LED error detection

LED2472G

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DocID024620 Rev 3

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LED error detection

The LED error detection implemented by the LED2472G is performed in order to detect

shorted LED and open LED conditions. The shorted LED condition is determined by

checking the voltage across each current generator. If this voltage is higher than the

threshold, programmed by bits CFG-3, CFG-4 and CFG-5 of the configuration register, the

LED connected to that generator is considered shorted.

The open LED condition is determined by measuring the current flowing through each

current generator. If this current is lower than half the expected current, the LED connected

to that generator is considered open. The error detection request and the acquisition of the

results of the detection are managed by the serial interface. The steps to follow for correct

performance of error detection are summarized as follows (see Figure 16):

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Enter the error detection. To do this, the appropriate digital key must be provided

(see Figure 9). There is both the possibility of “generic” error detection (open/short

detection) and the possibility to specifically select the type of failure (short

detection or open detection).

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Performing the error detection. When the ROE, GOE and BOE signals become

low, error detection starts. These signals must be kept low for at least 1 µs in order

to correctly complete the error detection process. After this time, at least one CLK

pulse must be provided in order to make the detection result available at the SDO

pin while the output enable signals are still low. The bit shifted out of SDO after this

clock pulse represents the first bit of the detection result word.

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Detection results. To complete the detection result acquisition, at least another

23 CLK pulses must be provided after the xOE signals have been set high again

(24 CLK pulses in total). The detection result will be always in RGB sequence

regardless of any different programmed data flow (CFG9-CFG11).

The detection result indicates “1” for each channel considered good, “0” for each channel

that has a failure (shorted or open LED). To check the status of all channels and to obtain an

accurate detection result, it is important to set all outputs to ON before starting the error

detection process. If this is not done, it is worth noting that the detection result will indicate a

“0” also for those channels not set to ON before the detection process, although they may

not actually have any failure.