TLC3541, TLC3545

SLAS345 − DECEMBER 2001

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PRINCIPLES OF OPERATION

control via pin 1 (CS, DSP interface)

All devices are compatible with this mode of operation. The FS signal from a DSP is connected directly to the

so that the conversion cycle is not terminated prematurely.

1

2

3

5

4

6

7

13

14

15

16

1

12

ts

tconv

t(PWRDWN)

SDO Data Is the Result of the Previous Sample

For TLC35xx, the LSB Is Presented on the Rising SCLK 14th Edge

MSB

MSB−1

MSB−2 MSB−3 MSB−4 MSB−5 MSB−6

LSB+2

LSB+1

LSB

LSB−1

LSB−2

SCLK

CS

SDO

MSB

MSB−1

The CS Input Signal Is

Generated by the FS Output

From a TMS320 DSP

24

Figure 16. DSP Cycle Timing Using the CS Input (FS = 1 for TLC3541 only)

control via pin 1 and pin 7 (CS and FS or FS only, DSP interface)

Only TLC3541 is compatible with this mode of operation. The CS input to the ADC can be controlled via a

general-purpose I/O pin from the DSP or tied to ground. The FS signal from the DSP is connected directly to

the FS input of the ADC. A rising FS edge releases the MSB to the SDO output. The falling edge on the FS input

while SCLK is high or low initiates the cycle. The CS input should remain low for the entire sampling time plus

4 SCLK decoding time after falling FS (24 falling SCLK edges) and can then be released at any time during the

remainder of the conversion cycle. The optimum DSP interface is achieved when tying CS to ground and using

only the FS input to control the ADC.

tconv

t(PWRDWN)

SDO Data Is the Result of the Previous Sample

For TLC35xx, the LSB Is Presented on the Rising SCLK 14th Edge

1

2

3

5

4

6

14

15

16

1

2

34

ts

MSB

MSB−1 MSB−2 MSB−3 MSB−4 MSB−5 LSB+1

LSB

LSB−1 LSB−2

MSB

MSB−1 MSB−2 MSB−3

The MSB Is Presented on the SDO Output After

a Rising Edge on the FS Input.

17

24

The Device Will Go Into the Power Down State After the Conversion Is

Complete. A Falling CS Edge or Rising FS Edge, Whichever Occurs First,

Removes the Device From Power Down.

SCLK

CS

SDO

FS

Figure 17. DSP Cycle Timing Using FS Only (or Using Both CS and FS for TLC3541)