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PCA9922 Datasheet(PDF) 7 Page - NXP Semiconductors |
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PCA9922 Datasheet(HTML) 7 Page - NXP Semiconductors |
7 / 27 page PCA9922 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved. Product data sheet Rev. 2 — 6 April 2011 7 of 27 NXP Semiconductors PCA9922 8-channel constant current LED driver with output error detection 7.2 LED output error detection The PCA9922 has built-in circuitry for detecting LED open-circuit and output short conditions. A predefined set of signal sequence on the input control lines must be initiated to perform the output error detection. Once the error data is captured by this sequence, error status can be read out of the device via the serial interface. The error detection mode is entered by the user via specific timing sequences presented on the CLK, OE and LE pins. There are three key sequences to be generated by the user: enter error detect, capture faults, and exit error detect. It is the responsibility of the user to enable all outputs that the user wants to test during the error detect sequence. Performing an error mode detection sequence consists of several operations: 1. Entering error detect mode. 2. Setting all bits that you want to test by enabling all outputs to logical 1s in the output latch. 3. Capture fault data. 4. Exit error detect. 7.2.1 Open-circuit detection principle The LED open-circuit detection compares the effective current level IO with the open load detection threshold current Ith(det). If IO is below Ith(det), the PCA9922 detects an open-load condition. This error status can be read as an error status code in the error detect mode. For open-circuit error detection, a channel must be on. For each LEDn 0 is on, 1 is off. Fig 5. Normal function timing diagram CLK SDI LE OE LED0 LED1 LED2 LED3 LED4 LED5 LED6 LED7 002aad203 |
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