Always 0 for

TPS56921

TPS56921

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SLVSBL4 – OCTOBER 2012

When the TPS56921 receives an address code it recognizes to be its own, it will respond by sending an ACK

(pulling down on the SDA bus during clock 9 on the SCL bus). If the address is not recognized, the TPS56921

data sent thereafter until the next START is begun.

If, after recognizing its address, the TPS56921 receives a valid data byte (checked by comparing the ChkSum

sent to the D[6:0] data), it will send an ACK and will set the output voltage to the desired value. If the byte is

deemed invalid, ACK will not be sent and the Master will need to retry by sending a new START sequence and

an initiating resend of the entire address/data packet.

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The 7-bit address of the TPS56921 can be any number between 34h (0110100) and 37h (0110111). The 5

MSBs are set internally and the 2 LSBs are customer-selectable via the A1 and A0 pins, allowing up to 4

TPS56921s to be controlled on the same serial bus. When the Master is sending the address as an 8-bit value,

the 7-bit address should be sent followed by a trailing 0 to indicate this is a WRITE operation. The following

codes assume this trailing zero.

Table 1. TPS56921 Address as a Function of A1 and A0 Pins

A1

A0

TPS56921 Address (binary)

TPS56921 Address (hex)

Ground (0)

Ground (0)

01101000

68h

Ground (0)

Open (1)

01101010

6Ah

Open (1)

Ground (0)

01101100

6Ch

Open (1)

Open (1)

01101110

6Eh

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The 8 bits of data sent over the serial bus controls the VOUT of the TPS56921. After the SoftStart time has

elapsed (SS pin voltage goes above approx. 1.23V), the serial interface becomes active and the user may

program VOUT by writing to the interface. The data is structured thus:

Table 2. Structure of TPS56921 Data byte

8

7

6

5

4

3

2

1

ChkSum

D6

D5

D4

D3

D2

D1

D0

D[6:0] – These bits are the 7-bit selector for one of 77 output voltages. The voltages are selected from the

following table:

Table 3. Ideal VOUT vs. Code

Code

Binary

VOUT

Code

Binary

VOUT

Code

Binary

VOUT

0

0000000

0.720

26

0011010

0.980

52

0110100

1.240

Copyright © 2012, Texas Instruments Incorporated

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