www.ti.com

V

(1 V/Div)

O

V (5 V/Div)

I

I (5 A/Div)

I

t - Time = 5 s/Div

m

Overcurrent Protection

Overtemperature Protection (OTP)

Output On/Off Inhibit

PTH12060W/L

SLTS217D–MAY 2003–REVISED OCTOBER 2005

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

(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 PTH12020, PTV12020, and PTH12030 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 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 will reduce 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.

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

has its own internal pull-up to a potential of 5 V to 13.2 V (see footnotes to specification table). The input is not

compatible with TTL logic devices. An open-collector (or open-drain) discrete transistor is recommended for

control.

15