PTB78560A Datasheet, PDF (20/29 Pages) Texas Instruments – 30-W, 24-V/48-V INPUT DC/DC CONVERTERS WITH AUTO-TRACK SEQUENCING

PTB78560A, PTB78560B
PTB78560C
SLTS249 – JUNE 2005
Track ⁵
U1
PTB78560B
+V_I
1 _+VI
+Sense ⁹
V_O Seq 11
V_O Bus ¹⁰
C_I
100 µF
2 _PEN
3 _NEN
V_O Adjust 8
V_O COM ⁶
−V_I
4 _−VI
7
−Sense
C2
220 µF
R1
5.36 kΩ
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2
Track
3
V_I
U2
6
PTH04000W VO
Inhibit GND Adjust
4
15
C3
47 µF
R2
2.32 kΩ
3 _VI
2
Track
U3
6
PTH04000W ^VO
Inhibit GND Adjust
4
5
C5
47 µF
15
R3
6.65 kΩ
V_O Seq
(3.3 V)
V_POL1
(2.5 V)
C4
47 µF
V_POL2
(1.8 V)
C6
47 µF
Figure 28. Power-Up Sequencing With Nonisolated POL Modules
Power-Up Sequencing Without A V_OSEQ Output (PTB78560A/C)
Although the PTB78560A or PTB78560C do not have a V_OSeq output, they can provide the input power and
coordinate the power-up sequencing to two or more nonisolated, Auto-Track compliant power modules. Figure 30
shows the PTB78560A (5 V) converter (U1) configured to provide both the input source and the power-up
sequence timing to two 5-V input nonisolated modules. The example shows two PTH04000W modules (U2 and
U3), each rated for up to 3 A of output current. In this case, the number of downstream modules, and their
respective output voltage and load current rating, is only limited by the amount of current available at the V_OBus
output.
The output voltage of the PTB78560 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 PTB78560A is selected and
adjusted for an output of 5 V. For 12-V input modules, the PTB78560C 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
again set to 2.5 V (R2 = 2.32 kΩ) and 1.8 V (R3 = 6.65 kΩ), respectively. Figure 29 shows the power-up
waveforms from Figure 30 when the Track control of all three modules are simply connected together.
The PTB78560 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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