Technical Specification
BASIC OPERATION AND FEATURES
The
PowerQor
series converter uses a two-stage power conver-
sion topology. The first stage is a buck-converter that keeps the
output voltage constant over variations in line, load, and temper-
ature. The second stage uses a transformer to provide the func-
tions of input/output isolation and voltage step-down to achieve
the low output voltage required.
Both the first stage and the second stage switch at a fixed fre-
quency for predictable EMI performance. Rectification of the
transformer’s output is accomplished with synchronous rectifiers.
These devices, which are MOSFETs with a very low on-state resis-
tance, dissipate far less energy than Schottky diodes. This is the
primary reason that the
PowerQor
converter has such high effi-
ciency, even at very low output voltages and very high output cur-
rents.
Dissipation throughout the converter is so low that it does not
require a heatsink for operation. Since a heatsink is not required,
the
PowerQor
converter does not need a metal baseplate or pot-
ting material to help conduct the dissipated energy to the
heatsink. The
PowerQor
converter can thus be built more simply
and reliably using high yield surface mount techniques on a PCB
substrate.
The
PowerQor
series of half-brick and quarter-brick converters
uses the industry standard footprint and pin-out configuration.
Input:
Output:
Current:
Package:
CONTROL FEATURES
35-75 V
1.8 V
40 A
Quarter-brick
REMOTE ON/OFF (Pin 2):
The ON/OFF input, Pin 2, permits
the user to control when the converter is
on
or
off.
This input is
referenced to the return terminal of the input bus, Vin(-). There are
two versions of the converter that differ by the sense of the logic
used for the ON/OFF input.
In the positive logic version, the ON/OFF input is active high
(meaning that a high turns the converter
on).
In the negative logic
version, the ON/OFF signal is active low (meaning that a low
turns the converter
on).
Figure A details five possible circuits for
driving the ON/OFF pin. Figure B is a detailed look of the inter-
nal ON/OFF circuitry.
REMOTE SENSE(+) (Pins 7 and 5):
The SENSE(+) inputs cor-
rect for voltage drops along the conductors that connect the con-
verter’s output pins to the load.
Pin 7 should be connected to Vout(+) and Pin 5 should be con-
nected to Vout(-) at the point on the board where regulation is
desired. A remote connection at the load can adjust for a voltage
drop only as large as that specified in this datasheet, that is
[
Vout(+) - Vout(-)
]
–
[V
sense(+) -
V
sense(-)
]
<
Sense Range % x Vout
Pins 7 and 5 must be connected for proper regulation of the out-
put voltage. If these connections are not made, the converter will
deliver an output voltage that is slightly lower than its specified
value.
Note: the output over-voltage protection circuit senses the voltage
ON/OFF
ON/OFF
ON/OFF
Vin(_
)
Remote Enable Circuit
Vin(_
)
Negative Logic
(Permanently Enabled)
ON/OFF
TTL/
CMOS
Vin(_)
Positive Logic
(Permanently Enabled)
V
in(+)
274k
ON/OFF
50k
5V
5V
ON/OFF
TTL
100pF
50k
Vin(_
)
Open Collector Enable Circuit
Vin(_
)
Direct Logic Drive
V
in(
_
)
Figure A:
Various circuits for driving the ON/OFF pin.
Product # PQ60018QTA40
Phone 1-888-567-9596
Figure B:
Internal ON/OFF pin circuitry
Doc.# 005-2QT618C Rev. C
09/08/05
Page 9
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