Daattaasshheeeett
BD2041AFJ
BD2051AFJ
3. Over current detection (OCD)
The over current detection circuit limits current (ISC) and outputs error flag (/OC) when current flowing in each switch
MOSFET exceeds a specified value. There are three types of response against over current. The over current detection
circuit works when the switch is on (EN,/EN signal is active).
3-1. When the switch is turned on while the output is in shortcircuit status
When the switch is turned on while the output is in shortcircuit status or so, the switch gets in current limit status
soon.
3-2. When the output shortcircuits while the switch is on
When the output shortcircuits or large capacity is connected while the switch is on, very large current flows until the
over current limit circuit reacts. When the current detection, limit circuit works, current limitation is carried out.
3-3. When the output current increases gradually
When the output current increases gradually, current limitation does not work until the output current exceeds the
over current detection value. When it exceeds the detection value, current limitation is carried out.
4. Under voltage lockout (UVLO)
UVLO circuit prevents the switch from turning on until the VIN exceeds 2.3V(Typ.). If the VIN drops below 2.2V(Typ.) while
the switch turns on, then UVLO shuts off the power switch. UVLO has hysteresis of a 100mV(Typ).
Under voltage lockout circuit works when the switch is on (EN,/EN signal is active).
5. Error flag (/OC) output
Error flag output is N-MOS open drain output. At detection of over current, thermal shutdown, low level is output.
Over current detection has delay filter. This delay filter prevents instantaneous current detection such as inrush current at
switch on, hot plug from being informed to outside.
/EN
V
Output shortcircuit
Thermal shut down
OUT
V
OUT
I
/OC
V
delay
Figure 36. Over current detection, thermal shutdown timing
(BD2041AFJ)
EN
V
Output shortcircuit
Thermal shut down
OUT
V
OUT
I
/OC
V
delay
Figure 37. Over current detection, thermal shutdown timing
(BD2051AFJ)
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08.Mar.2013 Rev.001
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