Vicor VI-J00 Family DC-DC Converters and Configurable Power Supplies - Manual (Page 8)

Design Guide & Applications Manual
For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies
VI-200 and VI-J00 Family Design Guide Rev 3.5 vicorpower.com
Page 7 of 98
Apps. Eng. 800 927.9474 800 735.6200
FOLDBACK CURRENT LIMITING
The VI-/ MI-200 modules with output voltages of 5 V or
3.3 V incorporate foldback current limiting. (Figure 4–1) In
this mode, the output voltage remains constant up to the
current knee, (Ic), which is 5 – 25% greater than full-rated
current, (Imax). Beyond Ic, the output voltage falls along
the vertical line Ic– Ifb until approximately 2 V. At
≤2 V, the
voltage and current folds back to short circuit current
point (20 – 80% of Imax). Typically, modules will
automatically recover when overcurrent is removed.
When bench testing modules with foldback current limiting,
use a constant resistance load as opposed to a constant
current load. Some constant current loads have the ability
to pull full current at near zero volts. This may cause a
latchup condition. Also when performing a short circuit
test it is recommended to use a mercury wetted relay to
induce the output short as other methods may induce
switch bounce that could potentially damage the converter.
STRAIGHT LINE CURRENT LIMITING
The VI-/ MI-200 modules with output voltages greater
than 5 V, 2 V (VI-/ MI-200 only) and all VI-/ MI-J00
modules incorporate a straight-line type current limit.
(Figure 4–2) As output current is increased beyond Imax,
the output voltage remains constant and within its
specified limits up to a point, Ic, which is 5 – 25% greater
than rated current, (Imax). Beyond Ic, the output voltage
falls along the vertical line to Isc. Typically, modules will
automatically recover after overcurrent is removed.
2 V
Vout
Ic
I fb
Imax
Iout
I short circuit
Vout
I short circuit
I c I max
I out
4. Overcurrent Protection
Figure 4–1 — Foldback current limiting Figure 4–2 — Straight-line current limiting