LM3414SDX National Semiconductor Corporation, LM3414SDX Datasheet - Page 17

• Manufacturer Part Number: LM3414SDX
• Description: Lm3414/lm3414hv 1a 60w* Common Anode Capable Constant Current Buck Led Driver Requires No External Current Sensing Resistor
• Manufacturer: National Semiconductor Corporation

DESIGN EXAMPLE
Figure 7 shows an example circuit for analog dimming control
using simple external biasing circuitry with a variable resistor.
30124827
FIGURE 7. Example Analog Dimming Control Circuit
In the figure, the variable resistor VR1 controls the base volt-
age of Q1 and eventually adjusts the bias voltage of current
to the IADJ pin (I
). As the resistance of VR1 increases and
EXT
the voltage across VR1 exceeds 1.255V + 0.7V, the LED cur-
rent starts to decrease as I
increases.
EXT
where
The analog dimming begins only when I
> 0.
EXT
DESIGN CONSIDERATIONS
The overall performance of the LED driver is highly depends
on the PCB layout and component selection. To minimize
connection losses and parasitic inductance of the traces, the
best practice is to keep the copper traces connecting the in-
ductor, power switch and rectifier short and thick . Long traces
on critical power paths will introduce voltage and current
spikes to the LM3414/LM3414HV. If the voltage spike level
exceeds the absolute maximum pin voltage of the LM3414, it
could damage the device and LEDs. To avoid physical dam-
age of the circuit, a Transient Voltage Suppressor (TVS) can
be added across VIN and GND pins to suppress the spike
voltage. This also helps in absorbing the input voltage spike
when the circuit is powered through physical switch upon
power up.
17
www.national.com