AAT2689 Analogic Corporation, AAT2689 Datasheet - Page 12

• Manufacturer Part Number: AAT2689
• Manufacturer: Analogic Corporation

Channel 1 Feedback and
Compensation Networks
The transfer function of the error amplifier is dominated
by the DC gain and the L C
tor. This output filter and its equivalent series resistor
(ESR) create a double pole at F
following equations:
12
SystemPower
Networks for Type III Voltage-Mode Control Loop.
Figure 1: AAT2689 Feedback and Compensation
Compensation
Feed-forward
Current Limit
COMP1
Network
Feedback
Table 2: AAT2689 Feedback, Feed-Forward, Compensation, and Current Limit Components
Eq. 2:
TM
C2
Eq. 1:
PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
C3
F
R1
ESR
F
LC
=
REF
=
2 · π · ESR · C
OUT
2 · π · L · C
Components
FB1
output filter of the regula-
LC
and a zero at F
1
R4
1
R3
R4
C8
R5
C2
C3
R1
C7
R2
R6
R7
R8
C8
R3
OUT
OUT
for V
R5
V
w w w . a n a l o g i c t e c h . c o m
OUT
OUT1
ESR
= 3.3V and V
in the
V
IN
V
OUT
= 12V fi xed
6.04kΩ
27.4kΩ
1.37kΩ
11.8kΩ
600kΩ
470pF
10kΩ
Open
11kΩ
56pF
22nF
1nF
= 3.3V
The feedback and compensation networks provide a
closed loop transfer function with the highest 0dB cross-
ing frequency and adequate phase margin for system
stability. Equation 3, 4, 5 and 6 relate the compensation
network’s poles and zeros to the components R1, R3,
R5, C2, C3, and C8:
Components of the feedback, feed-forward, compensa-
tion, and current limit networks need to be adjusted to
maintain the systems stability for different input and
output voltages applications as shown in Table 2.
OUT
= 5.0V.
Eq. 5:
Eq. 4:
V
IN
V
Eq. 6:
Eq. 3:
OUT
= 6V to 24V
6.04kΩ
27.4kΩ
24.3kΩ
133kΩ
330pF
470pF
220nF
499Ω
Open
56pF
F
2kΩ
2kΩ
F
= 3.3V
P1
Z2
PRODUCT DATASHEET
F
=
F
=
P2
Z1
2 · π · R
2 · π · ( R
=
=
2 · π · R
2 · π · R
AAT2689
1
1
3
1
1
1
·
+ R
1
5
V
C
C
· C
· C
IN
2
2
5
V
) · C
+ C
· C
OUT
= 6V to 24V
2
8
2689.2008.06.1.0
6.04kΩ
44.2kΩ
24.3kΩ
133kΩ
330pF
220pF
220nF
3
499Ω
Open
56pF
3
2kΩ
2kΩ
8
= 5.0V