Q24T25025 DC-DC Converter Data Sheet
18-36 VDC Input; 2.5 VDC @ 25A Output
may be connected directly to the ON/OFF input, in which
case it should be capable of sourcing or sinking up to 1 mA
depending on the signal polarity. See the Start-up Informa-
tion section for system timing waveforms associated with
use of the ON/OFF pin.
Operation
Input and Output Impedance
These power converters have been designed to be stable
with no external capacitors when used in low inductance in-
put and output circuits.
Remote Sense (Pins 5 and 7)
However, in many applications, the inductance associated
with the distribution from the power source to the input of the
converter can affect the stability of the converter. The addi-
tion of a 33 µF electrolytic capacitor with an ESR < 1 Ω
across the input helps ensure stability of the converter. In
many applications, the user has to use decoupling capaci-
tance at the load. The power converter will exhibit stable op-
eration with external load capacitance up to 30,000 µF.
The remote sense feature of the converter compensates for
voltage drops occurring between the output pins of the con-
verter and the load. The SENSE(-) (Pin 5) and SENSE(+)
(Pin 7) pins should be connected at the load or at the point
where regulation is required (see Fig. 3).
TM
Rw
Family
Q
Vout (+)
Vin (+)
Converter
100
SENSE (+)
(Top View)
ON/OFF (Pin 2)
Rload
ON/OFF
Vin (-)
TRIM
Vin
SENSE (-)
10
The ON/OFF pin is used to turn the power converter on or
off remotely via a system signal. There are two remote con-
trol options available, positive logic and negative logic and
both are referenced to Vin(-). Typical connections are shown
in Fig. 2.
Vout (-)
Rw
Fig. 3: Remote sense circuit configuration.
TM
If remote sensing is not required, the SENSE(-) pin must be
connected to the Vout(-) pin (Pin 4), and the SENSE(+) pin
must be connected to the Vout(+) pin (Pin 8) to ensure the
converter will regulate at the specified output voltage. If
these connections are not made, the converter will deliver an
output voltage that is slightly higher than the specified value.
Family
Q
Vin (+)
ON/OFF
Vin (-)
Vout (+)
SENSE (+)
TRIM
Converter
(Top View)
Rload
Vin
SENSE (-)
Vout (-)
CONTROL
INPUT
Because the sense leads carry minimal current, large traces
on the end-user board are not required. However, sense
traces should be located close to a ground plane to minimize
system noise and insure optimum performance. When wiring
discretely, twisted pair wires should be used to connect the
sense lines to the load to reduce susceptibility to noise.
Fig. 2: Circuit configuration for ON/OFF function.
The positive logic version turns on when the ON/OFF pin is
at logic high and turns off when at logic low. The converter is
on when the ON/OFF pin is left open.
The converter’s output over-voltage protection (OVP) senses
the voltage across Vout(+) and Vout(-), and not across the
sense lines, so the resistance (and resulting voltage drop)
between the output pins of the converter and the load should
be minimized to prevent unwanted triggering of the OVP.
The negative logic version turns on when the pin is at logic
low and turns off when the pin is at logic high. The ON/OFF
pin can be hard wired directly to Vin(-) to enable automatic
power up of the converter without the need of an external
control signal.
When utilizing the remote sense feature, care must be taken
not to exceed the maximum allowable output power capabil-
ity of the converter, equal to the product of the nominal out-
put voltage and the allowable output current for the given
conditions.
ON/OFF pin is internally pulled-up to 5 V through a resistor.
A mechanical switch, open collector transistor, or FET can
be used to drive the input of the ON/OFF pin. The device
must be capable of sinking up to 0.2 mA at a low level volt-
age of ≤ 0.8 V. An external voltage source of ±20 V max.
JUN 01, 2003 revised to NOV 22, 2006
Page 5 of 14
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