Vicor VI Chip PRM Evaluation Board - Manual (Page 25)

UG:013 vicorpower.com Applications Engineering: 800 927.9474 Page 25
Trim and soft-start adjustment in Remote Sense Operation
Trim and soft start adjustment in Remote Sense Operation is set by the reference voltage
network shown below. The PRM evaluation board is normally configured for a 20 V to
55 V trim range. Trim POT R44 is used to trim the output voltage in
Remote Sense Operation.
The slew rate of the output voltage during startup may be controlled by controlling
the rate-of-rise of the voltage at VREF node. This can be achieved using soft-start
capacitance C24. By default, C24 is populated with 0.1uF ceramic capacitance.
Sockets H55 and H56 can be used for installation of additional through-hole soft-start
capacitance. It is not recommended to extend the soft start beyond 10msec.
Current limit adjustment in Remote Sense Operation
In Remote Sense Operation, current feedback is provided externally. The current limit
set point is a function of the current sense amplifier gain, the shunt resistor and the
internal current limit threshold of PRM. Full chip PRM evaluation board has 5 mΩ
current shunt whereas half chip PRM evaluation board has 10mΩ current shunt. The
IFB current limit threshold is fixed at 2.0V. The gain of the current sense amplifier can be
changed per Equation 2 in order to adjust the current limit. Resistor R26 set the gain of
the current sense amplifier. R25 is the current shunt.
By default, R26 is installed for the current limit approximately 10% above rated
output current.
The current limit setpoint can be changed by adjusting the value of R26 and
appropriately setting the gain of the current sense IC.
G
CS
=
V
IFB_IL
I
LIMIT (SET) •
R
25
Equation 2
REF_EN_B
C23
0603
VREF
TP44
TP43
SGND
1206
R45
1206
R43
1206
C24
GN
D
3
IN
1
OUT
2
U12
SOT23_3
H 55
H 56
R44
VOLTAGE REFERENCE
Figure 15.
Voltage Reference circuit