LM3553 Datasheet, PDF (15/26 Pages) National Semiconductor (TI) – 1.2A Dual Flash LED Driver System with I2C Compatible

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LM3553
SNVS414B – FEBRUARY 2008 – REVISED MAY 2013
on
FEN
off
on
TX _off
flash
STATE torch
off
Safety
Timer
Figure 20. Safety Timer Terminated Pulse
on
FEN
off
on
TX _off
flash
STATE torch
off
Safety
Timer
Figure 21. TX Terminated Pulse
Application Information
INDUCTOR SELECTION
The LM3553 is designed to use a 2.2µH inductor. When the device is boosting (V_OUT > V_IN) the inductor is one of
the biggest sources of efficiency loss in the circuit. Therefore, choosing an inductor with the lowest possible
series resistance is important. Additionally, the saturation rating of the inductor should be greater than the
maximum operating peak current of the LM3553. This prevents excess efficiency loss that can occur with
inductors that operate in saturation and prevents over heating of the inductor and possible damage. For proper
inductor operation and circuit performance ensure that the inductor saturation and the peak current limit setting of
the LM3553 (2.6A or 1.8A) is greater than I_PEAK. I_PEAK can be calculated by:
I_LOAD V_OUT
I_PEAK = _K u _VIN + 'I_L
where
( ) ^VIN ^{u V}OUT ^{- V}IN
'I_L = _{2 u fSW u L u VOUT}
(1)
Manufacturer
Toko
Coilcraft
TDK
Table 4. Recommended Inductors
Part#
FDSE312-2R2M
LPS4012-222ML
VLF4014ST-2R2M1R9
L / I_SAT
2.2µH / 2.3A
2.2µH / 2.3A
2.2µH / 2.0A
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