1 TC7652 LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER ■ ■ ■ ■ ■ ■ ■ ■ 2 GENERAL DESCRIPTION FEATURES Low Offset Over Temperature Range ............ 10µV Ultra-Low Long-Term Drift ................. 150nV/Month Low Temperature Drift ............................. 100nV/°C Low DC Input Bias Current ............................. 15pA High Gain, CMRR and PSRR ................. 110dB Min Low Input Noise Voltage ......... 0.2µVP-P; DC to 1Hz Internally-Compensated for Unity-Gain Operation Clamp Circuit for Fast Overload Recovery The TC7652 is a lower noise version of the TC7650, sacrificing some input specifications (bias current and bandwidth) 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 external trim components. Like the TC7650, the TC7652 requires only two noncritical external caps for storing the chopped null potentials. There are no significant chopping spikes, internal effects or overrange lockup problems. 3 PIN CONFIGURATIONS CB 1 14 INT/EXT CA 2 EXT CLK 13 IN 12 INT CLK OUT NC 3 –INPUT 4 +INPUT 5 TC7652CPD 11 VDD CA 1 8 CB –INPUT 2 +INPUT 3 7 TC7652CPA VDD 6 OUTPUT 5 CLAMP VSS 4 10 OUTPUT NC 6 9 OUTPUT CLAMP VSS 7 8 CRET ORDERING INFORMATION Part No. Package Temperature Range TC7652CPA TC7652CPD 8-Pin Plastic DIP 14-Pin Plastic DIP 0°C to +70°C 0°C to +70°C NC = NO INTERNAL CONNECTION (MAY BE USED AS INPUT GUARD) 4 5 FUNCTIONAL BLOCK DIAGRAM TC7652 14-PIN DIP ONLY OUTPUT CLAMP (NOT ON "Z" PINOUT) OUTPUT CLAMP CIRCUIT INT/EXT EXT CLK IN CLK OUT OSCILLATOR 6 MAIN AMPLIFIER A INPUTS B OUTPUT CEXT NULL 7 INTERMOD COMPARATOR B B B A C EXT NULL AMPLIFIER A NULL CRET (NOTE 1) 8 VSS NOTE: 1. For 8-pin DIP connect to VSS, or to CRET on "Z" pinout. TC7652-7 9/11/96 TELCOM SEMICONDUCTOR, INC. 3-281 LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER TC7652 ABSOLUTE MAXIMUM RATINGS* Total Supply Voltage (VDD to VSS) ........................... +18V Input Voltage ........................ (VDD + 0.3V) to (VSS – 0.3V) Voltage on Oscillator Control Pins ................... VDD to VSS Duration of Output Short Circuit ......................... Indefinite Current Into Any Pin ................................................. 10mA While Operating (Note 1) ..................................100µA Package Power Dissipation (TA ≤ 70°C) 8-Pin Plastic DIP ............................................. 730mW 14-Pin Plastic DIP ........................................... 800mW Storage Temperature Range ................ – 65°C to +150°C Operating Temperature Range C Device ................................................ 0°C to +70°C I Device ............................................. – 25°C to +85°C Lead Temperature (Soldering, 10 sec) ................. +300°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 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. ELECTRICAL CHARACTERISTICS: VDD = +5V, VSS = – 5V, TA = +25°C, unless otherwise indicated. Symbol Parameter Test Conditions Min Typ Max Unit VOS Input Offset Voltage Average Temperature Coefficient of Input Offset Voltage Offset Voltage vs Time Input Bias Current (CLK On) — — — ±2 ±10 0.01 ±5 — 0.05 µV TCVOS TA = +25°C 0°C < TA < +70°C 0°C < TA < +70°C — — — — — — — — — 120 ±4.7 — – 4.3 150 30 100 250 15 35 100 25 1012 150 ±4.85 ±4.95 — — 100 — 1000 30 — — 150 — — — — +3.5 nV/mo pA CMVR = – 4.3V to +3.5V 120 140 — dB ±3V to ±8V 120 140 — dB RS = 100W, DC to 1Hz DC to 10Hz f = 10Hz — — — — — — 5 — 100 25 — 0.2 0.7 0.01 0.4 1 15 — 1 275 100 1 1.5 5 — — — — 16 3 — — — µVP-P µVP-P pA/√Hz MHz V/µsec % V mA Hz µA pA VOS/DT IBIAS IBIAS Input Bias Current (CLK Off) IOS RIN Input Offset Current Input Resistance Large Signal Voltage Gain Output Voltage Swing (Note 2) Common-Mode Voltage Range Common-Mode Rejection Ratio Power Supply Rejection Ratio Input Noise Voltage OL VOUT CMVR MRR PSRR eN IN GBW SR VDD, VSS IS fCH Input Noise Current Unity-Gain Bandwidth Slew Rate Overshoot Operating Supply Range Supply Current Internal Chopping Frequency Clamp ON Current (Note 3) Clamp OFF Current (Note 3) TA = +25°C 0°C < TA < +70°C – 25°C < TA < +85°C TA = +25°C 0°C < TA < +70°C – 25°C < TA < +85°C RL = 10kW, VOUT = ±4V RL = 10kW RL = 100kW CL = 50 pF, RL = 10kW No Load Pins 12 – 14 Open (DIP) RL = 100kW – 4V ≤ VOUT < +10V µV/°C pA pA W dB V V 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. 3-282 TELCOM SEMICONDUCTOR, INC. LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER 1 TC7652 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 uncontrolled 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 VSS. The external clock signal is then applied to the EXT CLK IN input (pin 13). An internal divide-by-two provides 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 VDD and VSS, with the logic threshold about 2.5V below VDD. The output of the internal oscillator, before the divideby-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 frequency. This prevents clock intermodulation effects when two TC7652's are used in a differential amplifier configuration. If the TC7652's output saturates, error voltages on the external capacitors will slow overload recovery. This condition 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 3 CA 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 filmtype capacitors (polyester or polypropylene) are recommended, although a lower grade (ceramic) may work in some applications. For quickest settling after initial turn-on, use low dielectric absorption capacitors (e.g., polypropylene). With ceramic capacitors, settling to 1µV takes several seconds. R2 1 MΩ R1 1 kΩ TC7652 – + C 0.1 µF R C OUTPUT 0.1 µF TELCOM SEMICONDUCTOR, INC. 4 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. 5 Latch-Up Junction-isolated CMOS circuits have a 4-layer (p-np-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. Establish 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 TEST CIRCUIT 2 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 proportional 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 3-283 6 7 8 LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER TC7652 CONNECTION OF INPUT GUARDS Inverting Amplifier R1 Follower R2 INPUT – – OUTPUT + + INPUT TC7652 OUTPUT TC7652 Noninverting Amplifier R2 – + OUTPUT R1 TC7652 INPUT 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 ultrahigh-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-coefficient connections. Keep power supply voltages and power dissipation to a minimum. Use high-impedance loads and seek maximum separation from surrounding heat-dissipating elements. Guarding To benefit from TC7652 low-input currents, take care assembling printed circuit boards. Clean boards with alcohol 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 currents may occur because input pins are next to pins at supply potentials. To reduce this leakage, use guarding to lower the 3-284 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 guarding. 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. Nullstoring 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 VDD by two capacitors from those pins to VSS) provides compatibility. Replacing the compensation capacitor between pins 1 and 8 by two capacitors to VSS 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. TELCOM SEMICONDUCTOR, INC. LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER 1 TC7652 Some Applications Figures 1 and 2 show basic inverting and noninverting amplifier circuits using the output clamping circuit to enhance overload recovery performance. The only limitations on replacing other op amps with the TC7652 are supply voltage (±8V maximum) and output drive capability (10kΩ load for full swing). Overcome these limitations with a booster circuit (Figure 3) to combine output capabilities of the LM741 (or other standard device) with input capabilities of the TC7652. These two form a composite device; therefore, when adding the feedback network, monitor loop gain stability. 0.1 µF Figure 4 shows the clamp circuit of a zero-offset comparator. Because the clamp circuit requires the inverting input to follow the input signal, problems with a chopperstabilized op amp are avoided. The threshold input must tolerate the output clamp current ≈VIN/R without disrupting other parts of the system. Figure 5 shows how the TC7652 can offset-null high slew-rate and wideband amplifiers. Mixing the TC7652 with circuits operating at ±15V requires a lower supply voltage divider with the TC7660 voltage converter circuit operated "backwards." Figure 6 shows an approximate connection. 0.1 µF 0.1 µF TC7652 0.1 µF + VIN OUTPUT R3 4 VOUT – CLAMP 3 TC7652 + INPUT 2 R2 – R1 200 k Ω to 2 MΩ CLAMP VTH 5 Figure 4. Low Offset Comparator Figure 1. Noninverting Amplifier With Optional Clamp R2 TC7652 – INPUT TC7652 + CLAMP R1 – OUTPUT + 22 k Ω 22 k Ω 6 + OUT IN 0.1 µF – 0.1 µF Figure 2. Inverting Amplifier With Optional Clamp FAST AMPLIFIER Figure 5. 1437 Offset-Nulled by TC7652 7 –7.5V 2 +15V + + IN 741 – OUT – –7.5V TC7652 0.1 µF 4 –15V 0.1 µF 10 µF 10 k Ω Figure 3. Using 741 to Boost Output Drive Capability TELCOM SEMICONDUCTOR, INC. 8 TC 3 7660 6 5 +15V +7.5V 10 µF 0V 1 MΩ Figure 6. Splitting +15V With the 7660 at >95% Efficiency 3-285 8 LOW NOISE, CHOPPER-STABILIZED OPERATIONAL AMPLIFIER TC7652 TYPICAL CHARACTERISTICS Output Resistance vs Output Voltage Supply Current vs ± Supply Voltage Positive Clamp Current 1400 1 mA 1000 800 600 400 0.01 mA –4.0 CLAMP CURRENT OUTPUT VOLTAGE (V) SUPPLY CURRENT (µA) 0.1 mA –5.0 1200 SINK SOURCE 0.01 µA 1 nA 0.1 nA 200 0.01 nA –3.0 0 1 µA 0.1 µA 2 3 4 5 6 7 ± SUPPLY VOLTAGE (V) 8 100 Negative Clamp Current 1k 10k 100k 1M 1 pA 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0 OUTPUT RESISTANCE (Ω) OUTPUT VOLTAGE (V) Noise at 0.1 Hz to 100 Hz Noise at 0.1 Hz to 10 Hz 1 mA 0.1 mA 2 µV/DIV 1 µA 0.1 µA 1 µV/DIV CLAMP CURRENT 0.01 mA 0.01 µA 1 nA 0.1 nA 0.01 nA 1 pA 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0 1 sec/DIV 1 sec/DIV OUTPUT VOLTAGE (V) Slew Rate Phase-Gain (Bode Plot)* 60 GAIN +240 +180 50 PHASE 1 µV/DIV 0.5V/DIV GAIN (dB) 40 +120 +60 30 0 20 –60 10 PHASE (deg) Noise at 0.1 Hz to 1 Hz –120 0 –180 –10 –20 5 µsec/DIV 1 sec/DIV 1 10 *NOTE: Input Offset Voltage vs Common-Mode Voltage 100 1k 10k 100k FREQUENCY (Hz) 1M ±5V, ±2.5V supplies; no load to 10k load. INPUT OFFSET VOLTAGE (µV) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 –6 –4 –2 0 2 4 COMMON-MODE VOLTAGE (V) 3-286 TELCOM SEMICONDUCTOR, INC.