AS1109_1 Datasheet, PDF (12/26 Pages) ams AG – Constant-Current, 8-Bit LED Driver with Diagnostics

AS1109
Data Sheet - Detailed Description
If there are multiple AS1109s 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 possi-
ble 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 AS1109, or LED produced the error.
Note: When no error has occurred, the detailed error report can be skipped, setting LD and subsequently OEN low.
Error Detection Functions
Open-LED Detection
The AS1109 open-LED detection is based on the comparison between VDS and VTHL. The open LED status is aquired
at the rising edge of OEN and stored internally. While detecting open-LEDs the output port must be turned on. Open
LED detection can be started with 1 clock pulse during error detection mode while the output port is turned on.
Note: LEDs which are turned off at test time cannot be tested.
Table 6. Open LED Detection Modes
Output Port State
On
On
Effective Output
Point Conditions
VDS < VTHL
VDS > VTHL
Detected Open-LED
Error Status Code
0
1
Meaning
Open Circuit
Normal
Shorted-LED
The AS1109 shorted-LED detection is based on the comparison between VDS and VTHH. The shortened LED status is
aquired at the rising edge of OEN and stored internally. While detecting shorted-LEDs the output port must be turned
on. Shorted-LED detection can be started with 2 clock pulses during error detection mode while the output port is
turned on.
For valid results, the voltage at OUTN0:OUTN7 must be lower then VTHH under low-current diagnostic mode operating
conditions. This can be achieved by reducing the VLED voltage or by adding additional diodes, resistors or LED’s.
Note: LEDs which are turned off at test time cannot be tested.
Table 7. Shorted LED Detection Modes
Output Port State
On
On
Effective Output
Point Conditions
VDS > VTHH
VDS < VTHH
Detected Shorted-LED
Error Status Code
0
1
Meaning
Short Circuit
Normal
Overtemperature
Thermal protection for the AS1109 is provided by continuously monitoring the device’s core temperature. The overtem-
perature status is aquired at the rising edge of OEN and stored internally.
Table 8. Overtemperature Modes
Output Port State
Don’t Care
Don’t Care
Effective Output
Point Conditions
Temperature > TOV1
Temperature < TOV1
Detected Overtemperature
Status Code
0
1
Meaning
Overtemperature
Condition
Normal
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Revision 1.18
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