Application Notes

ATH Series of Wide-Output Adjust Power

Modules (3.3/5-V Input)

North America (USA): 1-888-41-ASTEC

Europe (UK): 44(1384)842-211

Asia (HK): 852-2437-9662

Output On/Off Inhibit

For applications requiring output voltage on/off control,

each series of the ATH 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.

The power modules function normally when the Inhibit

pin is left open-circuit, providing a regulated output

respect to GND.

Figure 3-2 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.

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

sequence. A regulated output voltage is produced within

20 msec. Figure 3-3 shows the typical rise in both the

output voltage and input current, following the turn-off

a 5-A load.

Figure 3-2

Figure 3-3

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

Remote Sense

The ATH10, ATH12/15, ATH18/22, and ATH26/30

products incorporate an output voltage sense pin,

load circuit (see data sheet standard application). A re-

mote sense improves the load regulation performance of

the module by allowing it to compensate for any ‘IR’ voltage

drop between itself and the load. An IR drop is caused by

the high output current flowing through the small

amount of pin and trace resistance. Use of the remote

open-circuit. An internal low-value resistor (15-

Ω or

sures the output voltage remains in regulation.

With the sense pin connected, the difference between

amount of IR drop being compensated by the regulator.

This should be limited to a maximum of 0.3 V.

Note: The remote sense feature is not designed to compensate

for the forward drop of non-linear or frequency dependent

components that may be placed in series with the converter

output. Examples include OR-ing diodes, filter inductors,

ferrite beads, and fuses. When these components are enclosed

by the remote sense connection they are effectively placed

inside the regulation control loop, which can adversely affect

the stability of the regulator.

Over-Temperature Protection

The ATH18/22 and ATH26/30 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.

ATH15T05-9S