SM16705FN datasheet(12/15 Pages) SAMHOP

12 / 15 page

SAMHOP Microelectronics Corp.

8-BIT CONSTANT CURRENT LED DRIVER

Page 12

V.2.10

[1] Output Current (IOUT)

[2] Total supply voltage (VLED)

IOUT is set by the enternal resistor (R-EXT) as shown in Firgure1.

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).

[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.

PATTERN LAYOUT

VLED = 3 ~ 4 (V)

R-EXT

SERIAL-IN

LATCH

CLOCK

ENABLE

OUT0

OUT7

SERIAL-OUT

R-EXT

SERIAL-IN

LATCH

CLOCK

ENABLE

OUT7

GND

SERIAL-OUT

CPU

GND

VDD

OUT0

SCAN

SDM4953

SDM9435A

VDS

VDD

VOUT

SDM4952

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