AS1109 Datasheet, PDF (12/25 Pages) ams AG – Constant-Current, 8-Bit LED Driver with Diagnostics

AS1109
Datasheet - Detailed Description
8.5 Error Detection Functions
8.5.1 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
8.5.2 Shorted-LED
The AS1109 shorted-LED detection is based on the comparison between VDS and VTHH. The shortened LED status is acquired 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
8.5.3 Overtemperature
Thermal protection for the AS1109 is provided by continuously monitoring the device’s core temperature. The overtemperature 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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