AMC3100
APPLICATION INFORMATION
The basic AMC3100 application circuit is shown in Figure 1. External component selection is driven by load
requirement:
Adjustable Output Voltage:
In adjustable version, the output voltage is set by the below formula (1):
R
1
⎞
⎛
V
OUT
=
0 .6
V
⎜
1
+
⎟
R
2
⎠
⎝
R
1
⎛
V
OUT
⎞
−
1
⎟
⎜
⎝
0 . 6
V
⎠
0.6V≦V
OUT
≦5.5V
(1)
The external resistor divider sets the output voltage (see figure 1). Choose R1 around 1MΩ, R2 is then given by:
R
2
=
V
OUT
＝2.5V
V
IN
＝2.5V
to 5.5V
Rectified
L1
2.2uH
Table 1- Resistor Selection vs. Adjust Output Voltage.
R1
1MΩ
C1
22pF
V
OUT
1.2V
1.5V
C
OUT
10uF
R1
1M
Ω
, 1%
1M
Ω
, 1%
1M
Ω
, 1%
1M
Ω
, 1%
1M
Ω
, 1%
R2
1M
Ω
, 1%
667K
Ω
, 1%
500K
Ω
, 1%
316K
Ω
, 1%
222K
Ω
, 1%
VIN
SW
FB
AMC3100-ADJ
4.7uF
R2
316KΩ
C
IN
RUN
1.8V
2.5V
3.3V
GND
Figure 1
Inductor selection:
For most applications, the value of the inductor will fall in the range of 1uH to 4.7uH. Its value is chosen
based on the desired ripple current. Large value inductors lower ripple current, and small value inductors result in
higher ripple currents.
Higher V
IN
or V
OUT
also increases the ripple current as shown in the formula (2):
∆
I
L
=
V
OUT
fL
⎛
V
OUT
⎜
1
−
⎜
V
IN
⎝
⎞
⎟
⎟
⎠
Where,
f
= operating frequency, and
Δ
I
L
= ripple current in the inductor.
(2)
C
OUT
selection:
The output capacitor keeps output voltage ripple small and ensures regulation loop stable. The output capacitor
impedance shall be low in switching frequency. The output rippleΔV
OUT
approximately:
⎛
1
∆
V
OUT
≅ ∆
I
L
⎜
ESR
+
⎜
8
fC
OUT
⎝
⎞
⎟
⎟
⎠
Where, C
OUT
= output capacitance.
8
DD010_A --
JUNE 2006
Copyright
©
2006 ADDtek Corp.
ADDTEK [ ADDTEK CORP ]
