AN3981 datasheet(22/54 Pages) STMICROELECTRONICS

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16-bit LED array drivers

AN3981

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Doc ID 022217 Rev 1

The error detection process can be divided into three phases:

Entering detection mode. From “normal mode” the device can enter “error mode”

through a logic key (Figure 23), which is a logic sequence of the

and LE/DM1

signals over five CLK cycles. After these five CLK cycles, the device is in “error

detection mode” and ready for sampling data on the SDI pin

Error detection. Once the device has entered “error detection mode”, an 8-bit string

should be loaded into the shift register through the SDI pin in order to set the outputs in

accordance with the diagnostic demands (only the outputs that are on are checked by

the error detection process). Therefore, if the user wants to check all the outputs, a

string with all “1” must be sent. After that the outputs are ready for the detection

process, which starts when

is set low. The device drives LEDs in order to

analyze if an open or short condition has occurred. The

must remain low for

at least 1 µs to complete the detection process. As shown in Figure 25, during the

detection process, at least three clock pulses are necessary: two pulses as soon as the

is set low, one clock pulse before ending the detection process.

Once the

is set high, the error status code is available at the SDO pin. To

download the complete error string, at least 8 clock pulses are necessary

Resuming normal mode. The device quits detection mode and returns to normal mode

through an exit logic key (Figure 24), a logic sequence over five clock pulses.

For proper device operation, the entering sequence must be followed by a resuming

sequence as it is not possible to insert consecutive equal sequences.

Figure 25 shows an example of error detection where OUT15 and OUT0 are faulty, whereas

all other outputs are considered good.

OE DM2

⁄

OE DM2

⁄

OE DM2

⁄

OE DM2

⁄

–

OE DM2

⁄

Figure 23.

Digital key for entering error

detection mode in 16-bit LED

drivers

Figure 24.

Digital key for exiting error

detection mode in 16-bit LED

drivers

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