PCA9922BS NXP [NXP Semiconductors], PCA9922BS Datasheet - Page 7

• Manufacturer Part Number: PCA9922BS
• Description: 8-channel constant current LED driver with output error detection
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
PCA9922_1
Product data sheet
7.2.1 Open-circuit detection principle
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:
The LED open-circuit detection compares the effective current level I
detection threshold current I
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.
1. Entering error detect mode.
2. Setting all bits that you want to test by enabling all outputs to logical 1s in the output
3. Capture fault data.
4. Exit error detect.
Fig 5.
latch.
For each LEDn 0 is on, 1 is off.
Normal function timing diagram
LED0
LED1
LED2
LED3
LED4
LED5
LED6
LED7
CLK
SDI
OE
LE
8-channel constant current LED driver with output error detection
Rev. 01 — 15 January 2009
th(det)
. If I
O
is below I
th(det)
, the PCA9922 detects an open-load
O
PCA9922
with the open load
© NXP B.V. 2009. All rights reserved.
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