Technical Reference Notes

ALQ25B50 Bus Converter

DC Transformer

MODEL: ALQ25B50 SERIES

SHEET 7 OF 11

SEPTEMBER 11, 2003 - REVISION A (PRELIMINARY)

Basic Operation and Features

INPUT UNDER VOLTAGE LOCKOUT

To prevent any instability to the converter, which may affect the end system, the ALQ25B50 series have been designed to turn-

39-41 VDC.

INPUT OVER VOLTAGE PROTECTION

The ALQ25B50 employs a DC Transformer conversion scheme where the input and output relationship is dictated by the turns

ratio of the windings. The OVP circuit senses the input line and shuts down the entire module once the sensed voltage reaches

the OVP threshold. Restart is possible once the fault is removed and the input power is recycled.

OUTPUT ENABLE

The ALQ25B50 series comes with an Enable pin (PIN 2), which is primarily used to turn ON/OFF the converter. Both a

Positive (no part number suffix required) and a Negative (suffix “N” required) Enable Logic options are being offered. Please

refer to Table 2 for the Part Numbering Scheme.

For Positive Enable, the converter is turned on when the Enable pin is at logic HIGH or left open. The unit turns off when the

OVER CURRENT PROTECTION (OCP)

The Over Current Protection circuit comes in latching mode. The converter is latched off if the load current on the output

reaches the OCP threshold limit. The OCP latch can be reset either by cycling the input voltage or toggling the Enable signal

for 100ms. Consult factory for Auto-restart option.

OVER TEMPERATURE PROTECTION (OTP)

The Over Temperature Protection circuit will shutdown the converter once the average PCB temperature reaches the OTP

range. This feature prevents the unit from overheating and consequently going into thermal runaway, which may further

damage the converter and the end system. Such overheating may be an effect of operation outside the given power thermal

derating conditions. Restart is possible once the temperature of the sensed location drops to less than 110

°C.