PRODUCT DATASHEET
AAT1189
TM
SwitchReg
High Voltage Step-Down Regulator
1
1
Eq. 4:
F
=
FZ2 =
Eq. 2:
ESR
2 · π · ESR · COUT
2 · π · (R3 + R4) · C7
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:
1
Eq. 5:
FP1
=
C5 · C6
2 · π · R2 ·
C5 + C6
1
Eq. 6:
FP2
=
2 · π · R3 · C7
1
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.
Eq. 3:
FZ1
=
2 · π · R2 · C5
C6
C5
C7
VOUT
R3
R2
COMP
R4
FB
R5
REF
Figure 1: AAT1189 Feedback and Compensation Networks for Type III Voltage-Mode Control Loop.
Network
Components
VOUT = 3.3V
VOUT = 5.0V
R4
R5
C7
R3
C5
C6
R2
C4
R1
R6
R7
R8
27.4kΩ
6.02kΩ
330pF
499Ω
470pF
56pF
24.3kΩ
68nF
6.34kΩ
6.34kΩ
453kΩ
Open
44.2kΩ
6.02kΩ
330pF
499Ω
220pF
56pF
24.3kΩ
68nF
6.34kΩ
6.34kΩ
649kΩ
Open
Feedback
Feed-forward
Compensation
Current Limit
Table 2: AAT1189 Feedback and Compensation Network Components for VOUT =3.3V and VOUT = 5.0V.
w w w . a n a l o g i c t e c h . c o m
12
1189.2008.06.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
