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BD18378EFV-M

TSZ02201-0W1W0C500020-1-2

© 2015 ROHM Co., Ltd. All rights reserved.

www.rohm.co

m

TSZ22111・15・001

04. Dec. 2015 Rev.004

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PWM Fault Detection

PWM fault diagnostic can be performed at startup to test for wire connectivity. The chip is initialized with a

PWM fault condition that changes to PWM_OK immediately after the first falling edge on the PWM input(s).

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UVLO Under Voltage LockOut

By monitoring the Vcc pin an UVLO event can be detected. If Vcc is below UVLO_L then the chip is turned

off. If the Vcc voltage increases over the UVLO_H threshold then the chip is turned back on.

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Weak LED Supply Voltage Detection

By monitoring VSENSE pin, a low LED supply voltage can be detected.

After a Weak LED Supply voltage has been detected a corresponding one bit register flag is set and remains

high until cleared by the controller. The detection has its own status bit and is mapped to Open Drain Fault

Indicator. Note that this circuit is always active. A masking command that can be locked and read back is

implemented.

Figure 5. Startup diagram

Note: In Case II when the MASK_WLS will be activated a Weak LED Supply event will be signaled to the

internal logic. This is because the detection circuit itself is not disabled by the MASK_WLS command but only

the diagnostic is masked.

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Open Drain Fault Indicator

An emergency warning pin is available (ERR) to signal to the controller the most important faults of the

system.

The ERR output is activated (active=”LOW”) when a fault flag in the STATUS register or a flag in the

UNLOCK register is set. The flags can be masked using the WRITE_EN_ERR_PIN command. The content of

the EN_ERR_PIN register shows the flags that will activate the Open Drain Fault Indicator (ERR). The picture

below shows the ERR pin functionality:

Figure 6. Open Drain fault indicator (ERR)

ERR

All STATUS

and UNLOCK

bits

UVLO_H

realease

POINT

WLS detect

POINT

UVLO_H

realease

POINT

WLS detect

POINT

Case II

Case I

V

V

time

time

UVLO_L

Lockout

POINT

UVLO_L

Lockout

POINT