AS1123
Datasheet ꢀ Detailed Description
Figure 13. Switching Global Error Mode Timing Diagram
tTESTING
OEN
tGSW(ERROR)
tGSW(ERROR)
tSU(ERROR)
LD
tP(I/O)
tP(I/O)
tP(I/O)
tGSW(ERROR)
CLK
SDI
TFLAG(IN)
OFLAG(IN)
SFLAG(IN)
Don’t
Care
Don’t
Care
Don’t
Care
SDO
TFLAG
OFLAG
SFLAG
tP4
tSW(ERROR)
tSW(ERROR)
Acquisition of
Error Status
Error-Detection Mode
Acquisition of the error status occurs at the rising edge of OEN. Errorꢀdetection mode is started on the rising edge of LD when OEN is high. The
CLK signal must be low when entering error detection mode. Error detection for openꢀ and shortedꢀLEDs can only be performed for LEDs that
are switched on during test time. To switch between errorꢀdetection modes clock pulses are needed (see Table 5).
Note: To test all LEDs, a test pattern that turns on all LEDs must be input to the AS1123.
Global Error Mode
Global error mode is entered when errorꢀdetection mode is started. Clock pulses during this period are used to select between temperature,
openꢀLED, and shortedꢀLED tests, as well as lowꢀcurrent diagnostic mode and shutdown mode (see Table 5). In global error mode, an error flag
(TFLAG, OFLAG, SFLAG) is delivered to pin SDO if any errors are encountered.
Table 5. Global Error Mode Selections
Clock
Output Port
Don't Care
Enabled
Error-Detection Mode
OverꢀTemperature Detection
OpenꢀLED Detection
Global Error Flag/Shutdown Condition
TFLAG = SDO = 1: No overꢀtemperature warning.
TFLAG = SDO = 0: Overꢀtemperature warning.
OFLAG = SDO = 1: No openꢀLED error.
OFLAG = SDO = 0: OpenꢀLED error.
Pulses
0
1
SFLAG = SDO = 1: No shortedꢀLED error.
SFLAG = SDO = 0: ShortedꢀLED error.
2
3
4
Enabled
Don't Care
Don't Care
ShortedꢀLED Detection
LowꢀCurrent Diagnostic Mode
VTHH Level
SDI = 1: Level1, VTHH set to 54% VDD (default)
SDI = 0: Level2, VTHH set to 80% VDD
Note: For a valid result SDI must be 1 for the first device.
If there are multiple AS1123s in a chain, the error flag will be gated through all devices. To get a valid result at the end of the chain, a logic 1 must
be applied to the SDI input of the first device of the chain. If one device produces an error this error will show up after n*tP(I/O) + tSW(ERROR) at
pin SDO of the last device in the chain. This means it is not possible to identify which device in the chain produced the error. Therefore, if a global
error occurs, the detailed error report can be run to identify which AS1123, or LED produced the error.
Note: When no error has occurred, the detailed error report can be skipped, setting LD and subsequently OEN low.
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