PTB48560A_15 Datasheet, PDF (20/29 Pages) Texas Instruments – 30-W, 48-V INPUT DC/DC CONVERTERS WITH AUTO-TRACK™ SEQUENCING

PTB48560A, PTB48560B
PTB48560C
SLTS236A – MARCH 2005 – REVISED OCTOBER 2005
U1
5
Track
PTB48560A
9
+Sense
+V_I
1
+V_I
10
V_OBus
2
PEN
3
NEN
8
V_OAdjust
6
V_OCOM
-V _I
4
-V _I
7
-Sense
C1
47 mF
R1
14.3 kW
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U2
3 _VI
2
Track
PTH05050W
6
V_O
Inhibit GND Adjust
4
15
C2
100 mF
R2
698 W
U3
3
V_I
2
Track
PTH05050W
6
V_O
Inhibit GND Adjust
4
15
C4
100 mF
R3
8.87 kW
V_OBUS (5 V)
V_(POL)1 (3.3 V)
C3
100 mF
V_(POL)2 (1.5 V)
C5
100 mF
Figure 21. Power-Up Sequencing With Nonisolated POL Modules
The output voltage of the PTB48560 must be set to a valid intermediate supply voltage. This depends on the
input voltage requirements of the downstream modules. For 5-V input modules, the PTB48560A is selected and
adjusted for an output of 5 V. For 12-V input modules, the PTB48560C is used and adjusted for an output of
12 V. U2 and U3, can be set to any voltage over their applicable adjustment range. In this example, they are set
to 3.3 V (R2 = 698 Ω) and 1.5 V (R3 = 8.87 kΩ), respectively. Figure 22 shows the power-up waveforms from
Figure 21 when the Track control of all three modules are simply connected together.
The PTB48560 converter (U1) provides the required intermediate voltage from the V_OBus output to power the
downstream modules, while holding the common Track control at ground potential. After allowing times for U2
and U3 to initialize, U1 removes the ground from the Track control, allowing this voltage to rise. The outputs from
the two nonisolated modules then rise simultaneously to their respective set-point voltages.
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