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BD2226G Datasheet(PDF) 8 Page - Rohm |
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BD2226G Datasheet(HTML) 8 Page - Rohm |
8 / 13 page Technical Note 8/12 BD2226G, BD2227G www.rohm.com 2011.05 - Rev.B © 2011 ROHM Co., Ltd. All rights reserved. ● 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 150mΩ(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. 2. Thermal Shutdown Circuit (TSD) If over-current would continue, the temperature of the IC would increase drastically. If the junction temperature were beyond 135℃(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 115℃(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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