AAT2689 Datasheet, PDF (12/20 Pages) Advanced Analogic Technologies – PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters

DATA SHEET
AAT2689
PMIC Solution for 12V Adapter Systems
with 2-Output High Performance Step-Down Converters
Channel 1 Feedback and
Compensation Networks
C3
C2
R1
C8
R5
VOUT1
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:
COMP1
R3
FB1
R4
REF
Eq.
3:
F_Z1
=
2
·
π
1
· R₁
·
C₂
Eq.
4:
F_Z2
=
2
·
π
·
1
(R₃ +
R₅)
·
C₈
Figure 1: AAT2689 Feedback and Compensation
Networks for Type III Voltage-Mode Control Loop.
The transfer function of the error amplifier is dominated
by the DC gain and the L C_OUT output filter of the regula-
tor. This output filter and its equivalent series resistor
(ESR) create a double pole at F_LC and a zero at F_ESR in the
following equations:
Eq.
1:
F_LC
=
2
·
π
·
1
L
·
C_OUT
Eq.
2:
F_ESR
=
2
·
π
·
1
ESR
·
C_OUT
1
Eq. 5: _{FP1 =}
2 · π · R₁ ·
C₂ · C₃
C₂ + C₃
Eq. 6: F_P2 =
1
2 · π · R₅ · 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.
Network
Feedback
Feed-forward
Compensation
Current Limit
Components
R3
R4
C8
R5
C2
C3
R1
C7
R2
R6
R7
R8
V_OUT = 3.3V
V_IN = 12V fixed
6.04k
27.4k
470pF
1.37k
1nF
56pF
11.8k
22nF
10k
Open
11k
600k
V_OUT = 3.3V
V_IN = 6V to 24V
6.04k
27.4k
330pF
499
470pF
56pF
24.3k
220nF
2k
Open
2k
133k
V_OUT = 5.0V
V_IN = 6V to 24V
6.04k
44.2k
330pF
499
220pF
56pF
24.3k
220nF
2k
Open
2k
133k
Table 2: AAT2689 Feedback, Feed-Forward, Compensation, and Current Limit Components
for V_OUT = 3.3V and V_OUT = 5.0V.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
12
202035A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012