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LT6656 1A Precision Series Voltage Reference FeaTures
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DescripTion
The LT(R)6656 is a small precision voltage reference that draws less than 1A 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. 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 1F or larger output capacitance and operates with a wide range of output capacitor ESR. This reference is fully specified for operation from -40C to 85C, and is functional over the extreme temperature range of -55C to 125C. 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.
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Low Drift A Grade: 10 ppm/C Max B Grade: 20 ppm/C Max High Accuracy A Grade: 0.05% Max B Grade: 0.1% Max Ultralow Supply Current: 850nA High Output Drive Current: 5mA Min Low Dropout Voltage: 10mV Max Fully Specified from -40C to 85C Operational from -55C to 125C Wide Supply Range to 18V Reverse Input/Output Protection Available Output Voltage Options: 1.25V, 2.048V, 2.5V, 3V, 3.3V, 4.096V and 5V Thermal Hysteresis: 25ppm Low Profile (1mm) ThinSOTTM Package
applicaTions
n n n n n n
Precision A/D and D/A Converters Portable Gas Monitors Battery- or Solar-Powered Systems Precision Regulators Low Voltage Signal Processing Micropower Remote Sensing
Typical applicaTion
2.503
Output Voltage Temperature Drift LT6656-2.5
38 TYPICAL UNITS
Basic Connection
2.51V VIN 18V 0.1F LT6656-2.5 VIN VOUT GND VOUT 2.5V 1F
6656 TA01a
2.502
VOUT (V)
2.501
2.500
2.499
2.498 -40
-20
0 20 40 TEMPERATURE (C)
60
80
6652 TA01b
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LT6656 absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW GND* 1 GND 2 NC 3 6 VOUT 5 NC 4 VIN
Input Voltage...........................................................20V Output Voltage ........................................... -0.3V to 20V Output Voltage Above Input Voltage .........................20V Specified Temperature Range Commercial ............................................. 0C to 70C Industrial .............................................-40C to 85C Operating Temperature Range ............... -55C to 125C Output Short Circuit Duration ......................... Indefinite Junction Temperature .......................................... 150C Storage Temperature Range (Note 2)..... -65C to 150C Lead Temperature (Soldering, 10 sec.) (Note 3)................................................................. 300C
S6 PACKAGE 6-LEAD PLASTIC TSOT-23 TJMAX = 150C, JA = 230C/W *CONNECT PIN TO DEVICE GND (PIN 2)
orDer inForMaTion
LEAD FREE FINISH LT6656ACS6-1.25#PBF LT6656BCS6-1.25#PBF LT6656AIS6-1.25#PBF LT6656BIS6-1.25#PBF LT6656ACS6-2.048#PBF LT6656BCS6-2.048#PBF LT6656AIS6-2.048#PBF LT6656BIS6-2.048#PBF LT6656ACS6-2.5#PBF LT6656BCS6-2.5#PBF LT6656AIS6-2.5#PBF LT6656BIS6-2.5#PBF LT6656ACS6-3#PBF LT6656BCS6-3#PBF LT6656AIS6-3#PBF LT6656BIS6-3#PBF LT6656ACS6-3.3#PBF LT6656BCS6-3.3#PBF LT6656AIS6-3.3#PBF LT6656BIS6-3.3#PBF TAPE AND REEL LT6656ACS6-1.25#TRPBF LT6656BCS6-1.25#TRPBF LT6656AIS6-1.25#TRPBF LT6656BIS6-1.25#TRPBF LT6656ACS6-2.048#TRPBF LT6656BCS6-2.048#TRPBF LT6656AIS6-2.048#TRPBF LT6656BIS6-2.048#TRPBF LT6656ACS6-2.5#TRPBF LT6656BCS6-2.5#TRPBF LT6656AIS6-2.5#TRPBF LT6656BIS6-2.5#TRPBF LT6656ACS6-3#TRPBF LT6656BCS6-3#TRPBF LT6656AIS6-3#TRPBF LT6656BIS6-3#TRPBF LT6656ACS6-3.3#TRPBF LT6656BCS6-3.3#TRPBF LT6656AIS6-3.3#TRPBF LT6656BIS6-3.3#TRPBF PART MARKING* LTFNK LTFNK LTFNK LTFNK LTFNN LTFNN LTFNN LTFNN LTFGW LTFGW LTFGW LTFGW LTFNQ LTFNQ LTFNQ LTFNQ LTFNS LTFNS LTFNS LTFNS PACKAGE DESCRIPTION 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 SPECIFIED TEMPERATURE RANGE 0C to 70C 0C to 70C -40C to 85C -40C to 85C 0C to 70C 0C to 70C -40C to 85C -40C to 85C 0C to 70C 0C to 70C -40C to 85C -40C to 85C 0C to 70C 0C to 70C -40C to 85C -40C to 85C 0C to 70C 0C to 70C -40C to 85C -40C to 85C
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LT6656 orDer inForMaTion
LEAD FREE FINISH LT6656ACS6-4.096#PBF LT6656BCS6-4.096#PBF LT6656AIS6-4.096#PBF LT6656BIS6-4.096#PBF LT6656ACS6-5#PBF LT6656BCS6-5#PBF LT6656AIS6-5#PBF LT6656BIS6-5#PBF TAPE AND REEL LT6656ACS6-4.096#TRPBF LT6656BCS6-4.096#TRPBF LT6656AIS6-4.096#TRPBF LT6656BIS6-4.096#TRPBF LT6656ACS6-5#TRPBF LT6656BCS6-5#TRPBF LT6656AIS6-5#TRPBF LT6656BIS6-5#TRPBF PART MARKING* LTFNV LTFNV LTFNV LTFNV LTFNX LTFNX LTFNX LTFNX PACKAGE DESCRIPTION 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 SPECIFIED TEMPERATURE RANGE 0C to 70C 0C to 70C -40C to 85C -40C to 85C 0C to 70C 0C to 70C -40C to 85C -40C to 85C
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 OUTPUT VOLTAGE 1.250V 2.048V 2.500V 3.000V 3.300V 4.096V 5.000V INITIAL ACCURACY 0.05% 0.1% 0.05% 0.1% 0.05% 0.1% 0.05% 0.1% 0.05% 0.1% 0.05% 0.1% 0.05% 0.1% TEMPERATURE COEFFICIENT 10ppm/C 20ppm/C 10ppm/C 20ppm/C 10ppm/C 20ppm/C 10ppm/C 20ppm/C 10ppm/C 20ppm/C 10ppm/C 20ppm/C 10ppm/C 20ppm/C 0C to 70C ORDER PART NUMBER** LT6656ACS6-1.25 LT6656BCS6-1.25 LT6656ACS6-2.048 LT6656BCS6-2.048 LT6656ACS6-2.5 LT6656BCS6-2.5 LT6656ACS6-3 LT6656BCS6-3 LT6656ACS6-3.3 LT6656BCS6-3.3 LT6656ACS6-4.096 LT6656BCS6-4.096 LT6656ACS6-5 LT6656BCS6-5 -40C to 85C ORDER PART NUMBER** LT6656AIS6-1.25 LT6656BIS6-1.25 LT6656AIS6-2.048 LT6656BIS6-2.048 LT6656AIS6-2.5 LT6656BIS6-2.5 LT6656AIS6-3 LT6656BIS6-3 LT6656AIS6-3.3 LT6656BIS6-3.3 LT6656AIS6-4.096 LT6656BIS6-4.096 LT6656AIS6-5 LT6656BIS6-5
**See Order Information section for complete part number listing.
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LT6656 elecTrical characTerisTics
PARAMETER Output Voltage Error Output Voltage Temperature Coefficient (Note 4) Line Regulation LT6656A LT6656B LT6656A LT6656B VIN = (VOUT + 0.5V) to 18V LT6656-2.048, LT6656-2.5, LT6656-3, LT6656-3.3, LT6656-4.096, LT6656-5 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 0C TA 70C -40C TA 85C
l l l
The l denotes the specifications which apply over the specified temperature range, otherwise specifications are at TA = 25C. VIN = VOUT + 0.5V (for LT6656-1.25, VIN = 2.2V), CL = 1F IL = 0,unless , otherwise noted.
CONDITIONS MIN -0.05 -0.10 5 12 2 TYP MAX 0.05 0.10 10 20 25 40 25 40 150 375 175 425 10 40 370 500 UNITS % % ppm/C ppm/C ppm/V ppm/V ppm/V ppm/V ppm/mA ppm/mA ppm/mA ppm/mA mV mV mV mV
2
l
65
l
80
l
3
l
250
l
1.35
l l
1.5 1.6 1.8 1.0 1.5
V V V A A mA mA A A ppmP-P VRMS VRMS VRMS ms ms ms ppm/kHr ppm ppm
Supply Current
l
0.85 Short VOUT to GND Short VOUT to VIN VIN = -18V, VOUT = GND VIN = GND, VOUT = 18V 0.1Hz to 10Hz 10Hz to 1kHz, LT6656-1.25 10Hz to 1kHz, LT6656-2.5 10Hz to 1kHz, LT6656-5 LT6656-1.25, 0.1% Settling LT6656-2.5, 0.1% Settling LT6656-5, 0.1% Settling T = 0C to 70C T = -40C to 85C 18 4 80 30 30 50 80 140 15 30 60 50 25 70
Output Short Circuit Current Input Reverse Leakage Current Reverse Output Current Output Voltage Noise (Note 7)
Turn-On Time
Long Term Drift of Output Voltage (Note 8) Hysteresis (Note 9)
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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 25C, 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
10000 CHANGE IN OUTPUT VOLTAGE (ppm) ALL OPTIONS 9000 25 TYPICAL UNITS 8000 NORMALIZED AT 25C CL = 1F 7000 IL = 0 6000 5000 4000 3000 2000 1000 0 -1000 -60 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C) 200
Typical VOUT Distribution
Supply Current vs Input Voltage
100 1.25V OPTION TA = 125C TA = 85C TA = 25C TA = -40C TA = -55C
SUPPLY CURRENT (A)
NUMBER OF UNITS
ALL OPTIONS 180 CL = 1F IL = 0 160 T = 25C A 140 120 100 80 60 40 20 0 -0.10 -0.06 -0.02 0 0.02 0.06 OUTPUT VOLTAGE ERROR (%) 0.10
6656 G02
10
1
0.1
0
2
4
6 8 10 12 14 16 18 20 INPUT VOLTAGE (V)
6656 G17
6652 G01
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LT6656 Typical perForMance characTerisTics
Supply Current vs Input Voltage
100 2.048V TO 5V OPTIONS TA = 125C TA = 85C TA = 25C TA = -55C 2.0 MINIMUM SUPPLY VOLTAGE (V)
Minimum Supply Voltage vs Load Current
1.25V OPTION INITIAL VIN = 2.2V 1.8 VOUT = 0.1% 1.6 1.4 1.2 1.0 0.8 0.1 DROPOUT VOLTAGE (mV) 1000
Dropout Voltage vs Load Current
2.048V TO 5V OPTIONS VIN - VOUT INITIAL VIN = VOUT + 0.5V VOUT = 0.1%
SUPPLY CURRENT (A)
10
VON
100
1 2.5V OPTION SHOWN VON MOVES WITH VOLTAGE OPTION 0.1 0 2 4 6 8 10 12 14 16 18 20 INPUT VOLTAGE (V)
6656 G03
TA = 125C TA = 85C TA = 25C TA = -40C TA = -55C 1 10 100 1m LOAD CURRENT (A) 10m
6656 G18
10 TA = 125C TA = 85C TA = 25C TA = -55C 1 10 100 1m LOAD CURRENT (A) 10m
6656 G04
1 0.1
Load Regulation (Sourcing)
500 OUTPUT VOLTAGE CHANGE (ppm) OUTPUT VOLTAGE CHANGE (ppm) 1.25V OPTION VIN = 1.75V 250 CL = 1F 0 -250 -500 -750 750
Load Regulation (Sourcing)
2.048V TO 5V OPTIONS VIN = VOUT + 0.5V 500 CL = 1F 250 0 -250 -500 -750 0.1 TA = 125C TA = 85C TA = 25C TA = -55C 1 10 100 1m LOAD CURRENT (A) 10m
6656 G05
Load Regulation (Sinking)
5.0 OUTPUT VOLTAGE CHANGE (%) ALL OPTIONS 4.5 VIN = VOUT + 0.5V 4.0 CL = 1F 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -0.5 10 100 LOAD CURRENT (A) 1m
6656 G06
TA = 85C, 125C TA = 25C TA = -40C TA = -55C
-1000 0.1
TA = 125C TA = 85C TA = 25C TA = -40C TA = -55C 1 10 100 1m LOAD CURRENT (A) 10m
6656 G19
Line Regulation
1000 OUTPUT VOLTAGE CHANGE (ppm) POWER SUPPLY REJECTION RATIO (dB) ALL OPTIONS 900 I = 0 L 800 CL = 1F 700 600 2.5V OPTION SHOWN VON MOVES WITH 500 VOLTAGE OPTION 400 VON 300 200 100 0 -100 -200 0 2 4 6 8 10 12 14 16 18 20 INPUT VOLTAGE (V)
6656 G08
Power Supply Rejection Ratio vs Frequency
80 70 60 50 40 30 20 10 0 10 1.25V OPTION 2.5V OPTION 5V OPTION 100 1k FREQUENCY (Hz) 10k
6656 G09
Power Supply Rejection Ratio vs Frequency
90 POWER SUPPLY REJECTION RATIO (dB) 80 70 60 50 40 30 20 10 0 -10 10 IL = 0, CL = 1F IL = 0, CL = 10F IL = 1mA, CL = 1F IL = 1mA, CL = 10F 100 1k FREQUENCY (Hz) 10k
6656 G20
TA = 125C TA = 85C TA = 25C TA = -55C
90
VIN = VOUT + 0.5V CL = 1F IL = 0
2.5V OPTION VIN = 3V
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LT6656 Typical perForMance characTerisTics
Output Impedance vs Frequency
10k VIN = VOUT + 0.5V CL = 1F IL = 0 OUTPUT IMPEDANCE ( ) 10k
Output Impedance vs Frequency
2.5V OPTION VIN = 3V 1000
Ground Current vs Load Current
ALL OPTIONS VIN = VOUT + 0.5V CL = 1F
OUTPUT IMPEDANCE ( )
GROUND CURRENT (A)
1k
1k
100
100
100
10 TA = 125C TA = 85C TA = 25C TA = -55C 100 1m LOAD CURRENT (A) 10m
6656 G07
10 1.25V OPTION 2.5V OPTION 5V OPTION 10 100 1k FREQUENCY (Hz) 10k
6656 G21
10
1
1
IL = 0, CL = 1F IL = 0, CL = 10F IL = 100A, CL = 1F IL = 100A, CL = 10F 10 100 1k FREQUENCY (Hz) 10k
6656 G22
1 10
Reverse Input Current
1000 REVERSE INPUT CURRENT (A) REVERSE OUTPUT CURRENT (A) ALL OPTIONS VOUT = GND 100
Reverse Output Current
ALL OPTIONS VIN = GND OUTPUT NOISE (20ppm/DIV)
Output Noise 0.1Hz to 10Hz
ALL OPTIONS VIN = VOUT + 0.5V CL = 1F IL = 0
100
10
10
1
0
TA = 125C TA = 85C TA = 25C TA = -55C 0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 INPUT VOLTAGE (V)
6656 G11
1
TA = 125C TA = 85C TA = 25C TA = -55C 0 5 10 15 OUTPUT VOLTAGE (V) 20
6656 G12
TIME (1s/DIV)
6656 G13
Output Voltage Noise Spectrum
30 25 20 5V OPTION 15 10 5 0 2.5V OPTION 1.25V OPTION 10 100 1k FREQUENCY (Hz) 10k
6656 G24
Output Voltage Noise Spectrum vs Load Current
16 2.5V OPTION 14 VIN = 3V CL = 1F NOISE VOLTAGE (V/Hz) 12 10 8 6 4 2 0 10 100 1k FREQUENCY (Hz) 10k
6656 G14
Output Noise Voltage Spectrum vs Load Capacitance
40 2.5V OPTION 35 VIN = 3V CL = 47F IL = 0 NOISE VOLTAGE (V/Hz) 30 25 20 15 10 5 0 1 10 100 FREQUENCY (Hz) 1k
6656 G15
NOISE VOLTAGE (VRMS/Hz)
VIN = VOUT + 5V CL = 1F IL = 0
IL = 0 IL = 10A IL = 250A IL = 1mA
CL = 4.7F CL = 0.47F
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LT6656 Typical perForMance characTerisTics
Integrated 10Hz to 1kHz Noise vs Load Current
500 VIN = VOUT + 0.5V CL = 1F INTEGRATED NOISE (VRMS) 250
Integrated 10Hz to 1kHz Noise vs Load Current
2.5V OPTION 200
Long-Term Drift
ALL OPTIONS 150 CL = 1F IL = 0 LONG TERM DRIFT (ppm) 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
INTEGRATED NOISE (VRMS)
400
200
300 5V OPTION 200 2.5V OPTION
150
100 CL = 0.47F CL = 1F CL = 10F CL = 47F 1 10 100 LOAD CURRENT (A) 1m 10m
6656 G23
100 1.25V OPTION 0 0.1 1 10 100 LOAD CURRENT (A) 1m 10m
6656 G25
50
0 0.1
pin FuncTions
GND* (Pin 1): Internal Function. This pin must be tied to ground. GND (Pin 2): Device Ground. NC (Pin 3): Not internally connected. May be tied to VIN, VOUT, GND or floated. VIN (Pin 4): Power Supply. Bypass VIN with a 0.1F capacitor to ground. NC (Pin 5): Not internally connected. May be tied to VIN, VOUT, GND or floated. VOUT (Pin 6): Output Voltage. An output capacitor of 1F minimum is required for stable operation.
block DiagraM
VIN
NC
VOUT
BANDGAP
ERROR AMP NC
GND
GND
6656 BD
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LT6656 applicaTions inForMaTion
Long Battery Life 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 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 W, 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. Output Voltage Options 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. 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 0.1F input bypass capacitor placed within an inch of the input pin. An additional 2.2F 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 1F 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 (5 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.
VIN 3V CIN 0.1F R2 LT6656-2.5 CL 1F R1 2N7000
6656 F02
VIN 1V/DIV VOUT
1ms/DIV
6656 F01
Figure 1. LT6656-2.5 Turn-On Characteristics, CL = 1F
VGEN
3V
Figure 2. Transient Load Test Circuit
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LT6656 applicaTions inForMaTion
0A IOUT 100A
2.52V VOUT 2.50V 2.48V 5ms/DIV
6656 F03
Figure 3. Transient Response, 0A to 100A 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 5A, 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: Settling time 2(Deadband)(CL ) + ( VOUT )(0.8ms / V) IL
2.52V VOUT 2.50V 2.48V 5ms/DIV
6656 F04
Figure 4. Transient Response, 1mA to 2mA Load Step (R1 = R2 = 2.49k)
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 2A 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.
30 2.5V OPTION VIN = 3V 25 CL = 1F 20 15 10 5 0 0.001 IL = LOAD STEP TO 2A IL = ZERO TO LOAD STEP 0.01 0.1 LOAD STEP (mA) 1 10
6656 F06
VIN
3.25V 2.75V
2.7V VOUT 2.5V OUTPUT SETTLING TIME (ms) 2.3V 5ms/DIV
6656 F05
IL = LOAD STEP TO ZERO
Figure 5. Output Response to 0.5VP-P Step on VIN, CL = 1F 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.
Figure 6. Output Settling Time to 0.05% vs Load Step
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0
LT6656 applicaTions inForMaTion
VIN 3.25V 2.75V
input pulled to ground, the reverse output protection of the LT6656 limits the output current to typically less than 30A. The current versus reverse voltage is shown in the Typical Performance Characteristics section. Long-Term Drift 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 = 30C, 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. Hysteresis Hysteresis on the LT6656 is measured in two steps, for example, from 25C to -40C to 25C, then from 25C to 85C to 25C, 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 -40C to 85C, 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
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IL = 0 VOUT 10mV/DIV IL = 5A
5ms/DIV
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Figure 7. Detailed Output Response to a 0.5V Input Step, CIN = CL = 1F
The photo in Figure 7 shows the output response to a 0.5V input step in both a no-load and 5A 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. Output Noise 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 40A 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
LT6656 applicaTions inForMaTion
30 2.5V OPTION VIN = 3V 25 CL = 1F IL = 0 NUMBER OF UNITS 20 15 10 75 5 120s 0 -60 -40 -20 0 20 HYSTERESIS (ppm) 40 60
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0C TO 25C 70C TO 25C
300
380s
TP = 260C
225
TL = 217C TS(MAX) = 200C TS = 190C
RAMP DOWN
tP 30s tL 130s 40s
150
T = 150C RAMP TO 150C
0
0
2
4 6 MINUTES
8
10
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Figure 8. 0C to 70C Hysteresis
20 18 16 NUMBER OF UNITS 14 12 10 8 6 4 2 0 -160 -120 -80 -40 0 40 80 120 160 HYSTERESIS (ppm)
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Figure 10. Lead Free Reflow Profile Due to IR Reflow
7 2.5V OPTION VIN = 3V 6 C = 1F L IL = 0 5 4 3 2 1 0 0 20 60 100 140 180 220 CHANGE IN OUTPUT VOLTAGE (ppm)
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-40C TO 25C 85C TO 25C
2.5V OPTION VIN = 3V CL = 1F IL = 0 NUMBER OF UNITS
3 CYCLES 1 CYCLE
Figure 9. -40C to 85C Hysteresis
IR reflow. Common lead free IR reflow profiles reach over 250C, 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 = 260C
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.
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LT6656 Typical applicaTions
Regulator 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.
3V VIN 18V 0.1F IN LT6656-2.5 OUT MCU 10F VCC/VREF PB0/AIN0/AREF/MOSI PB1/INT0/AIN1/MISO/OC1A PB2/ADC1/SCK/T0/INT0 PB3/ADC2 PB4/ADC3 PB5/RESET/ADC0 GND
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Low Power ADC Reference Low power ADCs draw only a few As during their idle period and well over 100A 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 1A, during conversion the IQ jumps up to 160A. 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 160A, 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 26.4A. When taking into consideration the current drawn by the reference, the total current draw is only 27.4A. 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.
OUT 4.7F IN+ DIFFERENTIAL INPUT VREF * 0.5 (2.5V) REF VCC
5 6 7 2 3 1
Figure 12. Microcontroller Reference and Regulator
5.1V VIN 18V 0.1F
IN
LT6656-5
CS SCK SDO
LTC2480 IN-
AT 1sps, IQ = 27.4A
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Figure 13. Low Power ADC Reference
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LT6656 Typical applicaTions
Extended Supply Range Reference
VCC UP TO 160V 330k MMBT5551
BZX584C12 2.2F
0.1F
IN OUT LT6656-2.5 VOUT 1F
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Boosted Output Current Reference
3.6V VCC 18V 220 0.1F
+
10F 2N2905
IN OUT LT6656-2.5 1F
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VOUT 40mA MAX
Micropower Regulator, IQ = 2A, Sink Up to 8mA
3V VCC 18V IN 0.1F LT6656-2.5 OUT 1F
+
LT6003 2.5V
-
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ADC Reference and Bridge Excitation Supply
3.8V VIN 18V 0.1F IN LT6656-3.3 3.3V VCC 5.5V OUT 1F 10k 10k IN- VREF VCC CS SCK SDO 0.1F 10F
0.1F
LTC2452 IN+
10k
0.1F
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LT6656 Typical applicaTions
Low Power Precision High Voltage Supply Monitor, IQ = 1.4A, High Voltage Supply Load = 10A
100V 105V OVERVOLTAGE THRESHOLD VCC 3
9.53M 6.5V VCC 10V IN 0.1F LT6656-5 OUT 1F 475k
+ -
1, 2
7 OVERVOLTAGE FLAG 6
4
LTC1540 5
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2-Terminal Current Source
+
+
IN 0.1F LT6656-1.25 GND OUT VREF R1 1F R2 R3 -
IOUT VREF R2 1 R1 R3
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LT6003
-
Precision Current and Boosted Reference, IQ = 5.5A
249k VCC
2N5086 1A OUT
1k
+
LT6004
+
LT6004 2.75V 200k
-
3V VCC 16V IN 0.1F LT6656-2.5
-
2M OUT 2.5V 1F
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LT6656 package DescripTion
(Reference LTC DWG # 05-08-1636)
0.62 MAX 0.95 REF 2.90 BSC (NOTE 4)
S6 Package 6-Lead Plastic TSOT-23
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
0.95 BSC 0.80 - 0.90
0.30 - 0.45 6 PLCS (NOTE 3)
0.20 BSC DATUM `A' 1.00 MAX
0.01 - 0.10
0.30 - 0.50 REF
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
0.09 - 0.20 (NOTE 3)
1.90 BSC
S6 TSOT-23 0302 REV B
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LT6656 revision hisTory
REV A DATE 7/10 DESCRIPTION Voltage options added (1.25, 2.048, 3, 3.3), reflected throughout the data sheet PAGE NUMBER 1 to 18
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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.
LT6656 Typical applicaTion
Reference Regulator for Micropower DAC, Total IQ = 4.8A
5.1V VIN 18V 0.1F IN LT6656-5 OUT 5V 10F VREF CS SCK SDI LTC1662 DAC B GND
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VCC DAC A 0V TO 5V OUTPUT
0V TO 5V OUTPUT
relaTeD parTs
PART NUMBER LT1389 LTC1440 LT1460 LT1461 LT1495 LTC1540 LT1634 LT1790 LTC1798 LT6003 LT6650 LT6660 LT6700 DESCRIPTION Micropower Comparator with Reference Micropower Series Reference Micropower Precision LDO Series Reference 1.5A Precision Rail-to-Rail Dual Op Amp Nanopower Comparator with Reference Micropower Precision Shunt Voltage Reference Micropower Precision Series Reference 6A Low Dropout Series Reference 1.6V, 1A Precision Rail-to-Rail Op Amp Micropower Reference with Buffer Amplifier Tiny Micropower Series Reference Micropower, Low Voltage Dual Comparator with 40mV Reference COMMENTS 3.7A Max Supply Current, 1% 1.182V Reference, MSOP PDIP and SO-8 Packages , 0.075% Max, 10ppm/C Max Drift, 2.5V, 5V and 10V Versions,MSOP PDIP SO-8, , , SOT-23 and TO-92 Packages 3ppm/C Max Drift, 0C to 70C, -40C to 85C, -40C to 125C Options in SO-8 1.5A Max Supply Current, 100pA Max IOS 600nA Max Supply Current, 2% 1.182V Reference, MSOP and SO-8 Packages 0.05% Max, 10ppm/C Max Drift, 1.25V, 2.5V, 4.096V, 5V, 10A Maximum Supply Current 0.05% Max, 10ppm/C Max, 60A Supply, SOT23 Package Available in Adjustable, 2.5V, 3V, 4.096V and 5V 1A Max Supply Current, 1.6V Minimum Operating Voltage, SOT-23 Package 0.05% Max, 5.6A Supply, SOT-23 Package 0.2% Max, 20ppm/C Max, 20mA Output Current, 2mm x 2mm DFN 6.5A Supply Current, 1.4V Minimum Operating Voltage Nanopower Precision Shunt Voltage Reference 0.05% Max 10ppm/C Max, 800nA Supply
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
LT 0710 REV A * PRINTED IN USA
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2010

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