ZD-00376 Rev. 1.1.1, 19-Feb-10
Page 5 of 20
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QM48T/S14120 DC-DC Converter Data Sheet
36-75 VDC Input; 12 VDC @ 14 A Output
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, decrease the maximum
current (originally obtained from the derating curves)
by the same percentage to ensure the converter’s
actual output power remains at or below the
maximum allowable output power.
Output Voltage Adjust /TRIM (Pin 6)
The output voltage can be adjusted up 10% (VIN >
40 V) or down 20% relative to the rated output
voltage by the addition of an externally connected
resistor.
The TRIM pin should be left open if trimming is not
being used. To minimize noise pickup, a 0.1 F
capacitor is connected internally between the TRIM
and SENSE(-) pins.
To increase the output voltage, refer to Fig. C. A trim
resistor, RT-INCR, should be connected between the
TRIM (Pin 6) and SENSE(+) (Pin 7), with a value of:
10.22
1.225Δ
626
Δ)V
5.11(100
R
NOM
O
INCR
T
[k],
for non-paralleling option
RT-INCR = 45(100+)/(*N
P)
[k],
for paralleling option
where,
INCR
T
R
Required value of trim-up resistor [k]
NOM
O
V
Nominal value of output voltage [V]
100
X
V
)
V
(V
Δ
NOM
-
O
NOM
-
O
REQ
-
O
[%]
REQ
O
V
Desired (trimmed) output voltage [V].
Rload
Vin
Vin (+)
Vin (-)
ON/OFF
Vout (+)
Vout (-)
TRIM
SENSE (+)
SENSE (-)
R T-INCR
(Top View)
Converter
Series
QmaXTM
Fig. C: Configuration for increasing output voltage.
When trimming up, care must be taken not to exceed
the converter‘s maximum allowable output power.
See the previous section for a complete discussion
of this requirement.
To decrease the output voltage (Fig. D), a trim
resistor, RT-DECR, should be connected between the
TRIM (Pin 6) and SENSE(-) (Pin 5), with a value of:
10.22
|
Δ
|
511
R DECR
T
[k],
for non-paralleling option
RT-DECR = (511-5.6)/(*N
P)
[k],
for paralleling option
where,
DECR
T
R
Required value of trim-down resistor [k]
and Δ is defined above.
Note:
The above equations for calculation of trim resistor values match
those typically used in conventional industry-standard quarter-
bricks.
Rload
Vin
Vin (+)
Vin (-)
ON/OFF
Vout (+)
Vout (-)
TRIM
SENSE (+)
SENSE (-)
RT-DECR
(Top View)
Converter
Series
QmaXTM
QmaX
QmaXTM
Fig. D: Configuration for decreasing output voltage.
TRIM/SENSE Function Notes:
1. Trim/Sense Functions have limited capability for Vin < 40 V.
2. Trimming/sensing beyond 110% of the rated output voltage is
not an acceptable design practice, as this condition could cause
unwanted triggering of the output overvoltage protection (OVP)
circuit. The designer should ensure that the difference between
the voltages across the converter’s output pins and its sense pins
does not exceed 10% of VOUT(NOM), or:
X
NOM
-
O
SENSE
OUT
10%
V
)]
(
V
)
(
[V
)]
(
V
)
(
[V
[V]
This equation is applicable for any condition of output sensing
and/or output trim.