NR111E Datasheet, PDF (7/13 Pages) Sanken electric – Light Load High Efficiency

Light Load High Efficiency, 31V, Buck Regulator
NR110E series
Oct/23/2012
Typical Application Circuit
VIN
VIN_s
R1
C2
C1
GND
C9
R3
2
IN
7
EN
C10
1
BS
3
L1
SW
NR111E
R5
8
SS
GND
5
FB
ISET
R4
4
6
R7
R6
D1
Vo
Vo_s
C4 C5
GND
C1, C2: 10μF / 35V
C4, C5: 22μF / 16V
C9: 0.1μF
C10: 0.1μF
SW
R1: 1.7MΩ
L1: 10μH
R3: 22Ω
R4: 18kΩ, R5: 2.7kΩ (Vo=5.0V)
R6: 3.9kΩ
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), C9
・As large ripple current 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.
・C9 is a capacitor for soft start. In case soft start function is not used, please keep Pin No.2 open.
(4)Resistor R1, R2
・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.1.0
SANKEN ELECTRIC CO., LTD.
7
http://www.sanken-ele.co.jp