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TC7650 Fiches technique(PDF) 4 Page - Microchip Technology |
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TC7650 Fiches technique(HTML) 4 Page - Microchip Technology |
4 / 14 page TC7650 DS21463C-page 4 2001-2012 Microchip Technology Inc. 2.0 PIN DESCRIPTIONS The descriptions of the pins are listed in Table 2-1. TABLE 2-1: PIN FUNCTION TABLE 3.0 DETAILED DESCRIPTION 3.1 Theory of Operation Figure 3-1 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 exter- nal capacitors provide the required storage of the null- ing potentials and the necessary nulling loop time constants. The nulling arrangement operates over the full common mode and power supply ranges, and is also independent of the output level, thus giving excep- tionally high CMRR, PSRR and AVOL. Careful balancing of the input switches minimizes chopper frequency charge injection at the input termi- nals, and the feed forward type injection into the com- pensation 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 CA. The effective offset voltage at the null amplifier input is: EQUATION 3-1: After the nulling amplifier is zeroed, the main amplifier is zeroed; the A switches open and B switches close. The output voltage equation is: EQUATION 3-2: EQUATION 3-3: As desired, the device offset voltages are reduced by the high open loop gain of the nulling amplifier. 3.2 Output Stage/Loading The output circuit is a high impedance stage (approxi- mately 18k ). With loads less than this, the chopper amplifier behaves in some ways like a trans-conduc- tance amplifier whose open-loop gain is proportional to load resistance. For example, the open loop gain will be 17dB lower with a 1k load than with a 10k 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 1k load. In wideband applications, the best frequency response will be achieved with a load resistor of 10k or higher. This results in a smooth 6dB/octave response from 0.1Hz to 2MHz, with phase shifts of less than 10° in the transi- Pin Number Symbol Description 8-pin DIP 14-pin DIP 1,8 2,1 CA, CB Nulling capacitor pins 2 4 -INPUT Inverting Input 3 5 +INPUT Non-inverting Input 47 VSS Negative Power Supply 59 OUTPUT CLAMP Output Voltage Clamp 610 OUTPUT Output 711 VDD Positive Power Supply — 3,6 NC No internal connection —8 CRETN Capacitor current return pin — 12 INT CLK OUT Internal Clock Output — 13 EXT CLK IN External Clock Input — 14 INT/EXT Select Internal or External Clock V OSE 1 A N 1 + ------------------V OSN = VOUT = AMVOSM + (V + - V-) + A N(V + - V-) + A N VOSE V OUT A M A N V + V - – V OSM V OSN + A N ------------------------------------------- + = |
Numéro de pièce similaire - TC7650_13 |
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Description similaire - TC7650_13 |
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