MB39A102_05 Datasheet, PDF (17/32 Pages) Tyco Electronics – 4-ch DC/DC Converter IC

MB39A102
■ SETTING TIME CONSTANT FOR TIMER-LATCH SHORT-CIRCUIT PROTECTION CIRCUIT
Each channel uses the short-circuit detection comparator (SCP) to always compare the error amplifier′s output
level to the reference voltage.
While DC/DC converter load conditions are stable on all channels, the short-circuit detection comparator output
remains at “L” level, and the CSCP terminal (pin 11) is held at “L” level.
If the load condition on a channel changes rapidly due to a short-circuit of the load, causing the output voltage
to drop, the output of the short-circuit detection comparator on that channel goes to “H” level. This causes the
external short-circuit protection capacitor CSCP connected to the CSCP terminal (pin 11) to be charged at 1 µA.
Short-circuit detection time (tCSCP)
tCSCP (s) =: 0.70 × CSCP (µF)
When the capacitor CSCP is charged to the threshold voltage (VTH =: 0.70 V), the latch is set and the external
FET is turned off (dead time is set to 100%). At this point, the latch input is closed and the CSCP terminal (pin
11) is held at “L” level.
In addition, the short-circuit detection from external input is capable by using −INS terminal (pin 20) on the short-
circuit detection comparator (SCP Comp.) . The short-circuit detection operation starts when −INS terminal
voltage is less than threshold voltage (VTH =: 1 V) .
When the power supply is turn on back or VREF terminal (pin 7) voltage is less than 1.5 V (Min) by setting CTL
terminal (pin 6) to “L” level, the latch is released.
• Timer-latch short-circuit protection circuit
VO
FBx
R1
−INEx
R2
Error
Amp
−
+
1.24 V
VREF
−INS
20
83 kΩ
−
SCP
Comp.
+
1V
SCP
1 µA
CSCP
11
CSCP
CTL
SR
Latch
1.15 V
VREF
UVLO
To each channel
Drive
x : Each channel No.
17