SM16705 Datasheet, PDF (12/15 Pages) SamHop Microelectronics Corp. – 8-BIT CONSTANT CURRENT LED DRIVER

SAMHOP Microelectronics Corp.
8-BIT CONSTANT CURRENT LED DRIVER
[1] Output Current (IOUT)
IOUT is set by the enternal resistor (R-EXT) as shown in Firgure1.
[2] Total supply voltage (VLED)
This device can operate at 0.4~0.7V (VOUT). When a higher voltage is input to the device, the excess
voltage is consumed inside the device, that leads to more power dissipation.
In order to minimize power dissipation and loss, we would like to recommend to set the total supply voltage
as shown below,
VLED (total supply voltage)=VOUT (IC Supply Voltage)+ Vf (LED Forward voltage)
+ VDS (MOSFET Voltage Drop )
When the total supply is too high considering the power dissipation of this device, an additional R can
decrease the supply voltage (VOUT).
PATTERN LAYOUT
VDD
SCAN
CPU
VDD
ENABLE
CLOCK
LATCH
SERIAL-IN
R-EXT
VDD
OUT0
VOUT
OUT7
GND SERIAL-OUT
VLED = 3 ~ 4 (V)
SDM4952
SDM4953
VDS _SDM9435A
Vf
VDD
ENABLE
CLOCK
LATCH
VDD
Vf
OUT0
VOUT
SERIAL-IN
OUT7
R-EXT GND SERIAL-OUT
[3] Pattern Layout
This device has only one ground pin that means signal ground pin and power ground pin are common.
If ground pattern layout contains large inductance and impedance, and the voltage between ground
and LATCH, CLOCK terminals exceeds 2.5V by switching noise during operation, this device may miss-
operate. So we would advise you to pay attention to pattern layout to minimize ground inductance.
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