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BD2220G データシートの表示(PDF) - ROHM Semiconductor

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BD2220G Datasheet PDF : 13 Pages
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BD2220G, BD2221G
Technical Note
Functional Description
1. Switch Operation
VIN terminal and VOUT terminal are connected to the drain and the source of switch MOSFET respectively. And the VIN
terminal is used also as power source input to internal control circuit.
When the switch is turned on from EN,/EN control input, VIN terminal and VOUT terminal are connected by a
160m(Typ.) switch. In on status, the switch is bidirectional. Therefore, when the potential of VOUT terminal is higher
than that of VIN terminal, current flows from VOUT terminal to VIN terminal.
Since a parasitic diode between the drain and the source of switch MOSFET is canceled, in the off status, it is possible to
prevent current from flowing reversely from VOUT to VIN.
2. Thermal Shutdown Circuit (TSD)
If over current would continue, the temperature of the IC would increase drastically. If the junction temperature were
beyond 170°C(Typ.) in the condition of over current detection, thermal shutdown circuit operates and makes power switch
turn off and outputs fault flag (/OC). Then, when the junction temperature decreases lower than 150°C(Typ.), power
switch is turned on and fault flag (/OC) is cancelled. Unless the fact of the increasing chips temperature is removed or the
output of power switch is turned off, this operation repeats.
The thermal shutdown circuit operates when the switch is on (EN,/EN signal is active).
3. Over Current Detection (OCD)
The over current detection circuit limits current (ISC) and outputs fault 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. Fault Flag (/OC) Output
Fault 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.
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8/12
2011.05 - Rev.B

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