EVALA5970AD STMicroelectronics, EVALA5970AD Datasheet - Page 17

• Manufacturer Part Number: EVALA5970AD
• Description: BOARD EVAL FOR A5970AD REG
• Manufacturer: STMicroelectronics

Specifications of EVALA5970AD

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.235 ~ 35V
• Current - Output: 1A
• Voltage - Input: 4 ~ 36V
• Regulator Topology: Buck
• Frequency - Switching: 500kHz
• Board Type: Fully Populated
• Utilized Ic / Part: A5970AD
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

A5970AD
7.1
Error amplifier and compensation network
The output L-C filter of a step-down converter contributes with 180 degrees phase shift in
the control loop. For this reason a compensation network between the COMP pin and
GROUND is added. The simplest compensation network together with the equivalent circuit
of the error amplifier are shown in
open loop gain. CP does not significantly affect system stability but it is useful to reduce the
noise of the COMP pin.
The transfer function of the error amplifier and its compensation network is:
Equation 2
Where A
Figure 10. Error amplifier equivalent circuit and compensation network
The poles of this transfer function are (if C
Equation 3
Equation 4
A
0
vo
s ( )
= G
=
m
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
s
2
· R
•
R
o
0
•
(
C
0
+
C
Doc ID 14661 Rev 4
p
F
) R
•
P2
Figure
c
F
=
•
P1
------------------------------------------------------- -
2 π
A
C
•
V0
c
=
10. R
+
c
•
-------------------------------------
2 π
•
s
>> C
(
•
R
•
1
c
(
+
R
C
1
•
•
s
0
1
0
(
R
and C
C
•
+C
•
0
0
R
C
•
+
P
c
c
C
):
•
C
+
c
C
C
p
R
)
introduce a pole and a zero in the
c
0
)
•
(
C
0
+
C
p
)
+
R
c
Closing the loop
•
C
c
)
+
1
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