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TB62731FUG Fiches technique(PDF) 7 Page - Marktech Corporate

No de pièce TB62731FUG
Description  Step-up DC-DC Converter for White LED Driver
Download  17 Pages
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Fabricant  MARKTECH [Marktech Corporate]
Site Internet  http://www.marktechopto.com
Logo MARKTECH - Marktech Corporate

TB62731FUG Fiches technique(HTML) 7 Page - Marktech Corporate

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TB62731FUG
2004-09-14
7
Standby Operation
The SHDN pin is used to set normal or standby operation. When SHDN is set to Low, the operation is
standby; when the pin is High, the LED is turned on. Current consumption in Standby Mode is 1 µA (max).
Output-side capacitor setting
When the output-side capacitor (C2) = 0.1 µF, the peak current to be supplied to LEDs is expected to be the
set current +5~+8 mA.
When C2 = 0.01 µF, the peak current is expected to be the set current +20~30 mA; when C2 = 1 µF, it is the set
current +2~3 mA. Toshiba recommend C2 = 1 µF or more considering the LED max If.
The IC is used only for lighting LEDs. The IC does not finely control output current ripples. This is because
eliminating ripples is considered unnecessary as the LED emittance is recognized as the integral amount.
External inductance setting
The minimum external inductance is calculated as follows:
L (µH) = ((K × Po) − VIN min × Io) × (1/fOSC min) × 2 × (1/Ip min × Ip min) . . . formula 2
The above parameters are described below:
Po: output power (power required by LED load)
Po (W) = Vf LED × If LED + Vf schottky × If LED + R_sens × If LED × If LED
LED forward current: If LED (mA) = Set current: Io (mA), LED forward voltage: Vf LED (V),
schottky diode forward voltage: Vf schottky (V),
Setting resistance: R_sens (Ω)
VIN min (V): minimum input voltage (battery voltage)
If the input voltage includes a resistance component, take the voltage drop into consideration for the
minimum input voltage.
The input current IIN is roughly estimated as follows:
IIN (mA) = VfLED × Io × (1/η) × (1/VIN) . . . formula 3
When min VIN = 3.2 (V), VfLED = 16 (V), Io = 18 (mA), and η >= 75 (%), then IIN = 0.12 (mA). As a result,
the voltage drops by 1.2 V due to the 1-Ω DC resistance component. Because the IC’s minimum VCC =
3.0 V, the minimum VIN is 3.12 V (VIN >= 3.12 V).
Io (A): Mean current value set according to resistance R_sens (Ω)
fOSC (Hz): Switching frequency of internal MOS transistor
Specified values for fOSC (kHz): 275 min, 350 typ., 475 max
Ip (A): Peak current value supplied to external inductor
Specified values for Ip (A): 230 min, 240 typ., 270 max
K: Margin of output power K = 1.1~1.3
The ideal condition is to give 1.05 to 1.3 times the output power Po as the input power.
The loss of the IC is assumed to be included in the margin.
If K is too large, it may not be possible for the current characteristic to be the specified value. Note that
K > 1.


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