm/°C LT6656ACS6-2.5 LT6656BCS6-2.5 LT6656AIS6-2.5 LT6656BIS6-2.5 3.000V 0.05% 0.1% 10ppm/°C 20ppm/°C LT6656ACS6-3 LT6656BCS6-3 LT6656AIS6-3 LT6656BIS6-3 3.300V 0.05% 0.1% 10ppm/°C 20ppm/°C LT6656ACS6-3.3 LT6656BCS6-3.3 LT6656AIS6-3.3 LT6656BIS6-3.3 4.096V 0.05% 0.1% 10ppm/°C 20ppm/°C LT6656ACS6-4.096 LT6656BCS6-4.096 LT6656AIS6-4.096 LT6656BIS6-4.096 5.000V 0.05% 0.1% 10ppm/°C 20ppm/°C LT6656ACS6-5 LT6656BCS6-5 LT6656AIS6-5 LT6656BIS6-5 **See Order Information section for complete part number listing. 6656fa LT6656 Electrical Characteristics The l denotes the specifications which apply over the specified temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT + 0.5V (for LT6656-1.25, VIN = 2.2V), CL = 1μF, IL = 0,unless otherwise noted. PARAMETER CONDITIONS MIN Output Voltage Error LT6656A LT6656B –0.05 –0.10 Output Voltage Temperature Coefficient (Note 4) LT6656A LT6656B l l Line Regulation VIN = (VOUT + 0.5V) to 18V LT6656-2.048, LT6656-2.5, LT6656-3, LT6656-3.3, LT6656-4.096, LT6656-5 l VIN = 2.2V to 18V LT6656-1.25 Load Regulation (Note 5) IL = 5mA, Sourcing LT6656-2.048, LT6656-2.5, LT6656-3, LT6656-3.3, LT6656-4.096, LT6656-5 IL = 5mA, Sourcing LT6656-1.25 Dropout Voltage (Note 6) VIN – VOUT, ∆VOUT Error ≤ 0.1% IL = 0 LT6656-2.048, LT6656-2.5, LT6656-3, LT6656-3.3, LT6656-4.096, LT6656-5 IL = 5mA, Sourcing LT6656-2.048, LT6656-2.5, LT6656-3, LT6656-3.3, LT6656-4.096, LT6656-5 Minimum Input Voltage IL = 0, ∆VOUT Error ≤ 0.1% LT6656-1.25 0°C ≤ TA ≤ 70°C –40°C ≤ TA ≤ 85°C TYP UNITS 0.05 0.10 % % 5 12 10 20 ppm/°C ppm/°C 2 25 40 ppm/V ppm/V 2 25 40 ppm/V ppm/V 65 150 375 ppm/mA ppm/mA 80 175 425 ppm/mA ppm/mA 3 10 40 mV mV 250 370 500 mV mV 1.35 1.5 1.6 1.8 V V V 0.85 1.0 1.5 µA µA l l l l l l l Supply Current MAX l Output Short Circuit Current Short VOUT to GND Short VOUT to VIN 18 4 mA mA Input Reverse Leakage Current VIN = –18V, VOUT = GND 80 µA Reverse Output Current VIN = GND, VOUT = 18V 30 µA Output Voltage Noise (Note 7) 0.1Hz to 10Hz 10Hz to 1kHz, LT6656-1.25 10Hz to 1kHz, LT6656-2.5 10Hz to 1kHz, LT6656-5 30 50 80 140 ppmP-P µVRMS µVRMS µVRMS Turn-On Time LT6656-1.25, 0.1% Settling LT6656-2.5, 0.1% Settling LT6656-5, 0.1% Settling 15 30 60 ms ms ms 50 ppm/√kHr 25 70 ppm ppm Long Term Drift of Output Voltage (Note 8) Hysteresis (Note 9) ∆T = 0°C to 70°C ∆T = –40°C to 85°C 6656fa LT6656 Electrical Characteristics 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: If the parts are stored outside of the specified temperature range, the output may shift due to hysteresis. Note 3: The stated temperature is typical for soldering of the leads during manual rework. For detailed IR reflow recommendations, refer to the Applications 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 with a pulse from no load to the specified load current. Output changes due to die temperature change must be taken into account separately. Note 6: Excludes load regulation errors. Note 7: Peak-to-peak noise is measured with a 3-pole highpass filter at 0.1Hz and a 4-pole lowpass filter at 10Hz. The unit is enclosed in a still-air environment to eliminate thermocouple effects on the leads. The test time is 10 seconds. RMS noise is measured on 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 will also be 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 25°C, but the IC is cycled to the hot or cold temperature limit before successive measurements. For instruments that are stored at well controlled temperatures (within 20 or 30 degrees of operational temperature) hysteresis is usually not a dominant error source. Typical Performance Characteristics Output Voltage Temperature Drift 200 6000 5000 4000 3000 2000 120 100 80 60 40 0 20 6652 G01 Supply Current vs Input Voltage 100 ALL OPTIONS 180 CL = 1µF I =0 160 TL = 25°C A 140 1000 –1000 –60 –40 –20 0 20 40 60 80 100 120 TEMPERATURE (°C) Typical VOUT Distribution SUPPLY CURRENT (µA) ALL OPTIONS 9000 25 TYPICAL UNITS 8000 NORMALIZED AT 25°C CL = 1µF 7000 IL = 0 NUMBER OF UNITS CHANGE IN OUTPUT VOLTAGE (ppm) 10000 0 –0.10 –0.06 –0.02 0 0.02 0.06 OUTPUT VOLTAGE ERROR (%) 0.10 6656 G02 1.25V OPTION 10 TA = 125°C TA = 85°C TA = 25°C TA = –40°C TA = –55°C 1 0.1 0 2 4 6 8 10 12 14 16 18 20 INPUT VOLTAGE (V) 6656 G17 6656fa LT6656 Typical Performance Characteristics Minimum Supply Voltage vs Load Current Supply Current vs Input Voltage VON 1 2.5V OPTION SHOWN VON MOVES WITH VOLTAGE OPTION 0.1 0 2 4 1.25V OPTION INITIAL VIN = 2.2V 1.8 ∆VOUT = 0.1% 1.6 1.4 1.2 TA = 125°C TA = 85°C TA = 25°C TA = –40°C TA = –55°C 1.0 0.8 0.1µ 6 8 10 12 14 16 18 20 INPUT VOLTAGE (V) 1µ 10µ 100µ 1m LOAD CURRENT (A) 6656 G03 Load Regulation (Sourcing) TA = 125°C TA = 85°C TA = 25°C TA = –40°C TA = –55°C 1µ 10µ 100µ 1m LOAD CURRENT (A) 10m 0 –250 –500 –750 0.1µ 600 2.5V OPTION SHOWN VON MOVES WITH 500 VOLTAGE OPTION 400 VON 300 200 100 0 –100 –200 0 2 4 TA = 125°C TA = 85°C TA = 25°C TA = –55°C 1µ 6 8 10 12 14 16 18 20 INPUT VOLTAGE (V) 6656 G08 90 3.5 3.0 TA = 85°C, 125°C TA = 25°C TA = –40°C TA = –55°C 2.5 2.0 1.5 1.0 0.5 0 10µ 100µ 1m LOAD CURRENT (A) 10m –0.5 10µ 100µ LOAD CURRENT (A) 70 60 50 40 30 20 1.25V OPTION 2.5V OPTION 5V OPTION 10 0 10 100 1k FREQUENCY (Hz) 1m 6656 G06 Power Supply Rejection Ratio vs Frequency VIN = VOUT + 0.5V CL = 1µF IL = 0 80 10m ALL OPTIONS 4.5 VIN = VOUT + 0.5V 4.0 CL = 1µF 6656 G05 POWER SUPPLY REJECTION RATIO (dB) OUTPUT VOLTAGE CHANGE (ppm) 700 10µ 100µ 1m LOAD CURRENT (A) 6656 G04 Power Supply Rejection Ratio vs Frequency TA = 125°C TA = 85°C TA = 25°C TA = –55°C 1µ Load Regulation (Sinking) 250 Line Regulation ALL OPTIONS 900 I = 0 L 800 CL = 1µF TA = 125°C TA = 85°C TA = 25°C TA = –55°C 5.0 2.048V TO 5V OPTIONS VIN = VOUT + 0.5V 500 CL = 1µF 6656 G19 1000 1 0.1µ 10m OUTPUT VOLTAGE CHANGE (%) OUTPUT VOLTAGE CHANGE (ppm) OUTPUT VOLTAGE CHANGE (ppm) –250 –1000 0.1µ 10 Load Regulation (Sourcing) 0 –750 100 750 1.25V OPTION VIN = 1.75V 250 CL = 1µF 2.048V TO 5V OPTIONS VIN – VOUT INITIAL VIN = VOUT + 0.5V ∆VOUT = 0.1% 6656 G18 500 –500 DROPOUT VOLTAGE (mV) 10 TA = 125°C TA = 85°C TA = 25°C TA = –55°C 1000 10k 6656 G09 90 POWER SUPPLY REJECTION RATIO (dB) 2.048V TO 5V OPTIONS Dropout Voltage vs Load Current 2.0 MINIMUM SUPPLY VOLTAGE (V) SUPPLY CURRENT (µA) 100 2.5V OPTION VIN = 3V 80 70 60 50 40 30 20 IL = 0, CL = 1µF IL = 0, CL = 10µF IL = 1mA, CL = 1µF IL = 1mA, CL = 10µF 10 0 –10 10 100 1k FREQUENCY (Hz) 10k 6656 G20 6656fa LT6656 Typical Performance Characteristics Output Impedance vs Frequency 100 10 1.25V OPTION 2.5V OPTION 5V OPTION 100 1k FREQUENCY (Hz) 1k 100 10 1 10k IL = 0, CL = 1µF IL = 0, CL = 10µF IL = 100µA, CL = 1µF IL = 100µA, CL = 10µF 10 100 1k FREQUENCY (Hz) 6656 G21 TA = 125°C TA = 85°C TA = 25°C TA = –55°C 0 ALL OPTIONS VIN = GND TA = 125°C TA = 85°C TA = 25°C TA = –55°C 0 5 10 15 OUTPUT VOLTAGE (V) 15 10 2.5V OPTION 5 100 1k FREQUENCY (Hz) TIME (1s/DIV) 6656 G13 Output Noise Voltage Spectrum vs Load Capacitance IL = 0 IL = 10µA IL = 250µA IL = 1mA 12 10 8 6 4 10k 6656 G24 0 40 2.5V OPTION 35 VIN = 3V CL = 47µF IL = 0 30 25 20 CL = 4.7µF 15 CL = 0.47µF 10 5 2 1.25V OPTION 10 2.5V OPTION 14 VIN = 3V CL = 1µF NOISE VOLTAGE (µV/√Hz) NOISE VOLTAGE (µVRMS/√Hz) 5V OPTION 0 16 VIN = VOUT + 5V CL = 1µF IL = 0 20 ALL OPTIONS VIN = VOUT + 0.5V CL = 1µF IL = 0 20 Output Voltage Noise Spectrum vs Load Current Output Voltage Noise Spectrum 25 10m 6656 G12 6656 G11 30 100µ 1m LOAD CURRENT (A) Output Noise 0.1Hz to 10Hz 10 1 –2 –4 –6 –8 –10 –12 –14 –16 –18 –20 INPUT VOLTAGE (V) TA = 125°C TA = 85°C TA = 25°C TA = –55°C 6656 G07 OUTPUT NOISE (20ppm/DIV) 10 REVERSE OUTPUT CURRENT (µA) REVERSE INPUT CURRENT (µA) ALL OPTIONS VOUT = GND 100 0 10 Reverse Output Current 100 1 100 6656 G22 Reverse Input Current 1000 ALL OPTIONS VIN = VOUT + 0.5V CL = 1µF 1 10µ 10k NOISE VOLTAGE (µV/√Hz) 10 2.5V OPTION VIN = 3V 1000 GROUND CURRENT (µA) VIN = VOUT + 0.5V CL = 1µF IL = 0 1k 1 Ground Current vs Load Current Output Impedance vs Frequency 10k OUTPUT IMPEDANCE (Ω) OUTPUT IMPEDANCE (Ω) 10k 10 100 1k FREQUENCY (Hz) 10k 6656 G14 0 1 10 100 FREQUENCY (Hz) 1k 6656 G15 6656fa LT6656 Typical Performance Characteristics 250 VIN = VOUT + 0.5V CL = 1µF 400 INTEGRATED NOISE (µVRMS) INTEGRATED NOISE (µVRMS) 500 Integrated 10Hz to 1kHz Noise vs Load Current 300 5V OPTION 200 2.5V OPTION 100 ALL OPTIONS 150 CL = 1µF IL = 0 2.5V OPTION 200 150 100 CL = 0.47µF CL = 1µF CL = 10µF CL = 47µF 50 1.25V OPTION 0 0.1µ 1µ 10µ 100µ LOAD CURRENT (A) 1m 10m Long-Term Drift 200 0 0.1µ 1µ 10µ 100µ LOAD CURRENT (A) 6656 G25 1m 10m LONG TERM DRIFT (ppm) Integrated 10Hz to 1kHz Noise vs Load Current 100 50 0 –50 –100 –150 5 TYPICAL PARTS SOLDERED ONTO PCB –200 0 100 200 300 400 500 600 700 800 900 1000 HOURS 6656 G16 6656 G23 Pin Functions GND* (Pin 1): Internal Function. This pin must be tied to ground. NC (Pin 5): Not internally connected. May be tied to VIN, VOUT, GND or floated. GND (Pin 2): Device Ground. VOUT (Pin 6): Output Voltage. An output capacitor of 1µF minimum is required for stable operation. NC (Pin 3): Not internally connected. May be tied to VIN, VOUT, GND or floated. VIN (Pin 4): Power Supply. Bypass VIN with a 0.1µF capacitor to ground. Block Diagram VIN NC VOUT ERROR AMP BANDGAP NC GND GND 6656 BD 6656fa LT6656 Applications Information Long Battery Life Output Voltage Options Series references have a large advantage over shunt style references. Shunt references require a resistor from the power supply to operate. This resistor must be chosen to supply the maximum current that can be demanded by the load. When the load is not operating at this maximum current, the shunt reference must always sink this current, resulting in high dissipation and shortened battery life. The performance of the LT6656 is consistent for the 2.048V to 5V options. The 1.25V option has slightly reduced load regulation, and unlike the higher voltage options, the minimum operating supply voltage is limited by internal circuitry rather than the output voltage. The LT6656 series reference does not require a current setting resistor and is specified to operate with any supply from 1.5V to 18V, depending on the output voltage option, load current and operating temperature (see Dropout Voltage and Minimum Input Voltage in the Typical Performance Characteristics). When the load does not demand current, the LT6656 reduces its dissipation and battery life is extended. If the reference is not delivering load current, it dissipates only a few µW, yet the same connection can deliver 5mA of load current when required. Start-Up To ensure proper start-up, the output voltage should be between –0.3V and the rated output voltage. If the output load may be driven more than 0.3V below ground, a low forward voltage schottky diode from the output to ground is required. The turn-on characteristics can be seen in Figure 1. VIN 1V/DIV VOUT 1ms/DIV 6656 F01 Parameters that are based on changes in the output voltage, such as load regulation and hysteresis, remain proportional to the output voltage and are specified in relative units, for example, parts per million (ppm). Parameters that are not based on changes in the output voltage, such as supply current and reverse input current, are the same for all options. The bandwidth of the LT6656 decreases with higher output voltage. This causes parameters that are affected by both bandwidth and output voltage, such as wideband noise and output impedance, to increase less with higher output voltage. Bypass and Load Capacitance The LT6656 voltage reference needs a 0.1μF input bypass capacitor placed within an inch of the input pin. An additional 2.2μF capacitor should be used when the source impedance of the input supply is high or when driving heavy loads. The bypassing of other local devices may serve as the required components. The output of the LT6656 requires a capacitance of 1µF or larger. The LT6656 is stable with a wide variety of capacitor types including ceramic, tantalum and electrolytic due to its low sensitivity to ESR (5Ω or less). The test circuit in Figure 2 was used to test the response and stability of the LT6656 to various load currents. The resultant transient responses can be seen in Figure 3 and Figure 4. The large scale output response to a 500mV input step is shown in Figure 5 with a more detailed photo and description in the Output Settling section. Figure 1. LT6656-2.5 Turn-On Characteristics, CL = 1µF VIN 3V CIN 0.1µF R2 LT6656-2.5 3V VGEN CL 1µF R1 2N7000 6656 F02 Figure 2. Transient Load Test Circuit 6656fa LT6656 Applications Information 0µA IOUT 100µA 2.52V VOUT 2.50V 2.48V 5ms/DIV 6656 F03 Figure 3. Transient Response, 0µA to 100µA Load Step (R2 = 24.9k, R1 = Open) 1mA IOUT 2mA The settling time is typically less than 8ms for output loads up to 5mA, however the time required to settle when the load is turned off or in response to an input transient can be significantly longer due to the dead band (shown in Figure 7). During this interval the output stage is neither sourcing nor sinking current so the settling time is dominated by the ability of the application circuit to discharge the output capacitor to the voltage at which the sourcing circuitry in the output stage reactivates. Larger load currents will decrease the settling time and higher output capacitance will increase the settling time. In application circuits where the LT6656 is experiencing a load step greater than 5µA, such as an ADC reference and supply implementation, the settling time will typically remain less than 8ms, regardless of the output settling from a previous load step. The settling time can be estimated by the following equation: 2.52V VOUT 2.50V 2.48V 5ms/DIV 6656 F04 Figure 4. Transient Response, 1mA to 2mA Load Step (R1 = R2 = 2.49k) VIN Settling time ≈ The deadband is ≈7mV for the 2.5V option, is proportional to the voltage option (i.e., ≈14mV for the 5V option) and can double due to variations in processing. The graph in Figure 6 shows the settling time versus load step with no load and with a constant 2µA load applied. Note the settling time can be longer with load steps that are not large enough to activate the sinking side of the output stage. 3.25V 2.75V 2.7V 30 2.3V 5ms/DIV 6656 F05 Figure 5. Output Response to 0.5VP-P Step on VIN, CL = 1µF, IL = 0 Output Settling The output of the LT6656 is primarily designed to source current into a load, but is capable of sinking current to aid in output transient recovery. The output stage uses a class B architecture to minimize quiescent current and has a crossover dead band as the output transitions from sourcing to sinking current. OUTPUT SETTLING TIME (ms) VOUT 2.5V 10 2(Deadband)(CL ) + ( VOUT )(0.8ms / V) IL 2.5V OPTION VIN = 3V 25 CL = 1µF ∆IL = LOAD STEP TO ZERO 20 15 ∆IL = LOAD STEP TO 2µA 10 5 0 0.001 ∆IL = ZERO TO LOAD STEP 0.01 0.1 LOAD STEP (mA) 1 10 6656 F06 Figure 6. Output Settling Time to 0.05% vs Load Step 6656fa LT6656 Applications Information VIN input pulled to ground, the reverse output protection of the LT6656 limits the output current to typically less than 30µA. The current versus reverse voltage is shown in the Typical Performance Characteristics section. 3.25V 2.75V IL = 0 Long-Term Drift VOUT 10mV/DIV The photo in Figure 7 shows the output response to a 0.5V input step in both a no-load and 5µA load condition. In the no-load condition only the bias current of the internal bandgap reference (about 400nA) is available to discharge the output capacitor. Long-term drift cannot be extrapolated from accelerated high temperature testing. This erroneous technique gives drift numbers that are wildly optimistic. A more realistic way to determine long-term drift is to measure it over the time interval of interest. The LT6656 drift data was taken over 100 parts that were soldered onto PC boards in a typical application configuration. The boards were then placed into a constant temperature oven with TA = 30°C, their outputs scanned regularly and measured with an 8.5 digit DVM. The parts chosen in the Long Term Drift curves in the Typical Performance Characteristics section represent high, low and typical units. Output Noise Hysteresis IL = 5µA 5ms/DIV 6656 F07 Figure 7. Detailed Output Response to a 0.5V Input Step, CIN = CL = 1µF Low frequency noise is proportional to the output voltage and is insensitive to output current and moderate levels of output capacitance. Wideband noise increases less with higher output voltage and is proportional to the bandwidth of the output stage, increasing with higher load current and lower output capacitance. Peaking in the noise response is another factor contributing to the output noise level for a given frequency range. Noise peaking can be reduced by increasing the size of the output capacitor when driving heavier loads, or conversely, reducing the size of the output capacitor when driving lighter loads. Noise plots in the Typical Performance Curves section show noise spectrum with various load currents and output capacitances. Internal Protection The LT6656 incorporates several internal protection features that make it ideal for use in battery powered systems. Reverse input protection limits the input current to typically less than 40µA when either the LT6656 or the battery is installed backwards. In systems where the output can be held up by a backup battery with the Hysteresis on the LT6656 is measured in two steps, for example, from 25°C to –40°C to 25°C, then from 25°C to 85°C to 25°C, for the industrial temperature range. This two-step cycle is repeated several times and the maximum hysteresis from all the partial cycles is noted. Unlike other commonly used methods for specifying hysteresis, this ensures the worst-case hysteresis is included, whether it occurs in the first temperature excursion or the last. Results over both commercial and industrial temperature ranges are shown in Figure 8 and Figure 9. The parts cycled over the higher temperature range have a higher hysteresis than those cycled over the lower range. Power Dissipation The LT6656 will not exceed the maximum junction temperature when operating within its specified temperature range of –40°C to 85°C, maximum input voltage of 18V and specified load current of 5mA. IR Reflow Shift The different expansion and contraction rates of the materials that make up the LT6656 package may induce small stresses on the die that can cause the output to shift during 6656fa 11 LT6656 Applications Information 30 NUMBER OF UNITS 2.5V OPTION VIN = 3V 25 CL = 1µF IL = 0 0°C TO 25°C 70°C TO 25°C 300 380s TP = 260°C TL = 217°C TS(MAX) = 200°C 225 20 TS = 190°C 15 RAMP DOWN tP 30s T = 150°C 150 tL 130s RAMP TO 150°C 10 75 40s 5 120s 0 –60 –40 –20 0 20 HYSTERESIS (ppm) 40 0 60 0 2 6656 F08 Figure 8. 0°C to 70°C Hysteresis 20 18 12 10 8 6 4 10 6656 F10 2.5V OPTION VIN = 3V 6 C = 1µF L IL = 0 5 3 CYCLES 1 CYCLE 4 3 2 1 2 0 7 2.5V OPTION VIN = 3V CL = 1µF IL = 0 14 8 Figure 10. Lead Free Reflow Profile Due to IR Reflow NUMBER OF UNITS NUMBER OF UNITS 16 –40°C TO 25°C 85°C TO 25°C 4 6 MINUTES –160 –120 –80 –40 0 40 80 120 160 HYSTERESIS (ppm) 0 0 20 60 100 140 180 220 CHANGE IN OUTPUT VOLTAGE (ppm) 6656 F11 6656 F09 Figure 9. –40°C to 85°C Hysteresis IR reflow. Common lead free IR reflow profiles reach over 250°C, considerably more than lead solder profiles. The higher reflow temperature of the lead free parts exacerbates the issue of thermal expansion and contraction causing the output shift to generally be greater than with a leaded reflow process. The lead free IR reflow profile used to experimentally measure the output voltage shift in the LT6656-2.5 is shown in Figure 10. Similar results can be expected using a convection reflow oven. Figure 11 shows the change in output voltage that was measured for parts that were run through the reflow process for 1 cycle and also 3 cycles. The results indicate that the standard deviation of the output voltage increases with a positive mean shift of 120ppm. While there can be up to 220ppm of output voltage shift, additional drift of the LT6656 after IR reflow does not vary significantly. Figure 11. Output Voltage Shift Due to IR Reflow, Peak Temperature = 260°C PC Board Layout The mechanical stress of soldering a surface mount voltage reference to a PC board can cause the output voltage to shift and temperature coefficient to change. To reduce the effects of stress-related shifts, position the reference near the short edge of the PC board or in a corner. In addition, slots can be cut into the board on two sides of the device. See Application Note AN82 for more information. http://www.linear.com The input and output capacitors should be mounted close to the package. The GND and VOUT traces should be as short as possible to minimize the voltage drops caused by load and ground currents. Excessive trace resistance directly impacts load regulation. 6656fa 12 LT6656 Typical Applications Regulator Reference Low Power ADC Reference The robust input and output of the LT6656 along with its high output current make it an excellent precision low power regulator as well as a reference. The LT6656 would be a good match with a small, low power microcontroller. Using the LT6656 as a regulator reduces power consumption, decreases solution size and increases the accuracy of the microcontroller’s on board ADC. Low power ADCs draw only a few µAs during their idle period and well over 100µA during conversions. Despite these surges of current, the ADC in reality can have very low power consumption. Figure 13 shows the LTC2480, a low power delta sigma ADC. When the ADC is disabled its quiescent current (IQ) is roughly 1µA, during conversion the IQ jumps up to 160µA. In reality, the power consumption is not only based on the IQ during conversion, but the real power consumption of the ADC is set by the conversion time and the sample rate. The LTC2480 shown in Figure 13 has a conversion time of 160ms which sets the maximum sample rate of 6 samples per second. The maximum sample rate also sets the maximum current consumption to 160µA, but at slower sample rates the ADC will have significantly lower average current draw. If the ADC is sampled at 1 sample per second the average current drawn by the ADC during a 1 second interval would only be 26.4µA. When taking into consideration the current drawn by the reference, the total current draw is only 27.4µA. This system is greatly simplified because the precision reference does not need to be cycled on and off to save power. Furthermore, leaving the reference on continuously eliminates concern for turn-on settling time. 3V ≤ VIN ≤ 18V 0.1µF IN LT6656-2.5 OUT MCU VCC/VREF 10µF PB0/AIN0/AREF/MOSI PB1/INT0/AIN1/MISO/OC1A PB2/ADC1/SCK/T0/INT0 PB3/ADC2 PB4/ADC3 PB5/RESET/ADC0 5 6 7 2 3 1 GND 6656 TA02 Figure 12. Microcontroller Reference and Regulator 5.1V ≤ VIN ≤ 18V 0.1µF IN LT6656-5 OUT 4.7µF IN+ DIFFERENTIAL INPUT ±VREF • 0.5 (±2.5V) REF VCC LTC2480 IN– AT 1sps, IQ = 27.4µA CS SCK SDO 6656 TA05 Figure 13. Low Power ADC Reference 6656fa 13 LT6656 Typical Applications Extended Supply Range Reference VCC UP TO 160V 330k MMBT5551 BZX584C12 0.1µF 2.2µF IN VOUT OUT LT6656-2.5 1µF 6656 TA03 Boosted Output Current Reference 3.6V ≤ VCC ≤ 18V 2207 + 10µF 2N2905 0.1µF IN VOUT 40mA MAX OUT LT6656-2.5 1µF 6656 TA04 Micropower Regulator, IQ = 2µA, Sink Up to 8mA 3V ≤ VCC ≤ 18V IN LT6656-2.5 + OUT 0.1µF 1µF 2.5V LT6003 – 6656 TA06 ADC Reference and Bridge Excitation Supply 3.8V ≤ VIN ≤ 18V IN 0.1µF LT6656-3.3 3.3V ≤ VCC ≤ 5.5V OUT 1µF 10k 0.1µF 10k 0.1µF IN– VCC LTC2452 IN+ 10k VREF 10µF CS SCK SDO 0.1µF 6656fa 14 LT6656 Typical Applications Low Power Precision High Voltage Supply Monitor, IQ = 1.4µA, High Voltage Supply Load = 10µA 100V 105V OVERVOLTAGE THRESHOLD VCC 9.53M 3 + 4 – 6.5V ≤ VCC ≤ 10V IN LT6656-5 OUT 0.1µF 1µF 475k 7 OVERVOLTAGE FLAG LTC1540 5 6 1, 2 6656 TA08 2-Terminal Current Source + + IN LT6656-1.25 GND 0.1µF OUT VREF LT6003 R1 – 1µF R3 R2 – IOUT 6656 TA09 VREF ¥ R2 ´ 1 R1 §¦ R3 ¶µ Precision Current and Boosted Reference, IQ = 5.5µA 249k 2N5086 VCC 1k + + – – LT6004 2.75V LT6004 200k 1µA OUT 3V ≤ VCC ≤ 16V IN 0.1µF LT6656-2.5 2M OUT 2.5V 1µF 6656 TA10 6656fa 15 LT6656 Package Description S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 0.62 MAX 2.90 BSC (NOTE 4) 0.95 REF 1.22 REF 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 6 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 1.90 BSC S6 TSOT-23 0302 REV B 6656fa 16 LT6656 Revision History REV DATE DESCRIPTION PAGE NUMBER A 7/10 Voltage options added (1.25, 2.048, 3, 3.3), reflected throughout the data sheet 1 to 18 6656fa 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. 17 LT6656 Typical Application Reference Regulator for Micropower DAC, Total IQ = 4.8µA 5.1V ≤ VIN ≤ 18V IN LT6656-5 OUT 0.1µF 5V 10µF VREF VCC CS SCK SDI DAC A 0V TO 5V OUTPUT DAC B 0V TO 5V OUTPUT LTC1662 GND 6656 TA07 Related Parts PART NUMBER DESCRIPTION COMMENTS LT1389 Nanopower Precision Shunt Voltage Reference 0.05% Max 10ppm/°C Max, 800nA Supply LTC1440 Micropower Comparator with Reference 3.7µA Max Supply Current, 1% 1.182V Reference, MSOP, PDIP and SO-8 Packages LT1460 Micropower Series Reference 0.075% Max, 10ppm/°C Max Drift, 2.5V, 5V and 10V Versions,MSOP, PDIP, SO-8, SOT-23 and TO-92 Packages LT1461 Micropower Precision LDO Series Reference 3ppm/°C Max Drift, 0°C to 70°C, –40°C to 85°C, –40°C to 125°C Options in SO-8 LT1495 1.5µA Precision Rail-to-Rail Dual Op Amp 1.5µA Max Supply Current, 100pA Max IOS LTC1540 Nanopower Comparator with Reference 600nA Max Supply Current, 2% 1.182V Reference, MSOP and SO-8 Packages LT1634 Micropower Precision Shunt Voltage Reference 0.05% Max, 10ppm/°C Max Drift, 1.25V, 2.5V, 4.096V, 5V, 10µA Maximum Supply Current LT1790 Micropower Precision Series Reference 0.05% Max, 10ppm/°C Max, 60µA Supply, SOT23 Package LTC1798 6µA Low Dropout Series Reference Available in Adjustable, 2.5V, 3V, 4.096V and 5V LT6003 1.6V, 1µA Precision Rail-to-Rail Op Amp 1µA Max Supply Current, 1.6V Minimum Operating Voltage, SOT-23 Package LT6650 Micropower Reference with Buffer Amplifier 0.05% Max, 5.6µA Supply, SOT-23 Package LT6660 Tiny Micropower Series Reference 0.2% Max, 20ppm/°C Max, 20mA Output Current, 2mm × 2mm DFN LT6700 Micropower, Low Voltage Dual Comparator with 40mV Reference 6.5µA Supply Current, 1.4V Minimum Operating Voltage 6656fa 18 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LT 0710 REV A • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2010