TC7652

TC7652 TELCOM | Alldatasheet

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3-281TELCOM SEMICONDUCTOR, INC. TC7652 LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER FUNCTIONAL BLOCK DIAGRAM C A OUTPUT TC7652CPA –INPUT +INPUT VSS VSS VDD VDD C B CLAMP NC NC = NO INTERNAL CONNECTION (MAY BE USED AS INPUT GUARD) INT/EXT EXT CLK IN INT CLK OUT OUTPUT OUTPUT CLAMP RET C –INPUT +INPUT NC TC7652CPD C B C A TC7652 NULL NULL OUTPUT BB A C EXT C EXT C RET (NOTE 1) NULL AMPLIFIER MAIN AMPLIFIER OUTPUT CLAMP CIRCUIT INTERMOD COMPARATOR OSCILLATOR BA INT/EXT EXT CLK IN CLK OUT 14-PIN DIP ONLY BA INPUTS OUTPUT CLAMP (NOT ON "Z" PINOUT) NOTE: 1. For 8-pin DIP connect to VSS , or to CRET on "Z" pinout. VSS TC7652-7 9/11/96

FEATURES

n Internally-Compensated for Unity-Gain Operation n Clamp Circuit for Fast Overload Recovery GENERAL DESCRIPTION The TC7652 is a lower noise version of the TC7650, sacrificing some input specifications (bias current and band- width) to achieve a 10x reduction in noise. All the other benefits of the chopper technique are present, i.e. freedom from offset adjust, drift, and reliability problems from exter- nal trim components. Like the TC7650, the TC7652 re- quires only two noncritical external caps for storing the chopped null potentials. There are no significant chopping spikes, internal effects or overrange lockup problems. PIN CONFIGURATIONS

ORDERING INFORMATION

Part No. Package Range TC7652CPA 8-Pin Plastic DIP 0 °C to +70°C TC7652CPD 14-Pin Plastic DIP 0 °C to +70°C

3-282 TELCOM SEMICONDUCTOR, INC. TC7652 LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER ABSOLUTE MAXIMUM RATINGS * Package Power Dissipation (T A ≤ 70°C) Operating Temperature Range ELECTRICAL CHARACTERISTICS: VDD = +5V, VSS = – 5V, TA = +25°C, unless otherwise indicated. Symbol Parameter Test Conditions Min Typ Max Unit VOS Input Offset Voltage T A = +25°C— ±2 ±5 µV TCV OS Average Temperature Coefficient of 0 °C < TA < +70°C — 0.01 0.05 µV/°C Input Offset Voltage VOS /DT Offset Voltage vs Time — 150 — nV/mo IBIAS Input Bias Current T A = +25°C — 30 100 pA (CLK On) 0 °C < TA < +70°C — 100 — – 25°C < TA < +85°C — 250 1000 IBIAS Input Bias Current T A = +25°C — 15 30 pA (CLK Off) 0 °C < TA < +70°C— 3 5 — IOS Input Offset Current — 25 150 pA R IN Input Resistance — 10 12 —W OL Large Signal Voltage Gain R L = 10kW, VOUT = ±4V 120 150 — dB VOUT Output Voltage Swing R L = 10kW ±4.7 ±4.85 — V (Note 2) R L = 100kW — ±4.95 — CMVR Common-Mode – 4.3 — +3.5 V Voltage Range MRR Common-Mode CMVR = – 4.3V to +3.5V 120 140 — dB Rejection Ratio PSRR Power Supply ±3V to ±8V 120 140 — dB Rejection Ratio eN Input Noise Voltage R S = 100W, DC to 1Hz — 0.2 1.5 µVP-P DC to 10Hz — 0.7 5 µVP-P IN Input Noise Current f = 10Hz — 0.01 — pA/ √Hz GBW Unity-Gain Bandwidth — 0.4 — MHz SR Slew Rate C L = 50 pF, RL = 10kW — 1 — V/ µsec Overshoot — 15 — % VDD , VSS Operating Supply Range 5 — 16 V IS Supply Current No Load — 1 3 mA fCH Internal Chopping Frequency Pins 12 – 14 Open (DIP) 100 275 — Hz Clamp ON Current (Note 3) R L = 100kW 25 100 — µA Clamp OFF Current (Note 3) – 4V ≤ VOUT < +10V — 1 — pA NOTES: 1. Limiting input current to 100µA is recommended to avoid latch-up problems. Typically, 1mA is safe; however, this is not guaranteed. 2. Output clamp not connected. See typical characteristics curves for output swing versus clamp current characteristics. *Static-sensitive device. Unused devices must be stored in conductive material. Protect devices from static discharge and static fields. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. Exposure to Absolute Maximum Rating Conditions for extended periods may affect device reliability.

3-283TELCOM SEMICONDUCTOR, INC. Capacitor Connection Connect the null-storage capacitors to the CA and CB pins with a common connection to the CRET pin (14-pin TC7652) or to VSS (8-pin TC7652). When connecting to VSS , avoid injecting load current IR drops into the capacitive circuitry by making this connection directly via a separate wire or PC trace. Output Clamp In chopper-stabilized amplifiers, the output clamp pin reduces overload recovery time. When a connection is made to the inverting input pin (summing junction), a current path is created between that point and the output pin, just before the device output saturates. This prevents uncon- trolled differential input voltages and charge buildup on correction-storage capacitors. Output swing is reduced. Clock The TC7652 has a 550Hz internal oscillator, which is divided by two before clocking the input chopper switches. The 275Hz chopping frequency is available at INT CLK OUT (pin 12) on 14-pin devices. In normal operation, INT/EXT (pin 14), which has an internal pull-up, can be left open. An external clock can also be used. To disable the internal clock and use an external one, the INT/EXT pin must be tied to V SS . The external clock signal is then applied to the EXT CLK IN input (pin 13). An internal divide-by-two pro- vides a 50% switching duty cycle. The capacitors are only charged when EXT CLK IN is high, so a 50% to 80% positive duty cycle is recommended for higher clock frequencies. The external clock can swing between V DD and VSS , with the logic threshold about 2.5V below VDD . The output of the internal oscillator, before the divide- by-two circuit, is available at EXT CLK IN when INT/EXT is high or unconnected. This output can serve as the clock input for a second TC7652 (operating in a master/slave mode), so that both op amps will clock at the same fre- quency. This prevents clock intermodulation effects when two TC7652's are used in a differential amplifier configura- tion. If the TC7652's output saturates, error voltages on the external capacitors will slow overload recovery. This condi- tion can be avoided if a strobe signal is available. The strobe signal is applied to EXT CLK IN and the overload signal is applied to the amplifier while the strobe is LOW. In this case, neither capacitor will be charged. The low leakage of the capacitor pins allow long measurements to be made with negligible errors (typical capacitor drift is 10µV/sec). APPLICATION NOTES Component Selection C A and CB (external capacitors) should be in the 0.1µF to 1µF range. For minimum clock ripple noise, use a 1µF capacitor in broad bandwidth circuits. For limited bandwidth applications where clock ripple is filtered out, use a 0.1µF capacitor for slightly lower offset voltage. High-quality film- type capacitors (polyester or polypropylene) are recom- mended, although a lower grade (ceramic) may work in some applications. For quickest settling after initial turn-on, use low dielectric absorption capacitors (e.g., polypropy- lene). With ceramic capacitors, settling to 1µV takes several seconds. Static Protection Although input diodes static-protect all device pins, avoid strong electrostatic fields and discharges that can cause degraded diode junction characteristics and produce increased input-leakage currents. Latch-Up Junction-isolated CMOS circuits have a 4-layer (p-n- p-n) structure similar to an SCR. Sometimes this junction can be triggered into a low-impedance state and produce excessive supply current. Therefore, avoid applying voltage greater than 0.3V beyond the supply rails to any pin. Estab- lish the amplifier supplies at the same time or before any input signals are applied. If this is not possible, drive circuits must limit input current flow to under 1mA to avoid latch-up, even under fault conditions. Output Stage/Load Driving The output circuit is high impedance (about 18kΩ ). With lesser loads, the chopper amplifier behaves somewhat like a transconductance amplifier with an open-loop gain propor- tional to load resistance. (For example, the open-loop gain is 17dB lower with a 1kΩ load than with a 10kΩ load.) If the amp is used only for DC, the DC gain is typically greater than 120dB (even with a 1kΩ load), and this lower gain is inconsequential. For wideband, the best frequency response occurs with a load resistor of at least 10kΩ . This produces OUTPUT R 2 R 1 0.1 µF 0.1 µF TC7652 C R C 1 kΩ 1 MΩ TEST CIRCUIT LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER TC7652

3-284 TELCOM SEMICONDUCTOR, INC. a 6dB/octave response from 0.1Hz to 2MHz, with phase shifts of less than 2 degrees in the transition region, where the main amplifier takes over from the null amplifier. Thermoelectric Effects The thermoelectric (Seebeck) effects in thermocouple junctions of dissimilar metals, alloys, silicon, etc. limit ultra- high-precision DC amplifiers. Unless all junctions are at the same temperature, thermoelectric voltages around 0.1µV/ °C (up to tens of µV/°C for some materials) are generated. To realize the low offset voltages of the chopper, avoid temperature gradients. Enclose components to eliminate air movement, especially from power-dissipating elements in the system. Where possible, use low thermoelectric-coeffi- cient connections. Keep power supply voltages and power dissipation to a minimum. Use high-impedance loads and seek maximum separation from surrounding heat-dissipat- ing elements. Guarding To benefit from TC7652 low-input currents, take care assembling printed circuit boards. Clean boards with alco- hol or TCE, and blow dry with compressed air. To prevent contamination, coat boards with epoxy or silicone rubber. Even if boards are cleaned and coated, leakage cur- rents may occur because input pins are next to pins at supply potentials. To reduce this leakage, use guarding to lower the voltage difference between the inputs and adjacent metal runs. The guard (a conductive ring surrounding inputs) is connected to a low-impedance point at about the same voltage as inputs. The guard absorbs leakage currents from high-voltage pins. The 14-pin dual-in-line arrangement simplifies guard- ing. Like the LM108 pin configuration (but unlike the 101A and 741), pins next to inputs are not used. Pin Compatibility Where possible, the 8-pin device pinout conforms to such industry standards as the LM101 and LM741. Null- storing external capacitors connect to pins 1 and 8, which are usually for offset-null or compensation capacitors. Output clamp (pin 5) is similarly used. For OP05 and OP07 devices, replacement of the offset-null potentiometer (connected between pins 1 and 8 and V DD by two capacitors from those pins to VSS ) provides compatibility. Replacing the compensation capacitor between pins 1 and 8 by two capacitors to V SS is required. The same operation (with the removal of any connection to pin 5) works for LM101, µA748, and similar parts. Because NC pins provide guarding between input and other pins, the 14-pin device pinout conforms closely to the LM108. Because this device does not use any extra pins and does not provide offset-nulling (but requires a compensation capacitor), some layout changes are necessary to convert to the TC7652. CONNECTION OF INPUT GUARDS INPUT OUTPUT R 2R 1 Inverting Amplifier INPUT OUTPUT Follower INPUT OUTPUT R 2 R 1 Noninverting Amplifier TC7652 TC7652 TC7652 TC7652 LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER

3-286 TELCOM SEMICONDUCTOR, INC. TYPICAL CHARACTERISTICS 2345678 – SUPPLY VOLTAGE (V) 1400 1200 1000 800 600 400 200 SUPPLY CURRENT ( µA) Supply Current vs – Supply Voltage 1 sec/DIV 2 µV/DIV Noise at 0.1 Hz to 10 Hz OUTPUT VOLTAGE (V) 1 mA 0.1 mA 0.01 mA 1 µA 0.1 µA 0.01 µA 1 nA 0.1 nA 0.01 nA 1 pA CLAMP CURRENT Positive Clamp Current 1 sec/DIV 1 µV/DIV Noise at 0.1 Hz to 1 Hz OUTPUT VOLTAGE (V) 1 mA 0.1 mA 0.01 mA 1 µA 0.1 µA 0.01 µA 1 nA 0.1 nA 0.01 nA 1 pA CLAMP CURRENT Negative Clamp Current 1 10 100 1k 10k 100k 1M FREQUENCY (Hz) GAIN –20 –10 60GAIN (dB) Phase-Gain (Bode Plot)* *NOTE: –5V, –2.5V supplies; no load to 10k load. –180 –120 –60 +60 +120 +180 +240 PHASE (deg) 1 sec/DIV 1 µV/DIV Noise at 0.1 Hz to 100 Hz 5 µsec/DIV 0.5V/DIV Slew Rate SOURCE SINK Output Resistance vs Output Voltage 100 OUTPUT RESISTANCE ( Ω ) –3.0OUTPUT VOLTAGE (V) 1k 10k 100k 1M –5.0 –4.0 –6 –4 –2 0 2 4 COMMON-MODE VOLTAGE (V) Input Offset Voltage vs Common-Mode Voltage 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 INPUT OFFSET VOLTAGE ( µV) PHASE TC7652 LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER