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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



Protection circuitry and diagnostic

o

LED Short Detection

A short event is detected when the voltage across the LED falls below the short detection threshold

output current offset of 20µA. After a detected LED short event, the corresponding bit of the Gen_SHORT

detection register and the ANY_SHORT_OPEN_FLAG from the STATUS register remain high until cleared by

the controller. The SHORT detection is also performed, when the LED is not activated, using small sink

currents for small time intervals (20us) to avoid LED flicker. In order for the detection to be available at

non-activated LED state the PWM duty cycle must be <99.2% at a frequency of 200Hz.

o

LED Open Detection

active (PWM

= “LOW”), will cause a typical output current offset of 20µA. After a LED open event has been

detected the corresponding bit of the Gen_OPEN detection register and ANY_SHORT_OPEN_FLAG from the

STATUS register remain high until cleared by the controller. The OPEN detection is also performed, when the

LED is not activated, using small sink currents for small time intervals (20us) to avoid LED flicker. In order for

the detection to be available at non-activated LED state the PWM duty cycle must be <99.2% at a frequency of

200Hz.

Note: In order to distinguish between diagnostics (LED Short Detection and LED Open Detection) at ON and

OFF, the corresponding detection must be enabled and corresponding state of the channel must be checked

(enabled/disabled).

o

Short to Ground Detection

The chip can perform output short to ground diagnosis during non-activated LED state. After LED short and

open at channel off diagnosis, a short to ground can be also detected. In order for the detection to be available

at non-activated LED state the PWM duty cycle must be <99.2% at a frequency of 200Hz.

The diagnostic is activated or deactivated by the EN_SHORT_TO_GND register.

After an output short to ground has been detected the corresponding bit of the SHORT_TO_GND detection

register and ANY_SHORT_TO_GND_FLAG from the STATUS register remain high until cleared by the

controller.

Note: In case both the Open Detection and Short to GND Detection are active at the same time and the voltage

ANY_SHORT_OPEN_FLAG from the STATUS register remain high until cleared by the controller.

Figure 4. Diagnostic diagram

o

REXT_FAULT flag is set and latched and an internal current reference is used to set a typical output current of

EN_CHANNEL

PWM

Diagnostic

CHANNEL ACTIVE

CHANNEL NOT ACTIVE

PWM ACTIVE

PWM NOT ACTIVE

20us

SHORT/OPEN

@ON

PULL_UP@ON

PULL_UP@OFF

SHORT/

OPEN

@OFF

SHORT

TO GND