mb3881pff Fujitsu Microelectronics, Inc., mb3881pff Datasheet - Page 26

• Manufacturer Part Number: mb3881pff
• Description: 8-ch Dc/dc Converter Ic With Synchronous Rectifier For Voltage Step-up And Step-down
• Manufacturer: Fujitsu Microelectronics, Inc.

26
MB3881
SETTING TIME CONSTANT FOR TIMER-LATCH SHORT-CIRCUIT PROTECTION CIRCUIT
The short detection comparator (SCP comparator) in each channel monitors the output voltage.
While the switching regulator load conditions are stable on all channels, the LOG_SCP output remains at "H"
level, transistor Q1 is turned on, and the CSCP terminal (pin 26) is held at “L” level.
If the load condition on a channel changes rapidly due to a short of the load, causing the output voltage to drop,
the output of the short detection comparator on that channel goes to “H” level. This causes transistor Q1 to be
turned off and the external short protection capacitor C
When the capacitor C
FET is turned off (dead time is set to 100%). At this point, the latch input is closed and the CSCP terminal is
held at “L” level.
Short detection time (t
A.
R1
R2
CSCP
V
C
O
IN8(C)
IN8(C)
1
SCP
t
PE
46
IN1
26
(s) : = 0.70
7
8
Q1
1 A
1.0 V
SCP
PE
)
C
is charged to the threshold voltage (VTH : = 0.70 V), the latch is set and the external
SCP
( F)
Timer-latch short
protection circuit
S
Timer-latch short circuit protection circuit
SCP
Comp.1
SCP
Comp.8
bias
R
LOG_SCP
UVLO
SCP
connected to the CSCP terminal to be charged at 1.0
bias
Ref
ON/OFF CTL
Drive
Drive
Drive
Power
1 1
1 2
8
External PNP transistor
OUT1 1
OUT1 2
50
51
64
28
CTL 1
OUT8