LM3414SDX National Semiconductor Corporation, LM3414SDX Datasheet - Page 12

• 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

www.national.com
TABLE 1. Examples for f
To ensure accurate current regulation, the LM3414/14HV
should be operated in continuous conduction mode (CCM)
and the on time should not be shorter than 400 ns under all
operation condition.
SETTING LED CURRENT
The LM3414/14HV requires no external current sensing re-
sistor for LED current regulation. The average output current
of the LM3414/14HV is adjustable by varying the resistance
of the resistor, R
pins. The IADJ pin is internally biased to 1.255V. The LED
current is then governed by the following equation:
where 350 mA < I
FIGURE 1. Switching Frequency vs R
f
SW
1000
250
500
(kHz)
IADJ
LED
that connects across the IADJ and GND
< 1A
SW
Settings
R
FS
80
40
20
(kΩ)
30124845
FS
12
TABLE 2. Examples for I
The LED current can be set to any level in the range from 350
mA to 1A. In order to provide accurate LED current, R
should be a resistor with no more than 0.5% tolerance. If the
IADJ pin is accidentally shorted to GND (R
current will be limited to avoid damaging the circuit. When the
over current protection is activated, current regulation cannot
be maintained until the over-current condition is cleared.
MINIMUM SWITCH ON-TIME
As the LM3414 features a 400 ns minimum ON time, it is es-
sential to make sure the ON time of the internal switch is not
shorter than 400 ns when setting the LED driving current. If
the switching ON time is shorter than 400 ns, the accuracy of
the LED current may not maintain and exceed the rated cur-
rent of the LEDs. The ratio of the LED forward voltage to input
voltage is restricted by the following restriction:
PEAK SWITCH CURRENT LIMIT
The LM3414/14HV features an integrated switch current lim-
iting mechanism that protects the LEDs from being overdriv-
en. The switch current limiter will be triggered when the switch
current is three times exceeding the current level set by
R
switch turns OFF for 3.6 µs to allow the inductor to discharge
and cycles repetitively until the over current condition is re-
moved. The current limiting feature is exceptionally important
to avoid permanent damage of the LM3414/14HV application
circuit due to short circuit of LED string.
IADJ
. Once the current limiter is triggered, the internal power
I
OUT
1000
350
500
700
FIGURE 2. LED Current vs R
(mA)
OUT
Settings
R
IADJ
IADJ
8.93
6.25
4.46
3.13
IADJ
= 0), the output
(kΩ)
30124822
IADJ