www.ams.com/LED-Driver-ICs/AS1109 Revision 1.21 7 - 24
AS1109
Datasheet - Detailed Description
8 Detailed Description
The AS1109 is designed to drive up to 8 LEDs through a fast serial interface and 8 constant-current output drivers. Furthermore, the AS1109
provides diagnostics for detecting open- or shorted-LEDs, as well as over-temperature conditions for LED display systems, especially LED traffic
sign applications.
The AS1109 contains an 8-bit shift register and an 8-bit data register, which convert serial input data into parallel output format. At AS1109 output
stages, eight regulated current sinks are designed to provide uniform and constant current with excellent matching between ports for driving
LEDs within a wide range of forward voltage variations. External output current is adjustable from 0.5 to 100mA using an external resistor for
flexibility in controlling the brightness intensity of LEDs. The AS1109 guarantees to endure 15V maximum at the outputs.
The serial interface is capable of operating at a minimum of 30 MHz, satisfying the requirements of high-volume data transmission.
Using a multiplexed input/output technique, the AS1109 adds additional functionality to pins SDO, LD and OEN. These pins provide highly useful
functions (open- and shorted-LED detection, over-temperature detection), thus reducing pin count. Over-temperature detection will work on-the-
run, whereas the open- and shorted-LED detection can be used on-the-run or in low-current diagnostic mode (see page 14).
Figure 9. AS1109 - Block Diagram
8.1 Serial Interface
Data accesses are made serially via pins SDI and SDO. At each CLK rising edge, the signal present at pin SDI is shifted into the first bit of the
internal shift register and the other bits are shifted ahead of the first bit. The MSB is the first bit to be clocked in. In error-detection mode the shift
register will latch-in the corresponding error data of temperature-, open-, and short-error register with each falling edge of LD.
AS1109
REXT
OEN
CLK
SDI
LD
Current
Generators
Detailed
Error
Detection
8-Bit Data
Register
8-Bit Shift
Register
Temperature
Detection
8-Bit Open Detec-
tion & Error Reg-
ister
8-Bit Short
Detection & Error
Register
Global Error
Detection
SDO
Indicates 8 Bit Path
Control Logic
+VLED
OUTN0 OUTN1 OUTN2 OUTN3 OUTN4 OUTN5 OUTN6 OUTN7
