AS1181 datasheet(31/92 Pages) AMSOSRAM

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AS1181

Functional description

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7.2.1

High side safety monitors

7.2.1.1

Power switch / overcurrent detection

The current applied to the LEDs is measured and compared to an internal reference current in

the high side current path (LP node). This reference current defines the turn off threshold and

can be programmed in HSCS_SEL register (Address 0x1A30). The individual channel current

limits can be defined in CURR_LIM0 register (Address 0x1A12) to CURR_LIM7 register

(Address 0x1A20).

7.2.1.2

LP node open/short detection

LP shorts and open (anode connection of the LED) are detected using current sources in the

“short LP” section of Figure 26 while the power switch is off to prevent accidental illumination

or uncontrolled current paths outside the LEDs.

7.2.2

Low side safety monitors

7.2.2.1

Open and short LED detection

Checks for open and shorted LEDs are done at the cathode connection (LNx) of the LEDs. If

the voltage on the LNx pin is higher than a programmed threshold voltage a shorted LED is

detected and if the voltage on the LNx pin is lower than a programmed threshold open LEDs

are detected. The detection thresholds are pre-programmed in OTP and can be adjusted in the

COMP_LVL_SHORT register (Address 0x1A4C) and COMP_LVL_OPEN register (Address

0x1A4E).

AS1181 Datasheet(PDF) 31 Page - ams-OSRAM AG