TPS54383, TPS54386
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SLUS774B–AUGUST 2007–REVISED OCTOBER 2007
Dual Supply Operation
It is possible to operate a TPS5438x from two supply voltages. If this application is desired, then the sequencing
of the supplies must be such that PVDD2 is above the UVLO voltage before PVDD1 begins to rise. This level
requirement ensures that the internal regulator and the control circuitry are in operation before PVDD1 supplies
energy to the output. In addition, Output 1 must be held in the disabled state (EN1 high) until there is sufficient
voltage on PVDD1 to support Output 1 in regulation. (See the Operating Near Maximum Duty Cycle section.)
The preferred sequence of events is:
1. PVDD2 rises above the input UVLO voltage
2. PVDD1 rises with Output 1 disabled until PVDD1 rises above level to support Output 1 regulation.
With these two conditions satisfied, there is no restriction on PVDD2 to be greater than, or less than PVDD1.
DESIGN HINT
An R-C delay on EN1 may be used to delay the startup of Output1 for a long enough
period of time to ensure that PVDD1 can support Output 1 load.
Cascading Supply Operation
It is possible to source PVDD1 from Output 2 as depicted in Figure 34 and Figure 35. This configuration may be
preferred if the input voltage is high, relative to the voltage on Output 1.
V
IN
TPS54383
1
2
3
4
5
6
7
PVDD1 PVDD2 14
BOOT1 BOOT2 13
OUTPUT1
OUTPUT2
SW1
GND
EN1
EN2
FB1
SW2 12
BP 11
SEQ 10
ILIM2
FB2
9
8
UDG-07015
Figure 34. Schematic Showing Cascading PVDD1 from Output 2
Copyright © 2007, Texas Instruments Incorporated
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