MQFL-28V-12S Datasheet, PDF (11/19 Pages) SynQor Worldwide Headquarters – HIGH RELIABILITY DC-DC CONVERTER

Technical Specification
MQFL-28V-12S
Output: 12 V
Current: 8 A
Usually the converter has an EMI filter upstream of it, and the
source voltage is connected to the input of this EMI filter. When,
during compliance testing, the source voltage goes low during
an under-voltage transient, the input to the converter will go even
lower. This is because the inductance of the EMI filter (as well
as the parasitic source inductance) will cause an oscillatory ring
with the bulk capacitor. With the bulk capacitor that is present in
an MQME-28 filter, the peak of this under-voltage ring may be
approximately 2 volts if the source voltage drops to 6V (it will be
smaller than this at a higher transient source voltage due to the
lower current drawn by the converter). As a result, it is necessary
to add extra bulk capacitor across the converter’s input pins if the
source voltage is going to drop to 6V, as it does for MIL-STD-704(A)
or MIL-STD 1275B. It is recommended that a 100µF/0.25W ESR
capacitor be connected across the input pins of the converter be
used as a starting point. For MIL-STD-704(B-F), where the source
voltage drops to only 7V, a 47µF hold-up capacitor would be a
good starting point. The exact amount of capacitance required
depends on the application (source inductance, load power, rate
of fall of the source voltage, etc). Please consult the factory if
further assistance is required.
Because input system stability is harder to maintain as the
input voltage gets lower, the MQFL-28V series converters are
designed to give external access to the voltage node between the
boost-converter and the pre-regulator stages. This access, at the
“STABILITY” pin (pin 3), permits the user to add a stabilizing bulk
capacitor with series resistance to this node. Since the voltage at
this node stays above 16V, the amount of capacitance required
is much less than would be required on the converter’s input pins
where the voltage might drop as low as 5.5V. It is recommended
that a 22µF capacitor with an ESR of about 1W be connected
between the STABILITY pin and the INPUT RETURN pin (pin
2). Without this special connection to the internal node of the
converter, a 300µF stabilizing bulk capacitor would have been
required across the converter’s input pins.
Another advantage of the STABILITY pin is that it provides a
voltage source that stays above 16V when the under-voltage
transient occurs. This voltage source might be useful for other
circuitry in the system.
CONTROL FEATURES
ENABLE: The MQFL converter has two enable pins. Both must
have a logic high level for the converter to be enabled. A logic
low on either pin will inhibit the converter.
The ENA1 pin (pin 4) is referenced with respect to the converter’s
input return (pin 2). The ENA2 pin (pin 12) is referenced with
respect to the converter’s output return (pin 8). This permits the
converter to be inhibited from either the input or the output side.
Regardless of which pin is used to inhibit the converter, the
regulation and the isolation stages are turned off. However,
when the converter is inhibited through the ENA1 pin, the bias
supply is also turned off, whereas this supply remains on when
the converter is inhibited through the ENA2 pin. A higher input
standby current therefore results in the latter case.
Both enable pins are internally pulled high so that an open
connection on both pins will enable the converter. Figure A shows
the equivalent circuit looking into either enable pins. It is TTL
compatible.
SHUT DOWN: The MQFL converter will shut down in response
5.6V
PIN 4
(or PIN 12)
PIN 2
(or PIN 8)
1N4148
ENABLE
82K
250K
125K
TO ENABLE
CIRCUITRY
2N3904
IN RTN
Figure A: Equivalent circuit looking into either the ENA1 or ENA2
pins with respect to its corresponding return pin.
to only four conditions: ENA1 input low, ENA2 input low, VIN
input below under-voltage lockout threshold, or VIN input above
over-voltage shutdown threshold. Following a shutdown event,
there is a startup inhibit delay which will prevent the converter
from restarting for approximately 300ms. After the 300ms delay
elapses, if the enable inputs are high and the input voltage is
within the operating range, the converter will restart. If the VIN
input is brought down to nearly 0V and back into the operating
range, there is no startup inhibit, and the output voltage will rise
according to the “Turn-On Delay, Rising Vin” specification.
REMOTE SENSE: The purpose of the remote sense pins is to
correct for the voltage drop along the conductors that connect the
converter’s output to the load. To achieve this goal, a separate
conductor should be used to connect the +SENSE pin (pin 10)
directly to the positive terminal of the load, as shown in the
connection diagram. Similarly, the –SENSE pin (pin 9) should be
connected through a separate conductor to the return terminal of
the load.
NOTE: Even if remote sensing of the load voltage is not desired, the
+SENSE and the -SENSE pins must be connected to +Vout (pin 7)
and OUTPUT RETURN (pin 8), respectively, to get proper regulation
of the converter’s output. If they are left open, the converter will
have an output voltage that is approximately 200mV higher than
its specified value. If only the +SENSE pin is left open, the output
voltage will be approximately 25mV too high.
Product # MQFL-28V-12S
Phone [phone]
www.synqor.com
Doc.# 005-2MQ12VS Rev. C 04/24/09
Page 11