NJU6052 데이터 시트보기 (PDF) - Japan Radio Corporation
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NJU6052 Datasheet PDF : 23 Pages
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NJU6052
(9) APPLICATIONS INFORMATION
(9-1) PWM DUTY and LED CURRENT
The average LED current is programmed with the single resistor RLED and the PWM duty, as shown in
Formula (4).
I LED(avg)
=
I LED(max)
⋅
DUTY
100
I LED(max)
=
VREF
RLED
--- Formula (4)
(9-2) INDUCTOR SELECTION
Formula (5) is used to choose an optimum inductor, as shown below:
L
=
2
VOUT
η
− VIN ⋅
I2
LIMIT
⋅
f OSC
I LED
--- Formula (5)
η
: Power conversion efficiency (= 0.7 to 0.8)
The power supply voltage VIN may fluctuate in battery-powered applications. For this reason, the minimum
voltage should be applied to the VIN in Formula (5).
The NJU6052 has about 200ns of delay time (TDELAY), which is defined as the period from the reach of the
current limit 720mA to the MOS-switch-off. The TDELAY may cause an overshoot-inductor-current, which is called
the peak current IL,PEAK, and calculated by Formula (6). Therefore, it is recommended that an inductor with a
rating twice of the IL,PEAK and a low DCR (DC resistance) be used for high efficiency.
I L,PEAK
=
I LIMIT
+
VIN(max)
L
−
VDS
⋅ TDELAY
--- Formula (6)
VDS
: Drain-Source voltage of the MOS switch (=ILIMIT*RON)
VIN(MAX) : Maximum of VIN Voltage
(9-3) DIODE SELECTION
A Schottky diode with a low forward-voltage-drop and a fast switching-speed is ideal. And the diode must
have a rating greater than the output voltage and the output current in the system.
(9-4) CAPACITOR SELECTION
A low ESR (Equivalent Series Resistance) capacitor should be used at the output to minimize output ripples. A
multi-layer ceramic capacitor is the best selection for the NJU6052 application because of not only the low ESR
but its small package. A ceramic capacitor as the input decoupling-capacitor is also recommended and should be
placed as close to the NJU6052 as possible.
Ver.2004-02-26
- 11 -
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