PTB48560A_15 Datasheet, PDF (18/29 Pages) Texas Instruments – 30-W, 48-V INPUT DC/DC CONVERTERS WITH AUTO-TRACK™ SEQUENCING

PTB48560A, PTB48560B
PTB48560C
SLTS236A – MARCH 2005 – REVISED OCTOBER 2005
www.ti.com
Power-Up Sequencing With A V_O SEQ Output (PTB48560B)
Figure 19 shows the PTB48560B converter (U1) providing two 3.3-V sources. This allows it to both power and
sequence with one or more downstream nonisolated modules. The example shows two 3.3-V input PTH03050W
modules (U2 and U3), each rated for up to 6 A of output current. The selection and current rating of the
nonisolated modules depends on the requirements of a specific application. The number of modules, their
respective output voltage, and load current rating combine with the load required at the V_OSeq output. The total
must be supplied by the PTB48560B, and cannot exceed that available at the V_OBus output.
U1
5
Track
PTB48560B
V_OSEQ (3.3 V)
9
+Sense
11
+V_I
1
V_OSeq
+V_I
10
V_OBus
U2
3 _VI
2
Track
PTH03050W
6
V_O
V_(POL)1 (2.5 V)
2
PEN
3
NEN
8
V_OAdjust
6
V_OCOM
C1
47 mF
R1
5.36 kW
Inhibit GND Adjust
4
15
C2
100 mF
R2
2.21 kW
C3
100 mF
-V _I
4
-V _I
7
-Sense
U3
3
V_I
2
Track
PTH03050W
6
V_O
V_(POL)2 (1.8 V)
Inhibit GND Adjust
4
15
C4
100 mF
R3
5.49 kW
C5
100 mF
Figure 19. Power-Up Sequencing With Nonisolated POL Modules
The output voltage adjust range of the PTB48560B is 1.8 V to 3.6 V. In these applications, the output voltage
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 = 2.21 kΩ) and 1.8 V (R3 = 5.49 kΩ),
respectively. Figure 20 shows the power-up waveforms from Figure 19 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.
18