apu3073o APEC, apu3073o Datasheet - Page 12

• Manufacturer Part Number: apu3073o
• Description: Synchronous Pwm Controller With Over-current Protection / Ldo Controller
• Manufacturer: APEC

APU3073
In such configuration, the transfer function is given by:
The error amplifier gain is independent of the transcon-
ductance under the following condition:
By replacing Z
former function can be expressed as:
As known, transconductance amplifier has high imped-
ance (current source) output, therefore, consider should
be taken when loading the E/A output. It may exceed its
source/sink output current capability, so that the ampli-
fier will not be able to swing its output voltage over the
necessary range.
The compensation network has three poles and two ze-
ros and they are expressed as follows:
H(s) =
H(s) dB
F
F
F
g
V
Figure 12 - Compensation network with local
m
P1
P2
P3
V
OUT
Z
e
sR
Z
f
= 0
=
=
feedback and its asymptotic gain plot.
IN
>> 1
Gain(dB)
6
=
2p3R
(C
2p3R
R
C
1
8
1 + g
12
1 - g
10
+C
IN
F
V
1
Z
and Z
and
8
11
1
7
OUT
3C
m
3
m
)
Z
Z
3
R
R
(
IN
f
6
5
[
10
1
f
C
F
C
1+sR
according to Figure 7, the trans-
Vp=V
(1+sR
Z
12
12
g
2
Fb
3C
m
+C
Z
IN
7
11
REF
11
(
>>1
7
)
C
C
R
C
11
12
7
F
)3[1+sC
12
E/A
+C
P
C
2p3R
2
11
11
C
)]
12
1
3(1+sR
F
7
10
C
3C
P
---(20)
Comp
(R
3
11
6
Frequency
12
+R
8
8
Z
)]
C
Ve
f
10
)
Cross Over Frequency:
The stability requirement will be satisfied by placing the
poles and zeros of the compensation network according
to following design rules. The consideration has been
taken to satisfy condition (20) regarding transconduc-
tance error amplifier.
These design rules will give a crossover frequency ap-
proximately one-tenth of the switching frequency. The
higher the band width, the potentially faster the load tran-
sient speed. The gain margin will be large enough to
provide high DC-regulation accuracy (typically -5dB to -
12dB). The phase margin should be greater than 458 for
overall stability.
Based on the frequency of the zero generated by ESR
versus crossover frequency, the compensation type can
be different. The table below shows the compensation
type and location of crossover frequency.
Type II (PI)
Type III (PID)
Method A
Type III (PID)
Method B
Detail information is dicussed in application Note AN-
1043 which can be downloaded from the IR Web-Site.
Compensator
Table - The compensation type and location of zero
F
F
F
Where:
V
V
Lo = Output Inductor
Co = Total Output Capacitors
Type
Z1
Z2
O
IN
OSC
= R
=
=
= Maximum Input Voltage
= Oscillator Ramp Voltage
2p3R
2p3C
7
3C
10
1
Crossover Frequency
7
3
10
crossover frequency.
3C
F
F
F
3(R
Location of Zero
PO
1
PO
PO
V
V
11
< F
OSC
< F
< F
IN
6
+ R
3
O
ZO
O
(F
< f
< F
< F
2p3Lo3Co
O
8
)
)
S
/2 < F
ZO
O
< f
< f
1
2p3C
S
S
/2
/2
ZO
1
10
Electrolytic,
3R
Capacitor
Tantalum,
Tantalum
Ceramic
Ceramic
Typical
Output
---(21)
6
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