TC7650CPD

TC7650 TELCOM | Alldatasheet

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3-273TELCOM SEMICONDUCTOR, INC. CHOPPER-STABILIZED OPERATIONAL AMPLIFIER TC7650 GENERAL DESCRIPTION The TC7650 CMOS chopper-stabilized operational amplifier practically removes offset voltage error terms from system error calculations. The 5µV maximum V OS specification, for example, represents a 15 times improve- ment over the industry-standard OP07E. The 50nV/°C off- set drift specification is over 25 times lower than the OP07E. The increased performance eliminates V OS trim proce- dures, periodic potentiometer adjustment and the reliability problems caused by damaged trimmers. The TC7650 performance advantages are achieved without the additional manufacturing complexity and cost incurred with laser or "zener zap" V OS trim techniques. The TC7650 nulling scheme corrects both DC VOS errors and VOS drift errors with temperature. A nulling amplifier alternately corrects its own VOS errors and the main amplifier VOS error. Offset nulling voltages are stored on two user-supplied external capacitors. The capacitors connect to the internal amplifier V OS null points. The main amplifier input signal is never switched. Switching spikes are not present at the TC7650 output. The 14-pin dual-in-line package (DIP has an external oscillator input to drive the nulling circuitry for optimum noise performance. Both the 8 and 14-pin DIPs have an output voltage clamp circuit to minimize overload recovery time. PIN CONFIGURATIONS

FEATURES

n High Impedance Differential CMOS Inputs.... 1012Ω n Output Clamp Speeds Recovery Time n Compensated Internally for Stable Unity Gain Operation n Direct Replacement for ICL7650 n Available in 8-Pin Dip and 14-Pin Dip FUNCTIONAL BLOCK DIAGRAM

ORDERING INFORMATION

Part No. Package Range V OS TC7650CPA 8-Pin Plastic DIP 0 °C to +70°C5 µV TC7650CPD 14-Pin Plastic DIP 0 °C to +70°C5 µV TC7650 NULL NULL INPUTS OUTPUT CLAMP OUTPUT BB A C EXT C EXT FOR 8-PIN DIP, CONNECT TO VSS. NULL AMPLIFIER MAIN AMPLIFIER OUTPUT CLAMP CIRCUIT INTERMOD COMPENSATION OSCILLATOR AB INT/EXT EXT CLK IN CLK OUT 14-PIN DIP ONLY BA C RET* TC7650-5 9/11/96 C NC (GUARD) 8-Pin DIP VSS VSS INT/EXT EXT CLK INPUT INT CLK OUTPUT OUTPUT OUTPUT CLAMP RETN B CA C V DDTC7650CPD C OUTPUT A VDD TC7650CPA INPUT INPUT C B (+) (–) CLAMP INPUT(–) INPUT(+) NC (GUARD) 14-Pin DIP NC = NO INTERNAL CONNECTION

3-274 TELCOM SEMICONDUCTOR, INC. TC7650 CHOPPER-STABILIZED OPERATIONAL AMPLIFIER ELECTRICAL CHARACTERISTICS: VDD = +5V, VSS = –5V, CA = CB = 0.1µF, TA = 25°C, unless otherwise indicated. Symbol Parameter Test Conditions Min Typ Max Units Input VOS Input Offset Voltage T A = +25°C— ±0.7 ±5— Over Operating Temp Range — ± 1.0 — µV ΔVOS /ΔT Input Offset Voltage Operating Temperature Range — 0.01 0.05 µV/°C Average Temperature Coefficient Offset Voltage vs. Time — 100 — nV/ month IBIAS Input Bias Current T A = +25°C — 1.5 10 pA 0°C ≤ TA ≤ +70°C — 35 150 pA –25°C ≤ TA ≤ +85°C — 100 400 pA IOS Input Offset Current — 0.5 — pA eNP-P Input Noise Voltage R S = 100Ω , 0 to 10Hz — 2 — µVP-P IN Input Noise Current f = 10 Hz — 0.01 — pA/ √Hz R IN Input Resistance — 10 12 Ω CMVR Common-Mode – 5 – 5.2 +1.6 V Voltage Range to +2 CMRR Common-Mode CMVR = –5V to +1.5V 120 130 — dB Rejection Ratio Output A Large Signal Voltage R L = 10kΩ 120 130 — dB Gain VOUT Output Voltage Swing (Note 2) RL = 10kΩ± 4.7 ±4.85 — V R L = 100kΩ — ±4.95 — V Clamp ON Current R L = 100kΩ 25 70 200 µA (Note 1) Clamp OFF Current – 4V < V OUT < +4V — 1 — pA (Note 1) Dynamic BW Unity-Gain Bandwidth Unity Gain (+1) — 2.0 — MHz SR Slew Rate C L = 50 pF, RL = 10kΩ — 2.5 — V/ µsec tR Rise Time — 0.2 — µsec Overshoot — 20 — % fCH Internal Chopping Pins 12–14 Open (DIP) 120 200 375 Hz Frequency Package Power Dissipation (TA ≤ 70°C) *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 perma- nent 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. ABSOLUTE MAXIMUM RATINGS* Operating Temperature Range

3-275TELCOM SEMICONDUCTOR, INC. ELECTRICAL CHARACTERISTICS: VDD = +5V, VSS = – 5V, CA = CB = 0.1µF, TA = 25°C, unless otherwise specified. Symbol Parameter Test Conditions Min Typ Max Units Supply VDD , VSS Operating Supply Range 4.5 — 16 V IS Supply Current No Load — 2 3.5 mA PSRR Power Supply V S = ±3V to ±8V 120 130 dB Rejection Ratio NOTES: 1. See "Output Clamp" discussion. 2. Output clamp not connected. See typical characteristics curves for output swing versus clamp current characteristics. 3. Limiting input current to 100µA is recommended to avoid latch-up problems. CHOPPER-STABILIZED OPERATIONAL AMPLIFIER TC7650 Theory of Operation Figure 1 shows the major elements of the TC7650. There are two amplifiers (the main amplifier and the nulling amplifier), and both have offset-null capability. The main amplifier is connected full-time from the input to the output. The nulling amplifier, under the control of the chopping frequency oscillator and clock circuit, alternately nulls itself and the main amplifier. Two external capacitors provide the required storage of the nulling potentials and the necessary nulling-loop time constants. The nulling arrangement oper- ates over the full common-mode and power-supply ranges, and is also independent of the output level, thus giving exceptionally high CMRR, PSRR, and A VOL . Careful balancing of the input switches minimizes chop- per frequency charge injection at the input terminals, and the feed-forward-type injection into the compensation capacitor that can cause output spikes in this type of circuit. The circuit's offset voltage compensation is easily shown. With the nulling inputs shorted, a voltage almost identical to the nulling amplifier offset voltage is stored on C A. The effective offset voltage at the null amplifier input is: VOSE = VOSN (1) After the nulling amplifier is zeroed, the main amplifier is zeroed; the A switches open and B switches close. The output voltage equation is: VOUT = AM VOSM +(V+ – V–) + AN (V+– V–) + AN VOSE (3) As desired, the device offset voltages are reduced by the high open-loop gain of the nulling amplifier. Output Stage/Loading The output circuit is a high-impedance stage (approxi- mately 18kΩ ). With loads less than this, the chopper ampli- fier behaves in some ways like a transconductance amplifier whose open-loop gain is proportional to load resistance. For example, the open-loop gain will be 17dB lower with a 1kΩ load than with a 10kΩ load. If the amplifier is used strictly for DC, the lower gain is of little consequence, since the DC gain is typically greater than 120dB, even with a 1kΩ load. In wideband applications, the best frequency response will be achieved with a load resistor of 10kΩ or higher. This results in a smooth 6 dB/octave response from 0.1Hz to 2 MHz, with phase shifts of less than 10° in the transition region, where the main amplifier takes over from the null amplifier. The clock frequency sets the transition region. Intermodulation Previous chopper-stabilized amplifiers have suffered from intermodulation effects between the chopper frequency and input signals. These arise because the finite AC gain of the amplifier results in a small AC signal at the input. This is seen by the zeroing circuit as an error signal, which is chopped and fed back, thus injecting sum and difference frequencies, and causing disturbances to the gain and phase versus frequency characteristics near the chopping frequency. These effects are substantially reduced in the TC7650 by feeding the nulling circuit with a dynamic current corresponding to the compensation capacitor current in such a way as to cancel that portion of the input signal due to a finite AC gain. The intermodulation and gain/phase disturbances are held to very low values, and can generally be ignored. AN + 1 Substituting (1) → (2) and assuming AN >>1: VOUT = AM AN (V+ – V–) + ][ VOSM + VOSN AN

3-278 TELCOM SEMICONDUCTOR, INC. Figure 6. Input Guard Connection TC7650 to make measurements of high-impedance sources. is a conductive PC trace surrounding the input terminals. nections are shown in Figure 6. should be cleaned thoroughly and blown dry after soldering. Protective coatings will prevent future board contamination. should be scaled in proportion to the external clock, if used. seconds may be required to settle to 1µV.

3-279TELCOM SEMICONDUCTOR, INC. CHOPPER-STABILIZED OPERATIONAL AMPLIFIER TC7650 TYPICAL CHARACTERISTICS OUTPUT VOLTAGE (V) Positive Clamp Current vs. Output Voltage CLAMP CURRENT 1 mA 0.1 mA 0.01 mA 1 Aµ 0.1 A 0.01 A µ 1 nA 1 pA 0.01 nA 0.1 nA µ OUTPUT VOLTAGE (V) Negative Clamp Current vs. Output Voltage CLAMP CURRENT 3.0 2.6 2.2 1.8 1.4 Supply Current vs. Supply Voltage SUPPLY CURRENT (mA) Gain/Phase vs. Frequency –10 –20 –30 –40 –50 GAIN (dB) 225 180 135 –45 –90 –135 180 PHASE (deg) 1 mA 0.1 mA 0.01 mA 1 Aµ 0.1 A 0.01 A µ 1 nA 1 pA 0.01 nA 0.1 nA µ CLOSED-LOOP GAIN = 20 PHASE GAIN TA = +25°C VS = ±5V TA = +25°C VS = ±5V TA = +25°C