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SOFT-START POWER UP

12V

C

1000 F

I

m

C

330 F

O

m

GND

GND

3.3V

R

2k

0.1W

1%

SET

W

PTH12020W

7

10

4

5

6

2

3

9

Track

V

I

V

O

GND

Inhibit

1

Up Dn

Adjust

8

Sense

t − Time − 5 ms/div

OVERCURRENT PROTECTION

OVERTEMPERATURE PROTECTION (OTP)

PTH12030W/L

SLTS211F – MAY 2003 – REVISED FEBRUARY 2007

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

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.

Figure 10. Power-Up Application Circuit

Figure 11. Power-Up Waveforms

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.

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.

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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