Datasheet

V (2V/Div)
O
I (2 A/Div)
I
Q1Vds(5V/Div)
t-T
ime=10 msec/Div
PTH05020W
1
10
4
5
62
3
+
C
330 F
O
m
C
1,000 F
I
m
+
1=Inhibit
GND
V
O
V
I
9
V Sense
O
8
Q1
BSS138
R
SET
7
L
O
A
D
GND
PTH04040W
www.ti.com SLTS238C –SEPTEMBER 2005–REVISED JUNE 2010
OVERCURRENT PROTECTION
For protection against load faults, all modules incorporate output overcurrent protection. Applying a load that
exceeds the regulator’s overcurrent threshold causes the regulated output to shut down. Following shutdown, a
module periodically attempts to recover by initiating a soft-start powerup. This is described as a hiccup mode of
operation, whereby the module continues in a cycle of successive shutdown and power up until the load fault is
removed. During this period, the average current flowing into the fault is significantly reduced. Once the fault is
removed, the module automatically recovers and returns to normal operation.
OVERTEMPERATURE PROTECTION (OTP)
Products with a high output current capability (>20 A), incorporate overtemperature protection. This feature is
provided by an on-board temperature sensor that protects the module’s internal circuitry against excessively high
temperatures. A rise in the internal temperature may be the result of a drop in airflow, or a high ambient
temperature. If the internal temperature exceeds the OTP threshold, the module’s Inhibit control is automatically
pulled low. This turns the output off. The output voltage drops as the external output capacitors are discharged
by the load circuit. The recovery is automatic, and begins with a soft-start power up. It occurs when the sensed
temperature decreases by about 10°C below the trip point.
Note: The overtemperature protection is a last resort mechanism to prevent thermal stress to the regulator.
Operation at or close to the thermal shutdown temperature is not recommended, and reduces the long-term
reliability of the module. Always operate the regulator within the specified safe operating area (SOA) limits for
the worst-case conditions of ambient temperature and airflow.
OUTPUT ON/OFF INHIBIT
For applications requiring output voltage on/off control, each series of the PTH family incorporates an output
Inhibit control pin. The inhibit feature can be used wherever there is a requirement for the output voltage from the
regulator to be turned off.
The power modules function normally when the Inhibit pin is left open-circuit, providing a regulated output
whenever a valid source voltage is connected to V
in
with respect to GND.
Figure 13 shows the typical application of the inhibit function. Note the discrete transistor (Q1). The Inhibit control
has its own internal pull-up to V
I
potential. The input is not compatible with TTL logic devices. An open-collector
(or open-drain) discrete transistor is recommended for control.
Figure 13. Inhibit Control Circuit Figure 14. Power-Up from Inhibit Control
Turning Q1 on applies a low voltage to the Inhibit control and disables the output of the module. If Q1 is then
turned off, the module executes a soft-start powerup. A regulated output voltage is produced within 20 ms.
Figure 14 shows the typical rise in both the output voltage and input current, following the turn-off of Q1. The turn
off of Q1 corresponds to the rise in the waveform, Q1 Vds. The waveforms were measured with a 5-A constant
current load.
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