Technical Note

7/19

BD8113EFV

www.rohm.com

2011.07 - Rev.A

© 2011 ROHM Co., Ltd. All rights reserved.

・

Self-diagnostic functions

The operating status of the built-in protection circuitry is propagated to FAIL1 and FAIL2 pins (open-drain outputs). FAIL1

becomes low when UVLO, TSD, OVP, or SCP protection is engaged, whereas FAIL2 becomes low when open or short

LED is detected.

・

Operation of the Protection Circuitry

・

Under-Voltage Lock Out (UVLO)

The UVLO shuts down all the circuits other than REG when VREG ≦ 4.0V (TYP).

・

Thermal Shut Down (TSD)

The TSD shuts down all the circuits other than REG when the Tj reaches 175℃ (TYP), and releases when the Tj

becomes below 150℃ (TYP).

・

Over Current Protection (OCP)

The OCP detects the current through the power-FET by monitoring the voltage of the high-side resistor, and activates

when the CS voltage becomes less than VCC-0.6V (TYP).

When the OCP is activated, the external capacitor of the SS pin becomes discharged and the switching operation of

the DCDC turns off.

・

Over Voltage Protection (OVP)

The output voltage of the DCDC is detected with the OVP-pin voltage, and the protection activates when the OVP-pin

voltage becomes greater than 2.0V (TYP).

When the OVP is activated, the external capacitor of the SS pin becomes discharged and the switching operation of

the DCDC turns off.

・

Short Circuit Protection (SCP)

When the LED-pin voltage becomes less than 0.3V (TYP), the internal counter starts operating and latches off the circuit

approximately after 100ms (when FOSC = 300kHz). If the LED-pin voltage becomes over 0.3V before 100ms, then the

counter resets.

When the LED anode (i.e. DCDC output voltage) is shorted to ground, then the LED current becomes off and the LED-pin

voltage becomes low. Furthermore, the LED current also becomes off when the LED cathode is shorted to ground. Hence

in summary, the SCP works with both cases of the LED anode and the cathode being shorted.

・

LED Open Detection

When the LED-pin voltage

 0.3V (TYP) as well as OVP-pin voltage  1.7V (TYP) simultaneously, the device detects as

LED open and latches off that particular channel.

UVLO

TSD

OVP

OCP

S

R

Q

Counter

SCP

EN=Low

UVLO/TSD

FAIL1

OPEN

SHORT

S

R

Q

EN=Low

UVLO/TSD

FAIL2

MASK