Short-circuit detection PCA9955B

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Short-circuit detection PCA9955B

345 Views
wtrevine
Contributor I

Hello,

I have problems with the short circuit detection of the PCA9955B led drive.
The driver seems to be very sensitive, with short circuit alerts often occurring. They are false alerts, I can not rely on alerts. Even running your hands on channels, alerts appear, but that would not be a problem.
Open circuit detection works very well.

Any suggestion?

Sorry for my English.
Thank you.

3 Replies

182 Views
guoweisun
NXP TechSupport
NXP TechSupport

Hi

First please make sure your LED error detection is correct and refer to DS page22-7.3.16.

Especially after finished detection to read the fault bit

---Before reading the error flag register EFLAGn, user should verify if the FAULTTEST iscomplete by reading MODE2 register. MODE2[6] = 0 indicates that the test is complete

and the error status is ready in EFLAG0 and EFLAG1.

 

If both LED open and short-circuit conditions exist on

different LED outputs, the error status bits in error flag registers report only the

open-circuits first and disregards the short-circuits. If only one of the two conditions (that

is, LED open-circuits or short-circuits) exists, then the error status bits in error flag

registers will report all of those faulted channels. For all unused LED outputs, user must

program their LED outputs to the ‘OFF’ state (LDRx = 00) and IREFx value to 00h, and all

unused LED output pins must be pulled up to VDD with a recommended 100 kshared

resistor. The states of the unused LED channels have no effect upon the FAULTTEST and

always return 0s in EFLAG0/EFLAG1 registers.

 

 

182 Views
wtrevine
Contributor I

Hi G.w Sun, 
Thanks for the answer

I am using the final model "B" (PCA9955B) DS current 2.5.2017. On this model there is no automatic test as described. MODE2 [6] only reports if there is an error (report any error detection).
The errors are updated in real time in the flags. I need to cycle to turn on all the LEDs, to make sure all LEDs have been tested.
It works very well for open circuit detection (detected by current), but for short circuit detection (voltage detection), it seems to be sensitive and present non-real results.

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182 Views
guoweisun
NXP TechSupport
NXP TechSupport

Hi

If you configuration and registers setting no error,please test your false alerts channel Vo value to check it is real above 2.85V or not.

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