AMC3100 Datasheet, PDF (8/10 Pages) ADDtek Corp – 1.5MHz, 600mA SYNCHRONOUS STEP-DOWN CONVERTER

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):
V_OUT
= 0.6V ⎜⎛1 +
⎝
R1 _⎟⎞
R2 _⎠
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:
R2 =
R1
⎜⎛ ^{V OUT} − 1⎟⎞
⎝ ^0.6V ⎠
VIN＝2.5V to 5.5V
Rectified
CIN
4.7uF
VOUT＝2.5V
L1
2.2uH
R1 C1
1MΩ 22pF
VIN
SW
FB
AMC3100-ADJ R2
316KΩ
RUN
GND
COUT
10uF
Figure 1
Table 1- Resistor Selection vs. Adjust Output Voltage.
V_OUT
1.2V
1.5V
1.8V
2.5V
R1
1MΩ, 1%
1MΩ, 1%
1MΩ, 1%
1MΩ, 1%
R2
1MΩ, 1%
667KΩ, 1%
500KΩ, 1%
316KΩ, 1%
3.3V
1MΩ, 1%
222KΩ, 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
= ^VOUT
fL
⎜⎜⎝⎛¹
−
V_OUT
V_IN
⎟⎟⎠⎞
Where, f = operating frequency, andΔI_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:
∆V_OUT
≅
∆I _{L ⎜⎜⎝⎛} ESR +
1
8 fC_OUT
⎟⎟⎠⎞
Where, C_OUT = output capacitance.
Copyright © 2006 ADDtek Corp.
8
DD010_A -- JUNE 2006