TLC1549C_14 Datasheet, PDF (5/18 Pages) Texas Instruments – 10-BIT ANALOG-TO-DIGITAL CONVERTERS WITH SERIAL CONTROL

TLC1549C, TLC1549I, TLC1549M
10-BIT ANALOG-TO-DIGITAL CONVERTERS
WITH SERIAL CONTROL
SLAS059C – DECEMBER 1992 – REVISED MARCH 1995
mode 5: slow mode, CS inactive (high) between transfers, 11- to 16-clock transfer
In this mode, CS is inactive (high) between serial I/O CLOCK transfers and each transfer can be 11 to 16 clocks
long. The falling edge of CS begins the sequence by removing DATA OUT from the high-impedance state. The
rising edge of CS ends the sequence by returning DATA OUT to the high-impedance state within the specified
delay time. Also, the rising edge of CS disables I/O CLOCK within a setup time plus two falling edges of the
internal system clock.
mode 6: slow mode, CS active (low) continuously, 16-clock transfer
In this mode, CS is active (low) between serial I/O CLOCK transfers and each transfer must be exactly 16 clocks
long. After the initial conversion cycle, CS is held active (low) for subsequent conversions. The falling edge of
the sixteenth I/O CLOCK then begins each sequence by removing DATA OUT from the low state, allowing the
MSB of the previous conversion to appear immediately at DATA OUT. The device is then ready for the next 16
clock transfer initiated by the serial interface.
analog input sampling
Sampling of the analog input starts on the falling edge of the third I/O CLOCK, and sampling continues for seven
I/O CLOCK periods. The sample is held on the falling edge of the tenth I/O CLOCK.
converter and analog input
The CMOS threshold detector in the successive-approximation conversion system determines each bit by
examining the charge on a series of binary-weighted capacitors (see Figure 1). In the first phase of the
conversion process, the analog input is sampled by closing the S_C switch and all S_T switches simultaneously.
This action charges all the capacitors to the input voltage.
In the next phase of the conversion process, all S_T and S_C switches are opened and the threshold detector
begins identifying bits by identifying the charge (voltage) on each capacitor relative to the reference (REF –)
voltage. In the switching sequence, ten capacitors are examined separately until all ten bits are identified and
then the charge-convert sequence is repeated. In the first step of the conversion phase, the threshold detector
looks at the first capacitor (weight = 512). Node 512 of this capacitor is switched to the REF+ voltage, and the
equivalent nodes of all the other capacitors on the ladder are switched to REF –. If the voltage at the summing
node is greater than the trip point of the threshold detector (approximately one-half V_CC), a bit 0 is placed in the
output register and the 512-weight capacitor is switched to REF –. If the voltage at the summing node is less
than the trip point of the threshold detector, a bit 1 is placed in the register and this 512-weight capacitor remains
connected to REF + through the remainder of the successive-approximation process. The process is repeated
for the 256-weight capacitor, the 128-weight capacitor, and so forth down the line until all bits are determined.
With each step of the successive-approximation process, the initial charge is redistributed among the
capacitors. The conversion process relies on charge redistribution to determine the bits from MSB to LSB.
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