PTH12030W/L
www.ti.com
SLTS211F–MAY 2003–REVISED FEBRUARY 2007
SOFT-START POWER UP
The Auto-Track feature allows the power-up of multiple PTH modules to be directly controlled from the Track
pin. However, in a stand-alone configuration, or when the Auto-Track feature is not being used, the Track pin
should be directly connected to the input voltage, VI, see Figure 10.
When the Track pin is connected to the input voltage the Auto-Track function is permanently disengaged. This
allows the module to power up entirely under the control of its internal soft-start circuitry. When power up is
under soft-start control, the output voltage rises to the set-point at a quicker and more linear rate.
10 9
8
5
Up
Dn Track
Sense
V (5 V/div)
I
3.3 V
12 V
2
6
PTH12020W
VI
VO
V
O
(1 V/div)
Inhibit GND
3
Adjust
4
1
7
+
+
RSET
CI
1000 mF
CO
330 mF
2 kW
0.1 W
1%
GND
GND
I (5 V/div)
I
t − Time − 5 ms/div
Figure 11. Power-Up Waveforms
Figure 10. Power-Up Application Circuit
From the moment a valid input voltage is applied, the soft-start control introduces a short time delay (typically
8 ms-15 ms) before allowing the output voltage to rise. The output then progressively rises to the module’s
setpoint voltage. Figure 11 shows the soft-start power-up characteristic of the 18-A output product
(PTH12020W), operating from a 12-V input bus and configured for a 3.3-V output. The waveforms were
measured with a 5-A resistive load and the Auto-Track feature disabled. The initial rise in input current when the
input voltage first starts to rise is the charge current drawn by the input capacitors. Power-up is complete within
25 ms.
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 power-up. 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)
The PTH12020W and PTH12030W products have overtemperature protection. These products have 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 internally 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 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.
13
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