LTC6915 Zero Drift, Precision Instrumentation Amplifier with Digitally Programmable Gain U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC®6915 is a precision programmable gain instrumentation amplifier. The gain can be programmed to 0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, or 4096 through a parallel or serial interface. The CMRR is typically 125dB with a dual 5V supply with any programmed gain. The offset is below 10µV with a temperature drift of less than 50nV/°C. 14 Levels of Programmable Gain 125dB CMRR Independent of Gain Gain Accuracy 0.1% (Typ) Maximum Offset Voltage of 10µV Maximum Offset Voltage Drift: 50nV/°C Rail-to-Rail Input and Output Parallel or Serial (SPI) Interface for Gain Setting Supply Operation: 2.7V to ±5.5V Typical Noise: 2.5µVP-P (0.01Hz to 10Hz) 16-Lead SSOP and 12-Lead DFN Packages The LTC6915 uses charge balanced sampled data techniques to convert a differential input voltage into a single ended signal that is in turn amplified by a zero-drift operational amplifier. U APPLICATIO S ■ ■ ■ ■ ■ The differential inputs operate from rail-to-rail and the single-ended output swings from rail-to-rail. The LTC6915 can be used in single power supply applications as low as 2.7V, or with dual ±5V supplies. The LTC6915 is available in a 16-lead SSOP package and a 12-lead DFN surface mount package. Thermocouple Amplifiers Electronic Scales Medical Instrumentation Strain Gauge Amplifier High Resolution Data Acquisition , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATIO Differential Bridge Amplifier with Gain Programmed through the Serial Interface LTC6915 SSOP PACKAGE 3 IN + + OUT 15 3V 2 IN _ CS CH – SENSE 14 CF R < 10k RESISTOR ARRAY REF 13 11 PARALLEL_SERIAL MUX µP TO OTHER DEVICES 6 CS(D0) 7 DIN(D1) 8 CLK(D2) 9 DOUT(D3) 4-BIT LATCH HOLD_THRU 5 V+ 16 3V 0.1µF Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7 8-BIT SHIFT-REGISTER SHDN DGND V 1 10 – 4 6915 TA01 6915f 1 LTC6915 W W U W ABSOLUTE AXI U RATI GS (Note 1) Total Supply Voltage (V + to V –) ............................... 11V Input Current ...................................................... ±10mA |VIN+ – VREF| ....................................................... 5.5V |VIN– – VREF| ....................................................... 5.5V |V+ – VDGND| ....................................................... 5.5V |VDGND – V –| ....................................................... 5.5V Digital Input Voltage ......................................... V – to V + Operating Temperature Range LTC6915C .............................................–0°C to 70°C LTC6915I .............................................–40°C to 85°C LTC6915H .........................................–40°C to 125°C Junction Temperature (GN Package) ................................................... 150°C (DFN Package).................................................. 125°C Storage Temperature (GN Package) ....................................–65°C to 150°C (DFN Package)...................................–65°C to 125°C Lead Temperature (Soldering 10 sec)................... 300°C U W U PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW IN– 1 12 V + IN+ 2 11 OUT V– 3 10 REF CS(D0) 4 9 PARALLEL_SERIAL 8 DGND 7 DOUT(D3) DIN(D1) CLK(D2) 5 6 DE12 PACKAGE 12-LEAD (4mm × 3mm) PLASTIC DFN UNDERSIDE METAL CONNECTED TO V– TJMAX = 125°C, θJA = 160°C/W ORDER PART NUMBER TOP VIEW SHDN 1 LTC6915CDE LTC6915IDE IN – 2 15 OUT IN + 3 14 SENSE V– 4 HOLD_THRU 5 DFN PART MARKING 16 V+ 13 REF 12 NC CS(D0) 6 11 PARALLEL_SERIAL DIN(D1) 7 10 DGND CLK(D2) 8 9 6915 6915I LTC6915CGN LTC6915IGN LTC6915HGN GN PART MARKING DOUT(D3) GN PACKAGE 16-LEAD NARROW PLASTIC SSOP 6915 6915I 6915H TJMAX = 150°C, θJA = 135°C/W Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. SYMBOL V+ = 3V, V – PARAMETER CONDITIONS MIN TYP MAX UNITS 0 0.075 % = 0V, VREF = 200 mV Gain Error (Note 2) AV = 1 (RL =10k) ● –0.075 Gain Error (Note 2) AV = 2 to 32 (RL = 10k) ● –0.5 0 0.5 % Gain Error (Note 2) AV = 64 to 1024 (RL = 10k) ● –0.6 –0.1 0.6 % Gain Error (Note 2) AV = 2048, 4096 (RL = 10k) ● –1 –0.2 1.0 % Gain Nonlinearity AV = 1 ● 3 15 ppm Input Offset Voltage (Note 3) VCM = 200mV –3 ±10 µV Average Input Offset Drift (Note 3) TA = –40°C to 85°C TA = 85°C to 125°C ● ● ±50 ±100 nV/°C nV/°C IB Average Input Bias Current (Note 4) VCM = 1.2V ● 5 10 nA IOS Average Input Offset Current (Note 4) VCM = 1.2V ● 1.5 3 nA VOS 6915f 2 LTC6915 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V+ = 3V, V – = 0V, VREF = 200 mV CMRR Common Mode Rejection Ratio AV = 1024, VCM = 0V to 3V, LTC6915C AV = 1024, VCM = 0.1V to 2.9V, LTC6915I AV = 1024, VCM = 0V to 3V, LTC6915I AV = 1024, VCM = 0.1V to 2.9V, LTC6915H AV = 1024, VCM = 0V to 2.97V, LTC6915H ● ● ● ● ● 100 100 95 100 85 119 119 119 dB dB dB dB dB PSRR Power Supply Rejection Ratio (Note 5) VS = 2.7V to 6V ● 110 116 dB Output Voltage Swing High (Referenced to V–) Sourcing 200µA Sourcing 2mA ● ● 2.95 2.75 2.98 2.87 V V Output Voltage Swing Low (Referenced to V–) Sinking 200µA Sinking 2mA ● ● 18 130 50 300 mV mV Supply Current, Parallel Mode No Load at OUT, VCM = 200mV ● 0.88 1.3 mA Supply Current, Serial Mode (Note 6) No Load at OUT, Capacitive Load at DOUT (CL) = 15pF, Continuous CLK Frequency = 4MHz, CS= LOW, Gain Control Code = 0001 ● 1.1 1.65 mA Supply Current Shutdown VSHDN = 2.7V (Hardware Shutdown) VSHDN = 1V, Gain Control Code = 0000 (Software Shutdown ) ● ● 1 125 4 180 µA µA SHDN Input High ● SHDN Input Low ● 2.7 1 V V SHDN and HOLD_THRU Input Current (Note 2) ● 5 µA Internal Op Amp Gain Bandwidth 200 kHz Slew Rate 0.2 V/µs –0.5 3 kHz Internal Sampling Frequency V+ = 5V, V– = 0V, VREF = 200mV VOS Gain Error (Note 2) AV = 1 (RL = 10k) ● –0.075 0 0.075 % Gain Error (Note 2) AV = 2 to 32 (RL= 10k) ● –0.5 0 0.5 % Gain Error (Note 2) AV = 64 to 1024 (RL = 10k) ● –0.6 –0.1 0.6 % Gain Error (Note 2) AV = 2048, 4096 (RL = 10k) ● –1 –0.2 1 % Gain Nonlinearity AV = 1 ● 3 15 ppm Input Offset Voltage (Note 3) VCM = 200mV Average Input Offset Drift (Note 3) TA = –40°C to 85°C TA = 85°C to 125°C ● –3 ±10 µV ±50 ±100 nV/°C nV/°C Average Input Bias Current (Note 4) VCM = 1.2V ● 5 10 nA IOS Average Input Offset Current (Note 4) VCM = 1.2V ● 1.5 3 nA CMRR Common Mode Rejection Ratio AV = 1024, VCM = 0V to 5V, LTC6915C AV = 1024, VCM = 0.1V to 4.9V, LTC6915I AV = 1024, VCM = 0V to 5V, LTC6915I AV = 1024, VCM = 0.1V to 4.9V, LTC6915H AV = 1024, VCM = 0V to 4.97V, LTC6915H ● ● ● ● ● PSRR Power Supply Rejection Ratio (Note 5) VS = 2.7V to 6V ● Output Voltage Swing High Sourcing 200µA Sourcing 2mA ● ● Output Voltage Swing Low Sinking 200µA Sinking 2mA ● ● 105 105 95 100 85 125 125 125 dB dB dB dB dB 110 116 dB 4.95 4.80 4.99 4.93 V V 17 120 50 300 mV mV 6915f 3 LTC6915 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. SYMBOL V+ PARAMETER = 5V, V – = 0V, V CONDITIONS MIN VOS MAX UNITS REF = 200mV Supply Current, Parallel Mode No Load at OUT, VCM = 200mV ● 0.95 1.48 mA Supply Current, Serial Mode (Note 6) No Load at OUT, Capacitive Load at DOUT (CL) = 15pF, Continuous CLK Frequency = 4MHz, CS = LOW, Gain Control Code = 0001 ● 1.4 2 mA Supply Current, Shutdown VSHDN = 4.5V (Hardware Shutdown) VSHDN = 1V, Gain Control Code = 0000 (Software Shutdown) ● ● 2 135 10 200 µA µA 1 V SHDN Input High ● SHDN Input Low ● SHDN and HOLD_THRU Input Current (Note 2) ● 4.5 V 5 µA Internal Op Amp Gain Bandwidth 200 kHz Slew Rate 0.2 V/µs 3 kHz Internal Sampling Frequency V + = 5V, V– TYP = –5V, VREF = 0V Gain Error (Note 2) AV = 1 (RL = 10k) ● –0.075 0 0.075 % Gain Error (Note 2) AV = 2 to 32 (RL = 10k) ● Gain Error (Note 2) AV = 64 to 1024 (RL = 10k) ● –0.5 0 0.5 % –0.6 –0.1 0.6 % Gain Error (Note 2) AV = 2048, 4096 (RL = 10k) ● Gain Nonlinearity AV = 1 ● –1 –0.2 1 % 3 15 ppm ±20 nV nV/°C nV/°C VCM = 0mV Average Input Offset Drift (Note 3) TA = –40°C to 85°C TA = 85°C to 125°C ● ● Average Input Bias Current (Note 4) VCM = 1V ● 4 10 nA Average Input Offset Current (Note 4) VCM = 1V ● 1.5 3 nA CMRR Common Mode Rejection Ratio AV = 1024, VCM = –5V to 5V, LTC6915C AV = 1024, VCM = –4.9V to 4.9V, LTC6915I AV = 1024, VCM = –5V to 5V, LTC6915I AV = 1024, VCM = –4.9V to 4.9V, LTC6915H AV = 1024, VCM = –5V to 4.97V, LTC6915H ● ● ● ● ● PSRR Power Supply Rejection Ratio (Note 5) VS = 2.7V to 11V ● Output Voltage Swing High Sourcing 200µA Sourcing 2mA ● ● Output Voltage Swing Low Sinking 200µA Sinking 2mA ● ● –4.98 –4.90 –4.92 –4.70 mV mV Supply Current, Parallel Mode No Load, VCM = 200mV ● 1.1 1.6 mA Supply Current, Serial Mode (Note 6) No Load at OUT, Capacitive Load at DOUT (CL) = 15pF, Continuous CLK Frequency = 4MHz, CS = LOW, Gain Control Code = 0001 ● 1.73 2.48 mA Supply Current, Shutdown VSHDN = 4V (Hardware Shutdown) VSHDN = 1V, Gain Control Code = 0000 (Software Shutdown ) ● ● 160 25 240 µA µA IOS 5 ±50 ±100 Input Offset Voltage (Note 3) SHDN Input High ● SHDN Input Low ● 105 105 100 100 90 123 123 123 dB dB dB dB dB 110 116 dB 4.97 4.90 4.99 4.96 V V 4 V 1 V 6915f 4 LTC6915 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V + = 5V, V– = –5V, VREF = 0V SHDN and HOLD_THRU Input Current (Note 2) 5 ● µA Internal Op Amp Gain Bandwidth 200 kHz Slew Rate 0.2 V/µs 3 kHz Internal Sampling Frequency Digital I/O, All Digital I/O Voltage Referenced to DGND VIH Digital Input High Voltage ● VIL Digital Input Low Voltage ● 2.0 V 0.8 V+ – 0.3 V VOH Digital Output High Voltage Sourcing 500µA ● VOL Digital Output Low Voltage Sinking 500µA ● 0.3 V Digital Input Leakage V+ = 5V, V– = –5V, V ● ±2 µA Timing, V + = 2.7V to 4.5V, V – IN = 0V to 5V V = 0V (Note 7) t1 DIN Valid to CLK Setup ● t2 DIN Valid to CLK Hold ● 0 ns t3 CLK Low ● 100 ns t4 CLK High ● 100 ns t5 CS/LD Pulse Width ● 60 ns t6 LSB CLK to CS/LD ● 60 ns t7 CS/LD Low to CLK ● 30 t8 DOUT Output Delay t9 CLK Low to CS/LD Low CL = 15pF 60 ns ns 125 ● ns ● 0 ns Timing, V+ = 4.5V to 5.5V, V – = 0V (Note 7) t1 DIN Valid to CLK Setup ● 30 ns t2 DIN Valid to CLK Hold ● 0 ns t3 CLK Low ● 50 ns t4 CLK High ● 50 ns t5 CS/LD Pulse Width ● 40 ns t6 LSB CLK to CS/LD ● 40 ns t7 CS/LD Low to CLK ● 20 ns t8 DOUT Output Delay t9 CLK Low to CS/LD Low CL = 15pF 85 ● ns ● 0 ns Timing, Dual ±4.5V to ±5.5V Supplies (Note 7) t1 DIN Valid to CLK Setup ● 30 ns t2 DIN Valid to CLK Hold ● 0 ns t3 CLK High ● 50 ns t4 CLK Low ● 50 ns t5 CS/LD Pulse Width ● 40 ns t6 LSB CLK to CS/LD ● 40 ns t7 CS/LD Low to CLK ● 20 ns t8 DOUT Output Delay t9 CLK Low to CS/LD Low CL = 15pF 85 ● ● 0 ns ns 6915f 5 LTC6915 ELECTRICAL CHARACTERISTICS Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: These parameters are tested at ±5V supply; at 3V and 5V supplies they are guaranteed by design. Note 3: These parameters are guaranteed by design. Thermocouple effects preclude measurement of these voltage levels in high speed automatic test systems. VOS is measured to a limit set by test equipment capability. Note 4: If the total source resistance is less than 10k, no DC errors result from the input bias current or mismatch of the input bias currents or the mismatch of the resistances connected to IN – and IN+. Note 5: The PSRR measurement accuracy depends on the proximity of the power supply bypass capacitor to the device under test. Because of this, the PSRR is 100% tested to relaxed limits at final test. However, their values are guaranteed by design to meet the data sheet limits. Note 6: Supply current is dependent on the clock frequency. A higher clock frequency results in higher supply current. Note 7: Guaranteed by design, not subject to test. U W TYPICAL PERFOR A CE CHARACTERISTICS Input Offset Voltage vs Input Common Mode –4 –6 AV = 4096 –8 AV = 256 –10 AV = 16 –12 AV = 1 –2 –8 AV = 256 –10 –12 AV = 16 –14 –16 –16 –18 2.5 1.0 1.5 2.0 0.5 INPUT COMMON MODE VOLTAGE (V) AV = 4096 –6 6915 G01 5 0 TA = 125°C –5 TA = 85°C TA = 25°C –15 –20 TA = 70°C –6 AV = 256 AV = 16 –8 –10 –14 AV = 1 –5 –4 –3 –2 –1 0 1 2 3 4 INPUT COMMON MODE VOLTAGE (V) 2.5 1.0 1.5 2.0 0.5 INPUT COMMON MODE VOLTAGE (V) 15 10 5 TA = 125°C 0 –5 TA = 85°C TA = 25°C –10 TA = 70°C 6915 G04 –20 0 10 5 VS = ±5V VREF = 0V AV = 16 TA = –50°C TA = 25°C TA = 125°C 0 –5 –10 TA = 85°C TA = 70°C –15 –20 TA = –50°C 3.0 5 6915 G03 20 –15 TA = –50°C 0 AV = 4096 –4 Input Offset Voltage vs Input Common Mode VS = 5V VREF = 0.2V AV = 16 15 INPUT OFFSET VOLTAGE (µV) INPUT OFFSET VOLTAGE (µV) 20 10 –10 0 –2 Input Offset Voltage vs Input Common Mode VS = 3V VREF = 0.2V AV = 16 15 2 6915 G02 Input Offset Voltage vs Input Common Mode 20 4 –12 AV = 1 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT COMMON MODE VOLTAGE (V) 3.0 VS = ±5V VREF = 0V TA = 25°C 6 –4 –14 0 8 VS = 5V VREF = 0.2V TA = 25°C 0 INPUT OFFSET VOLTAGE (µV) INPUT OFFSET VOLTAGE (µV) –2 2 Input Offset Voltage vs Input Common Mode INPUT OFFSET VOLTAGE (µV) VS = 3V VREF = 0.2V TA = 25°C INPUT OFFSET VOLTAGE (µV) 0 Input Offset Voltage vs Input Common Mode 2 3 1 4 INPUT COMMON MODE VOLTAGE (V) 5 6915 G05 –25 –5 3 –3 1 –1 INPUT COMMON MODE VOLTAGE (V) 5 6915 G06 6915f 6 LTC6915 U W TYPICAL PERFOR A CE CHARACTERISTICS 20 RS = 15k –20 RS = 20k –30 VS = 3V RS VREF = 0.2V + R+ = R– = RS CIN –40 CIN < 100pF – AV = 16 RS TA = 25°C –50 2.5 0 1.0 1.5 2.0 0.5 INPUT COMMON MODE VOLTAGE (V) 10 RS = 10k RS = 15k 0 RS = 5k RS –10 + CIN –20 3.0 1 3 4 2 INPUT COMMON MODE VOLTAGE (V) Error Due to Input RS Mismatch vs Input Common Mode Error Due to Input RS Mismatch vs Input Common Mode ADDITIONAL OFFSET (µV) R+ = 15k, R– = 0k –20 R+ –40 + CIN R 0 R+ = 0k, R– = 15k 0 + – R = 15k, R = 0k –10 R+ –20 + – –30 R –40 3.0 Offset Voltage vs Temperature VS = ±5V VREF = 0V 20 CIN < 100pF AV = 16 TA = 25°C 10 5 R+ = 0k, R– = 20k R+ = 0k, R– = 15k 0 –10 R+ –20 CIN R+ = 15k, R– = 0k R+ = 20k, R– = 0k + – R– VOS vs REF (Pin 13) + 20 VIN = VIN = REF AV = 16 TA = 25°C 10 5 –5 –4 –3 –2 –1 0 1 2 3 4 INPUT COMMON MODE VOLTAGE (V) 6915 G12 VOS vs REF (Pin 13) 2 – VIN+ = VIN– = REF AV = 16 TA = 25°C 10 –3 VS = ±5V VS = 5V VS = 3V VOS (µV) 0 5 VOS (µV) INPUT OFFSET VOLTAGE (µV) –3 1 3 –1 INPUT COMMON MODE VOLTAGE (V) 6915 G11 15 –8 VS = 5V VS = 3V –13 –5 –10 –50 –5 –30 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT COMMON MODE VOLTAGE (V) 6915 G10 0 – RS R+ = 20k, R– = 0k – 2.5 1.0 1.5 2.0 0.5 INPUT COMMON MODE VOLTAGE (V) + Error Due to Input RS Mismatch vs Input Common Mode R+ = 0k, R– = 20k 10 R+ = 20k, R– = 0k – RS –10 30 VS = 5V 30 VREF = 0.2V CIN < 100pF 20 AV = 16 TA = 25°C CIN – –60 RS = 5k 6915 G09 40 0 RS = 15k 0 –20 5 6915 G08 VS = 3V = 0.2V V 60 REF CIN < 100pF R+ = 0k, R– = 20k A = 16 40 V TA = 25°C R+ = 0k, R– = 15k 20 RS = 10k CIN 6915 G07 80 10 RS = 20k – RS 0 VS = ±5V VREF = 0V R+ = R– = RS CIN < 100pF AV = 16 TA = 25°C RS = 20k ADDITIONAL OFFSET (µV) ADDITIONAL OFFSET (µV) RS = 10k –10 ADDITIONAL OFFSET (µV) RS = 5k 0 ADDITIONAL OFFSET (µV) 20 VS = 5V VREF = 0.2V R+ = R– = RS CIN < 100pF AV = 16 TA = 25°C ADDITIONAL OFFSET (µV) 10 –80 Error Due to Input RS vs Input Common Mode Error Due to Input RS vs Input Common Mode Error Due to Input RS vs Input Common Mode VS = 10V –10 –20 –30 –25 50 25 0 75 TEMPERATURE (°C) 100 125 6915 G13 –18 0 0.5 1.0 1.5 2.0 2.5 VREF (V) 3.0 3.5 4.0 6915 G14 –40 0 1 2 3 4 5 6 VREF (V) 7 8 9 10 6915 G15 6915f 7 LTC6915 U W TYPICAL PERFOR A CE CHARACTERISTICS Gain Nonlinearity at Gain = 1 (Gain Nonlinearity Decreases for Gain > 1) Supply Current vs Supply Voltage VS = ±2.5V 4 VCM = VREF = 0V R = 10k 3 AL = 1 V 2 TA = 25°C –1 –2 120 TA = 85°C 1.05 TA = 125°C 0.95 TA = 0°C 0.90 0.80 –4 0.75 + 1.8 0.70 2.4 70 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 SUPPLY VOLTAGE (V) 200 VS = 5V 150 VS = 3V 100 50 10 100 1000 FREQUENCY (Hz) 3 VS = 3V TA = 25°C 2 1 0 –1 –2 –3 1 10000 0 2 4 6 TIME (s) 5 4 OUTPUT VOLTAGE SWING (V) VS = 3V, SOURCING 2.0 1.5 0.5 0 0.01 VS = 3V, SINKING VS = 5V, SINKING 1 0.1 OUTPUT CURRENT (mA) –1 –2 VS = ±5V TA = 25°C 6915 G22 2 4 6 TIME (s) 8 SOURCING 7 2 1 0 –1 –2 6 VS = 5V dVOUT = 1V G ≤ 100 TA = 25°C 5 4 3 2 –3 –5 0.01 10 8 Low Gain Settling Time vs Settling Accuracy 3 –4 10 0 6915 G21 SETTLING TIME (ms) VS = 5V, SOURCING 2.5 1.0 0 Output Voltage Swing vs Output Current 3.5 3.0 1 6915 G20 Output Voltage Swing vs Output Current 4.0 VS = 5V TA = 25°C 2 –3 10 8 6915 G19 TA = 25°C 1000 Input Referred Noise in 10Hz Bandwidth INPUT REFFERED NOISE VOLTAGE (µV) INPUT REFFERED NOISE VOLTAGE (µV) INPUT REFERRED NOISE DENSITY (nV/√Hz) VS = ±5V 10 100 FREQUENCY (Hz) 1 6915 G18 3 250 R+ = 0k, R– = 10k 6915 G17 Input Referred Noise in 10Hz Bandwidth AV = 16 TA = 25°C – R– Input Voltage Noise Density vs Frequency OUTPUT VOLTAGE SWING (V) R+ TA = –50°C 6915 G16 4.5 R+ = 10k, R– = 0k 80 –5 –2.4 –1.8 –1.2 –0.6 0 0.6 1.2 OUTPUT VOLTAGE (V) 5.0 R+ = R– = 10k 100 90 0.85 –3 R+ = R– = 1k 110 1.00 CMRR (db) 0 0 VS = 3V, 5V, ±5V VIN = 1VP-P 1.10 1 300 CMRR vs Frequency 130 1.15 SUPPLY CURRENT (mA) GAIN NONLINEARITY (ppm) 5 1 SINKING 1 0.1 OUTPUT CURRENT (mA) 10 6915 G23 0 0.0001 0.01 0.001 SETTLING ACCURACY (%) 0.1 6915 G24 6915f 8 LTC6915 U W TYPICAL PERFOR A CE CHARACTERISTICS Internal Clock Frequency vs Supply Voltage Settling Time vs Gain 35 20 15 10 3.30 TA = 125°C 3.25 TA = 85°C 3.20 3.15 5 0 ADDITIONAL GAIN ERROR (%) 25 0.1 3.35 CLOCK FREQUENCY (kHz) SETTLING TIME (ms) 3.40 VS = 5V dVOUT = 1V 0.1% ACCURACY TA = 25°C 30 Additional Gain Error vs Load Resistance 10 100 GAIN (V/V) 1000 10000 3.10 2.5 4.5 6.5 8.5 SUPPLY VOLTAGE (V) 6915 G25 U U U PI FU CTIO S AV = 16 –0.1 AV = 256 –0.2 –0.3 AV = 4096 TA = –55°C TA = 25°C 1 0 10.5 6915 G26 –0.4 0 2 6 8 4 LOAD RESISTANCE RL (k) 10 6915 G27 (DFN/GN Packages) IN– (Pin 1/Pin 2): Inverting Analog Input. SHDN (Pin 1 GN Package Only): Shutdown Pin. The IC is shut down when SHDN is tied to V +. An internal current source pulls this pin to V – when floating. IN+ (Pin 2/Pin 3): Noninverting Analog Input. V– (Pin 3/Pin 4): Negative Supply. CS(D0) (Pin 4/Pin 6): TTL Level Input. When in serial control mode, this pin is the chip select input (active low); in parallel control mode, this pin is the LSB of the parallel gain control code. DIN(D1) (Pin 5/Pin 7): TTL Level Input. When in serial control mode, this pin is the serial input data; in parallel mode, this pin is the second LSB of the parallel gain control code. HOLD_THRU (Pin 5 GN Package Only): TTL Level Input for Parallel Control Mode. When HOLD_THRU is high, the parallel data is latched in an internal D-latch. CLK(D2) (Pin 6/Pin 8): TTL Level Input. When in serial control mode, this pin is the clock of the serial interface; in parallel mode, this pin is the third LSB of the parallel gain control code. DOUT(D3) (Pin 7/Pin 9): TTL Level Input. When in serial control mode, this pin is the output of the serial data; in parallel mode, this pin is the MSB of the 4-bit parallel gain control code. In parallel mode operation, if the data in to DOUT (Pin 9) is from a voltage source greater than V+ (Pin 12), then connect a resistor between the voltage source and DOUT to limit the current into Pin 9 to 5mA or less. DGND (Pin 8/Pin 10): Digital Ground. PARALLEL_SERIAL (Pin 9/Pin 11): Interface Selection Input. When tied to V+, the interface is in parallel mode, i.e., the PGA gain is defined by the parallel codes (D3 ~ D0), i.e., CS(D0), DATA(D1), CLK(D2), and D OUT(D3). When PARALLEL_SERIAL pin is tied to V –, the PGA gain is set by the serial interface. REF (Pin 10/Pin 13): Voltage Reference for PGA output. OUT (Pin 11/Pin 15): Amplifier Output. The typical current sourcing/sinking of the OUT pin is 1mA. For minimum gain error, the load resistance should be 1k or greater (refer to the Output Voltage Swing vs Output Current and Gain Error vs Load Resistance in the Typical Performance Characteristics section). V+ (Pin 12/Pin 16): Positive Supply. SENSE (Pin 14 GN Package Only): Sense Pin. When the PGA drives a low resistance load and the interconnect resistance between the OUT pin and the load is not negligible, tying the SENSE pin as close as possible to the load can improve the gain accuracy. 6915f 9 LTC6915 W BLOCK DIAGRA S (GN Package Only) IN + 3 + 15 CS IN – CH 2 – 14 CF OUT SENSE GAIN CONTROL RESISTOR ARRAY 13 PARALLEL_SERIAL 11 CS(D0) DIN(D1) CLK(D2) DOUT(D3) 5 4-BIT LATCH MUX 1 6 7 Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7 8-BIT SHIFT-REGISTER 8 16 10 4 9 REF HOLD_THRU SHDN V+ DGND V– 6915 BD01 (DFN Package Only) IN + 2 + 11 CS IN – 1 CH OUT – CF GAIN CONTROL RESISTOR ARRAY 10 PARALLEL_SERIAL 9 MUX CS(D0) DIN(D1) CLK(D2) DOUT(D3) 4 5 6 REF 4-BIT LATCH DGND Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7 8-BIT SHIFT-REGISTER 12 8 3 7 V+ DGND V– 6915 BD02 6915f 10 LTC6915 WU W TI I G DIAGRA Timing Diagram of the Serial Interface t4 t1 t2 t6 t3 t7 CLK t9 D3 DIN D2 D1 D0 D7 • • • • D4 D3 t5 CS/LD t8 DOUT D4 D3 D2 PREVIOUS BYTE D1 D0 D7 • • • • D4 CURRENT BYTE D3 6915 TD U OPERATIO Theory of Operation (Refer to Block Diagrams) The LTC6915 uses an internal capacitor (CS) to sample a differential input signal riding on a DC common mode voltage (the sampling rate is 3kHz and the input switch-on resistance is 1k to 2k, depending on the power supply voltage). This capacitor’s charge is transferred to a second internal hold capacitor (CH) translating the common mode voltage of the input differential signal to that of REF pin. The resulting signal is amplified by a zero-drift op amp in the noninverting configuration. Gain control within the amplifier occurs by switching resistors from a matched resistor array. The LTC6915 has 14 levels of gain, controlled by the parallel or serial interface. A feedback capacitor CF helps to reduce the switching noise. Due to the input sampling, an LTC6915 may produce aliasing errors for input signals greater than 1.5kHz (one half the 3kHz sampling frequency). However, if the input signal is bandlimited to less than 1.5kHz then an LTC6915 is useful as instrumentation or as a differential to single-ended AC amplifier with programmable gain. Parallel Interface As shown in Figure 1, connecting PARALLEL_SERIAL to V+ allows the gain control code to be set through the parallel lines (D3, D2, D1, D0). When HOLD_THRU is low (referenced to DGND) or floating, the parallel gain control bits (D3 ~ D0) directly control the PGA gain. When HOLD_THRU is high, the parallel gain control bits are read into and held by a 4-bit latch. Any change at D3 ~ D0 will not affect the PGA gain when HOLD_THRU is high. Note that the DFN12 package does not have the HOLD_THRU pin. Instead, it is tied to DGND internally. The DOUT(D3) pin is bidirectional (output in serial mode, input in parallel mode). In parallel mode, the voltage at DOUT(D3) cannot exceed V+; otherwise, large currents can be injected to V+ through the parasitic diode (see Figure 2). Connecting a 10k resistor at the DOUT(D3) pin if parallel mode is selected (see Figure 1) is recommended for current limiting. Serial Interface Connecting PARALLEL_SERIAL to V – allows the gain control code to be set through the serial interface. When CS is low, the serial data on DIN is shifted into an 8-bit shiftregister on the rising edge of the clock, with the MSB transferred first (see Figure 3). Serial data on DOUT is shifted out on the clock’s falling edge. A high CS will load the 4 LSBs of the shift-register into a 4-bit D-latch, which are the gain control bits. The clock is disabled internally when CS is pulled high. Note: CLK must be low before CS is pulled low to avoid an extra internal clock pulse. 6915f 11 LTC6915 U OPERATIO DOUT is always active in serial mode (never tri-stated). This simplifies the daisy chaining of the multiple devices. DOUT cannot be “wire-or” to other SPI outputs. In addition, DOUT does not return to zero at the end of transmission, i.e. when CS is pulled high. A LTC6915 may be daisy-chained with other LTC6915s or other devices having serial interfaces by connecting the DOUT to the DIN of the next chip while CLK and CS remain common to all chips in the daisy chain. The serial data is clocked to all the chips then the CS signal is pulled high to update all of them simultaneously. Figure 4 shows an example of two LTC6915s in a daisy chained SPI configuration. 5V 1 2 VIN LTC6915 V+ SHDN IN – OUT 3 IN+ SENSE 4 V– REF 5 6 7 8 HOLD_THRU NC CS(D0) P/S DIN(D1) DGND CLK(D2) DOUT(D3) 5V LTC6915 1 16 0.1µF 2 15 VOUT 14 3 VIN 13 4 12 5 11 10 µP 9 V+ SHDN D0 6 D1 7 D2 8 IN– OUT IN+ SENSE V– REF HOLD_THRU NC CS(D0) P/S DIN(D1) DGND CLK(D2) DOUT(D3) 16 0.1µF 15 VOUT 14 13 12 11 10 10k 9 D3 PARALLEL GAIN CONTROL CODE = 1010 VOUT = 29 VIN = 512VIN GAIN IS SET BY MICROPROCESSOR. A 10k RESISTOR ON DOUT(D3) PROTECT THE DEVICE WHEN VD3 > V + 6915 F01 Figure 1. PGA in the Parallel Control Mode V+ 4-BIT GAIN CONTROL CODE 4-BIT LATCH CS DOUT(D3) DGND (INTERNAL NODE) Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7 8-BIT SHIFT-REGISTER DIN V– DOUT 6915 F01 CLK (D3) 6915 F02 Figure 2. Bidirectional Nature of DOUT/D3 Pin Figure 3. Diagram of Serial Interface (MSB First Out) 6915f 12 LTC6915 U OPERATIO 1 0.1µF 2 VIN 3 4 –5V 0.1µF 5 CS 6 DIN 7 CLK 8 µP LTC6915 SHDN #1 IN– V+ OUT IN+ SENSE V– REF HOLD_THRU NC CS(D0) P/S DIN(D1) DGND CLK(D2) DOUT(D3) 16 15 1 0.1µF 0.1µF 2 VOUT 14 VIN 13 –5V 0.1µF 12 11 IN – V+ OUT 3 IN+ SENSE 4 V– REF 5 6 –5V LTC6915 SHDN #2 10 7 9 8 HOLD_THRU NC CS(D0) P/S DIN(D1) DGND CLK(D2) DOUT(D3) 16 15 0.1µF VOUT 14 13 12 11 –5V 10 9 DOUT CLK DIN D15 D11 D10 D9 D8 D7 D3 D2 D1 D0 GAIN CODE FOR #1 GAIN CODE FOR #2 CS/LD 6915 F04 Figure 4. 2 PGAs in a Daisy Chain The amplifier’s gain is set as follows: D3, D2, D1, D0 Gain 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101~ 1111 0 1 2 4 8 16 32 64 128 256 512 1024 2048 4096 Input Voltage Range ±5 Volt Operation The input common mode voltage range of the LTC6915 is rail-to-rail. However, the following equation limits the size of the differential input voltage: When using the LTC6915 with supplies over 5.5V, care must be taken to limit the maximum difference between any of the input pins (IN+ or IN– ) and the REF pin to 5.5V, i.e., V – ≤ (VIN+ – VIN –) + VREF ≤ V+ – 1.3 Where VIN+ and VIN– are the voltage of the differential input pins, V+ and V – are the positive and negative supply voltages respectively and VREF is the voltage of REF pin. In addition, VIN+ and VIN– must not exceed the power supply voltages, i.e., V – < VIN+ < V+ and V – < VIN– < V+ |VIN + – VREF| < 5.5 and |VIN– – VREF| < 5.5 If not, the device will be damaged. For example, if rail-torail input operation is desired when the supplies are at ±5V, the REF pin should be 0, ±0.5V. As a second example, if the V+ pin is 10V, and the V – and REF pins are at 0, the inputs should not exceed 5.5V. 6915f 13 LTC6915 U OPERATIO Settling Time The sampling rate is 3kHz and the input sampling period during which CS is charged to the input differential voltage, VIN, is approximately 150µs. First assume that on each input sampling period, CS is charged fully to VIN . Since CS = CH (= 1000pF), a change in the input will settle to N bits of accuracy at the op amp noninverting input after N clock cycles or 333µs(N). The settling time at the OUT pin is also affected by the internal op amp. Since the gain bandwidth of the internal op amp is typically 200kHz, the settling time is dominated by the switched-capacitor front end for gains below 100 (see the Low Gain Settling Time vs Settling Accuracy and the Settling Time vs Gain graphs in the Typical Performance Characteristics section). In addition, the worst case settling time after a device-enable (active low on Pin 1 of a GN package) is equal to the settling due to the gain plus the input settling time (333µs • N). For example, if an LTC6915 is enabled with a logic high on Pin 1 then, the maximum settling time to 10 bits of accuracy (0.1%) and a gain equal to 100 is 8.33ms ([333µs • 1024] + 5ms). Input Current Whenever the differential input VIN changes, CH must be charged up to the new input voltage via CS. This results in an input charging current during each input sampling period. Eventually, CH and CS will reach VIN and ideally, the input current would go to zero for DC inputs. In reality, there are additional parasitic capacitors which disturb the charge on CS every cycle even if VIN is a DC voltage. For example, the parasitic bottom plate capacitor on CS must be charged from the voltage on the REF pin to the voltage on the IN– pin every cycle. The resulting input charging current decays exponentially during each input sampling period with a time constant equal to RSCS. If the voltage disturbance due to these currents settles before the end of the sampling period, there will be no errors due to source resistance or the source resistance mismatch between IN+ and IN–. With RS less than 10k, no DC errors occur due to input current mismatch. In the Typical Performance Characteristics section of this data sheet, there are curves showing the additional error from non-zero source resistance in the inputs. If there are no large capacitors across the inputs, the amplifier is less sensitive to source resistance and source resistance mismatch. When large capacitors are placed across the inputs, the input charging currents are placed across the inputs. The input charging currents described above result in larger DC errors, especially with source resistor mismatches. Power Supply Bypassing In a dual supply operation, connect a 0.1µF bypass capacitor from each power supply pin (V+ and V–) to an analog round plance surrounding an LTC6915. The bypass capacitor trace to the supply pins must be less than 0.2 inches (an X7R or X5R capacitor type is recommended). In single supply operation, connect the V– pin to the analog ground plane and bypass the V+ pin. Shutdown Modes The IC has two shutdown modes, hardware shutdown and software shutdown. When SHDN is tied to V+, the IC is in hardware shutdown mode. During this shutdown mode, the gain setting digital interface (serial or parallel) and the main op amp are both disabled, thus the PGA dissipates very small supply current (see the Electrical Characteristic table). When SHDN is floating, an internal current source will pull it down to V –. The digital interface is turned on to read the gain setting codes. The IC is in normal amplification mode as long as the gain control code is other than 0000. If the gain control code is 0000, the IC operates in software shutdown mode, i.e., the main op amp is turned off so that the PGA dissipates less power. The DFN package does not have hardware shutdown. Setting the Voltage at the REF Pin The current coming out of the REF pin may affect the reference voltage at the REF pin (VREF). If VREF is set by a resistive divider then the VREF voltage is a function of the VOUT voltage (see Figure 5). In order to minimize the VREF variations, the total resistance of R1 plus R2 should be much less than 32k (5k or less) or use a voltage reference to set VREF. LTC6915 + OUT V+ VOUT – R1 V – VREF IREF = OUT 32k R = 32k VREF 0.1µF REF V+ V V– VREF = + OUT + • (R1 R2 32k) R1 32k R2 R2 V– 6915 F05 Figure 5 6915f 14 LTC6915 U TYPICAL APPLICATIO Multiplexing Two LTC6915’s 5V 5V 0.1µF 0.1µF SHDN V+ LTC6915 #1 IN– OUT Send a gain code of 0000 to one IC to set its output to a high impedance state and send a gain code other than 0000 to the second IC to set it for normal amplification. If both devices are ON, the 200Ω resistors protect the outputs. The sense pin connection maintains gain accuracy for loads 1k or greater. VIN1 VIN2 IN+ V –5V 0.1µF SENSE – REF HOLD_THRU DATA µP SELECT (TTL LEVELS) CLOCK SHDN V+ LTC6915 200Ω #2 IN– OUT 200Ω –5V 0.1µF NC –5V IN+ V SENSE – VOUT REF NC HOLD_THRU CS PAR_SER CS PAR_SER DIN DGND DIN DGND CLK DOUT CLK DOUT –5V 6915 F06 Figure 6. A 2:1 Multiplexing Two LTC6915’s with Daisy Chained Gain Control U PACKAGE DESCRIPTIO DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695) 4.00 ±0.10 (2 SIDES) 7 0.58 ±0.05 3.40 ±0.05 1.70 ±0.05 2.24 ±0.05 (2 SIDES) 3.00 ±0.10 (2 SIDES) 1.70 ± 0.10 (2 SIDES) PIN 1 NOTCH PACKAGE OUTLINE (UE12/DE12) DFN 0802 6 0.25 ± 0.05 0.75 ±0.05 0.200 REF 3.30 ±0.05 (2 SIDES) 0.38 ± 0.10 12 R = 0.20 TYP PIN 1 TOP MARK 0.25 ± 0.05 R = 0.115 TYP 0.50 BSC 3.30 ±0.10 (2 SIDES) 0.00 – 0.05 1 0.50 BSC BOTTOM VIEW—EXPOSED PAD RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING PROPOSED TO BE A VARIATION OF VERSION (WGED) IN JEDEC PACKAGE OUTLINE M0-229 2. ALL DIMENSIONS ARE IN MILLIMETERS 3. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 4. EXPOSED PAD SHALL BE SOLDER PLATED GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .189 – .196* (4.801 – 4.978) .045 ±.005 16 15 14 13 12 11 10 9 .254 MIN .009 (0.229) REF .150 – .165 .229 – .244 (5.817 – 6.198) .0165 ± .0015 .150 – .157** (3.810 – 3.988) 3. DRAWING NOT TO SCALE *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE .0250 TYP RECOMMENDED SOLDER PAD LAYOUT 1 .015 ± .004 × 45° (0.38 ± 0.10) .007 – .0098 (0.178 – 0.249) .053 – .068 (1.351 – 1.727) 2 3 4 5 6 7 NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 8 .004 – .0098 (0.102 – 0.249) 0° – 8° TYP .016 – .050 (0.406 – 1.270) .008 – .012 (0.203 – 0.305) .0250 (0.635) BSC GN16 (SSOP) 0502 6915f 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. 15 LTC6915 U TYPICAL APPLICATIO V+ V+ 9 X1 4MHz 10 C5 0.1µF 20 VDD PIC16LF73 RC5/SDO OSC1/ RC4/SDI/SDA CLKIN RC3/SCK/SCL OSC2/ CLKOUT RC2/CCP1 RC1/T1OSI/CCP2 V+ 1 BRIDGE SENSOR 10k ZETEK ZXM61P02F R < 10K 16 MOSI 15 MISO 13 CS1 LTC6915 IN – 3 IN+ SENSE V– REF 5 12 CS2 V+ SHDN 2 4 14 SCLK 6 28 RB7 MCLR/ 7 RAS/AN4/SS VPP 6 RA4/T0CLK1 VSS VSS 8 1 7 8 OUT HOLD_THRU NC CS(D0) PAR_SER DIN(D1) DGND CLK(D2) DOUT(D3) C1 0.1µF 16 C2 0.1µF 15 1 14 VCC 13 2 REF+ 12 SDO LTC2431 3 REF – 4 IN+ CS 5 IN – FO SCK 11 10 1.25V 9 8 9 7 10 GND 19 6 0V 10k MEASURE STANDBY V+ V+ CONTROL SIGNAL 4 C3 0.1µF VIN GND1 1 V+ VOUT 6 C3 1µF LT1790-1.25 GND2 2 6915 F07 Figure 7. Bridge Amplifier with Programmable Gain and Analog to Digital Conversion. (Standby Current Less than 100µA) RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1043 Dual Precision Instrumentation Switched-Capacitor Building Block Rail-to-Rail Input, 120dB CMRR LTC1100 Precision Zero-Drift Instrumentation Amplifier Fixed Gains of 10 or 100, 10µV Offset, 50pA Input Bias Current LTC1101 Precision, Micropower, Single Supply Instrumentation Amplifier Fixed Gain of 10 or 100, IS < 105µA LTC1167 Single Resistor Gain Programmable, Precision Instrumentation Amplifier Single Gains Set Resistor, G = 1 to 10,000 Low Noise: 7.5nV/√Hz LTC1168 Low Power Single Resistor Gain Programmable, Precision Instrumentation Amplifiers IS = 530µA LTC1789-1 Single Supply, Rail-to-Rail Output, Micropower Instrumentation Amplifier IS = 80µA Max LTC2050 Zero-Drift Operational Amplifier SOT-23 Package LTC2051 Dual Zero-Drift Operational Amplifier MS8 Package LTC2052 Quad Zero-Drift Operational Amplifier GN16 Package LTC2053 Rail-to-Rail Input and Output, Zero-Drift Instrumentation Amplifier with Resistor-Programmable Gain MS8 Package, 10µV Max VOS, 50nV/°C Max Drift LTC6800 Rail-to-Rail Input and Output, Instrumentation Amplifier with Resistor-Programmable Gain MS8 Package, 100µV Max VOS, 250nV/°C Max Drift 6915f 16 Linear Technology Corporation LT/TP 0204 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2003