Datasheet

Micrel, Inc. MIC4680
March 2008 10
M9999-032808
Applications Information
Adjustable Regulators
Adjustable regulators require a 1.23V feedback signal.
Recommended voltage-divider resistor values for
common output voltages are included in Figure 1b.
For other voltages, the resistor values can be
determined using the following formulas:
⎟
⎠
⎞
⎜
⎝
⎛
+= 1
R2
R1
VV
REFOUT
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−= 1
V
V
R2R1
REF
OUT
,
1
V
V
R1
2R
REF
OUT
−
=
V
REF
= 1.23V
SW
L1
IN
FB
GND
SHDN C
OUT
R1
R2D1
V
OUT
MIC4680BM
C
IN
V
IN
SHUTDOWN
ENABLE
5–8
4
32
1
Figure 1a. Adjustable Regulator Circuit
V
OUT
R1*† R2*† C
IN
D1 L1 C
OUT
1.8V 3.01k 6.495k
2.5V 3.01k 2.915k
3.3V 3.01k 1.788k
5.0V 3.01k 982Ω
6.0V 3.01k 776Ω
15µF 35V
AVX TPSE156035R0200
2A 60V Schottky
B260A Vishay-Diode, Inc***
or
SS26 General Semiconductor
68µH 1.5A
Coiltronics UP2B-680
or
Sumida CDRH125-680MC**
or
Sumida CDRH124-680MC**
220µF 10V
AVX TPSE227010R0060
* All resistors 1%
** Shielded magnetics for low RFI applications
*** Vishay-Diode, Inc. (805) 446-48600
† Nearest available resistor values
Figure 1b. Recommended Components for Common Output Voltages