MAX8513 MAXIM [Maxim Integrated Products], MAX8513 Datasheet - Page 25

• Manufacturer Part Number: MAX8513
• Description: Wide-Input, High-Frequency, Triple-Output Supplies with Voltage Monitor and Power-On Reset
• Manufacturer: MAXIM [Maxim Integrated Products]

Use 6.8kΩ.
Use 4.7nF.
Use 620Ω.
Use 680pF.
Pick f
and 1/2 the switching frequency.
Use 33pF.
The modulator gain at f
The output capacitor’s ESR zero frequency is higher
than the LC double-pole frequency but lower than the
closed-loop crossover frequency. Here the modulator
already has a -20dB/decade slope; therefore, the error-
amplifier gain must have a 0dB/decade slope at f
the loop crosses over at the desired -20dB/decade
slope. The error-amplifier circuit configuration is the
same as Case 1; however, the closed-loop crossover
frequency is now between f
Figure 4.
C
Wide-Input, High-Frequency, Triple-Output Supplies
R
Case 2: Electrolytic Output Capacitor (operating at
5
I
C
11
=
C
=
P3
12
R
=
f
π
P
= 700kHz, which is the midpoint between f
4
2
2
=
=
×
R
π
R
=
(
(
G
3
×
2
2
×
lower switching frequencies, f
3
MOD fc
π
π
R
R
×
×
G
R
2
1
1
×
×
4
1
EA fZ fZ
f
PMOD
f
PMOD
C
4 7
×
×
-
( )
.
(
5
f
______________________________________________________________________________________
P
R
R
nF
×
2
I
C
1
I
-
R
with Voltage Monitor and Power-On Reset
5
=
=
=
=
×
3
2
C
2
)
4 7
6 8
×
G
π
π
13 3
is:
.
.
13 3
f
P
MOD DC
=
×
×
nF
k
.
3
.
620
Ω
P2
)
6 8
6 8
k
k
423
-1
Ω
.
×
.
Ω
(
and f
700
k
Ω
k
×
1
Ω
kHz
-
Ω
2
)
×
×
583
583
f
kHz
f
423
×
PMOD
ZESR C
17 4
P3
×
17 4
Ω
.
Ω
, as illustrated in
kHz
)
0 479
kHz
.
-1
f
=
.
2
kHz
=
609
=
ZESR
33 7
=
607
.
5 38
Ω
=
.
pF
583
pF
< f
C
ZESR
nF
, so
Ω
C
)
The equations that define the error amplifier’s poles
and zeroes (f
Case 1. However, f
crossover frequency.
The error-amplifier gain at f
And the gain of the error amplifier between f
f
Due to the underdamped (Q > 1) nature of the output LC
double pole, the error-amplifier zero frequencies must be
set less than the LC double-pole frequency to provide
adequate phase boost. Set the first zero of the error
amplifier, f
the second zero, f
Set the second pole, f
Figure 4. Case 2: Error-Amplifier Compensation Circuit (Closed-
Loop and Error-Amplifier Gain Plot)
GAIN
Z2
(dB)
V
OUT1
is:
G
EA fZ fZ
C11
Z1
R1
(
, at 1/4th the LC double-pole frequency. Set
Z1
1
f
R2
Z1
−
, f
G
R4
CLOSED-LOOP GAIN
2
Z2
EA fc
f
)
Z2
Z2
P2
, f
( )
=
V
, at the LC double-pole frequency.
P2
REF
is now lower than the closed-loop
G
P2
, at f
EA fc
, and f
f
=
P2
( )
C
ZESR
G
EA
is:
MOD fc
f
f
Z
P
f
C
2
2
R3
P3
C12
1
.
=
) are the same as for
( )
f
P3
f G
P
2
C5
MOD fc
f
Z
EA GAIN
2
V
COMP
( )
FREQUENCY
Z1
and
25