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ICL7104 Datasheet(PDF) 11 Page - Intersil Corporation |
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ICL7104 Datasheet(HTML) 11 Page - Intersil Corporation |
11 / 21 page 5-16 Detailed Description ANALOG SECTION Figure 6 shows the equivalent Circuit of the Analog Section of both the ICL7104/8052 and the ICL7104/8068 in the 3 different phases of operation. If the Run/Hold pin is left open or tied to V+, the system will perform conversions at a rate determined by the clock frequency: 131,072 for - 16 and 32,368 for - 14 clock periods per cycle (see Figure 8 conversion timing). Auto-Zero Phase I (Figure 6A) During Auto-Zero, the input of the buffer is shorted to analog ground thru switch 2, and switch 1 closes a loop around the integrator and comparator. The purpose of the loop is to charge the Auto-Zero capacitor until the integrator output no longer changes with time. Also, switches 4 and 9 recharge the reference capacitor to VREF. Input Integrate Phase II (Figure 6B) During input integrate the Auto-Zero loop is opened and the analog input is connected to the buffer input thru switch 3. (The reference capacitor is still being charged to VREF during this time.) If the input signal is zero, the buffer, integrator and comparator will see the same voltage that existed in the previous sate (Auto-Zero). Thus the integrator output will not change but will remain stationary during the entire Input Integrate cycle. If VIN is not equal to zero, an unbalanced condition exists compared to the Auto-Zero phase, and the integrator will generate a ramp whose slope is proportional to VIN. At the end of this phase, the sign of the ramp is latched into the polarity F/F. Deintegrate Phase III (Figures 6C and 6D) During the Deintegrate phase, the switch drive logic uses the output of the polarity F/F in determining whether to close switches 6 and 9 or 7 and 8. If the input signal was positive, switches 7 and 8 are closed and a voltage which is VREF more negative than during Auto-Zero is impressed on the buffer input. Negative inputs will cause +VREF to be applied to the buffer input via switches 6 and 9. Thus, the reference capacitor generates the equivalent of a (+) reference or a (-) reference from the single reference voltage with negligible error. The reference voltage returns the output of the integra- tor to the zero-crossing point established in Phase I. The time, or number of counts, required to do this is proportional to the input voltage. Since the Deintegrate phase can be twice as long as the Input integrate phase, the input voltage required to give a full scale reading = 2VREF. NOTE: Once a zero crossing is detected, the system automatically reverts to Auto-Zero phase for the leftover Deintegrate time (unless RUN/HOLD is manipulated, see RUN/HOLD input in detailed description, digital section). FIGURE 5. HANDSHAKE MODE TIMING DIAGRAM CLOCK 1 H L (PIN 25) EITHER: MODE PIN OR INTERNAL LATCH PULSE IF MODE “HI” H L H L UART NORM DON’T CARE DON’T CARE DON’T CARE STABLE DATA VALID, STABLE DATA VALID, STABLE EXT EXT tMW tSM tCWH H L H L H L H L INTERNAL MODE IGNORED IGNORED CE/LD SEN (EXTERNAL SIGNAL) HBEN O/R, POL 01-14 LBEN BITS 1-5 tME tMB tCEL tCEH tSS tCBL tCDH tCDL tCBH tCBZ tCEZ THREE-STATE WITH PULLUP THREE-STATE -16 HAS EXTRA (MBEN) PHASE HANDSHAKE MODE OR TRIGGERED BY ICL8052/ICL7104, ICL8068/ICL7104 |
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Similar Description - ICL7104 |
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