SAMES SA8803 Datasheet

sames

LIGHT EMITTING DIODE DRIVER

FEATURES

n Drives 24 LED's under control of Serial

Interface

n Light Emitting Diode intensity

programmable using a single resistor

n Automatic lamp test facility on reset

(MRST)

n Minimal external components
n LED intensity constant, regardless of

number of LED's illuminated

DESCRIPTION

The block Diagram of the SA8803 is shown in
Fig. 1. A control word is clocked into the
device via the DATA pin with a local clock
provided to pin CLK. The control word
comprises a 3-bit chip address, a 5-bit LED
address and a Status (on/off) bit. Provided
that the Chip Adress matches the setting on
pins AD0..AD2 then the LED State Register is
addressed and the state of the selected LED
is set according to the Status bit in the Control
word.

The LEDs are driven by banks of Constant
Current Sources in which the value of the
current in all six banks is set by a single
external resistor connected between pin
INTENS and VEE. The total current drained
by the device and the LEDs may be fixed at
six times the LED current by connecting pin
CC to GND.

The status of all LEDs can be verified at any
time by pulling the TEST pin low. When tis
happens the contents of the LED Status
Register are clocked out of the SA8803 on the
pin DOUT. An additional test feature is that
al LEDs are illuminated for a short period after
power up to simplify system testing.

4159

SA8803

n 11 Bit Information word controls up to

192 LED's (using eight SA8803s)

n Readback of LED status
n Requires a local clock of 8 times the

data rate

n Constant current from power supply

option

PIN CONNECTIONS

7

LED 1

8

LED 2

9

LED 3

10

LED 4

11

V

EE

12

LED 5

13

LED 6

14

LED 7

15

V

DD

16

LED 8

17

LED 9

DR-00593

DD

V

65432

18 19

LED 10

AD 2

CC

EE

V

AD 1

DOUT

AD 0

1

DATA

44 43 42

SA8803

LED 12

LED 11

23

24 25 26

DD

V

INTENS

LED 13

20 21 22

PDS039-SA8803-001 REV. C 07-03-96

GND

MRST

LED 14

LED 15

CLK

41 40

27 28

EE

V

N.C.

39

38

37

36

35

34

33

32

31

30

29

LED 16

TEST
LED 24
LED 23
LED 22
V

EE

LED 21
LED 20
LED 19
V

DD

LED 18
LED 17

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SA8803

FIGURE 1: BLOCK DIAGRAM

INTENS
CC

DATA

CLK

AD0....AD2

MRST

TEST
DR-00594

START

BIT

DETECTION

S

CLK

CLOCK

SYNC

SIN
CLK

11 - BIT SHIFT REGISTER

RESET

START

BIT

COMPARATOR

ADDRESS
DECODER

RESET

LAMP TEST

LOGIC

LED

3-BIT

STOP

CHIP

BIT

ADDRESS

LED

SELECTION

BUS

24-BIT

LED

STATE

REGISTER

LED

DRIVERS

TEST

CONTROL

LOGIC

LED1

LED24

DOUT

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sames

SA8803

PIN DESCRIPTION

Pin Designation Description

1..3 AD0..AD2 Device address input pins. The binary code set up on
these pins, must match the address field of the control
word, before device access may be achieved. These
Schmitt-triggered inputs have on-chip pull-up resistors.

4 DOUT This output is used for the manufacturers test requirements

and MUST be left open.

5 CC Constant Current Drain Select.This Schmitt-triggered

input has on-chip pullup provided.

7..10, LED1..LED4, High current LED drive terminal outputs.

12..14, LED5..LED7

16..18, LED8..LED10,

20..21, LED11..LED12,

24..26 LED13..LED15,

28..30 LED16..LED18,

32..34, LED19..LED21,

36..38 LED22..LED24

22 INTENS This analog input is used to set the drive current supplied

to the LED's. A resistor is connected from this pin to VEE.

39 TEST Active low input that enables the internal LED status word

to be output from the DOUT pin. This Schmitt-triggered
input has on-chip pullup provided.

40 NC Internally Unconnected.
41 CLK External clock Schmitt-triggered input runs at 8X the data

rate (Baud rate).

42 MRST This active low Schmitt-Trigger input may be used to

reset all internal registers. When active (low) this input
will cause all LED's to be driven for the duration of MRST
(lamp test). When MRST goes inactive all LED's will be
turned off. On-chip pullup provided.

43 GND 0V Supply Input for logic (0V)
44 DATA Serial data input. Accept data in the form of an 11-bit

information word. This Schmitt-triggered input has on­chip pullup provided.

11, 19, VEE Negative Supply Inputs (-5V)
27, 35

6, 15, VDD Positive Supply Inputs (+5V)
23, 31

Note: All inputs and outputs are CMOS compatible, unless otherwise specified.

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