MB3886 Fujitsu Microelectronics, Inc., MB3886 Datasheet - Page 19

• Manufacturer Part Number: MB3886
• Description: 2-channel Dc/dc Converter Ic With Overcurrent Protection Symmetrical-phase Type
• Manufacturer: Fujitsu Microelectronics, Inc.

MB3886
SETTING THE TIME CONSTANT FOR TIMER-LATCH SHORT-CIRCUIT
PROTECTION CIRCUIT
Each channel uses the short-circuit detection comparator (SCP Comp.) to always compare the error amplifier’s
output level to the reference voltage.
While the DC/DC converter load conditions are stable on both channels, the short-circuit detection comparator
keeps its output at the “H” level and the CSCP terminal (pin 25) remains at the input standby voltage (V
: = 50
STB
mV) .
If a load condition changes rapidly due to a short circuit of the load, causing the output voltage to drop, the short-
circuit detection comparator changes its output to the “L” level. This causes the external short-circuit protection
capacitor Cscp connected to the CSCP terminal to be charged at 10 A.
Short-circuit detection time : tscp
tscp (s) : = 0.068
Cscp ( F)
When the capacitor Cscp is charged to the threshold voltage (V
: = 0.68 V) , the protection circuit sets the latch
TH
and turns off the external FET (setting the dead time to 100 ) . At this time, the latch input is closed and the
CSCP terminal is held at the input latch voltage (V
: = 50 mV) . The protection circuit shuts off both channels
I
even when a short circuit is detected on only either.
PROCESSING WITHOUT USING THE CSCP TERMINAL
When the timer-latch short-circuit protection circuit is not used, the CSCP terminal (pin 25) should be shorted
to SGND using the shortest possible connection.
6
SGND
CSCP
25
< Operation Without Using the CSCP Terminal >
19