PTB78560A Datasheet, PDF (19/29 Pages) Texas Instruments – 30-W, 24-V/48-V INPUT DC/DC CONVERTERS WITH AUTO-TRACK SEQUENCING

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PTB78560A, PTB78560B
PTB78560C
SLTS249 – JUNE 2005
must always be set to 3.3 V (R1 = 5.36 kΩ). This sets the output voltage of both the V_OBus and V_OSeq outputs.
The output voltage of the 3.3-V input (nonisolated) modules, U2 and U3, can be set to any voltage over the
range, 0.8 V to 2.5 V. In this example, they are set to 2.5 V (R2 = 2.32 kΩ) and 1.8 V (R3 = 6.65 kΩ),
respectively. Figure 27 shows the power-up waveforms from Figure 28 when the Track input to all three modules
are simply connected together.
The converter provides input power to the downstream nonisolated modules via the V_OBus output. This output
rises first to allow the nonisolated modules to complete their power-up initialization. The V_OSeq (3.3 V), V_(POL)1
(2.5 V) and V_(POL)2 (1.8 V), outputs supply the load circuit, and rise simultaneously when the converter removes
the internal ground signal to its own Track input. The V_OSeq output rises with the outputs from the nonisolated
modules, until it reaches its set-point voltage.
V_OBus (1 V/div)
V_OSeq (1 V/div)
V_(POL)1 (1 V/div)
V_(POL)2 (1 V/div)
t_d = 20 ms
t − 20 ms/div
Figure 27. Power-Up Waveforms with POL Modules
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