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DM114
、DM115
點晶科技股份有限公司
SILICON TOUCH TECHNOLOGY INC.
8-BIT CONSTANT CURRENT LED DRIVERS with 3.3V~5V supply voltage
Version:A.002
Page 12
Preliminary
System Configuration Example
[1] Output current (IOUT)
Sink current is set by the external resistor as shown in figure (Iout vs. Rext).
[2] LED supply voltage (VLED) setup
VLED
= V
CE ( Tr Vsat ) + Vf ( LED forward voltage ) + VO ( IC supply voltage)
To prevent too much power dissipated by the device due to higher V
LED , an additional R can
be used to reduce the Vout when the outputs consume current:
R =
(max)
(max)
(min)
Bit
I
V
V
V
O
O
f
LED
•
−
−
Note
This device has only one ground pin shared by signal, output sink current, and power ground.
It is advisable to pattern the ground layout with minimized inductance such that the switching
noise induced by the input signals and the output sink current would not cause chip malfunction. To
prevent the drivers’ outputs from damage by overshoot stress, it is also advisable not to turn off the
drivers and scan transistors simultaneously.
V DD
SER I A L -O U T
R
V LE D = 3~4 (V )
OU T 7
OU T 0
GN D
R-E X T
LA T C H
CP U
SER I A L -IN
EN ABL E
SC AN
CL O C K
SER I A L -O U T
OU T 7
OU T 0
GN D
R-E X T
LA T C H
SER I A L -IN
EN ABL E
CL O C K
Vo
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