Datasheet

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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 V
EN2
<
enable threshold voltage
Tie EN1 to < enable threshold voltage
for BP to be active when V
EN2
>
BP Sequential, Output 2 then Output 1 Active
enable threshold voltage
Tie EN1 to > enable threshold voltage
for low quiescent current (BP inactive)
when V
EN2
> enable threshold voltage
Ignored by the device.when V
EN1
<
enable threshold voltage
Tie EN2 to < enable threshold voltage
for BP to be active when V
EN1
>
GND Sequential, Output 1 then Output 2 Active
enable threshold voltage
Tie EN2 to > enable threshold voltage
for low quiescent current (BP inactive)
when V
EN1
> enable threshold voltage
Independent or Ratiometric, Output 1 Active. EN1 and EN2 must be tied Active. EN1 and EN2 must be tied
(floating)
and Output 2 together for Ratio-metric startup. 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
µ s 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 µ s 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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Product Folder Link(s): TPS54383 TPS54386