SAMHOP Microelectronics Corp.
WHITE / BLUE LED DRIVER FOR LI- ION BATTERY APPLICATION
APPLICATION INFORMATION
Enable (EN/CTRL pin)
The EN/CTRL pin serves two functions. One is the enable and disable of the device the other is the output
sink current programming of the device. If the digital interface is not required the CTRL pin can be used as
a standard enable pin for the device. Pulling the CTRL pin high will enable the device beginning sink
current on LED pins. Pulling the CTRL pin to ground for a period of time > 480us will shutdown the device
reducing the shutdown cruuent to typical 0.1 uA.
This pin should not be left floating and need to be terminated.
Digital interface (EN/CTRL pin)
When power on the chip and pull high the EN/CTRL pin, the LED pins will start sink the initial sink current.
The maximum LED sink current is I
LEDMAX
(20mA). Pulling the EN/CTRL pin low for a period of time can
program the output sink current. When pulling the CTRL pin to "low" between 9 us to 30 us, the internal
controller decreases its output sink current by one step (1 mA). When pulling the CTRL pin to "low"
between 125us to 175us, the internal controller increases its output sink current by one step. There are
total 16 steps that control LED output sink current range from I
LEDMAX
down to I
LEDMAX/4
. Between the
"low" pulses, EN/CTRL should keep at "high" for at last 10 us.
Decrease One Step
Increase One Step
9~30us
Time
125~175us
Time
Disable
Hold time
480us
Time
10us
Time
Supply Voltage and Li-ion battery low warning
SM6802/3/4 works with supply voltage range from 3.0V to 5.0V. The white/blue LED forward voltage is in
the range of 2.9V to 3.5V at 20mA current. The supply voltage range and LED forward voltage (Vf) should
be set to fully ultilize Li-ion battery energy. For example, the maximum white LED forward voltage limit at
3.2V (@ 20mA) when Li-ion battery discharge reaches 3.275V (normally around 1%~3% power left in the
battery). When Li-ion battery voltage is lower than the preset low level, the LED current (brightness) will
start to decrease.
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V.1.0 July 12,2007
SAMHOP [ SAMHOP MICROELECTRONICS CORP. ]
