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AS1109

Datasheet - Detailed Descr i p ti on

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