AAT1189 Datasheet, PDF (12/19 Pages) Advanced Analogic Technologies – High Voltage Step-Down Regulator

SwitchReg^TM
Eq.
2:
F_ESR
=
2
·
π
·
1
ESR
·
C_OUT
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. Equations 3, 4, 5 and 6 relate the compensa-
tion network’s poles and zeros to the components R2,
R3, R4, C5, C6, and C7:
Eq.
3:
F_Z1
=
2
·
π
1
· R₂
·
C₅
PRODUCT DATASHEET
AAT1189
High Voltage Step-Down Regulator
Eq.
4:
F_Z2
=
2
·
π
·
1
(R₃ +
R₄)
·
C₇
1
Eq. 5: _{FP1 =}
2 · π · R₂ ·
C₅ · C₆
C₅ + C₆
Eq. 6: F_P2 =
1
2 · π · R₃ · C₇
Components of the feedback, feed forward, compensa-
tion, and current limit networks need to be adjusted to
maintain system stability for different input and output
voltage applications as shown in Table 2.
C6
C5
R2
C7
R3
V_OUT
COMP
R4
FB
R5
REF
Figure 1: AAT1189 Feedback and Compensation Networks for Type III Voltage-Mode Control Loop.
Network
Feedback
Feed-forward
Compensation
Current Limit
Components
R4
R5
C7
R3
C5
C6
R2
C4
R1
R6
R7
R8
V_OUT = 3.3V
27.4kΩ
6.02kΩ
330pF
499Ω
470pF
56pF
24.3kΩ
68nF
6.34kΩ
6.34kΩ
453kΩ
Open
V_OUT = 5.0V
44.2kΩ
6.02kΩ
330pF
499Ω
220pF
56pF
24.3kΩ
68nF
6.34kΩ
6.34kΩ
649kΩ
Open
Table 2: AAT1189 Feedback and Compensation Network Components for V_OUT =3.3V and V_OUT = 5.0V.
12
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1189.2008.06.1.0