NR120E Datasheet, PDF (7/13 Pages) Sanken electric – 3A, 18V, Buck Regulator

3A, 18V, Buck Regulator
NR120E series
Nov./10/2015
External Components Design Guide
(1)Diode D1
・The schottky-barrier diode must be used for D1. If other diodes like fast recovery diodes are used, IC may be
damaged because of the reverse voltage applied by the recovery voltage or ON voltage.
(2)Choke coil L1
・If the winding resistance of the choke coil is too high, the efficiency may go down to the extent that it is out of the rating.
・As the start current of the over current protection is approximately 4A, attention must be paid to the heating of the choke
coil by the magnetic saturation due to overload or short-circulated load.
(3)Capacitor C1(C2), C4(C5), C7
・As large ripple currents across C1 (C2) and C4 (C5), capacitors with high frequency and low impedance for SMPS must
be used. Especially when the impedance of C4 (C5) is high, the switching waveform may not be normal at low
temperature.
・C7 is a capacitor for soft start. A soft-start controls the over-shoot of the output voltage rising and rush current.
(4)Resistor R4, R5, R6
・R4, R5, R6 are resistor to the Output Voltage. I_ADJ is required to set to 0.2mA.
R4, R5, R6 are calculated by the equation (1).
R4  R5  ^{Vo  VFB}  ^{Vo  0.8} ， R6  ^VFB  ^0.8 ≒ 4.0k
I _ADJ
0.2 10^3
IADJ _{0.2 10}3
------- (1)
In order to have optimum operating condition, each component must be connected with the minimum distance.
Rev.1.1
SANKEN ELECTRIC CO., LTD.
7
http://www.sanken-ele.co.jp