Datasheet

TLC2543C, TLC2543I, TLC2543M

12-BIT ANALOG-TO-DIGITAL CONVERTERS

WITH SERIAL CONTROL AND 11 ANALOG INPUTS

SLAS079F – DECEMBER 1993 – REVISED NOVEMBER 2001

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

data output length

The next two bits (D3 and D2) of the data register select the output data length. The data-length selection is

valid for the current I/O cycle (the cycle in which the data is read). The data-length selection, being valid for the

current I/O cycle, allows device start-up without losing I/O synchronization. A data length of 8, 12, or 16 bits can

be selected. Since the converter has 12-bit resolution, a data length of 12 bits is suggested.

With D3 and D2 set to 00 or 10, the device is in the 12-bit data-length mode and the result of the current

conversion is output as a 12-bit serial data stream during the next I/O cycle. The current I/O cycle must be exactly

12 bits long for proper synchronization, even when this means corrupting the output data from a previous

conversion. The current conversion is started immediately after the twelfth falling edge of the current I/O cycle.

With bits D3 and D2 set to 11, the 16-bit data-length mode is selected, which allows convenient communication

with 16-bit serial interfaces. In the 16-bit mode, the result of the current conversion is output as a 16-bit serial

data stream during the next I/O cycle with the four LSBs always reset to 0 (pad bits). The current I/O cycle must

be exactly 16 bits long to maintain synchronization even when this means corrupting the output data from the

previous conversion. The current conversion is started immediately after the sixteenth falling edge of the current

I/O cycle.

With bits D3 and D2 set to 01, the 8-bit data-length mode is selected, which allows fast communication with 8-bit

serial interfaces. In the 8-bit mode, the result of the current conversion is output as an 8-bit serial data stream

during the next I/O cycle. The current I/O cycle must be exactly eight bits long to maintain synchronization, even

when this means corrupting the output data from the previous conversion. The four LSBs of the conversion

result are truncated and discarded. The current conversion is started immediately after the eighth falling edge

of the current I/O cycle.

Since D3 and D2 take effect on the current I/O cycle when the data length is programmed, there can be a conflict

with the previous cycle when the data-word length is changed from one cycle to the next. This may occur when

the data format is selected to be least significant bit first, since at the time the data length change becomes

effective (six rising edges of I/O CLOCK), the previous conversion result has already started shifting out.

In actual operation, when different data lengths are required within an application and the data length is changed

between two conversions, no more than one conversion result can be corrupted and only when it is shifted out

in LSB-first format.

sampling period

During the sampling period, one of the analog inputs is internally connected to the capacitor array of the

converter to store the analog input signal. The converter starts sampling the selected input immediately after

the four address bits have been clocked into the input data register. Sampling starts on the fourth falling edge

of I/O CLOCK. The converter remains in the sampling mode until the eighth, twelfth, or sixteenth falling edge

of the I/O CLOCK depending on the data-length selection. After the EOC delay time from the last I/O CLOCK

falling edge, the EOC output goes low indicating that the sampling period is over and the conversion period has

begun. After EOC goes low, the analog input can be changed without affecting the conversion result. Since the

delay from the falling edge of the last I/O CLOCK to EOC low is fixed, time-varying analog input signals can be

digitized at a fixed rate without introducing systematic harmonic distortion or noise due to timing uncertainty.

After the 8-bit data stream has been clocked in, DATA INPUT should be held at a fixed digital level until EOC

goes high (indicating that the conversion is complete) to maximize the sampling accuracy and minimize the

influence of external digital noise.