AS1122
Datasheet ꢀ Detailed Description
Status Information Data (SID)
The AS1122 contains an integrated status information register. After latching the correct identifier with a 16 bit data word the input shift register
data is replaced with status information data.
With the next 16 clock cycles the Open LED information, the OvertemperatureꢀWarning and ꢀError flag as well as the powerꢀon reset (POR) flag
can be read out at pin SDO. The status information data packet is 16 bits wide. Bits 11:0 contain the open LED detection status of each channel.
Bit 12 is the overtemperatureꢀwarning flag, bit 13 is the overtemperatureꢀerror flag and bit 14 indicates if the POR was triggered. The complete
status information data packet is shown in Figure 34.
Figure 34. Status Information Data Packet Format
Note: Bit14 (POR) is set to ‘1’ after startꢀup and after triggering a powerꢀon reset due to a supply voltage drop. Must be set to ‘0’ manually.
Readback the Status Information Data
To read out the SID the read bit in the command data needs to be set to “1”. After the new command data is lachted into the device the SID is
shifted to the SDO register and will be shifted out with the next running clk cycles on CLKI. After keeping the clk low for the time tlow, the device
is reset again and can be programmed with need information.
Figure 35. Reading of the Status Information Register
Setting Maximum Channel Current
The maximum output current per channel is programmed by a single resistor RIREF, which is placed between pin IREF and GND. The voltage on
pin IREF is set by an internal band gap VIREF (1.27V typ). The maximum channel current is equivalent to the current flowing through RIREF mulꢀ
tiplied by a factor of 31.5. The maximum output current is calculated as:
VIREF
IMAX =
x 31.5
(EQ 3)
RIREF
Where:
VIREF = 1.27V;
RIREF = Userꢀselected external resistor.
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