AS1105 데이터 시트보기 (PDF) - austriamicrosystems AG

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AS1105

Serially Interfaced, 4-Digit LED Driver

austriamicrosystems AG 

Data Sheet AS1105

When the LOAD signal finally goes to high all shift registers

are latched. The first four devices have got no-operation

commands and only the fifth device sees the intended

command and updates its register.

Reset and external Clock Register3

This register is addressed via the serial interface. It allows

to switch the device to external clock mode (If D0=1 the

CLK pin of the serial interface operates as system clock

input.) and to apply an external reset (D1). This brings all

registers (except reg. E) to default state. For standard

operation the register contents should be "00h".

Mode

Address

Register Data

code (hex) D7 D6 D5 D4 D3 D2 D1 D0

Normal Operation,

internal clock

0xXE

XXXXXX0 0

Normal Operation,

external clock

0xXE

XXXXXX0 1

Reset state,

internal clock

0xXE X X X X X X 1 0

Reset state,

external clock

0xXE X X X X X X 1 1

Table 11: Reset and external Clock register (address (hex) = 0xXE)

Applications Information

Supply Bypassing and Wiring

In order to achieve optimal performance the AS1105 shall

be placed very close to the LED display to minimize effects

of electromagnetic interference and wiring inductance.

Furthermore it is recommended to connect a 10µF

electrolytic and a 0.1µF ceramic capacitor between VDD

and GND to avoid power supply ripple. Also, both GNDs

must be connected to ground.

Selecting RSET Resistor and Using External Drivers

The current through the segments is controlled via the

external resistor RSET. Segment current is about 100 times

the current in ISET. The right values for ISET are given in

table 12. The maximum current the AS1105 can drive is

40mA. If higher currents are needed, external drivers must

be used. In that case it is no longer necessary that the

AS1105 drives high currents. A recommended value for

RSET is 47kΩ. In cases that the AS1105 only drives few

digits table 9 specifies the maximum currents and RSET must

be set accordingly. Refer to absolute maximum ratings to

calculate acceptable limits for ambient temperature,

segment current, and the LED forward-voltage drop.

ISEG (mA)

40

30

20

10

VLED (V)

1.5 2.0 2.5 3.0 3.5

12.2 11.8 11.0 10.6 9.69

17.8 17.1 15.8 15.0 14.0

29.8 28.0 25.9 24.5 22.6

66.7 63.7 59.3 55.4 51.2

Table 12: RSET vs. segment current and LED forward voltage

3 This register is not used by MAX7219, since it does not support

software reset and external clocks

Revision 1.32, Oct. 2004

Page 8 of 12

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