amc3202 ADDtek Corp, amc3202 Datasheet - Page 9

• Manufacturer Part Number: amc3202
• Description: 1.5a 280khz Boost Regulators
• Manufacturer: ADDtek Corp

V
capacitor. Ceramic capacitors have the lowest ESR, but too low ESR may cause loop stability problems. Aluminum
Electrolytic capacitors exhibit the highest ESR, resulting in the poorest AC response. One option is to parallel a ceramic
capacitor with an Aluminum Electrolytic capacitor.
Frequency Compensation
the stability of the system. A typical compensation network, as shown in the typical application circuit, provides a
frequency response of two poles and one zero. The loop frequency compensation is performed on the output of the error
amplifier (COMP pin) with a series RC network. The main pole is formed by the series capacitor and the output
impedance of the error amplifier. The series resistor creates a zero, which improves loop stability and transient response.
A second capacitor is sometimes used to reduce the switching frequency ripple on the COMP pin.
Soft Start
prevents the COMP pin from slamming high during startup, thereby inhibiting the inductor current from rising at a high
slope. Referring to the figure shown in the following, the soft-start circuitry requires a minimum number of components
and allows the soft-start circuitry to be activated any time when the EN pin is used to restart the converter.
starts to come up, charging capacitor C
switching begins when COMP reaches the COMP threshold, typically 1.05V. Therefore, C
the circuit by limiting the voltage on the COMP pin. The soft-start time increases with the size of C
part, the cathode of D
Copyright © 2006 ADDtek Corp.
OUT
The V
ripple comes from two major sources, namely ESR of output capacitor and the charging/discharging of the output
The goal of frequency compensation is to achieve desirable transient response and DC regulation while ensuring
Through the addition of an external circuit, a soft-start function can be added to the AMC3202. Soft-start circuitry
Resistor R
Diode D
IN
f
f
f
P
Z
P
SS
ripple is determined by the product of the inductor current ripple and the ESR of input capacitor, and the
1
1
2
P
=
=
discharges C
=
and capacitors C
2
2
2
π
π
π
SS
C
C
C
1
1
P
1
P
should be connected to V
P
1
1
2
R
R
R
O
P
P
SS
when the voltage on the EN pin is low. If the shutdown function is not used with this
where, R
P1
and C
SS
V
V
through internal transistor Q, clamping the voltage at the COMP pin such that
E N
I N
P2
O
= error amplifier output resistance;
form the compensation network. At turn on, the voltage at the COMP pin
D
C
IN
S S
S S
.
9
4
3
E N
S S
4 u A
Q
C
5
P 2
V
C C
1
C O M P
R
C
P
P 1
SS
DD074_B -- AUGUST 2006
slows down the startup of
SS
AMC3202
.