Datasheet TC7652 (Microchip) - 7

TC7652 4.3 Output Stage/Load Driving
with a 1k load), and this lower gain is inconsequential. For wide band, the best frequency response occurs The output circuit is high impedance (about 18k). with a load resistor of at least 10k. This produces a With lesser loads, the chopper amplifier behaves 6dB/octave response from 0.1Hz to 2MHz, with phase somewhat like a transconductance amplifier with an shifts of less than 2 degrees in the transition region, open-loop gain proportional to load resistance. (For where the main amplifier takes over from the null ampli- example, the open-loop gain is 17dB lower with a 1k. fier. load than with a 10k load.) If the amp is used only for DC, the DC gain is typically greater than 120dB (even
FIGURE 4-1: CONNECTION OF INPUT GUARDS
Inverting Amplifier Follower R R 1 2 Input
TC7652 TC7652
- - Output Output + + Input Noninverting Amplifier R2
TC7652
- Output + R1 Input
4.4 Thermoelectric Effects 4.5 Guarding
The thermoelectric (Seebeck) effects in thermocouple To benefit from TC7652 low input currents, take care junctions of dissimilar metals, alloys, silicon, etc. limit assembling printed circuit boards. Clean boards with ultra high precision DC amplifiers. Unless all junctions alcohol or TCE and blow dry with compressed air. To are at the same temperature, thermoelectric voltages prevent contamination, coat boards with epoxy or sili- around 0.1V/C (up to tens of V/C for some materi- cone rubber. als) are generated. To realize the low offset voltages of Even if boards are cleaned and coated, leakage cur- the chopper, avoid temperature gradients. Enclose rents may occur because input pins are next to pins at components to eliminate air movement, especially from supply potentials. To reduce this leakage, use guarding power dissipating elements in the system. Where pos- to lower the voltage difference between the inputs and sible, use low thermoelectric co-efficient connections. adjacent metal runs. The guard (a conductive ring sur- Keep power supply voltages and power dissipation to a rounding inputs) is connected to a low impedance point minimum. Use high impedance loads and seek maxi- at about the same voltage as inputs. The guard mum separation from surrounding heat disipating ele- absorbs leakage currents from high voltage pins. ments. 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.  2001-2012 Microchip Technology Inc. DS21464C-page 7 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