Error detection feature

AN3090

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Doc ID16496 Rev 1

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Error detection feature

The output error detection feature allows LED functionality checks by means of output status

detection. This feature covers two types of detection: open-circuit and short-circuit

detection.

The schematic in Figure 4 shows a typical application where multiple STP16DPPS05

devices are cascaded.

Figure 4.

Typical application of the STP16DPPS05 device

From “normal mode”, the device is switched to “error detection mode” (EDM) by a logic

sequence on the LE/DM1 and OE/DM2 pins. In order to switch on all the outputs during the

detection time, the sixteen data bits must be set to “1”.

The data are latched by the LE/DM1, after which the outputs are ready for the detection

process.

When the microcontroller switches the OE/DM2 to low, the device drives the LEDs to check

if an open or short condition has occurred. The acquisition time (OE/DM2 to low) necessary

to allow for correct LED feedback is typically 1 µs. Two CLK pulses must be sent after the

minimum detection time (typical: 500-600 ns), in order to set the SDO pin to the correct

output error detection value. In this way, the data loaded in the shift register is updated

(rewritten) with the error detection data when the OE/DM2 signal goes high.

In synchronization with the rising edge of the CLK signal, the LED status is provided by the

SDO pin: a “1” logic level signals a good output, while a “0” logic level signals an output fault

condition (short or open condition).