PTB48520W Datasheet, PDF (12/18 Pages) Texas Instruments – 25-A, 48-V INPUT ISOLATED DC/DC CONVERTER WITH AUTO-TRACK™ SEQUENCING

PTB48520W
SLTS233A – NOVEMBER 2004 – REVISED APRIL 2005
www.ti.com
Typical Power-Up Sequencing Configuration
Figure 10 shows how the converter (U1) can be configured to provide two 3.3-V sources, that allow it to both
power and sequence with one or more non-isolated POL modules. The example shows two PTH03050W
modules (U2 and U3), each rated for up 6 A of output current. Additional voltages, as well as modules with a
higher output current capability can also be specified to meet a specific application. The number of downstream
modules, their respective output voltage and load current rating is only limited by the amount of current available
at the V_O Bus output. This is 25 A, less the current allocated to the load circuit via the V_O Seq output.
The output voltage adjust range is 1.8 V to 3.6 V, which is compatible with the 3.3-V input non-isolated POL
modules. In these applications, the output voltage must always be set to 3.3 V (R1 = 887 Ω). Note that this sets
the output voltage of both the V_O Bus and V_O Seq outputs. The 3.3-V input non-isolated 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 = 2.21 kΩ)
and 1.8 V (R3 = 5.49 kΩ), respectively. Figure 9 shows the power-up waveforms from Figure 10 when the Track
control input to all three modules are simply connected together.
The converter provides input power to the downstream non-isolated modules via the V_O Bus output. This output
rises first to allow the downstream modules to complete their power-up initialization. V_O Seq (3.3 V), and the
outputs V_(POL)1 (2.5 V) and V_(POL)2 (1.8 V), supply the load circuit. These three outputs are controlled by the track
control voltage, which the converter holds at ground potential for 20 ms. When the track control voltage is finally
allowed to rise, the three outputs rise simultaneously to their respective set-point voltages.
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 9. Power-Up Waveforms with POL Modules
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