datasheetbank_Logo     Integrated circuits, Transistor, Semiconductors Search and Datasheet PDF Download Site

LM3414 View Datasheet(PDF) - National ->Texas Instruments

Part NameDescriptionManufacturer
LM3414 1A 60W* Common Anode Capable Constant Current Buck LED Driver Requires No External Current Sensing Resistor National-Semiconductor
National ->Texas Instruments National-Semiconductor
LM3414 Datasheet PDF : 20 Pages
First Prev 11 12 13 14 15 16 17 18 19 20
30124845
FIGURE 1. Switching Frequency vs RFS
fSW (kHz)
250
500
1000
RFS (kΩ)
80
40
20
TABLE 1. Examples for fSW Settings
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, RIADJ that connects across the IADJ and GND
pins. The IADJ pin is internally biased to 1.255V. The LED
current is then governed by the following equation:
where 350 mA < ILED < 1A
30124822
FIGURE 2. LED Current vs RIADJ
IOUT (mA)
350
500
700
1000
RIADJ (kΩ)
8.93
6.25
4.46
3.13
TABLE 2. Examples for IOUT Settings
The LED current can be set to any level in the range from 350
mA to 1A. In order to provide accurate LED current, RIADJ
should be a resistor with no more than 0.5% tolerance. If the
IADJ pin is accidentally shorted to GND (RIADJ = 0), the output
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
RIADJ. Once the current limiter is triggered, the internal power
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.
www.national.com
12
Direct download click here

 

Share Link : 

All Rights Reserved © datasheetbank.com 2014 - 2020 [ Privacy Policy ] [ Request Datasheet ] [ Contact Us ]