JFC050C Datasheet, PDF (9/20 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)
Overcurrent Protection (continued)
The current-limit set point can be reduced by connect-
ing a resistor between the overcurrent trim (OCTRIM)
pin and SENSE(–) pin. The resistor value is derived by
the following equation:
Rcl-adj
=


1----1-1---.-I-1-t_--r_5--i_-m_---I--r-–_-a---t1-_{e---.d-1---–-5----I-I-t-}r_-r-a_-i-m-t_--e_---d_{-}
kΩ
Where:
Rcl-adj is the value of an external resistor between the
OCTRIM pin and SENSE(–) pin.
Irated is the output current rating of the module.
(not the output current-limit inception).
Itrim is the trimmed value of the output current-limit
set point.
Remote On/Off
There are two remote on/off signals, a primary refer-
enced signal and a secondary referenced signal. Both
signals must be asserted on for the module to deliver
output power. If either signal is asserted off, the module
will not deliver output power. Both signals have internal
pull-up circuits and are designed to interface with an
open collector pull-down device. Typically one on/off
signal will be permanently enabled by hardwiring it to
its return while the other on/off signal is used exclu-
sively for control.
Primary Remote On/Off
The primary remote on/off signal (ON/OFF) is available
with either positive or negative logic. Positive logic turns
the module on during a logic high and off during a logic
low. Negative logic remote on/off turns the module off
during a logic high and on during a logic low. Negative
logic (code suffix 1) is the factory-preferred configura-
tion.
To turn the power module on and off, the user must sup-
ply a switch to control the voltage between the primary
remote on/off terminal (Von/off, pri) and the VI(–) terminal.
The switch can be an open collector or equivalent (see
Figure 11). A logic low is Von/off, pri = 0 V to 1.2 V. The
maximum Ion/off, pri during a logic low is 1 mA. The switch
should maintain a logic-low voltage while sinking 1 mA.
During a logic high, the maximum Von/off, pri generated by
the power module is 15 V. The maximum allowable
leakage current of the switch at Von/off, pri = 15 V is 50
µA.
Tyco Electronics Corp.
If not using the primary remote on/off feature, do one of
the following:
s For negative logic, short the ON/OFF pin to VI(–).
s For positive logic, leave the ON/OFF pin open.
Secondary Remote On/Off
The secondary remote on/off signal (S-ON/OFF pin) is
only available with negative logic. The negative logic sig-
nal turns the module off during a logic high and on during
a logic low. To turn the power module on and off, the user
must supply a switch to control the voltage between the
S-ON/OFF pin and the SENSE(–) pin (i.e., Von/off, sec).
The switch can be an open collector or equivalent (see
Figure 11). A logic low is Von/off, sec = 0 V to 1.2 V. The
maximum Ion/off, sec during a logic low is 1 mA. The switch
should maintain a logic-low voltage while sinking 1 mA.
During a logic high, the maximum Von/off, sec generated
by the power module is 15 V. The maximum allowable
leakage current of the switch at Von/off, sec = 15 V is 50
µA.
If not using the secondary remote on/off feature, short
the S-ON/OFF pin to the SENSE(–) pin.
Ion/off, pri
+
V on/off, pri
–
VI(+)
ON/OFF
(PRIMARY)
SENSE(–)
Ion/off, sec
S- ON/OFF
(SECONDARY) ⁺
Von/off, sec
–
VI(–)
8-1398 (C)
Figure 11. Remote On/Off Implementation
Remote Sense
Remote sense minimizes the effects of distribution
losses by regulating the voltage at the remote-sense
connections. The voltage between the remote-sense
pins and the output terminals must not exceed the out-
put voltage sense range given in the Feature Specifica-
tions table, i.e.:
[VO(+) – VO(–)] – [SENSE(+) – SENSE(–)] ð 0.5 V
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), see Figure 12.
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