Under split rail configuration, VIN, VCC bias, and EN are the signals to enable the part. For start-up sequence,

TI recommends that at least one of VIN UVLO rising threshold or EN rising threshold is satisfied later than VCC

UVLO rising threshold. A practical start-up sequence example is:

1. VIN applied

2. External VCC bias applied

3. EN signal goes high

Similarly, for power-down sequence, TI recommends that at least one of the VIN UVLO falling threshold or the

EN falling threshold is satisfied before the external VCC bias supply turns off. If the external VCC bias supply

turns off first, the internal LDO of the device prevents the VCC voltage from dropping below 3.0-V and be loaded

by other circuits powered by the external VCC bias supply.

CIN

MSEL

VOUT

VIN: 4 V

16 V

SS

AGND

PG

FB

BOOT

SW

GOSNS

VCC

EN

VIN

ILIM

VOSNS+

VOSNS-

CBOOT

COUT

RFB_T

RFB_B

CFF, Optional

CSS

RMSEL

RILIM

RPG

CVCC

PGOOD

EN

LOUT

PGND

VCC bias

Figure 7-2. Split Rail Configuration with External VCC Bias

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TPS54KB20

SLVSGP3 – MAY 2023

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