SQ24 Power-One, SQ24 Datasheet - Page 3

• Manufacturer Part Number: SQ24
• Description: Sq24 Series Dc-dc Converter Data Sheet 18-36 Vdc Input; Standard Outputs From 1-12 Vdc
• Manufacturer: Power-One

Operation
Input and Output Impedance
These power converters have been designed to be stable
with no external capacitors when used in low inductance
input and output circuits.
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
addition of a 100 µF electrolytic capacitor with an ESR < 1Ω
across the input helps 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
1000 µF on 12 V, 2,200 µF on 8.0 V, 10,000 µF on 5.0 V –
6.0 V, and 15,000 µF on 3.3 V – 1.0 V outputs.
ON/OFF (Pin 2)
The ON/OFF pin is used to turn the power converter on or
off remotely via a system signal.
control options available, positive logic and negative logic
and both are referenced to Vin(-). Typical connections are
shown in Fig. A.
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 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.
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 0.2mA at a low level
voltage of ≤ 0.8V. An external voltage source (±20V
maximum) may be connected directly to the ON/OFF input,
AUG 25, 2006 revised to MAR 19, 2007
Vin
CONTROL
Fig. A: Circuit configuration for ON/OFF function.
INPUT
Vin (+)
ON/OFF
Vin (-)
Semi
Converter
(Top View)
Q
TM
Family
.
SENSE (+)
SENSE (-)
There are two remote
Vout (+)
Vout (-)
TRIM
18-36 VDC Input; Standard Outputs from 1-12 VDC
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SQ24 Series DC-DC Converter Data Sheet
in which case it must be capable of sourcing or sinking up to
1mA depending on the signal polarity. See the Start-up
Information section for system timing waveforms associated
with use of the ON/OFF pin.
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).
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.
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.
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.
When utilizing the remote sense feature, care must be taken
not to exceed the maximum allowable output power
capability of the converter, equal to the product of the
nominal output voltage and the allowable output current for
the given conditions.
When using remote sense, the output voltage at the
converter can be increased by as much as 10% above the
nominal rating in order to maintain the required voltage
across the load. Therefore, the designer must, if necessary,
Vin
Fig. B: Remote sense circuit configuration.
Vin (+)
ON/OFF
Vin (-)
Semi
Converter
(Top View)
Q
TM
Family
SENSE (+)
SENSE (-)
Vout (+)
Vout (-)
TRIM
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Rw
Rw
Rload