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SILICON TOUCH TECHNOLOGY INC.

8-bit Constant Current LED Driver with Error Detection

Version:A.001

Page 12

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DM117

Alarm Function

It can detect the operating status by connecting a pull-high resistor to the open-drain ALARM

pin. The ALARM pin is kept ‘H’ for normal conditions, and shifted to ‘L’ if there is any failure like

LED open/short, overheating or both occurrence. User can determine the different status from the

truth table below:

ALARM

EN

OS

Status

H

L

don't care

Normal Operation

H→L

L

L

LED Open or Thermal issue

H→L

L

H

LED Short or Thermal issue

H→L

H

don't care

Thermal Alarm or Shutdown

When the latch is at its rising edge, the ALARM pin will reset to high level and start to detect

once again. It will send out the test result after the next clock pulse. The detection cycle of the alarm

signal will continue until it reaches the rising edge of the latch pulse again. Please see the timing

diagram below:

ALARM

normal

LED open/short or theraml alarm/shutdown

normal

status1

CLK

LAT

ALARM

(SDO=`L`)

(SDO=`H`)

normal

abnormal

normal

status2

For actual application, the controller could connect all the ALARM pins with one pull-high

resistor to simplify circuit designs and feedback loops