SC4509 Semtech Corporation, SC4509 Datasheet - Page 7

• Manufacturer Part Number: SC4509
• Description: Highly Integrated Step-Up Converter
• Manufacturer: Semtech Corporation

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Programming the LED Current
Please refer to the Typical Application Circuit on page 1.
The LED current is programmed by connecting a resistor
(R1) between the FB pin and GND. The LED current in
mA is given by the following equation:
where R1 value is in Ohms.
Setting the Output Voltage
The non-inverting input of the internal error amplifi er is
tied to a 199mV voltage reference. A simple voltage divider
(R1 at the top and R2 at the bottom) sets the converter
output voltage. Please refer to the Application Circuit for
OLED Panels on the next page. The voltage feedback gain
h = 0.199/Vo is related to the divider resistors value as
Once either R1 or R2 is chosen, the other can be calcu-
lated for the desired output voltage Vo. Since the number
of standard resistance values is limited, the calculated
resistance may not be available as a standard value resis-
tor. As a result, there will be a set error in the converter
output voltage. This non-random error is caused by the
feedback voltage divider ratio. It cannot be corrected by
the feedback loop.
© 2007 Semtech Corp.
POWER MANAGEMENT
Applications Information
h
I
LED
R1
= 199/R1
R2
R2
7
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SC4509