Datasheet

 
 
SLVS391B − OCTOBER 2001 − REVISED FEBRUARY 2002
14
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APPLICATION INFORMATION
DSP supply with sequencing
This application shows a power supply for a typical DSP. DSPs usually have core voltages in the 1-V to 2.5-V
range, whereas the voltage at the I/O-pins (I/O voltage) is typically 3.3 V to interface with external logic and
converters. Therefore, a power supply with two output voltages is required. The application works with an input
voltage in the range of 3.5 V to 6.5 V. The maximum output current is 150 mA on each output.
The supply is enabled by pulling the enable pin (EN
of the TPS60503) to GND. The step-down charge pump
starts and its power good (PG) output goes high. This enables the LDO which powers the I/O lines and generates
a reset signal for the DSP. Figure 27 shows the timing diagram of the start-up/shutdown procedure.
t
d
V
I/O
V
(NOM)
V
IT
PG
1
0
1
0
EN
t
1
0
RS
‡
V
(CORE)
V
(NOM)
V
IT
t
t
t
t
OUT
OUT
FB
RESET
VIN
VIN
EN
GND
47 kΩ
1 MΩ10 MΩ
PG
OUT
FB
VIN
EN
GND
1 MΩ
47 µF
1 µF
1 µF
C1F+
C1F−
C2F+
C2F−
V
I/O
RESET
TPS60503
TPS77133
10 µF†
10 µF†
3.3 V
1.5 V
V
(CORE)
V
I
ENABLE
GND
†
Recommended value for stability, DSP may require higher capacitance.
‡
RS
is the RESET output of the TPS77133.
t
d
t
d
Figure 27. DSP Supply With Sequencing