PCA9922

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© 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

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

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