Application Notes

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PTH Series of Wide-Output Adjust

Power Modules (3.3/5-V Input)

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 wher-

ever there is a requirement for the output voltage from

the regulator to be turned off.

Vo (2V/Div)

Iin (2A/Div)

Q1Vds (5V/Div)

HORIZ SCALE: 10ms/Div

PTH05020W

V

IN

1

10

4

5

6

2

3

L

O

A

D

C

IN

1,000 µF

C

OUT

330 µF

1 =Inhibit

GND

GND

V

OUT

9

V

8

Q

1

BSS138

R

SET

7

From the moment a valid input voltage is applied, the

soft-start control introduces a short time delay (typically

5 ms-10 ms) before allowing the output voltage to rise.

The output then progressively rises to the module’s set-

point voltage. Figure 3-2 shows the soft-start power-up

characteristic of the 22-A output product (PTH05020W),

operating from a 5-V input bus and configured for a 3.3-V

output. The waveforms were measured with a 5-A resistive

load, with Auto-Track 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 15 ms.

Over-Current Protection

For protection against load faults, all modules incorporate

output over-current protection. Applying a load that

exceeds the regulator’s over-current threshold will cause

the regulated output to shut down. Following shutdown

a module will periodically attempt 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.

Over-Temperature Protection

The PTHxx020 and PTHxx030 series of products have

over-temperature 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 automatically pulled low. This

turns the output off. The output voltage will drop 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 tem-

perature decreases by about 10 °C below the trip point.

Note: The over-temperature protection is a last resort mecha-

nism to prevent thermal stress to the regulator. Operation at

or close to the thermal shutdown temperature is not recom-

mended 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.

off, the module will execute a soft-start power-up. A

regulated output voltage is produced within 20 msec.

Figure 3-4 shows the typical rise in both the output volt-

Figure 3–4

The power modules function normally when the Inhibit

pin is left open-circuit, providing a regulated output

respect to GND.

Figure 3-3 shows the typical application of the inhibit

input is not compatible with TTL logic devices. An open-

collector (or open-drain) discrete transistor is recommended

for control.

Figure 3–3