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QLS20ZG

DC-DC Series Data Sheet 25A Quarter-Brick

Power-One Inc. 

QLS25 DC-DC Series Data Sheet

25A Quarter-Brick

Typical Application

Figure 7 shows the recommended connections for

the QLS25 Series converter.

Figure 7. Typical application of QLS25 Series

The QLS25 Series converters do not require any

external components for proper operation. However,

if the distribution of the input voltage to the converter

contains significant inductance, the capacitor C1

may be required to enhance performance of the

converter. A minimum of a 33μF electrolytic

capacitor with the ESR<0.7Ω is recommended for

the QLS25 Series.

Refer to the “Inrush Current Control Application

Note” on www.power-one.com for suggestions on

how to limit the magnitude of the inrush current.

For output decoupling we recommend to use a 10μF

tantalum and a 1μF ceramic capacitors connected

directly across the output pins of the converter.

Note, that the capacitors do not substitute the

filtering required by the load.

When the ON/OFF pin is used to achieve remote

control, the user must take care to insure that the pin

reference for the control is really the -Vin pin. The

control signal must not be referenced ahead of EMI

filtering, or remotely from the unit. Optically coupling

the information and locating the optical coupler

directly at the module will solve any of these

problems.

Note:

If the ON/OFF pin is not used, it can be left floating (positive logic),

or connected to the -Vin pin (negative logic).

Output Voltage Trim

The trim feature allows the user to adjust the output

voltage from the nominal. This can be used to

accommodate a different requirement or to do

production margin testing. There are two variances

available in the QLS25 Series.

Negative Trim

The QLS25 negative trim units trim up with a resistor

from the TRIM pin to the –Sense pin and trim down

with a resistor from the TRIM pin to the +Sense pin

as shown in Figure 8.

The negative trim schematic is shown in Figure 8.

Shutdown Feature Description

The ON/OFF pin in the QLS25 Series converters

functions as a normal soft shutdown. It is referenced

to the –Vin pin (see Figure 7). With the positive

logic, when the ON/OFF pin is pulled low, the output

is turned off and the unit goes into a very low input

power mode.

With negative logic, when the ON/OFF pin is pulled

low, the unit is turned on.

An open collector switch is recommended to control

the voltage between the ON/OFF pin and the -Vin

pin of the converter. The ON/OFF pin is pulled up

internally, so no external voltage source is required.

The user should avoid connecting a resistor between

the ON/OFF pin and the +Vin pin.

Figure 8. QLS25 Series Negative Trim Schematic

The general equation (1) for changing the output

voltage on the negative trim modules is invariant, but

the constants in the equation change due to different

internal values.

RTRIM

=

A − B × ΔV

ΔV

,

kΩ

(1)

SEP 12, 2003 revised to OCT 26, 2006

Page 5 of 8

www.power-one.com

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