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NJW4160 Datasheet(PDF) 13 Page - New Japan Radio

Part No. NJW4160
Description  Switching Regulator IC for Buck Converter
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Manufacturer  NJRC [New Japan Radio]
Direct Link  http://www.njr.co.jp/index_e.htm
Logo NJRC - New Japan Radio

NJW4160 Datasheet(HTML) 13 Page - New Japan Radio

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NJW4160
- 13 -
Ver.2014-04-01
Application Information
Inductors
Large currents flow into inductor, therefore you
must provide current capacity that does not
saturate.
Reducing L, the size of the inductor can be
smaller. However, peak current increases and
adversely affecting efficiency.
On the other hand, increasing L, peak current
can be reduced at switching time. Therefore
conversion efficiency improves, and output ripple
voltage reduces. Above a certain level, increasing
inductance windings increases loss (copper loss)
due to the resistor element.
Ideally, the value of L is set so that inductance current is in continuous conduction mode. However, as the load
current decreases, the current waveform changes from (1) CCM: Continuous Conduction Mode
(2) Critical Mode
(3) DCM: Discontinuous Conduction Mode (Fig. 6.).
In discontinuous mode, peak current increases with respect to output current, and conversion efficiency tend to
decrease. Depending on the situation, increase L to widen the load current area to maintain continuous mode.
Catch Diode
When the switch element is in OFF cycle, power stored in the inductor flows via the catch diode to the output
capacitor. Therefore during each cycle current flows to the diode in response to load current. Because diode's
forward saturation voltage and current accumulation cause power loss, a Schottky Barrier Diode (SBD), which has a
low forward saturation voltage, is ideal.
An SBD also has a short reverse recovery time. If the reverse recovery time is long, through current flows when
the switching transistor transitions from OFF cycle to ON cycle. This current may lower efficiency and affect such
factors as noise generation.
Switching Element
You should use a switching element (Pch MOSFET) that is specified for use as a switch. And select sufficiently low
RON MOSFET at less than VGS=5V because the NJW4160 OUT pin voltage is clamped V
+-5.35V (typ.).
However, when the supply voltage of the NJW4160 is low, the OUT pin voltage becomes low. You should select a
suitable MOSFET according to the supply voltage specification. (Ref. Driver section)
Large gate capacitance is a source of decreased efficiency. That is charge and discharge from gate capacitance
delays switching rise and fall time, generating switching loss.
The spike noise might occur at the time of charge/discharge of gate by the parasitic inductance element. You
should insert resistance between the OUT pin and the gate and limit the current for gate protection when gate
capacitance is small. However, it should be noted that the efficiency might decrease because the shape of waves
may become duller when resistance is too large. The last fine-tuning should be done on the actual device and
equipment.
0
Inductor
Current IL
tOFF
tON
Peak Current Ipk
Frequency
fOSC
Current
(1) Continuous
Conduction Mode
(2) Critical Mode
(3) Continuous
Conduction Mode
Fig. 6. Inductor Current State Transition
NJW4160 Application Manual
Technical Information


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