SLMA002 datasheet(24/46 Pages) TI1

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Dual Supply Operation

Cascading Supply Operation

PVDD2

BOOT2

SW2

PVDD1

BOOT1

SW1

GND

TPS55383

SEQ

ILIM2

FB2

EN1

EN2

FB1

OUTPUT1

OUTPUT2

UDG-08043

COMP2

COMP1

TPS55383

,, TPS55386

SLUS818 – SEPTEMBER 2008 ......................................................................................................................................................................................... www.ti.com

DESIGN HINT

The OCP threshold refers to the peak current in the internal switch. Be sure to add

one-half of the peak inductor ripple current to the dc load current in determining how

close the actual operating point is to the OCP threshold.

It is possible to operate a TPS5538x 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 Output 1 for a long enough

period of time to ensure that PVDD1 can support Output 1 load.

It is possible to source PVDD1 from Output 2 as depicted in Figure 27 and Figure 28. This configuration may be

preferred if the input voltage is high, relative to the voltage on Output 1.

Figure 27. Schematic Showing Cascading PVDD1 from Output 2

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SLMA002 Datasheet(PDF) 24 Page - Texas Instruments

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