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AS1108
4-Digit LED Display Driver
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Datasheet
1 General Description
The AS1108 is a compact display driver for 7-segment
numeric displays of up to 4 digits. The device can be
programmed via SPI, QSPI, and Microwire as well as a
conventional 4-wire serial interface.
The device includes an integrated BCD code-B/HEX
decoder, multiplex scan circuitry, segment and display
drivers, and a 32-bit memory. Internal memory stores
the LED settings, eliminating the need for continuous
device reprogramming.
Every segment can be individually addressed and
updated separately. Only one external resistor (RSET) is
required to set the current through the LED display. LED
brightness can be controlled by analog or digital means.
The device can be programmed to use the internal
code-B/HEX decoder to display numeric digits or to
directly address each segment.
The AS1108 features an extremely low shutdown cur-
rent of typically 3µA, and an operational current of less
than 500µA. The number of digits can be programmed,
the device can be reset by software, and an external
clock is also supported. Additionally, segment blinking
can be synchronized across multiple drivers.
The AS1108 provides several test modes for easy appli-
cation debugging.
The device is available in a SOIC 20-pin package.
Figure 1. AS1108 - Typical Application Diagram
2 Key Features
10MHz SPI-, QSPI-, Microwire-Compatible
Serial I/O
Individual LED Segment Control
Segment Blinking Control (can be synchronized
across multiple drivers)
Hexadecimal- or BCD-Code/No-Decode
Digit Selection
3µA Low-Power Shutdown Current (typ;
data retained)
Extremely Low Operating Current 0.5mA in
Open-Loop
Digital and Analog Brightness Control
Display Blanked on Power-Up
Drive Common-Cathode LED Displays
Supply Voltage Range: +2.7 to +5.5V
Software Reset
Optional External Clock
SOIC 20-pin package
3 Applications
The AS1108 is ideal for bar-graph displays, instrument-
panel meters, LED matrix displays, dot matrix displays,
set-top boxes, white goods, professional audio equip-
ment, medical equipment, industrial controllers and
panel meters.
AS1108
4-Digit Microprocessor Display
DIG0 to
DIG3
SEG A to G
SEP DP
4 Digits
8 Segments
I/O
I/O
SCK
VDD
ISET
DIN
CLK
GND
GND
LOAD/CSN
+5V
9.53kΩ
Micro-
processor
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AS1108
Datasheet - Pinout
4 Pinout
Pin Assignments
Figure 2. Pin Assignments (Top View)
Pin Descriptions
Table 1. Pin Descriptions
Pin Number Pin Name Description
1DOUT Serial-Data Output. The data into pin DIN is valid at pin DOUT 16.5 clock
cycles later. This pin is used to daisy-chain several AS1108 devices and is
never high-impedance.
2DIN Serial-Data Input. Data is loaded into the internal 16-bit shift register on the
rising edge of pin CLK.
3, 5, 6, 8 DIG 0:DIG 3 Digit Drive Lines. 4 four-digit drive lines that sink current from the display
common cathode. The AS1108 pulls the digit outputs to VDD when turned off.
4, 7 GND Ground. Both GND pins must be connected.
9LOAD/CSN
Load-Data Input. The last 16 bits of serial data are latched on the rising edge
of this pin.
Chip-Select Input (AS1108 SPI-enabled only). Serial data is loaded into the
shift register while this pin is low. The last 16 bits of serial data are latched on
the rising edge of this pin.
10 CLK
Serial-Clock Input. 10MHz maximum rate. Data is shifted into the internal
shift register on the rising edge of this pin. Data is clocked out of DOUT on the
falling edge of this pin. On the AS1108 SPI-enabled, the CLK input is active
only while pin LOAD/CSN is low.
11, 12, 13, 14,
17, 18, 19, 20 SEG A:SEG G,
SEG DP
Seven Segment and Decimal Point Drive Lines. 8 seven-segment drives
and decimal point drive that source current to the display. When a segment
driver is turned off it is pulled to GND.
15 ISET Set Segment Current. Connect to VDD through RSET to set the peak segment
current (see Selecting RSET Resistor Value and Using External Drivers on
page 14).
16 VDD Positive Supply Voltage. Connect to +2.7 to +5.5V supply.
20
19
18
17
16
15
14
13
12
11
1
2
3
4
5
6
7
8
9
10
SEG D
SEG DP
SEG E
SEG C
VDD
ISET
SEG G
SEG B
SEG F
SEG A
DOUT
DIN
DIG 0
GND
DIG 2
DIG 3
GND
DIG 1
LOAD/CSN
CLK
AS1108
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AS1108
Datasheet - Absolute Maximum Ratings
5 Absolute Maximum Ratings
Stresses beyond those listed in Table 2 may cause permanent damage to the device. These are stress ratings only,
and functional operation of the device at these or any other conditions beyond those indicated in Section 6 Electrical
Characteristics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may
affect device reliability.
Table 2. Absolute Maximum Ratings
Parameter Min Max Units Notes
Electrical Parameters
VDD to GND -0.3 7 V
All other pins to GND -0.3 VDD + 0.3
(max 7V) V
Current
DIG 0:DIG 3 Sink Current 500 mA
SEG A:SEG G, SEG DP 100 mA
Latch-Up Immunity ±200 mA All pins except AS1108 pin 11: ±180 mA
Norm: JEDEC 78
Electrostatic Discharge
Digital outputs 1000 V Norm: MIL 883 E method 3015
All other pins 1000 V
Continuous Power Dissipation (TA = +85°C)
Wide SOIC 941 mW Derate 11.8mW/ºC
above +70ºC
Temperature Ranges and Storage Conditions
Storage Temperature Range -55 +150 ºC
Package Body Temperature (Wide SOIC) +260 ºC
The reflow peak soldering temperature (body
temperature) specified is in accordance with IPC/
JEDEC J-STD-020 “Moisture/Reflow Sensitivity
Classification for Non-Hermetic Solid State Surface
Mount Devices”.
The lead finish for Pb-free leaded packages is
matte tin (100% Sn).
Humidity 5 85 % Non-condensing
Moisture Sensitive Level 3 Represents a max. floor life time of 168h
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AS1108
Datasheet - Electrical Characteristics
6 Electrical Character istics
VDD = 2.7V to 5.5V, RSET = 9.53kΩ±1%, TAMB = TMIN to TMAX (unless otherwise specified). All limits are guaranteed.
The parameters with min and max values are guaranteed with production tests or SQC (Statistical Qualification Con-
trol) methods.
Table 3. Electrical Characteristics
Parameter Symbol Conditions Min Typ Max Unit
Operating Temperature Range TAMB 0 +70 °C
Operating Supply Voltage VDD 2.7 5.0 5.5 V
Shutdown Supply Current IDDSD All digital inputs at VDD or GND,
TAMB = +25ºC 10 µA
Operating Supply Current IDD RSET = open circuit. 1 mA
All segments and decimal point
on; ISEG = -40mA. 330
Display Scan Rate fOSC 4 digits scanned 1000 1600 2600 Hz
Digit Drive Sink Current IDIGIT VOUT = 0.65V 320 mA
Segment Drive Source Current ISEG VDD = 5.0V, VOUT = (VDD -1V) -30 -40 -45 mA
Segment Drive Current Matching ∆ISEG 3.0 %
Digit Drive Source Current IDIGIT Digit off, VDIGIT = (VDD - 0.3V) -2 mA
Segment Drive Sink Current ISEG Segment off, VSEG = 0.3V 5 mA
Slow Segment Blink Period (ON
phase, Internal Oscillator) tSLOWBLINK 0.64 1 1.65 s
Fast Segment Blink Period
(ON phase, Internal Oscillator) tFASTBLINK 0.32 0.5 0.83 s
Fast or Slow Segment Blink Duty
Cycle (Guaranteed by design) 49.9 50 50.1 %
Table 4. Logic Inputs/Outputs Characteristics
Parameter Symbol Conditions Min Typ Max Unit
Input Current DIN, CLK, LOAD/CSN IIH, IIL VIN = 0V or VDD -1 1 µA
Logic High Input Voltage VIH 0.7 x VDD V
Logic Low Input Voltage VIL VDD = 5.0V ± 10% 0.8 V
VDD = 3.0V ± 10% 0.6
Output High Voltage VOH
DOUT, ISOURCE = -1mA,
VDD = 5.0V ± 10% VDD - 1 V
DOUT, ISOURCE = -1mA,
VDD = 3.0V ± 10% VDD - 0.5
Output Low Voltage VOL DOUT, ISINK = 1.6mA 0.4 V
Hysteresis Voltage ∆VIDIN, CLK, LOAD/CSN 1 V
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AS1108
Datasheet - Electrical Characteristics
Table 5. Timing Characteristics (see Figure 10 on page 8)
Parameter Symbol Conditions Min Typ Max Unit
CLK Clock Period tCP 100 ns
CLK Pulse Width High tCH 50 ns
CLK Pulse Width Low tCL 50 ns
CSMFall-to-CLK Rise Setup Time
(AS1108 SPI-programmed) tCSS 25 ns
CLK Rise-to -LOAD/CSN Rise Hold Time tCSH 0 ns
DIN Setup Time tDS 25 ns
DIN Hold Time tDH 0 ns
Output Data Propagation Delay tDO CLOAD = 50pF 25 ns
LOAD Rising Edge-to-Next Clock Rising Edge tLDCK 50 ns
Minimum LOAD/CSN Pulse High tCSW 50 ns
Data-to-Segment Delay tDSPD 2.25 ms
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AS1108
Datasheet - Typical Operating Characteristics
7 Typical Operating Characteristics
VDD = 5V, RSET = 9.53k
Ω
, TAMB = 25ºC (unless otherwise specified).
Figure 3. Scan Frequency vs.Temperature Figure 4. Scan Frequency vs. VDD
Figure 5. ISEG vs. Temperature Figure 6. ISEG vs. VDD
Figure 7. ISEG vs. VOUT Figure 8. ISEG vs. VOUT
1860
1880
1900
1920
1940
1960
1980
-40 -20 0 20 40 60 80
TAMB (°C)
FOSC (Hz)
1800
1820
1840
1860
1880
1900
1920
1940
1960
23456
VDD (V)
FOSC (Hz)
0
5
10
15
20
25
30
35
40
45
50
-40 -20 0 20 40 60 80
TAMB (°C)
ISEG (mA)
0
10
20
30
40
50
60
2 2.5 3 3.5 4 4.5 5 5.5 6
VDD (V)
ISEG (mA)
V
DD
= 5V, V
OUT
= 2.4V
V
DD
= 5V, V
OUT
= 4V
V
DD
= 2.7V, V
OUT
= 2V
V
DD
= 2.7V, V
OUT
= 2.4V
V
OUT
= 1.7V
V
OUT
= 2.4V
V
OUT
= 4V
0
5
10
15
20
25
30
35
40
45
50
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
VOUT (V)
ISEG (mA)
VDD = 2.7V
0
5
10
15
20
25
0 0.5 1 1.5 2 2.5
VOUT (V)
ISEG (mA)
R
SET
= 10kΩ
R
SET
= 20kΩ
R
SET
= 40kΩR
SET
= 40kΩ
R
SET
= 10kΩ
R
SET
= 20kΩ
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AS1108
Datasheet - Detailed Description
8 Detailed Description
Serial-Addressing Format
Programming the AS1108 is accomplished by writing to the device’s internal registers (see Digit- and Control-Registers
on page 9) via the 4-wire serial interface. A programming sequence consists of 16-bit packages as depicted in Table 6.
The data is shifted into the internal 16-bit register with the rising edge of the CLK signal. With the rising edge of the
LOAD/CSN signal the data is latched into a digit- or control-register. The LOAD/CSN signal must go high after the 16th
rising clock edge.
The LOAD/CSN signal can also come later but this must happen just before the next rising edge of CLK, otherwise the
data will be lost. The contents of the internal shift register are applied 16.5 clock cycles later to pin DOUT. The data is
clocked out at the falling edge of CLK.
The first 4 bits (D15:D12) are “don't care” settings, bits D11:D8 contain the register address, and bits D7:D0 contain the
data. The first bit is D15, the most significant bit (MSB). The exact timing is shown in Figure 10.
Initial Power-Up
On initial power-up, the AS1108 registers are reset to their default values, the display is blanked, and the device goes
into shutdown mode. All registers should be programmed for normal operation at this time.
Note: The default settings enable only scanning of one digit; the internal decoder is disabled and the Intensity Control
Register (see page 12) is set to the minimum values.
Figure 10. Interface Timing
Table 6. 16-Bit Serial Data Format
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
X X X X Register Address (see Table 7) MSB Data LSB
t
CL
LOAD/
CSN
CLK
DIN
DOUT
D15 D14 D1 D0
t
DO
t
CSS
t
DS
t
DH
t
CH
t
CP
t
CSH
t
CSW
t
LDCK
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AS1108
Datasheet - Detailed Description
Shutdown Mode
The AS1108 features a shutdown mode, consuming only 10µA (max) current. Shutdown mode is entered via a write to
the Shutdown Register (see Table 8). At that point, all segment current sources are pulled to ground and all digit driv-
ers are connected to VDD, so that all segments are blanked.
Note: During shutdown mode the Digit-Registers maintain their data.
Shutdown mode can either be used as a means to reduce power consumption or for generating a flashing display
(repeatedly entering and leaving shutdown mode). For minimum supply current in shutdown mode, logic input should
be at GND or VDD (CMOS logic level).
The device needs typically 250µs to exit shutdown mode, and during shutdown mode the AS1108 is fully programma-
ble. Only the display test mode (see page 11) overrides shutdown mode.
When entering or leaving shutdown mode, the Feature Register is reset to its default values (all 0s) when Shutdown
Register bit D7 (page 10) = 0. When bit D7 = 1, the Feature Register is left unchanged when entering or leaving shut-
down mode.
Note: If the AS1108 is used with an external clock, Shutdown Register bit D7 should be set to 1 when writing to the
Shutdown Register.
Digit- and Control-Registers
The AS1108 contains four Digit-Registers and six control-registers, which are listed in Table 7. All registers are
selected using a 4-bit address word, and communication is done via the serial interface.
Digit Registers – These registers are realized with an on-chip 32-bit memory. Each digit can be controlled directly
without rewriting the whole register contents.
Control Registers – These registers consist of decode mode, display intensity, number of scanned digits, shut-
down, display test and features selection registers.
Table 7. Register Address Map
Register HEX Code Address Page
D15:D12 D11 D10 D9 D8
No-Op 0xX0 X 0 0 0 0 13
Digit 0 0xX1 X 0 0 0 1 N/A
Digit 1 0xX2 X 0 0 1 0 N/A
Digit 2 0xX3 X 0 0 1 1 N/A
Digit 3 0xX4 X 0 1 0 0 N/A
Decode-Mode 0xX9 X 1 0 0 1 10
Intensity Control 0xXA X 1 0 1 0 12
Scan Limit 0xXB X 1 0 1 1 12
Shutdown 0xXC X 1 1 0 0 10
N/A 0xXD X 1 1 0 1 N/A
Feature 0xXE X 1 1 1 0 13
Display Test 0xXF X 1 1 1 1 11
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AS1108
Datasheet - Detailed Description
Shutdown Register (0xXC)
The Shutdown Register controls AS1108 shutdown mode (see Shutdown Mode on page 9).
Decode Enable Register (0xX9)
The Decode Enable Register sets the decode mode. BCD/HEX decoding (either BCD code – characters 0:9, E, H, L,
P, and -, or HEX code – characters 0:9 and A:F) is selected by bit D2 (page 13) of the Feature Register. The Decode
Enable Register is used to select the decode mode or no-decode for each digit. Each bit in the Decode Enable Regis-
ter corresponds to its respective display digit (i.e., bit D0 corresponds to digit 0, bit D1 corresponds to digit 1 and so
on). Table 10 lists some examples of the possible settings for the Decode Enable Register bits.
Note: A logic high enables decoding and a logic low bypasses the decoder altogether.
When decode mode is used, the decoder looks only at the lower-nibble (bits D3:D0) of the data in the Digit-Registers,
disregarding bits D6:D4. Bit D7 sets the decimal point (SEG DP) independent of the decoder and is positive logic (bit
D7 = 1 turns the decimal point on). Table 10 lists the code-B font; Table 11 lists the HEX font.
When no-decode mode is selected, data bits D7:D0 of the Digit-Registers correspond to the segment lines of the
AS1108. Table 12 shows the 1:1 pairing of each data bit and the appropriate segment line.
Figure 11. Standard 7-Segment LED Intensity Control and Inter-Digit Blanking
Table 8. Shutdown Register Format (Address (HEX) = 0xXC))
Mode HEX Code Register Data
D7 D6 D5 D4 D3 D2 D1 D0
Shutdown Mode,
Reset Feature Register to Default Settings 0x00 0 X X X X X X 0
Shutdown Mode, Feature Register Unchanged 0x80 1 X X X X X X 0
Normal Operation,
Reset Feature Register to Default Settings 0x01 0 X X X X X X 1
Normal Operation, Feature Register Unchanged 0x81 1 X X X X X X 1
Table 9. Decode Enable Register Format (Address (HEX) = 0xX9))
Decode Mode HEX Code Register Data
D7 D6 D5 D4 D3 D2 D1 D0
No decode for digits 3:0 0x00 X X X X 0 0 0 0
Code-B/HEX decode for digit 0. No decode for digits 3:1 0x01 X X X X 0 0 0 1
Code-B/HEX decode for digits 3:0 0xFF X X X X 1 1 1 1
Table 10. Code-B Font
7-Segment
Character Register Data On Segments = 1
D7
†
D6:D4
D3
D2
D1
D0
DP
†
A
B
C
D
E
F
G
0 X 0000 1111110
1 X 0001 0110000
2 X 0010 1101101
3 X 0011 1111001
4 X 0100 0110011
5 X 0101 1011011
A
B
G
F
E
D
C
DP
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AS1108
Datasheet - Detailed Description
Display-Test Register (0xXF)
The AS1108 can operate in two modes: normal mode and display test mode. In display test mode all LEDs are
switched on at maximum brightness (duty cycle is 15/16). The device remains in display-test mode until the Display-
Test Register is set for normal operation.
Note: All settings of the Digit- and Control-Registers are maintained.
6 X 0110 1011111
7 X 0111 1110000
8 X 1000 1111111
9 X 1001 1111011
- X 1010 0000001
E X 1011 1001111
H X 1100 0110111
L X 1101 0001110
P X 1110 1100111
Blank X 1111 0000000
†
The decimal point is enabled by setting bit D7 = 1.
Table 11. HEX Font
7-Segment
Character Register Data On Segments = 1
D7
†
D6:D4
D3
D2
D1
D0
DP
†
A
B
C
D
E
F
G
0 X 0 0 0 0 1 1 1 1 1 1 0
1 X 0 0 0 1 0 1 1 0 0 0 0
2 X 0 0 1 0 1 1 0 1 1 0 1
3 X 0 0 1 1 1 1 1 1 0 0 1
4 X 0 1 0 0 0 1 1 0 0 1 1
5 X 0 1 0 1 1 0 1 1 0 1 1
6 X 0 1 1 0 1 0 1 1 1 1 1
7 X 0 1 1 1 1 1 1 0 0 0 0
8 X 1 0 0 0 1 1 1 1 1 1 1
9 X 1 0 0 1 1 1 1 1 0 1 1
A X 1 0 1 0 1 1 1 0 1 1 1
b X 1 0 1 1 0 0 1 1 1 1 1
C X 1 1 0 0 1 0 0 1 1 1 0
d X 1 1 0 1 0 1 1 1 1 0 1
E X 1 1 1 0 1 0 0 1 1 1 1
F X 1 1 1 1 1 0 0 0 1 1 1
†
The decimal point is enabled by setting bit D7 = 1.
Table 12. No-Decode Mode Data Bits and Corresponding Segment Lines
D7 D6 D5 D4 D3 D2 D1 D0
Corresponding Segment Line DP A B C D E F G
Table 13. Display-Test Register Format (Address (HEX) = 0xXF))
Mode Register Data
D7 D6 D5 D4 D3 D2 D1 D0
Normal Operation X X X X X X X 0
Display Test Mode X X X X X X X 1
Table 10. Code-B Font (Continued)
7-Segment
Character Register Data On Segments = 1
D7
†
D6:D4
D3
D2
D1
D0
DP
†
A
B
C
D
E
F
G
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AS1108
Datasheet - Detailed Description
Intensity Control Register (0xXA)
The brightness of the display can be controlled by digital means using the Intensity Control Register and by analog
means using RSET (see Selecting RSET Resistor Value and Using External Drivers on page 14).
Display brightness is controlled by an integrated pulse-width modulator which is controlled by the lower-nibble of the
Intensity Control Register. The modulator scales the average segment-current in 16 steps from a maximum of 31/32
down to 1/32 of the peak current set by RSET.
Scan-Limit Register (0x0B)
The Scan-Limit Register controls which of the digits are to be displayed. When all 4 digits are to be displayed, the
update frequency is typically 1600Hz. If the number of digits displayed is reduced, the update frequency is increased.
The frequency can be calculated using 8fOSC/N, where N is the number of digits. Since the number of displayed digits
influences the brightness, RSET should be adjusted accordingly. Table 16 lists the maximum allowed current when
fewer than 4 digits are used.
Note: To avoid differences in brightness this register should not be used to blank parts of the display (leading zeros).
Table 14. Intensity Register Format (Address (HEX) = 0xXA))
Duty Cycle HEX Code Register Data
AS1108 D7 D6 D5 D4 D3 D2 D1 D0
1/32 (min on) 0xX0 X X X X 0 0 0 0
3/32 0xX1 X X X X 0 0 0 1
5/32 0xX2 X X X X 0 0 1 0
7/32 0xX3 X X X X 0 0 1 1
9/32 0xX4 X X X X 0 1 0 0
11/32 0xX5 X X X X 0 1 0 1
13/32 0xX6 X X X X 0 1 1 0
15/32 0xX7 X X X X 0 1 1 1
17/32 0xX8 X X X X 1 0 0 0
19/32 0xX9 X X X X 1 0 0 1
21/32 0xXA X X X X 1 0 1 0
23/32 0xXB X X X X 1 0 1 1
25/32 0xXC X X X X 1 1 0 0
27/32 0xXD X X X X 1 1 0 1
29/32 0xXE X X X X 1 1 1 0
31/32 (max on) 0xXF X X X X 1 1 1 1
Table 15. Scan-Limit Register Format (Address (HEX) = 0xXB))
Scan Limit HEX Code Register Data
D7 D6 D5 D4 D3 D2 D1 D0
Display digit 0 only (see Table 16) 0xX0 X X X X X 0 0 0
Display digits 0:1 (see Table 16) 0xX1 X X X X X 0 0 1
Display digits 0:2 (see Table 16) 0xX2 X X X X X 0 1 0
Display digits 0:3 0xX3 X X X X X 0 1 1
Table 16. Maximum Segment Current for 1-, 2-, or 3-Digit Displays
Number of Digits Displayed Maximum Segment Current (mA)
1 10
2 20
3 30
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AS1108
Datasheet - Detailed Description
Feature Register (0xXE)
The Feature Register is used for switching the device into external clock mode, applying an external reset, selecting
code-B or HEX decoding, enabling or disabling blinking, enabling or disabling the SPI-compatible interface, setting the
blinking rate, and resetting the blink timing.
Note: At power-up the Feature Register is initialized to 0.
No-Op Register (0xX0)
The No-Op Register is used when multiple AS1108 devices are cascaded in order to support displays with more than 4
digits. The cascading must be done in such a way that all DOUT pins are connected to DIN of the next AS1108 (see
Figure 12 on page 16). The LOAD/CSN and CLK signals are connected to all devices.
For example, if five devices are cascaded, in order to perform a write operation to the fifth device, the write-command
must be followed by four no-operation commands. When the LOAD/CSN signal goes high, all shift registers are
latched. The first four devices will receive no-operation commands and only the fifth device will receive the intended
operation command, and subsequently update its register.
Table 17. Feature Register Summary
D7 D6 D5 D4 D3 D2 D1 D0
blink_
start sync blink_
freq_sel blink_en spi_en decode_sel reg_res clk_en
Table 18. Feature Register Bit Descriptions (Address (HEX) = 0xXE))
Addr: 0xXE Feature Register
Enables and disables various device features.
Bit Bit Name Default Access Bit Description
D0 clk_en 0 R/W External clock select.
0 = Internal oscillator is used for system clock.
1 = Pin CLK of the serial interface operates as system clock input.
D1 reg_res 0 R/W
Resets all control registers except the Feature Register.
0 = Reset Disabled. Normal operation.
1 = All control registers are reset to default state (except the Feature
Register) identically after power-up.
Note: The Digit Registers maintain their data.
D2 decode_sel 0 R/W Selects display decoding.
0 = Enable Code-B decoding (see Table 10 on page 10).
1 = Enable HEX decoding (see Table 11 on page 11).
D3 spi_en 0 R/W Enables the SPI-compatible interface.
0 = Disable SPI-compatible interface.
1 = Enable the SPI-compatible interface.
D4 blink_en 0 R/W Enables blinking.
0 = Disable blinking.
1 = Enable blinking.
D5 blink_freq_sel 0 R/W Sets blink with low frequency (with the internal oscillator enabled):
0 = Blink period typically is 1 second (0.5s on, 0.5s off).
1 = Blink period is 2 seconds (1s on, 1s off).
D6 sync 0 R/W
Synchronizes blinking on the rising edge of pin LOAD/CSN. The
multiplex and blink timing counter is cleared on the rising edge of pin
LOAD/CSN. By setting this bit in multiple AS1108 devices, the blink
timing can be synchronized across all the devices.
D7 blink_start 0 R/W
Start Blinking with display enabled phase. When bit D4 (blink_en) is set,
bit D7 determines how blinking starts.
0 = Blinking starts with the display turned off.
1 = Blinking starts with the display turned on.
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AS1108
Datasheet - Typical Application
9 Typical Application
Supply Bypassing and Wiring
In order to achieve optimal performance the AS1108 should be placed very close to the LED display to minimize
effects of electromagnetic interference and wiring inductance.
Furthermore, a 10µF electrolytic and a 0.1µF ceramic capacitor should be connected between pins VDD and GND to
avoid power supply ripple (see Figure 12 on page 16).
Note: Both GND pins must be connected to ground.
Selecting RSET Resistor Value and Using External Drivers
Brightness of the display segments is controlled via RSET. The current that flows between VDD and ISET defines the
current that flows through the LEDs.
Segment current is about 200 times the current in ISET. Typical values for RSET for different segment currents, operat-
ing voltages, and LED voltage drop (VLED) are given in Tables 19 - 23. The maximum current the AS1108 can drive is
40mA. If higher currents are needed, external drivers must be used, in which case it is no longer necessary that the
device drive high currents.
In cases where the device drives only a few digits, Table 16 specifies the maximum currents, and RSET must be set
accordingly.
Note: The display brightness can also be logically controlled (see Selecting RSET Resistor Value and Using External
Drivers on page 14).
Table 19. RSET vs. Segment Current and LED Forward Voltage, VDD = 2.7V
ISEG (mA) VLED(V)
1.5 2.0
40 5kΩ4.4kΩ
30 6.9kΩ5.9kΩ
20 10.7kΩ9.6kΩ
10 22.2kΩ20.7kΩ
Table 20. RSET vs. Segment Current and LED Forward Voltage, VDD = 3.3V
ISEG (mA) VLED(V)
1.5 2.0 2.5
40 6.7kΩ6.4kΩ5.7kΩ
30 9.1kΩ8.8kΩ8.1kΩ
20 13.9kΩ13.3kΩ12.6kΩ
10 28.8kΩ27.7kΩ26kΩ
Table 21. RSET vs. Segment Current and LED Forward Voltage, VDD = 3.6V
ISEG (mA) VLED(V)
1.5 2.0 2.5 3.0
40 7.5kΩ7.2kΩ6.6kΩ5.5kΩ
30 10.18kΩ9.8kΩ9.2kΩ7.5kΩ
20 15.6kΩ15kΩ14.3kΩ13kΩ
10 31.9kΩ31kΩ29.5kΩ27.3kΩ
Table 22. RSET vs. Segment Current and LED Forward Voltage, VDD = 4.0V
ISEG (mA) VLED(V)
1.5 2.0 2.5 3.0 3.5
40 8.6kΩ8.3kΩ7.9kΩ7.6kΩ5.2kΩ
30 11.6kΩ11.2kΩ10.8kΩ9.9kΩ7.8kΩ
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AS1108
Datasheet - Typical Application
20 17.7kΩ17.3kΩ16.6kΩ15.6kΩ13.6kΩ
10 36.89kΩ35.7kΩ34.5kΩ32.5kΩ29.1kΩ
Table 23. RSET vs. Segment Current and LED Forward Voltage, VDD = 5.0V
ISEG (mA) VLED (V)
1.5 2.0 2.5 3.0 3.5 4.0
40 11.35kΩ11.12kΩ10.84kΩ10.49kΩ10.2kΩ9.9kΩ
30 15.4kΩ15.1kΩ14.7kΩ14.4kΩ13.6kΩ13.1kΩ
20 23.6kΩ23.1kΩ22.6kΩ22kΩ21.1kΩ20.2kΩ
10 48.9kΩ47.8kΩ46.9kΩ45.4kΩ43.8kΩ42kΩ
Table 24. Package Thermal Data
Package Thermal Resistance (ΘJA)
20 Wide SOIC +85°C/W
Table 22. RSET vs. Segment Current and LED Forward Voltage, VDD = 4.0V (Continued)
ISEG (mA) VLED(V)
1.5 2.0 2.5 3.0 3.5
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AS1108
Datasheet - Typical Application
4x8 LED Dot Matrix Driver
The application example in Figure 12 shows the AS1108 as a 4x8 LED dot matrix driver.
The LED columns have common cathodes and are connected to the DIG0:3 outputs. The rows are connected to the
segment drivers. Each of the 32 LEDs can be addressed separately. The columns are selected via the digits as listed
in Table 7 on page 9.
The Decode Enable Register (see page 10) must be set to ‘00000000’ as described in Table 9 on page 10. Single
LEDs in a column can be addressed as described in Table 12 on page 11, where bit D0 corresponds to segment G and
bit D7 corresponds to segment DP.
Note: For a multiple-digit dot matrix, multiple AS1108 devices must be cascaded.
Figure 12. Application Example as LED Dot Matrix Driver
Cascading Drivers
If more than 4 digits or 32 LEDs are needed, it is recommended to use the AS1106/AS1107, although several AS1108
devices can be cascaded.
The example in Figure 4 drives 2 dot matrix digits using a 4-wire microprocessor interface. All Scan-Limit Registers
should be set to the same value so that one display will not appear brighter than the other.
For example, to display 6 digits, set both Scan-Limit Registers to display 3 digits so that both displays have a 1/3 duty
cycle per digit. If 5 digits are needed, set both Scan-Limit Registers to display 3 digits and leave one digit unconnected.
Otherwise, if one driver is set to display 3 digits and the other to display 2 digits one display will appear brighter
because its duty cycle per digit will be 1/2 and the other display’s duty cycle will be 1/3.
Note: Refer to No-Op Register (0xX0) on page 13 for additional information.
SEG G
DIG0:3
ISET
DIN
GND
GND
LOAD/CSN
CLK
VDD
SEG A:G
SEG DP
9.53kΩ
DIG0:3
ISET
DIN
GND
GND
LOAD/CSN
CLK
VDD
SEG A:G
SEG DP
9.53kΩ
DOUT
4x8 LED
Dot Matrix
Diode Arrangement
V
BAT
V
BAT
Micro-
Processor
SEG A
SEG DP
SEG B
SEG C
SEG D
SEG E
SEG F SEG G
4x8 LED
Dot Matrix
SEG A
SEG DP
SEG B
SEG C
SEG D
SEG E
SEG F
AS1108AS1108
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AS1108
Datasheet - Package Drawings and Markings
10 Package Drawings and Markings
Figure 13. SOIC 20-pin Marking
Table 25. Packaging Code YYWWRZZ
YY WW Q ZZ
last two digits of the current year manufacturing week plant identifier free choice / traceability code
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www.austriamicrosystems.com/LED-Driver-ICs/AS1108 Revision 2.13 19 - 20
AS1108
Datasheet - Ordering Information
11 Ordering Information
The AS1108 is available as the standard products shown in Table 26.
Note: All products are RoHS compliant and austriamicrosystems green.
Buy our products or get free samples online at ICdirect: http://www.austriamicrosystems.com/ICdirect
Technical Support is found at http://www.austriamicrosystems.com/Technical-Support
For further information and requests, please contact us mailto:sales@austriamicrosystems.com
or find your local distributor at http://www.austriamicrosystems.com/distributor
Table 26. Ordering Information
Ordering Code Marking Description Temperature Range Delivery Form Package
AS1108WL AS1108WL 4-Digit LED Display Driver 0 to +70ºC Tubes SOIC 20-pin
AS1108WL-T AS1108WL 4-Digit LED Display Driver 0 to +70ºC Tape and Reel SOIC 20-pin
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AS1108
Datasheet
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austriamicrosystems AG reserves the right to change specifications and prices at any time and without notice.
Therefore, prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for
current information. This product is intended for use in normal commercial applications. Applications requiring
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