ADP2442-EVALZ Analog Devices, ADP2442-EVALZ Datasheet - Page 23

• Manufacturer Part Number: ADP2442-EVALZ
• Description: Power Management IC Development Tools Eval board
• Manufacturer: Analog Devices
• Type: DC/DC Converters, Regulators & Controllersr
• Series: ADP2442r

Specifications of ADP2442-EVALZ

• Rohs: yes
• Tool Is For Evaluation Of: ADP2442
• Factory Pack Quantity: 1

Data Sheet
Correspondingly, there are three transfer functions:
where:
V
I
g
250 µA/V.
G
V
V
Z
forms a pole at the origin and a zero, as expressed in Equation 17.
Z
where s is the angular frequency, which can be written as s = 2πf.
The overall loop gain, H(s), is obtained by multiplying the three
transfer functions previously mentioned as follows:
When the switching frequency (f
output inductor (L), and output capacitor (C
L
m
COMP
FILT
COMP
OUT
REF
CS
is the inductor current.
is the transconductance of the error amplifier and equals
is the current sense gain and equals 2 A/V.
(s) is the impedance of the output filter and is expressed as
is the internal reference voltage and equals 0.6 V.
is the output voltage of the regulator.
Z
Z
H
V
V
V
(s) is the impedance of the RC compensation network that
V
is the comparator voltage.
COMP
FILT
COMP
COMP
OUT
I
(
OUT
I
L
s
L
(
)
(
s
(
=
s
(
)
(
)
s
(
(
s
(
s
)
s
s
)
s
g
)
)
)
)
=
=
m
=
=
=
1
×
Z
1
G
+
V
V
G
FILT
+
s
CS
OUT
REF
CS
×
s
×
(
R
×
s
R
s
R
LOAD
)
×
V
×
LOAD
V
COMP
g
OUT
C
REF
m
COMP
×
×
×
×
C
Z
C
OUT
Z
COMP
COMP
COMP
SW
), output voltage (V
(
s
(
)
s
)
×
Z
FILT
OUT
(
) values are
s
)
OUT
),
(14)
(15)
(16)
(17)
(18)
(19)
Rev. 0 | Page 23 of 36
selected, the unity crossover frequency can be set to 1/12 of the
switching frequency.
At the crossover frequency, the gain of the open-loop transfer
function is unity.
This yields Equation 21 for the RC compensation network
impedance at the crossover frequency.
Placing s = f
To ensure that there is sufficient phase margin at the crossover
frequency, place the compensator zero at 1/8 of the crossover
frequency, as shown in the following equation:
Solving Equation 21, Equation 22, and Equation 23 yields the
values for the resistor and capacitor in the RC compensation
network, as shown in Equation 24 and Equation 25.
Using these equations allows calculating the compensations for
the voltage loop.
Z
Z
COMP
COMP
H(f
C
R
f
ZERO
(
(
COMP
COMP
f
CROSSOVER
f
CROSSOVER
CROSSOVER
=
CROSSOVER
=
=
2
0
2
×
9 .
×
) = 1
π
×
)
π
)
×
=
=
2
×
R
1
×
in Equation 17,
2
COMP
f
+
ZERO
×
π
1
g
2
π
×
1
m
×
×
f
2
×
×
π
×
CROSSOVER
×
C
f
G
R
CROSSOVER
g
×
π
COMP
CS
m
COMP
f
×
CROSSOVER
×
G
f
CROSSOVER
≈
CS
×
f
×
CROSSOVER
C
C
OUT
×
OUT
8
V
R
×
COMP
×
REF
C
×
V
COMP
V
OUT
V
OUT
×
REF
ADP2442
C
COMP
(20)
(21)
(22)
(23)
(24)
(25)