JFC050C Datasheet, PDF (11/20 Pages) Tyco Electronics – dc-dc Converters; 18 to 36 Vdc Input; 15 Vdc Output; 50 W to 100 W

Data Sheet
October 1999
JFC050C, JFC075C, JFC100C Power Modules:
dc-dc Converters; 18 to 36 Vdc Input, 15 Vdc Output; 50 W to 100 W
Feature Descriptions (continued)
Output Voltage Set-Point Adjustment
(Trim) (continued)
The amount of power delivered by the module is
defined as the voltage at the output terminals multiplied
by the output current. When using remote sense and
trim, the output voltage of the module can be
increased, which at the same output current would
increase the power output of the module. Care should
be taken to ensure that the maximum output power of
the module remains at or below the maximum rated
power.
VI(+)
VO(+)
ON/OFF SENSE(+)
CASE
TRIM
Radj-up
RLOAD
VI(–)
SENSE(–)
VO(–)
8-715 (C).d
Figure 15. Circuit Configuration to Increase
Output Voltage
Note: The output voltage of this module may be
increased to a maximum of 0.5 V. The 0.5 V is
the combination of both the remote-sense and
the output voltage set-point adjustment (trim).
Do not exceed 15.5 V between the VO(+) and
VO(–) terminals.
The following equation determines the required exter-
nal-resistor value to obtain a percentage output voltage
change of ý%.
Radj-up
=


-V----^O---⁽---1---0---0-----⁺-----^∆----%------⁾
1.225 ∆ %
–
(_{---1---0----0---∆-}+_---%--2----∆_----%------)
kΩ
Only trim up to 0.5 V maximum. See note above.
The test results for this configuration are displayed in
Figure 16. For applications requiring voltage between
15 V and 24 V, consider using the JFC050H, JFC075H,
JFC100H, or JFC150H (24 V) trimmed down.
The voltage between the VO(+) and VO(–) terminals
must not exceed the output overvoltage shutdown volt-
age. This limit includes any increase in voltage due to
remote-sense compensation and output voltage set-
point adjustment (trim).
100M
10M
1M
100k
0
2
4
6
8
10
% CHANGE IN OUTPUT VOLTAGE (∆%)
8-2082 (C)
Figure 16. Resistor Selection for Increased Output
Voltage
Output Overvoltage Protection
The output overvoltage shutdown consists of control
circuitry, independent of the primary regulation loop,
that monitors the voltage on the output terminals. The
control loop of the clamp has a higher voltage set point
than the primary loop (see Feature Specifications
table). This provides a redundant voltage control that
reduces the risk of output overvoltage and latches the
converter off if an overvoltage occurs.
Recovery from latched shutdown is accomplished by
cycling the dc input power off for at least 1.0 second or
by toggling the primary or secondary referenced
remote on/off signal for at least 1.0 second.
The overvoltage shutdown set point can be lowered by
placing a resistor between the overvoltage trim
(OVTRIM) pin and SENSE(–) pin. This feature is useful
if the output voltage of the converter has been trimmed
down and a corresponding reduction in overvoltage trip
point is desired.
The resistance required from a given overvoltage nom-
inal set point is derived from the following equation:
Rov-adj
=


-1--V-7---.-_o-6-_v---_--^–_s---_e-2--_t--_–--V---1-^o--7-^v--^-_.--^s_6--^e---^t_
kΩ
Where:
Rov-adj is the value of an external resistor between the
OVTRIM pin and SENSE(–) pin.
Vov-set is the nominal adjusted set point of the overvolt-
age shutdown threshold.
Tyco Electronics Corp.
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