DESCRIPTION FEATURES APPLICATIONS TYPICAL APPLICATION. LT1218/LT1219 Precision Rail-to-Rail Input and Output Op Amps

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1 Precision Rail-to-Rail Input and Output Op Amps FEATURES Rail-to-Rail Input and Output 9µV V OS(MAX) for V CM = V to V High Common Mode Rejection Ratio: 97dB Min C-Load TM Stable Version (LT29) High A VOL : 5V/mV Minimum Driving kω Load Wide Supply Range: 2V to ±5V (LT28/LT29) 2V to ±5V (LT28L/LT29L) Shutdown Mode: I S < 3µA Low Supply Current: 42µA Max Low Input Bias Current: 8nA Typical 3kHz Gain-Bandwidth Product (LT28) Slew Rate:.V/µs (LT28) APPLICATIONS U Driving A/D Converters Test Equipment Amplifiers MUX Amplifiers, LTC and LT are registered trademarks of Linear Technology Corporation. C-Load is a trademark of Linear Technology Corporation. DESCRIPTION U The LT 28/LT29 are bipolar op amps which combine rail-to-rail input and output operation with precision specifications. Unlike other rail-to-rail amplifiers, the LT28/ LT29 s input offset voltage is a low 9µV across the entire rail-to-rail input range, not just a portion of it. Using a patented technique, both input stages of the LT28/ LT29 are trimmed: one at the negative supply and the other at the positive supply. The resulting common mode rejection of 97dB minimum is much better than other railto-rail input op amps. A minimum open-loop gain of 5V/mV into a k load virtually eliminates all gain error. The LT28 has conventional compensation which assures stability for capacitive loads of pf or less. The LT29 has compensation that requires the use of a.µf output capacitor, which improves the amplifier s supply rejection and reduces output impedance at high frequencies. The output capacitor s filtering action also reduces high frequency noise, which is beneficial when driving A/D converters. High and low voltage versions of the devices are offered. Operation is specified for 3V, 5V and ±5V supplies for the LT28L/LT29L and 3V, 5V and ±5V for the LT28/ LT29. TYPICAL APPLICATION V IN V IN2 INPUT SELECT 74HCO4 U MUX Amplifier 5V LT28L 5V LT28L SHDN SHDN V OUT MAXIMUM IN TO OUT ERROR = µv FOR.5V V IN 4.8V R L = k 28/9 TA ERROR (mv).. Voltage Follower Input to Output Error V S = 5V A V = NO LOAD MAX ERROR = µv.5v V IN 4.8V INPUT VOLTAGE (V) LT28/9 TA2

2 ABSOLUTE MAXIMUM RATINGS W W W Supply Voltage LT28/LT29... ±8V LT28L/LT29L... ±8V Input Current... ±5mA Output Short-Circuit Duration (Note )...Continuous Operating Temperature Range... 4 C to 85 C Specified Temperature Range (Note 3)... 4 C to 85 C Storage Temperature Range C to 5 C Junction Temperature... 5 C Lead Temperature (Soldering, sec)... 3 C U PACKAGE/ORDER INFORMATION V OS TRIM IN 2 IN 3 V 4 N8 PACKAGE 8-LEAD PDIP TOP VIEW 8 V OS TRIM 7 V 6 OUT 5 SHDN S8 PACKAGE 8-LEAD PLASTIC SO T JMAX = 5 C, θ JA = 3 C/ W (N8) T JMAX = 5 C, θ JA = 9 C/ W (S8) Consult factory for Industrial and Military grades. U W U ORDER PART NUMBER LT28CN8 LT28CS8 LT28LCN8 LT28LCS8 LT29CN8 LT29CS8 LT29LCN8 LT29LCS8 S8 PART MARKING L 29L ELECTRICAL CHARACTERISTICS T A = 25 C, V S = 5V, V; V S = 3V, V; V CM = V O = half supply, V SHDN = V, unless otherwise noted. V OS Input Offset Voltage V CM = V 25 9 µv V CM = V 25 9 µv V OS Input Offset Voltage Shift V CM = V to V 5 7 µv I B Input Bias Current V CM = V 3 7 na V CM = V 7 8 na I B Input Bias Current Shift V CM = V to V 5 4 na I OS Input Offset Current V CM = V 5 8 na V CM = V 2 8 na I OS Input Offset Current Shift V CM = V to V 5 8 na e n Input Noise Voltage Density f = khz 33 nv/ Hz i n Input Noise Current Density f = khz.9 pa/ Hz A VOL Large-Signal Voltage Gain V S = 5V, V O = 5mV to 4.8V, R L = k 25 V/mV V S = 3V, V O = 5mV to 2.8V, R L = k 2 75 V/mV CMRR Common Mode Rejection Ratio V S = 5V, V CM = V to V 97 db V S = 3V, V CM = V to V 92 6 db PSRR Power Supply Rejection Ratio V S = 2.3V to 2V, V CM = V, V O =.5V 9 db V OL Output Voltage Swing LOW No Load 4 2 mv I SINK =.5mA 45 9 mv I SINK = 2.5mA 2 24 mv V OH Output Voltage Swing HIGH No Load V.2 V.3 V I SOURCE =.5mA V.3 V.65 V I SOURCE = 2.5mA V.4 V.2 V I SC Short-Circuit Current V S = 5V 5 ma V S = 3V 4 7 ma I S Supply Current V S = 5V µa V S = 3V 37 4 µa Positive Supply Current, SHDN V S = 5V, V SHDN = V 9 3 µa V S = 3V, V SHDN = V 6 2 µa 2

3 ELECTRICAL CHARACTERISTICS T A = 25 C, V S = 5V, V; V S = 3V, V; V CM = V O = half supply, V SHDN = V, unless otherwise noted. SR Slew Rate (LT28/LT28L) A V =. V/µs (LT29/LT29L) A V =.5 V/µs GBW Gain Bandwidth Product (LT28/LT28L) A V =.3 MHz (LT29/LT29L) A V =.5 MHz C T A 7 C, V S = 5V, V; V S = 3V, V; V CM = V O = half supply, V SHDN = V, unless otherwise noted. V OS Input Offset Voltage V CM = V 75 2 µv V CM = V 75 2 µv V OS TC Input Offset Drift (Note 2) 3 µv/ C V OS Input Offset Voltage Shift V CM = V to V 25 8 µv I B Input Bias Current V CM = V 3 75 na V CM = V 75 8 na I B Input Bias Current Shift V CM = V to V 5 5 na I OS Input Offset Current V CM = V 5 25 na V CM = V 3 25 na I OS Input Offset Current Shift V CM = V to V 5 25 na A VOL Large-Signal Voltage Gain V S = 5V, V O = 5mV to 4.8V, R L = k 25 V/mV V S = 3V, V O = 5mV to 2.8V, R L = k 5 75 V/mV CMRR Common Mode Rejection Ratio V S = 5V, V CM = V to V 96 4 db V S = 3V, V CM = V to V 9 6 db PSRR Power Supply Rejection Ratio V S = 2.3V to 2V, V CM = V, V O =.5V 88 db V OL Output Voltage Swing LOW No Load 4 4 mv I SINK =.5mA 45 mv I SINK = 2.5mA 3 29 mv V OH Output Voltage Swing HIGH No Load V.4 V.4 V I SOURCE =.5mA V.5 V.75 V I SOURCE = 2.5mA V.48 V.24 V I SC Short-Circuit Current V S = 5V 4 7 ma V S = 3V 3 6 ma I S Supply Current V S = 5V µa V S = 3V µa Positive Supply Current, SHDN V S = 5V, V SHDN = V 9 36 µa V S = 3V, V SHDN = V 6 26 µa 4 C T A 85 C, V S = 5V, V; V S = 3V, V; V CM = V O = half supply, V SHDN = V, unless otherwise noted. (Note 3) V OS Input Offset Voltage V CM = V.5 4 µv V CM = V.5 4 µv V OS TC Input Offset Drift (Note 2) 4 µv/ C V OS Input Offset Voltage Shift V CM = V.5 to V µv I B Input Bias Current V CM = V.5 8 na V CM = V.5 8 na I B Input Bias Current Shift V CM = V.5 to V.5 6 na I OS Input Offset Current V CM = V.5 4 na V CM = V.5 4 na I OS Input Offset Current Shift V CM = V.5 to V.5 4 na 3

4 ELECTRICAL CHARACTERISTICS 4 C T A 85 C, V S = 5V, V; V S = 3V, V; V CM = V O = half supply, V SHDN = V, unless otherwise noted. (Note 3) A VOL Large-Signal Voltage Gain V S = 5V, V O = 5mV to 4.8V, R L = k 5 5 V/mV V S = 3V, V O = 5mV to 2.8V, R L = k 5 V/mV CMRR Common Mode Rejection Ratio V S = 5V, V CM = V.5 to V db V S = 3V, V CM = V.5 to V.5 88 db PSRR Power Supply Rejection Ratio V S = 2.3V to 2V, V CM = V, V O =.5V 86 db V OL Output Voltage Swing LOW No Load 5 5 mv I SINK =.5mA 5 5 mv I SINK = 2.5mA 3 3 mv V OH Output Voltage Swing HIGH No Load V.5 V.4 mv I SOURCE =.5mA V.6 V.7 mv I SOURCE = 2.5mA V.5 V.25 mv I SC Short-Circuit Current V S = 5V 4 7 ma V S = 3V 3 7 ma I S Supply Current V S = 5V 4 55 µa V S = 3V µa Positive Supply Current, SHDN V S = 5V, V SHDN = V 5 5 µa V S = 3V, V SHDN = V 3 4 µa LT28L/LT29L only; T A = 25 C, V S = ±5V, V CM = V, V O = V, V SHDN = 5V, unless otherwise noted. V OS Input Offset Voltage V CM = V 35 4 µv V CM = V 35 4 µv V OS Input Offset Voltage Shift V CM = V to V 2 7 µv I B Input Bias Current V CM = V 3 7 na V CM = V 7 8 na I B Input Bias Current Shift V CM = V to V 5 4 na I OS Input Offset Current V CM = V 5 8 na V CM = V 2 8 na I OS Input Offset Current Shift V CM = V to V 5 8 na A VOL Large-Signal Voltage Gain V O = 4.7V to 4.7V, R L = k 5 28 V/mV V O = 4.5V to 4.5V, R L = 2k 3 3 V/mV CMRR Common Mode Rejection Ratio V CM = V to V 3 4 db V OL Output Voltage Swing LOW No Load V.4 V.2 V I SINK =.5mA V.45 V.9 V I SINK = 5mA V.8 V.525 V V OH Output Voltage Swing HIGH No Load V.2 V.3 V I SOURCE =.5mA V.3 V.65 V I SOURCE = 5mA V.8 V.35 V I SC Short-Circuit Current 6 2 ma I S Supply Current 4 43 µa Positive Supply Current, SHDN V SHDN = V 4 µa SR Slew Rate (LT28/LT28L) A V =, R L = Open, V O = ±3.5V.6. V/µs (LT29/LT29L) A V =, R L = Open, V O = ±3.5V.3.5 V/µs GBW Gain-Bandwidth Product (LT28/LT28L) A V =.2.3 MHz (LT29/LT29L) A V =..5 MHz 4

5 ELECTRICAL CHARACTERISTICS LT28L/LT29L only; C T A 7 C, V S = ±5V, V CM = V, V O = V, V SHDN = 5V, unless otherwise noted. LT28/LT29 V OS Input Offset Voltage V CM = V 25 µv V CM = V 25 µv V OS Input Offset Voltage Shift V CM = V to V 3 9 µv I B Input Bias Current V CM = V 3 75 na V CM = V 75 8 na I B Input Bias Current V CM = V to V 5 5 na I OS Input Offset Current V CM = V 5 25 na V CM = V 3 25 na I OS Input Offset Current Shift V CM = V to V 5 2 na A VOL Large-Signal Voltage Gain V O = 4.7V to 4.7V, R L = k V/mV V O = 4.5V to 4.5V, R L = 2k V/mV CMRR Common Mode Rejection Ratio V CM = V to V db V OL Output Voltage Swing LOW No Load V.4 V.4 V I SINK =.5mA V.45 V. V I SINK = 5mA V.2 V.58 V V OH Output Voltage Swing HIGH No Load V.4 V.4 V I SOURCE =.5mA V.5 V.75 V I SOURCE = 5mA V.92 V.45 V I SC Short-Circuit Current 5 ma I S Supply Current µa Positive Supply Current, SHDN V SHDN = V 54 µa LT28L, LT29L only; 4 C T A 85 C, V S = ±5V; V CM = V, V O = V, V SHDN = 5V, unless otherwise noted. (Note 3) V OS Input Offset Voltage V CM = V µv V CM = V µv V OS Input Offset Voltage Shift V CM = V.5 to V µv I B Input Bias Current V CM = V.5 8 na V CM = V.5 8 na I B Input Bias Current V CM = V.5 to V.5 6 na I OS Input Offset Current Shift V CM = V.5 4 na V CM = V.5 4 na I OS Input Offset Current Shift V CM = V.5 to V.5 4 na A VOL Large-Signal Voltage Gain V O = 4.7V to 4.7V, R L = k 3 2 V/mV V O = 4.5V to 4.5V, R L = 2k 2 6 V/mV CMRR Common Mode Rejection Ratio V CM = V.5 to V db V OL Output Voltage Swing LOW No Load V.5 V.5 V I SINK =.5mA V.5 V.5 V I SINK = 2.5mA V.2 V.62 V V OH Output Voltage Swing HIGH No Load V.5 V.4 V I SOURCE =.5mA V.6 V.7 V I SOURCE = 2.5mA V. V.4 V I SC Short-Circuit Current 5 ma I S Supply Current µa Positive Supply Current, SHDN V SHDN = V 8 6 µa 5

6 ELECTRICAL CHARACTERISTICS LT28/LT29 only; T A = 25 C, V S = ±5V, V CM = V, V O = V, V SHDN = 5V, unless otherwise noted. V OS Input Offset Voltage V CM = V 85 2 µv V CM = V 85 2 µv V OS Input Offset Voltage Shift V CM = V to V 3 7 µv I B Input Bias Current V CM = V 3 7 na V CM = V 7 8 na I B Input Bias Current V CM = V to V 5 4 na I OS Input Offset Current V CM = V 5 8 na V CM = V 2 8 na I OS Input Offset Current Shift V CM = V to V 5 8 na A VOL Large-Signal Voltage Gain V O = 4.7V to 4.7V, R L = k 4 V/mV V O = V to V, R L = 2k 5 2 V/mV CMRR Common Mode Rejection Ratio V CM = V to V 3 2 db PSRR Power Supply Rejection Ratio V S = ±5V to ±5V db V OL Output Voltage Swing LOW No Load V.4 V.2 V I SINK =.5mA V.45 V.9 V I SINK = 5mA V.27 V.525 V V OH Output Voltage Swing HIGH No Load V.2 V.3 V I SOURCE =.5mA V.3 V.65 V I SOURCE = 5mA V.8 V.58 V I SC Short-Circuit Current 2 ma I S Supply Current µa Positive Supply Current, SHDN V SHDN = V 5 4 µa SR Slew Rate (LT28/LT28L) A V =. V/µs (LT29/LT29L A V =.5 V/µs GBW Gain Bandwidth Product (LT28/LT28L) A V =.28 MHz (LT29/LT29L) A V =.5 MHz LT28/LT29 only; C T A 7 C, V S = ±5V, V CM = V, V O = V, V SHDN = 5V, unless otherwise noted. V OS Input Offset Voltage V CM = V 2 3 µv V CM = V 2 3 µv V OS Input Offset Voltage Shift V CM = V to V 5 5 µv I B Input Bias Current V CM = V 3 75 na V CM = V 75 8 na I B Input Bias Current V CM = V to V 5 5 na I OS Input Offset Current V CM = V 5 25 na V CM = V 3 25 na I OS Input Offset Current Shift V CM = V to V 5 2 na A VOL Large-Signal Voltage Gain V O = 4.7V to 4.7V, R L = k 75 3 V/mV V O = V to V, R L = 2k 5 5 V/mV CMRR Common Mode Rejection Ratio V CM = V to V 9 4 db PSRR Power Supply Rejection Ratio V S = ±5V to ±5V 97 db V OL Output Voltage Swing LOW No Load V.4 V.4 V I SINK =.5mA V.45 V. V I SINK = 5mA V.3 V.58 V V OH Output Voltage Swing HIGH No Load V.4 V.3 V I SOURCE =.5mA V.5 V.75 V I SOURCE = 5mA V.92 V.7 V 6

7 ELECTRICAL CHARACTERISTICS LT28/LT29 only; C T A 7 C, V S = ±5V, V CM = V, V O = V, V SHDN = 5V, unless otherwise noted. LT28/LT29 I SC Short-Circuit Current 8 7 ma I S Supply Current 45 6 µa Positive Supply Current, SHDN V SHDN = V 2 54 µa LT28, LT29 only; 4 C T A 85 C, V S = ±5V; V CM = V = V O = V, V SHDN = 5V, unless otherwise noted. (Note 3) V OS Input Offset Voltage V CM = V µv V CM = V µv V OS Input Offset Voltage Shift V CM = V.5 to V µv I B Input Bias Current V CM = V.5 8 na V CM = V.5 8 na I B Input Bias Current V CM = V.5 to V.5 6 na I OS Input Offset Current V CM = V.5 4 na V CM = V.5 4 na I OS Input Offset Current Shift V CM = V.5 to V.5 4 na A VOL Large-Signal Voltage Gain V O = 4.7V to 4.7V, R L = k 5 3 V/mV V O = V to V, R L = 2k 4 V/mV CMRR Common Mode Rejection Ratio V CM = V.5 to V db PSRR Power Supply Rejection Ratio V S = ±5V to ±5V 96 db V OL Output Voltage Swing LOW No Load V.5 V.5 V I SINK =.5mA V.5 V.5 V I SINK = 2.5mA V.2 V.62 V V OH Output Voltage Swing HIGH No Load V.5 V.4 V I SOURCE =.5mA V.6 V.7 V I SOURCE = 2.5mA V. V.4 V I SC Short-Circuit Current 5 4 ma I S Supply Current 65 µa Positive Supply Current, SHDN V SHDN = V 6 µa The denotes specifications which apply over the full operating temperature range. Note : A heat sink may be required to keep the junction temperature below the Absolute Maximum Rating when the output is shorted indefinitely. Note 2: This parameter is not % tested. Note 3: The LT28/LT29 are designed, characterized and expected to meet these extended temperature limits, but are not tested at 4 C and 85 C. Guaranteed I grade part are available: consult factory. 7

8 TYPICAL PERFORMANCE CHARACTERISTICS U W PERCENT OF UNITS (%) V OS Distribution, V CM = V V S = 5V, V V CM = V PERCENT OF UNITS (%) V OS Shift, V CM = V to 5V V S = 5V, V V CM = V TO 5V PERCENT OF UNITS (%) V OS Distribution, V CM = 5V V S = 5V, V V CM = 5V INPUT OFFSET VOLTAGE (µv) INPUT OFFSET VOLTAGE (µv) INPUT OFFSET VOLTAGE (µv) LT28/9 TPC LT28/9 TPC2 LT28/9 TPC3 SUPPLY CURRENT (µa) Supply Current vs Temperature 5 V S = ±5V CHANGE IN OFFSET VOLTAGE (µv) Minimum Supply Voltage 2 T A = 4 C 5 T A = 25 C T A = 85 C 5 INPUT BIAS CURRENT (na) 5 Input Bias Current vs Common Mode Voltage V S = 5V, V T A = 25 C T A = 25 C T A = 4 C T A = 85 C TEMPERATURE ( C) TOTAL SUPPLY VOLTAGE (V) COMMON MODE VOLTAGE (V) 7 LT28/9 TPC4 LT28/9 TPC5 LT28/9 TPC6 Output Saturation Voltage vs Load Current (Output Low) V S = 5V, V Output Saturation Voltage vs Load Current (Output High) V S = 5V, V.Hz to Hz Output Voltage Noise V CM = V SATURATION VOLTAGE (V).. T A = 85 C T A = 25 C T A = 4 C SATURATION VOLTAGE (V).. T A = 25 C T A = 85 C T A = 4 C OUTPUT VOLTAGE (4nV/DIV).... LOAD CURRENT (ma).... LOAD CURRENT (ma) TIME (s/div) LT28/9 TPC7 LT28/9 TPC8 LT28/9 TPC9 8

9 TYPICAL PERFORMANCE CHARACTERISTICS U W NOISE VOLTAGE (nv/ Hz) Noise Voltage Spectrum V S = 5V, V V CM = 4V V CM = 2.5V FREQUENCY (Hz) LT28/9 TPC CURRENT NOISE (pa/ Hz) Noise Current Spectrum V CM = 4V V CM = 2.5V V S = 5V, V FREQUENCY (Hz) LT28/9 TPC VOLTAGE GAIN (db) LT28 Gain and Phase Shift vs Frequency GAIN PHASE LT28/9 TPC2 PHASE SHIFT (DEG) VOLTAGE GAIN (db) LT29 Gain and Phase Shift vs Frequency C L =.µf GAIN PHASE LT28/9 TPC3 PHASE SHIFT (DEG) LT28 Gain Bandwidth and Phase Margin vs Supply Voltage PHASE MARGIN GBW SUPPLY VOLTAGE (V) LT28/9 TPC PHASE MARGIN (DEG) COMMON MODE REJECTION RATIO (db) LT28 Common Mode Rejection Ratio vs Frequency LT28/9 TPC5 POWER SUPPLY REJECTION RATIO (db) LT29 Power Supply Rejection Ratio vs Frequency POSITIVE SUPPLY NEGATIVE SUPPLY LT28/9 TPC6 9

10 TYPICAL PERFORMANCE CHARACTERISTICS U W POWER SUPPLY REJECTION RATIO (db) LT28 Power Supply Rejection Ratio vs Frequency NEGATIVE SUPPLY POSITIVE SUPPLY LT28/9 TPC7 OUTPUT IMPEDANCE (Ω)... LT28 Closed Loop Output Impedance vs Frequency A V = A V = LT28/9 TPC8 OUTPUT IMPEDANCE (Ω)... LT29 Closed Loop Output Impedance vs Frequency C L =.µf A V = A V = LT28/9 TPC9 OVERSHOOT (%) LT28 Capacitive Load Handling A V = 4 3 A V = 5 2 OVERSHOOT (%) LT29 Overshoot vs Load Current, A V = C L =.22µF C L =.47µF OVERSHOOT (%) LT29 Overshoot vs Load Current, V S = ±5V V S = ±5V A V = C L =.22µF C L =.47µF A V = C L =.µf C L =.µf CAPACITIVE LOAD (pf) 5 5 LOAD CURRENT (ma) 5 5 LOAD CURRENT (ma) LT28/9 TPC2 LT28/9 TPC2 LT28/9 TPC22 OFFSET VOLTAGE CHANGE (µv) Open-Loop Gain, V S = ±5V V S = ±5V R L = k R L = 2k CHANGE IN OFFSET VOLTAGE (µv) Input Offset Drift vs Time V S = ±5V THD NOISE (%).. THD Noise vs Frequency V S = ±.5V V IN = 2V P-P R L = k A V = A V = OUTPUT VOLTAGE (V) TIME AFTER POWER-UP (SEC)... LT28/9 TPC23 LT28/9 TPC24 LT28/9 TPC25

11 TYPICAL PERFORMANCE CHARACTERISTICS U W THD Noise vs Peak-to-Peak Voltage f = khz R L = k (ALL CURVES) Small-Signal Response V S = ±5V Large-Signal Response V S = ±5V THD NOISE (%).. V S = ±.5V A V = V S = ±.5V A V = A V = A V = INPUT VOLTAGE (PEAK-TO-PEAK) A V = V S = ±5V LT28/8 TPC27 A V = V S = ±5V LT28/8 TPC28 LT28/9 TPC26 APPLICATIONS INFORMATION Rail-to-Rail Operation U W U U The LT28/LT29 differ from conventional op amps in the design of both the input and output stages. Figure shows a simplified schematic of the amplifier. The input stage consists of two differential amplifiers, a PNP stage Q/Q2 and an NPN stage Q3/Q4, which are active over different portions of the input common mode range. Lateral devices are used in both input stages, eliminating the need for clamps across the input pins. Each input stage is trimmed for offset voltage. A complementary output configuration (Q23 through Q26) is employed to create an TRIM V SHDN BIAS CONTROL Q5 I Q Q V D4 D5 Q6 Q7 D6 Q2 V D7 Q24 Q23 V C OUT IN IN V 3mV V Q2 Q6 Q3 Q4 V D Q D3 Q2 D2 Q7 V Q8 Q9 Q3 C C Q4 Q5 D7 V Q8 Q2 Q9 V Q22 C2 V Q25 Q26 D8 LT28/9 F Figure. LT28 Simplified Schematic Diagram

12 APPLICATIONS INFORMATION U W U U output stage with rail-to-rail swing. The amplifier is fabricated on Linear Technology s proprietary complementary bipolar process, which ensures very similar DC and AC characteristics for the output devices Q24 and Q26. A simple comparator Q5 steers current from current source I between the two input stages. When the input common mode voltage V CM is near the negative supply, Q5 is reverse biased, and I becomes the tail current for the PNP differential pair Q/Q2. At the other extreme, when V CM is within about.3v from the positive supply, Q5 diverts I to the current mirror D3/Q6, which furnishes the tail current for the NPN differential pair Q3/Q4. The collector currents of the two input pairs are combined in the second stage, consisting of Q7 through Q. Most of the voltage gain in the amplifier is contained in this stage. Differential amplifier Q4/Q5 buffers the output of the second stage, converting the output voltage to differential currents. The differential currents pass through current mirrors D4/Q7 and D5/Q6, and are converted to differential voltages by Q8 and Q9. These voltages are also buffered and applied to the output Darlington pairs Q23/Q24 and Q25/Q26. Capacitors C and C2 form local feedback loops around the output devices, lowering the output impedance at high frequencies. Input Offset Voltage Since the amplifier has two input stages, the input offset voltage changes depending upon which stage is active. The input offsets are random, but bounded voltages. When the amplifier switches between stages, offset voltages may go up, down or remain flat; but will not exceed the guaranteed limits. This behavior is illustrated in three distribution plots of input offset voltage in the Typical Performance Characteristics section. Overdrive Protection Two circuits prevent the output from reversing polarity when the input voltage exceeds the common mode range. When the noninverting input exceeds the positive supply by approximately 3mV, the clamp transistor Q2 (Figure ) turns on, pulling the output of the second stage low, which forces the output high. For input below the negative supply, diodes D and D2 turn on, overcoming the saturation of the input pair Q/Q2. When overdriven, the amplifier draws input current that exceeds the normal input bias current. Figures 2 and 3 show typical input current as a function of input voltage. The input current must be less than ma for the phase reversal protection to work properly. When the amplifier is severely overdriven, an external resistor should be used to limit the overdrive current. INPUT BIAS CURRENT (na) INPUT BIAS CURRENT (na) MEASURED AS A FOLLOWER 3 V S COMMON MODE VOLTAGE RELATIVE TO POSITIVE SUPPLY (mv) MEASURED AS A FOLLOWER T = 7 C T = 85 C T = 55 C T = 25 C T = 7 C T = 85 C T = 25 C T = 55 C 3 5 LT28/9 F2 Figure 2. Input Bias Current vs Common Mode Voltage V S 2 COMMON MODE VOLTAGE RELATIVE TO NEGATIVE SUPPLY (mv) LT28/9 F3 Figure 3. Input Bias Current vs Common Mode Voltage 2

13 APPLICATIONS INFORMATION U W U U Shutdown The biasing of the LT28/LT29 is controlled by the SHDN pin. When the SHDN pin is low, the part is shut down. In the shutdown mode, the output looks like a 4pF capacitor and the supply current is less than 3µA. The SHDN pin is referenced to the positive supply through an internal bias circuit (see Figure ). The SHDN pin current with the pin low is typically 3µA. The switching time between the shutdown and active states is about 2µs, however, the total time to settle will be greater by the slew time of the amplifier. For example, if the DC voltage at the amplifier output is V in shutdown and 2V in the active mode, an additional 2µs is required. Figures 4a and 4b show the switching waveforms for a sinusoidal and a 2V DC input to the LT28. The SHDN pin can be driven directly from CMOS logic if the logic and the LT28/LT29 are operated from the same supplies. For higher supply operation, an interface is required. An easy way to interface between supplies is to use open-drain logic, an example is shown in Figure 5. Because the SHDN pin is referenced to the positive supply, the logic used should have a breakdown voltage greater than the positive supply. 5V 5V 5V SHDN LT28/ LT29 SHDN 74C96 V LT28/9 F5 V OUT Figure 5. Shutdown Interface Trim Pins SHDN V Trim pins are provided for compatibility with other single op amps. Input offset voltage can be adjusted over a ±2.3mV range with a k potentiometer. V OUT R L = V Figure 4a LT28/9 F4a V 2 3 k 8 LT28/ LT29 7 V OUT 4 V LT28/9 F6 SHDN R L = V Figure 4b LT28/9 F4a V Figure 6. Optional Offset Nulling Improved Supply Rejection in the LT29 The LT29 is a variation of the LT28 offering greater supply rejection and lower high frequency output impedance. The LT29 requires a.µf load capacitance for 3

14 APPLICATIONS INFORMATION U W U U compensation. The output capacitance forms a filter, which reduces pickup from the supply and lowers the output impedance. This additional filtering is helpful in mixed analog/digital systems with common supplies or systems employing switching supplies. Filtering also reduces high frequency noise, which may be beneficial when driving A/D converters. Figures 7a and 7b show the outputs of the LT28/LT29 perturbed by a 2mV P-P 5kHz square wave added to the positive supply. The LT29 power supply rejection is about ten times greater than that of the LT28 at 5kHz. Note the 5-to- scale change in the output voltage traces. The tolerance of the external compensation capacitor is not critical. The plots of Overshoot vs Load Current in the Typical Performance Characteristics section illustrate the effect of a capacitive load. V (AC) V (AC) V OUT V OUT LT28/9 F7a Figure 7a. LT28 Power Supply Rejection Test LT28/9 F7b Figure 7b. LT29 Power Supply Rejection Test TYPICAL APPLICATIONS U Buffer for 2-Bit A/D Converter 3V High-Side Current Source V CC R SENSE.2Ω V IN LT29.µF.µF µf V REF IN V CC CLK 8 7 LTC285 IN D OUT 6 GND CS/SHDN 5 LT28/9 TA3 TO µp LT4-.2 R P k 4k Q2 2N434 LT28 k.33µf Ω I LOAD Q MTP23P6 5V < V CC < 3V A < I LOAD < A AT V CC = 5V ma < I LOAD < 6mA AT V CC = 3V LT28/9 TA4 4

15 TYPICAL APPLICATIONS U Positive Supply Current Sense V CC R 2Ω LOAD R S.2Ω I LOAD LT28 V O = (I LOAD )(R S )( R2 R ) = (I LOAD )(2Ω) Q TP6L V O R2 2k 28/9 TA6 PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. U N8 Package 8-Lead PDIP (Narrow.3) (LTC DWG # 5-8-5) ( ) (.43.65).3 ±.5 (3.32 ±.27).4* (.6) MAX.9.5 ( ) ( ).65 (.65) TYP.5 (.27) MIN. ±. (2.54 ±.254) *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED. INCH (.254mm).25 (3.75) MIN.8 ±.3 (.457 ±.76).5 (.38) MIN.255 ±.5* (6.477 ±.38) N8 695 S8 Package 8-Lead Plastic Small Outline (Narrow.5) (LTC DWG # 5-8-6).89.97* ( ) ( )..2 ( ) 45 8 TYP ( ).4. (..254) ( ).5.57** ( ) ( ) *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED.6" (.52mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED." (.254mm) PER SIDE.5 (.27) TYP 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 SO

16 TYPICAL APPLICATION 5V U 8-Channel, 2-Bit Data Acquisition System with Programmable Gain µf 5V INPUTS CH 2 CH 3 CH2 4 CH3 5 CH4 6 CH5 7 CH6 8 CH7 6 V 5 D 4 V 3 D OUT 2 D IN CS CLK 9 GND LTC39 8-CHANNEL MUX GAIN MUX CHANNEL GAIN LT29L 64R 32R 6R 8R 4R 2R R R µf 2 CH 2 CH 22 CH2 23 CH3 24 CH4 CH5 2 CH6 3 CH7.µF 8 MUXOUT 8 COM 8-CHANNEL MUX 7 6 5, 9 µf ADCIN V REF V CC 2-BIT SAMPLING ADC LTC598 GND 4, 9 CSADC 6 CSMUX 5, 4 CLK D OUT 7 D IN NC 2 NC 3 5V 28/9 TA5 µp/µc RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC 52 Rail-to-Rail Input and Output, Zero-Drift Op Amp High DC Accuracy, µv V OS(MAX), nv/ C Drift,.7MHz GBW,.5V/µs Slew Rate, Maximum Supply Current 3mA LT366/LT367 Dual/Quad Precision, Rail-to-Rail Input and Output 475µV V OS(MAX), 4kHz GBW,.3V/µs Slew Rate, Op Amps Maximum Supply Current 52µA per Op Amp LT466/LT467 Dual/Quad Micropower, Rail-to-Rail Input and Output Maximum Supply Current 75µA per Op Amp, 39µV V OS(MAX), Op Amps 2kHz Gain Bandwidth 6 Linear Technology Corporation 63 McCarthy Blvd., Milpitas, CA (48) FAX: (48) TELEX: f LT/TP 697 7K PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 997