Datasheet TC7652 (Microchip) - 6

TC7652 3.0 DETAILED DESCRIPTION FIGURE 3-1: TEST CIRCUIT
R2
3.1 Capacitor Connection
1MΩ Connect the null storage capacitors to the CA and CB R pins with a common connection to the C 1
TC7652
RET pin (14-pin 1kΩ TC7652) or to V - SS (8-pin TC7652). When connecting to VSS, avoid injecting load current IR drops into the Output + capacitive circuitry by making this connection directly C R via a separate wire or PC trace. C 0.1µF 0.1µF
3.2 Output Clamp
In chopper stabilized amplifiers, the output clamp pin If the TC7652's output saturates, error voltages on the reduces overload recovery time. When a connection is external capacitors will slow overload recovery. This made to the inverting input pin (summing junction), a condition can be avoided if a strobe signal is available. current path is created between that point and the out- The strobe signal is applied to EXT CLK IN and the put pin, just before the device output saturates. This overload signal is applied to the amplifier while the prevents uncontrolled differential input voltages and strobe is LOW. In this case, neither capacitor will be charge build-up on correction storage capacitors. Out- charged. The low leakage of the capacitor pins allow put swing is reduced. long measurements to be made within eligible errors (typical capacitor drift is 10V/sec).
3.3 Clock
The TC7652 has a 550Hz internal oscillator, which is
4.0 TYPICAL APPLICATIONS
divided by two before clocking the input chopper switches. The 275Hz chopping frequency is available
4.1 Component Selection
at INT CLK OUT (Pin 12) on 14-pin devices. In normal operation, INT/EXT (Pin 14), which has an internal pull- CA and CB (external capacitors)should be in the 0.1F up, can be left open. to 1F range. For minimum clock ripple noise, use a 1F capacitor in broad bandwidth circuits. For limited An external clock can also be used. To disable the bandwidth applications where clock ripple is filtered internal clock and use an external one, the INT/EXT pin out, use a 0.1F capacitor for slightly lower offset volt- must be tied to VSS. The external clock signal is then age. High quality, film type capacitors (polyester or applied to the EXT CLK IN input (Pin 13). An internal polypropylene) are recommended, although a lower divide-by-two provides a 50% switching duty cycle. The grade ceramic may work in some applications. For capacitors are only charged when EXT CLK IN is high, quickest settling after initial turn-on, use low dielectric so a 50% to 80% positive duty cycle is recommended absorption capacitors (e.g., polypropylene). With for higher clock frequencies. The external clock can ceramic capacitors, settling to 1V takes several sec- swing between VDD and VSS, with the logic threshold onds. about 2.5V below VDD. The output of the internal oscillator, before the divide-
4.2 Static Protection
by-two circuit, is available at EXT CLK IN when INT/ Although input diodes static protect all device pins, EXT is high or unconnected. This output can serve as avoid strong electrostatic fields and discharges that the clock input for a second TC7652 (operating in a can cause degraded diode junction characteristics and master/slave mode), so that both op amps will clock at produce increased input-leakage currents. the same frequency. This prevents clock intermodula- tion effects when two TC7652's are used in a differen- tial amplifier configuration. DS21464C-page 6  2001-2012 Microchip Technology Inc. Document Outline 1.0 Electrical Characteristics 2.0 pin descriptions TABLE 2-1: pin function table 3.0 detailed description 3.1 Capacitor Connection 3.2 Output Clamp 3.3 Clock Figure 3-1: TEST CIRCUIT 4.0 TYPICAL APPLICATIONS 4.1 Component Selection 4.2 Static Protection 4.3 Output Stage/Load Driving Figure 4-1: CONNECTION OF INPUT GUARDS 4.4 Thermoelectric Effects 4.5 Guarding 4.6 Pin Compatibility 4.7 Some Applications Figure 4-2: Noninverting amplifier with optional clamp Figure 4-3: inverting amplifier with optional clamp Figure 4-4: using 741 to boost output drive capability Figure 4-5: low offset comparator Figure 4-6: 1437 offset nulled by tc7652 Figure 4-7: splitting +15v with the 7660 at >95% efficiency 5.0 typical characteristics 6.0 packaging information 6.1 Package Marking Information 6.2 Package Dimensions 7.0 Revision History Corporate Office Atlanta Boston Chicago Cleveland Fax: 216-447-0643 Dallas Detroit Indianapolis Toronto Fax: 852-2401-3431 Australia - Sydney China - Beijing China - Shanghai India - Bangalore Korea - Daegu Korea - Seoul Singapore Taiwan - Taipei Fax: 43-7242-2244-393 Denmark - Copenhagen France - Paris Germany - Munich Italy - Milan Spain - Madrid UK - Wokingham Worldwide Sales and Service