QM48T/S14120 DC-DC Converter Data Sheet
36-75 VDC Input; 12 VDC @ 14 A Output
Vin(-) to enable automatic power up of the converter
without the need of an external control signal.
Operations
Input and Output Impedance
The ON/OFF pin is internally pulled up to 5 V
These power converters have been designed to be
stable with no external capacitors when used in low
inductance input and output circuits.
through a resistor. A properly debounced 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 voltage of 0.8 V. An external voltage source
(±20 V maximum) may be connected directly to the
ON/OFF input, in which case it must be capable of
sourcing or sinking up to 1 mA depending on the
signal polarity. See the Startup Information section
for system timing waveforms associated with use of
the ON/OFF pin.
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 addition of a 33 µF electrolytic capacitor with an
ESR < 1 ꢀ across the input helps to ensure stability
of the converter. In many applications, the user has
to use decoupling capacitance at the load. The
power converter will exhibit stable operation with
external load capacitance up to 2,200 µF on 12 V
output.
Remote Sense (Pins 5 and 7)
The remote sense feature of the converter
compensates for voltage drops occurring between
the output pins of the converter 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. B).
Additionally, see the EMC section of this data sheet
for discussion of other external components which
may be required for control of conducted emissions.
Paralleling Option
The QM48T/S14120-wxyP is a droop parallelable
version and is designed with a 600 mV output
voltage droop that is proportional to output current.
For any input voltage > 40 V, the converter will have
an open current output voltage of 12.3 V @ Io = 0,
and the nominal output voltage of 11.7 V @ Io =
14 A. The nominal output at 50% load will be 12 V.
TM Series
Rw
QmaX
Vout (+)
Vin (+)
Converter
100
SENSE (+)
(Top View)
Rload
ON/OFF
Vin (-)
TRIM
Vin
SENSE (-)
10
Vout (-)
Rw
ON/OFF (Pin 2)
The ON/OFF pin is used to turn the power converter
on or off remotely via a system signal. There are two
remote control options available, positive and
negative logic, with both referenced to Vin(-). A
typical connection is shown in Fig. A.
Fig. B: Remote sense circuit configuration.
CAUTION
If remote sensing is not utilized, 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 data
sheet value.
TM Series
QmaX
Vin (+)
ON/OFF
Vin (-)
Vout (+)
SENSE (+)
TRIM
Converter
(Top View)
Rload
Vin
SENSE (-)
Vout (-)
Because the sense leads carry minimal current,
large traces on the end-user board are not required.
However, sense traces should be run side by side
and located close to a ground plane to minimize
system noise and ensure optimum performance.
CONTROL
INPUT
Fig. A: Circuit configuration for ON/OFF function.
The converter’s output overvoltage 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 positive logic version turns on when the ON/OFF
pin is at a logic high and turns off when at a logic
low. The converter is on when the ON/OFF pin is left
open. See the Electrical Specifications for logic
high/low definitions.
The negative logic version turns on when the pin is
at a logic low and turns off when the pin is at a logic
high. The ON/OFF pin can be hardwired directly to
When utilizing the remote sense feature, care must
be taken not to exceed the maximum allowable
output power capability of the converter, which is
ZD-00376 Rev. 1.1.1, 19-Feb-10
Page 4 of 20
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