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Revision 1.21

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AS1109

Datasheet - Application In form atio n

9.2 Cascading Devices

To cascade multiple AS1109 devices, pin SDO must be connected to pin SDI of the next AS1109 (see Figure 23). At each rising edge of CLK the

LSB of the shift register will be written into the shift register SDI of the next AS1109 in the chain. Data at the SDI pin is clocked in at the rising

edge of the CLK pulse and is clocked out at the SDO pin 8.5 clock cycles later at the falling edge of the CLK pulse.

Note:

When n*AS1109 devices are in one chain, n*8 clock pulses are needed to latch-in the input data.

Figure 23. Cascading AS1109 Devices

9.3 Constant Current

In LED display applications, the AS1109 provides virtually no current variations from channel-to-channel and from AS1109-to-AS1109. This is

mostly due to 2 factors:



≥ 50mA, the maximum current skew is less than ±2% between channels and less than ±2% between AS1109 devices.



In the saturation region, the characteristics curve of the output stage is flat (see Figure 5 on page 6). Thus, the output current can be kept

9.4 Adjusting Output Current

(EQ 1)

(EQ 2)

(EQ 3)

Where:

Ω, 50.52mA at 372Ω and 25.26mA at 744Ω. Figure 3 on page 6

AS1109 #n-1

SDI

SDO

CLK

LD

OEN

SDI

CLK

LD

OEN

AS1109 #1

SDI

SDO

CLK

LD

OEN

AS1109 #2

SDI

SDO

CLK

LD

OEN