MIC4680_08 Datasheet, PDF (10/15 Pages) Micrel Semiconductor – 1A 200kHz SuperSwitcher Buck Regulator

Micrel, Inc.
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:
V_OUT
=
V_REF
⎜⎛
⎝
R1
R2
+
1⎟⎞
⎠
R1
=
R2_{⎜⎜⎝⎛}
V_OUT
V_REF
− 1_{⎟⎟⎠⎞} ,
R2 =
R1
V_{OUT − 1}
V_REF
V_REF = 1.23V
MIC4680
V_IN
MIC4680BM
2 _IN
SW ³
L1
C_IN
R1
SHUTDOWN
ENABLE
1 _SHDN
FB ⁴
GND
D1
R2
5–8
V_OUT
C_OUT
Figure 1a. Adjustable Regulator Circuit
V_OUT
1.8V
2.5V
3.3V
5.0V
6.0V
R1*†
3.01k
3.01k
3.01k
3.01k
3.01k
R2*†
6.495k
2.915k
1.788k
982Ω
776Ω
C_IN
15µF 35V
AVX TPSE156035R0200
D1
2A 60V Schottky
B260A Vishay-Diode, Inc***
or
SS26 General Semiconductor
L1
68µH 1.5A
Coiltronics UP2B-680
or
Sumida CDRH125-680MC**
or
Sumida CDRH124-680MC**
* 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
C_OUT
220µF 10V
AVX TPSE227010R0060
March 2008
10
M9999-032808