BD8179MUV Просмотр технического описания (PDF) - ROHM Semiconductor

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BD8179MUV

5V Input Multi-channel System Power Supply IC

ROHM Semiconductor 

BD8179MUV

Technical Note

●Under Voltage Lock Out (UVLO)

The UVLO circuit compares the input voltage at IN with the UVLO threshold (2.4V rising, 2.2V falling, typ) to ensure the input

voltage is high enough for reliable operation.

The 200mV (typ) hysteresis prevents supply transients from causing a restart. Once the input voltage exceeds the UVLO

rising threshold, startup begins. When the input voltage falls below the UVLO falling threshold, the controller turns off the

main step-up regulator, turns off the linear-regulator outputs, and disables the Gate Shading controller.

●Thermal Shut Down (TSD)

The TSD prevents excessive power dissipation from overheating the BD8179MUV. When the junction temperature exceeds

Tj=175℃(Typ), a thermal sensor immediately activates. The fault protection, which shuts down all outputs except the

reference, allowing the device to cool down. Once the device cools down by approximately 15℃ reactivate the device.

●Over Voltage Protection (OVP)

The Step up DC/DC converter has OVP circuit.

The OVP circuit compares the input Voltage at SUP with the OVP threshold (19V rising, 18.5V falling, Typ) to protect the step

up DC/DC output exceed the absolute maximum voltage. Once the SUP Voltage exceeds the OVP rising threshold, turn off

the main Step-up regulator.

Then, the SUP Voltage falls bellow the OVP falling threshold,reactivate the main Step-Up regulator.

●Over Current Protection (OCP)

The Step-Up DC/DC converter, linear-regulator and Operational Amplifier have OCP circuit respectively.

The OCP circuit restricts to load current, when an OCP activated, one’s own output only restricted.

However, if the output continue to overload, the device is possible to activate thermal shutdown or short current protection.

●Timer Latch Mode Short Current Protection (SCP)

BD8179MUV has SCP circuit feature to prevent the large current flowing when the output is shorted to GND.

This function is monitoring VMAIN, VGON, and VGOFF Voltage and starts the timer when at least one of the outputs operating

properly (when the output voltage was lower than expected).

After 150ms (Typ.) of this abnormal state, the device will shutdown the all outputs and latch the state.

VMAIN

FB

＋

－

VGON

FBP

＋

－

VGOFF

FB N

－

＋

150ms typ

Counter

reset

all outputs

shut down.

Fig.13 SCP Block Diagram

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© 2009 ROHM Co., Ltd. All rights reserved.

7/12

2009.07 - Rev.B

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