LM3509SDEV National Semiconductor, LM3509SDEV Datasheet - Page 10

• Manufacturer Part Number: LM3509SDEV
• Description: BOARD EVALUATION FOR LM3509SD
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3509SDEV

• Current - Output / Channel: 40mA
• Outputs And Type: 2, Non-Isolated
• Voltage - Output: 21V
• Features: Dimmable, I²C Interface
• Voltage - Input: 2.7 ~ 5.5V
• Utilized Ic / Part: LM3509
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Applications Information
LED Current Setting/Maximum LED
Current
Resistor R
LED current. The board is shipped with a 12.1kΩ for R
giving a maximum LED current of 20mA/string. For higher or
lower maximum LED currents the 12.1kΩ can be removed
and replaced with another value for R
R
where SET provides the constant 1.244V output. Typically the
MAIN and SUB current sinks can provide up to 30mA.
Output Voltage Setting (OLED
Mode)
For applications that require a constant output voltage + a
single LED string (such as OLED panel powering) the
SET
to I
LED_MAX
SET
connected from SET to GND sets the maximum
relationship is:
SET
. In this case the
SET
10
LM3509 features an OLED mode (OLED bit = '1'). In OLED
mode connect feedback resistors from the converters output
to SUB/FB to GND to set the output voltage (see R1 and R2
in Figure 1. First select R2 < 100kΩ then calculate R1 such
that:
In OLED mode the MAIN current sink continues to regulate
the current through MAIN, however, V
lated. To avoid dropout and ensure proper current regulation
the application must ensure that V
MAIN
MAIN
> 0.3V.
is no longer regu-