TLC5618, TLC5618A

PROGRAMMABLE DUAL 12-BIT DIGITAL-TO-ANALOG CONVERTERS

SLAS156G – JULY 1997 – REVISED APRIL 2001

16

POST OFFICE BOX 655303

APPLICATION INFORMATION

changing the latch B data from zero to full code

Assuming that latch B starts at zero code (e.g., after power-up), the latch can be filled with 1s by writing (bit D15

on the left, D0 on the right).

0X00 1111 1111 1111

to the serial interface. Bit D14 can be zero to select slow mode or one to select fast mode. The data (bits D0

to D11) are written to both the double buffer and latch B.

The latch A contents and the DAC A output are not changed by this write.

double-buffered change of both DAC outputs

Assuming that DACs A and B start at zero code (e.g., after power-up), if DAC A is to be driven to mid-scale and

DAC B to full-scale, and if the outputs are to begin rising at the same time, this can be achieved as follows:

First,

0d01 1111 1111 1111

is written (bit D15 on the left, D0 on the right) to the serial interface. This loads the full-scale code into the double

buffer but does not change the latch B contents and the DAC B output voltage. The latch A contents and the

DAC A output are also unaffected by this write operation.

Changing from fast to slow or slow to fast mode changes the supply current which can glitch the outputs, and

so D14 (designated by d in the above data word) should be set to maintain the speed mode set by the previous

write.

Next,

1X0X 1000 0000 0000

is written (bit D15 on the left, D0 on the right) to the serial interface. Bit D14 can be zero to select slow mode

or one to select fast mode. The other X can be zero or one (don’t care). This writes the mid-scale code

(100000000000) to latch A and also copies the full-scale code from the double buffer to latch B. Both DAC

outputs thus begin to rise after the second write.

DSP serial interface

Utilizing a simple 3-wire serial interface shown in Figure 22, the TLC5618A can be interfaced to TMS320

compatible serial ports. The 5618A has an internal state machine that will count 16 clocks after receiving a falling

edge of CS and then disable further clocking in of data until the next falling edge is received on CS. Therefore

CS can be connected directly to the FS pins of the serial port and only the leading falling edge of the DSP will

be used to start the write process. The TLC5618A is designed to be used with the TMS320Cxx DSP in burst

mode serial port transmit operation.