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PDF SA8803 Data sheet ( Hoja de datos )
| Número de pieza | SA8803 | |
| Descripción | LIGHT EMITTING DIODE DRIVER | |
| Fabricantes | Sames | |
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SA8803
LIGHT EMITTING DIODE DRIVER
FEATURES
n Drives 24 LED's under control of Serial n 11 Bit Information word controls up to
Interface
192 LED's (using eight SA8803s)
n Light Emitting Diode intensity n Readback of LED status
programmable using a single resistor n Requires a local clock of 8 times the
n Automatic lamp test facility on reset
data rate
(MRST)
n Constant current from power supply
n Minimal external components
option
n LED intensity constant, regardless of
number of LED's illuminated
DESCRIPTION
PIN CONNECTIONS
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.
LED 1 7
LED 2 8
LED 3 9
LED 4 10
V EE 11
LED 5 12
LED 6 13
LED 7 14
V DD 15
LED 8 16
LED 9 17
6 5 4 3 2 1 44 43 42 41 40
39 TEST
38 LED 24
37 LED 23
36 LED 22
SA8803
35 V EE
34 LED 21
33 LED 20
32 LED 19
31 V DD
30 LED 18
29 LED 17
18 19 20 21 22 23 24 25 26 27 28
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.
DR-00593
4159
PDS039-SA8803-001
1/10
REV. C 07-03-96
1 page  
SA8803
3. LED Intensity Control
The LED "on" current (ID), is determined by the current flowing from the INTENS pin
through the external resistor. The values of ID can be calculated as follows:
I
D
=
K.
T
VX
R
KT - Current Transfer Ratio of the Internal Current Mirror (typically 10.0)
R - The programming resistor value
V - The voltage drop across the external resistor (internally controlled to 5.0V)
X
4. Constant Current Mode
When the CC pin is pulled high, the device will draw a constant current from the VDD
supply which is equal to all LED's in the "on"condition regardless of the status of the
LED's.
5. Clock Characteristics
S is the internal synchronous clock derived from the asynchronous external clock
CLK
applied at the CLK input pin. It divides the external clock by 8. Theoretically the
rising edge of S (synchronous Clock) should be in the middle of every bit, as
CLK
shown in Figure 4. Because of phase shift due to the clock frequency being more
or less than 8 times the baud rate, this edge may shift its position with regard to the
bit period (B ). The extreme case that may still be tolerated is an edge arriving at
P
either the beginning, or end of bit 11. This represents the maximum shift that can
be tolerated for valid data to be received for an inaccurate input clock frequency
(F ).
O
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