A5974ADTR STMicroelectronics, A5974ADTR Datasheet - Page 20

• Manufacturer Part Number: A5974ADTR
• Description: IC REG SW STEP-DOWN 2A 8SOIC
• Manufacturer: STMicroelectronics
• Series: -r
• Type: Step-Down (Buck), PWMr

Specifications of A5974ADTR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.235 V ~ 35 V
• Current - Output: 2A
• Frequency - Switching: 500kHz
• Voltage - Input: 4 V ~ 36 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width) Exposed Pad
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 497-11423-2

Closing the loop
7.1
20/49
Error amplifier and compensation network
The output LC filter of a step-down converter contributes with 180-degree 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
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
vo
A
0
= G
s ( )
m
=
· R
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -
s
2
⋅
o
R
0
⋅
(
C
0
+
Figure
Doc ID 018762 Rev 1
C
p
F
) R
P2
⋅
10. R
c
=
F
⋅
P1
C
--------------------------------------------------- -
2 π R
A
c
⋅ ⋅
V0
C
=
+
c
and C
s
⋅
--------------------------------- -
2 π R
>> C
(
⋅
⋅
1
(
c
R
+
⋅
1
⋅
(
0
s
1
0
C
C
⋅
+C
⋅
0
0
C
R
introduce a pole and a zero in the open
⋅
+
c
c
P
C
+
C
⋅
):
c
C
R
p
)
c
0
)
⋅
(
C
0
+
C
p
)
+
R
c
⋅
C
c
)
+
1
A5974AD