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BD18378EFV-M Datasheet(PDF) 5 Page - Rohm |
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BD18378EFV-M Datasheet(HTML) 5 Page - Rohm |
5 / 30 page 5/26 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 VSCth. The SHORT detection current which is flowing during LED active (PWM =”LOW”), will cause a typical 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 During an open event the output device will be fully ON, pulling VDx low. An open event is detected when voltage VDx at the output pin falls below VOth. The OPEN detection current, Ipulldown which is flowing during LED 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 VDx at the output pin falls below VSGth also 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. Figure 4. Diagnostic diagram o IREF Fault Detection (Limp Home functionality) The chip can perform IREF short and open diagnostic on the external resistor. In case of an error the REXT_FAULT flag is set and latched and an internal current reference is used to set a typical output current of IREF_LH. If the fault condition is removed the chip can be reset to the normal operating state by a POR event. EN_CHANNEL PWM Diagnostic CHANNEL ACTIVE CHANNEL NOT ACTIVE PWM ACTIVE PWM NOT ACTIVE tdiag_off 20us SHORT/OPEN @ON PULL_UP@ON PULL_UP@OFF SHORT/ OPEN @OFF SHORT TO GND |
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