MCD10085 Rev. 1.1, 08-Jul-10 Page 3 of 30 www.power-one.com
SQM48 Series Data Sheet
SemiQ
TM
Family 25A DC-DC Converters
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.
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
across the input helps ensure stability of the converter. In
many applications, the user has to use decoupling capacit-
ance at the load. The power converter will exhibit stable op-
eration with external load capacitance up to 20,000 µF on
2.5 – 1.2 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. 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. A.
Rload
Vin
CONTROL
INPUT
Vin (+)
Vin (-)
ON/OFF
Vout (+)
Vout (-)
TRIM
SENSE (+)
SENSE (-)
(Top View)
Converter
Semi
Q
TM
Family
Fig. A: 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 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 0.2 mA at a low level vol-
tage of 0.8 V. An external voltage source of ±20 V max.
may be connected directly to the ON/OFF input, in which
case it should be capable of sourcing or sinking (depending
on the signal polarity) up to 1 mA. See the Start-up Informa-
tion 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 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. B).
100
10
Rw
Rw
Rload
Vin
Vin (+)
Vin (-)
ON/OFF
Vout (+)
Vout (+)
TRIM
SENSE (+)
SENSE (-)
(Top View)
Converter
SemiQ
TM
Family
Fig. B: Remote sense circuit configuration.
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 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.
When utilizing the remote sense feature, care must be taken
not to exceed the maximum allowable output power capabili-
ty of the converter, equal to the product of the nominal out-
put voltage and the allowable output current for the given
conditions.
When using remote sense, the output voltage at the conver-
ter 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, decrease
the maximum current (originally obtained from the derating
curves) by the same percentage to ensure the converter’s
