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TC7650CPD Arkusz danych(PDF) 4 Page - TelCom Semiconductor, Inc |
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TC7650CPD Arkusz danych(HTML) 4 Page - TelCom Semiconductor, Inc |
4 / 7 page 3-276 TELCOM SEMICONDUCTOR, INC. Clock Operation The internal oscillator is set for a 200Hz nominal chop- ping frequency on both the 8- and 14-pin DIPs. With the 14-pin DIP TC7650, the 200Hz internal chopping frequency is available at the internal clock output (pin 12). A 400Hz nominal signal will be present at the external clock input pin (pin 13) with INT/EXT high or open. This is the internal clock signal before a divide-by-two operation. Figure 1. TC7650 Contains a Nulling and Main Amplifier. Offset Correction Voltages Are Stored on Two External Capacitors. The 14-pin DIP device can be driven by an external clock. The INT/EXT input (pin 14) has an internal pull-up and may be left open for internal clock operation. If an external clock is used, INT/EXT must be tied to VSS (pin 7) to disable the internal clock. The external clock signal is applied to the external clock input (pin 13). The external clock amplitude should swing between VDD and ground for power supplies up to ±6V and between V+ and V+ – 6V for higher supply voltages. At low frequencies the external clock duty cycle is not critical, since an internal divide-by-two gives the desired 50% switching duty cycle. The offset storage correction capacitors are charged only when the external clock input is high. A 50% to 80% external clock positive duty cycle is desired for frequencies above 500Hz to guarantee tran- sients settle before the internal switches open. The external clock input can also be used as a strobe input. If a strobe signal is connected at the external clock input so that it is LOW during the time an overload signal is applied, neither capacitor will be charged. The leakage currents at the capacitors pins are very low. At 25 °C a typical TC7650 will drift less than 10 µV/sec. Output Clamp Chopper-stabilized systems can show long recovery times from overloads. If the output is driven to either supply rail, output saturation occurs. The inputs are no longer held at a "virtual ground." The VOS null circuit treats the differen- tial signal as an offset and tries to correct it by charging the external capacitors. The nulling circuit also saturates. Once the input signal returns to normal, the response time is lengthened by the long recovery time of the nulling amplifier and external capacitors. Through an external clamp connection, the TC7650 Figure 2. Nulling Capacitor Connection Nulling Capacitor Connection The offset voltage correction capacitors are connected to CA and CB. The common capacitor connection is made to VSS (pin 4) on the 8-pin packages and to capacitor return (CR, pin 8) on the 14-pin packages. The common connec- tion should be made through a separate PC trace or wire to avoid voltage drops. The capacitors outside foil, if possible, should be connected to CR or VSS. NULL MAIN AMPLIFIER NULL AMPLIFIER GAIN = A B A B A – + CB CA TC7650 NULL – + V – V + GAIN = A , OFFSET = V N OSN VOUT ANALOG INPUT M VDD VSS 6 4 8 1 3 2 7 CA CB + – VDD TC7650 10 1 8 2 5 4 11 CA CB + – 7 VSS 14-PIN PACKAGE 8-PIN PACKAGE TC7650 TC7650 CHOPPER-STABILIZED OPERATIONAL AMPLIFIER |
Podobny numer części - TC7650CPD |
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Podobny opis - TC7650CPD |
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