TPS54386PWPR datasheet(14/52 Pages) TI

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Output Voltage Sequencing

5-V VOUT1

(2 V/div)

3.3-V VOUT2

(2 V/div)

T - Time - 1 ms/div

SEQ = BP

Sequential

CH2 then CH1

T - Time - 1 ms/div

SEQ = GND

Sequential

CH1 then CH2

5-V VOUT1

(2 V/div)

3.3-V VOUT2

(2 V/div)

TPS54383,, TPS54386

SLUS774B – AUGUST 2007 – REVISED OCTOBER 2007

The TPS5438x allows single-pin programming of output voltage startup sequencing. During power-on, the state

of the SEQ pin is detected. Based on whether the pin is tied to BP, to GND, or left floating, the outputs behave

as described in Table 1.

Table 1. Sequence States

SEQ PIN STATE

MODE

EN1

EN2

Ignored by the device.when VEN2 <

enable threshold voltage

Tie EN1 to < enable threshold voltage

for BP to be active when VEN2 >

Sequential, Output 2 then Output 1

Active

enable threshold voltage

Tie EN1 to > enable threshold voltage

for low quiescent current (BP inactive)

when VEN2 > enable threshold voltage

Ignored by the device.when VEN1 <

enable threshold voltage

Tie EN2 to < enable threshold voltage

for BP to be active when VEN1 >

GND

Sequential, Output 1 then Output 2

Active

enable threshold voltage

Tie EN2 to > enable threshold voltage

for low quiescent current (BP inactive)

when VEN1 > enable threshold voltage

Independent or Ratiometric, Output 1

Active. EN1 and EN2 must be tied

(floating)

and Output 2

together for Ratio-metric startup.

If the SEQ pin is connected to BP, then when Output 2 is enabled, Output 1 is allowed to start approximately 400

µs after Output 2 has reached regulation; that is, sequential startup where Output 1 is slave to Output 2. If EN2 is

allowed to go high after the outputs have been operating, then both outputs are disabled immediately, and the

output voltages decay according to the load that is present.

If the SEQ pin is connected to GND, then when Output 1 is enabled, Output 2 is allowed to start approximately

400

µs after Output 1 has reached regulation; that is, sequential startup where Output 2 is slave to Output 1. If

EN1 is allowed to go high after the outputs have been operating, then both outputs are disabled immediately,

and the output voltages decay according to the load that is present.

Figure 18. SEQ Pin TIed to BP

Figure 19. SEQ Pin Tied to GND

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