Texas Instruments TPS3801, Отчет о приложении

Страница: 18 / 28

Applications
14 SLVA075
5 Applications
5.1 A TPS3801 Supervises a DSP
The standard task of a supply voltage supervisor is supervising a processor
supply voltage and triggering a reset, if this voltage falls below the threshold
voltage. The application example of Figure 17 shows a TPS3801K33, which
supervises the 3.3 V power line of the DSP TMS320LC542. This DSP has the
same supply voltage for the core and the I/O part. If the supply voltage falls below
2.93 V, which is the typical threshold voltage of a TPS3801K33, a reset is
asserted. The reset output keeps active until the supply voltage increases again
above the threshold voltage plus 200 ms of delay time.
A push button can be used to trigger a reset manually, a pullup resistor is not
needed. A capacitor of 100 nF between the V
DD
terminal of the supervisor and
GND ensures proper operation of the supervisor and is recommended.
VDD
MR
TPS3801K33
RESET
GND
VDD
TMS320LC542
RESET
GND
100 nF
VDD 3.3 V
Figure 17. TPS3801 Supervises the TMS320LC542-DSP
5.2 Switching the Power Supply With a TPS3801
Figure 18 illustrates an application to turn system power on and off with a
TPS3801. The TPS2051, a power distribution switch of Texas Instruments has
a high-active enable input, so that it can be directly connected to the reset output
of the supervisor.
Typically, the TPS2051 has R
DSon
of less than 100 m
Ω
. To keep the on-state
resistance low, the device has two input terminals and three output terminals.
The manual reset input of the TPS3801 allows a remote power control. This input
can be connected with an output of a DSP, which turns the power of a subsystem
on (
⇒
with a logical high signal) and off (
⇒
with a logical low signal). The
low-active OC terminal signals overcurrent or overtemperature conditions. The
output will remain asserted until the overcurrent or overtemperature condition is
removed. Due to the open-drain output, a resistor must be placed between the
OC terminal and the supply voltage.
When V
in
is below V
IT
, the reset output of the TPS3801is low and the power
distribution switch is disabled. When V
in
is above V
IT
, the reset output is high and
the TPS2051 is enabled.