AAT2687 Datasheet, PDF (11/20 Pages) Advanced Analogic Technologies – PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters

DATA SHEET
AAT2687
PMIC Solution for 24V Systems
with 2 High Performance Step-Down Converters
Channel 1 Feedback and
Compensation Networks
C6
C5
R1
C10
R5
VOUT1
COMP1
R3
FB1
R4
REF
Figure 1: AAT2687 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
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, C5, C6, and C10:
Eq.
3:
F_Z1
=
2
·
π
1
· R₁
·
C₅
Eq.
4:
F_Z1
=
2
·
π
·
1
(R₃ +
R₅)
·
C₁₀
1
Eq. 5: _{FP1 =}
2 · π · R₁ ·
C₅ · C₆
C₅ + C₆
Eq. 6: F_P2 =
1
2 · π · R₅ · C₁₀
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 1.
Channel 1 Thermal Protection
The AAT2687 has an internal thermal protection circuit
which will turn on when the device die temperature
exceeds 135°C. The internal thermal protection circuit
will actively turn off the high side regulator output
device to prevent the possibility of over temperature
damage. The Buck regulator output will remain in a
shutdown state until the internal die temperature falls
back below the 135°C trip point. The combination and
interaction between the short circuit and thermal protec-
tion systems allows the Buck regulator to withstand
indefinite short-circuit conditions without sustaining per-
manent damage.
Network
Feedback
Feed-forward
Compensation
Current Limit
Components
R4
R3
C10
R5
C5
C6
R1
C4
R2
R6
R7
R8
V_OUT =3.3V
V_IN = 6V-24V
1.96kΩ
8.87kΩ
2.2nF
453Ω
2.2nF
150pF
3.92kΩ
220nF
2kΩ
Open
2kΩ
165kΩ
V_OUT = 5.0V
V_IN = 6V-24V
1.96kΩ
8.87kΩ
2.2nF
453Ω
2.2nF
150pF
3.92kΩ
220nF
2kΩ
Open
2kΩ
165kΩ
Table 1: AAT2687 Feedback, 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
202033A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012
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