參數(shù)資料
型號: ISL6532ACRZ
廠商: INTERSIL CORP
元件分類: 穩(wěn)壓器
英文描述: PWM Control Circuit 16-SOIC 0 to 70
中文描述: 3 A SWITCHING CONTROLLER, 280 kHz SWITCHING FREQ-MAX, PQCC28
封裝: 6 X 6 MM, ROHS COMPLIANT, PLASTIC, MO-220VJJC, QFN-28
文件頁數(shù): 12/16頁
文件大?。?/td> 504K
代理商: ISL6532ACRZ
12
The PWM wave is smoothed by the output filter (L
O
and C
O
).
The modulator transfer function is the small-signal transfer
function of V
OUT
/V
E/A
. This function is dominated by a DC
Gain and the output filter (L
O
and C
O
), with a double pole
break frequency at F
LC
and a zero at F
ESR
. The DC Gain of
the modulator is simply the input voltage (V
IN
) divided by the
peak-to-peak oscillator voltage
V
OSC
.
Modulator Break Frequency Equations
The compensation network consists of the error amplifier
(internal to the ISL6532A) and the impedance networks Z
IN
and Z
FB
. The goal of the compensation network is to provide
a closed loop transfer function with the highest 0dB crossing
frequency (f
0dB
) and adequate phase margin. Phase margin
is the difference between the closed loop phase at f
0dB
and
180 degrees. The equations below relate the compensation
network’s poles, zeros and gain to the components (R
1
, R
2
,
R
3
, C
1
, C
2
, and C
3
) in Figure 5. Use these guidelines for
locating the poles and zeros of the compensation network:
1. Pick Gain (R
2
/R
1
) for desired converter bandwidth.
2. Place 1
ST
Zero Below Filter’s Double Pole (~75% F
LC
).
3. Place 2
ND
Zero at Filter’s Double Pole.
4. Place 1
ST
Pole at the ESR Zero.
5. Place 2
ND
Pole at Half the Switching Frequency.
6. Check Gain against Error Amplifier’s Open-Loop Gain.
7. Estimate Phase Margin - Repeat if Necessary.
Compensation Break Frequency Equations
Figure 6 shows an asymptotic plot of the DC-DC converter’s
gain vs. frequency. The actual Modulator Gain has a high
gain peak due to the high Q factor of the output filter and is
not shown in Figure 6. Using the above guidelines should
give a Compensation Gain similar to the curve plotted. The
open loop error amplifier gain bounds the compensation
gain. Check the compensation gain at F
P2
with the
capabilities of the error amplifier. The Closed Loop Gain is
constructed on the graph of Figure 6 by adding the
Modulator Gain (in dB) to the Compensation Gain (in dB).
This is equivalent to multiplying the modulator transfer
function to the compensation transfer function and plotting
the gain.
The compensation gain uses external impedance networks
Z
FB
and Z
IN
to provide a stable, high bandwidth (BW) overall
loop. A stable control loop has a gain crossing with
-20dB/decade slope and a phase margin greater than 45
degrees. Include worst case component variations when
determining phase margin.
Feedback Compensation - AGP LDO Controller
Figure 7 shows the AGP LDO power and control stage. This
LDO, which uses a MOSFET as the linear pass element,
requires feedback compensation to insure stability of the
system. The LDO requires compensation because of the
output impedance of the error amplifier.
FIGURE 5. VOLTAGE-MODE BUCK CONVERTER
COMPENSATION DESIGN AND OUTPUT
VOLTAGE SELECTION
V
DDQ
REFERENCE
L
O
C
O
ESR
V
IN
V
OSC
ERROR
AMP
PWM
DRIVER
(PARASITIC)
Z
FB
+
-
REFERENCE
R
1
R
3
R
2
C
3
C
1
C
2
COMP
V
DDQ
FB
Z
FB
ISL6532A
Z
IN
COMPARATOR
DRIVER
DETAILED COMPENSATION COMPONENTS
PHASE
V
E/A
+
-
+
-
Z
IN
OSC
R
4
V
DDQ
0.8
1
R
1
R
4
------
+
×
=
FLC
2
π
x
LO
x
CO
------------------------------------------
=
FESR
ESR
x
CO
------ x
=
F
Z1
R
2
x C
2
------ x
=
F
Z2
+
2
x
R
1
R
3
x
C
3
------------------------------------------------------
=
F
P1
2
π
x
R
2
x
C
2
1
C
2
+
---------------------
---------------------------------------- x
=
F
P2
x
R
3
x
C
3
-----------------------------------
=
100
80
60
40
20
0
-20
-40
-60
F
P1
F
Z2
10M
1M
100K
10K
1K
100
10
OPEN LOOP
ERROR AMP GAIN
F
Z1
F
P2
20LOG
(R
2
/R
1
)
F
LC
F
ESR
COMPENSATION
GAIN
CLOSED LOOP
GAIN
G
FREQUENCY (Hz)
20LOG
(V
IN
/
V
OSC
)
MODULATOR
GAIN
FIGURE 6. ASYMPTOTIC BODE PLOT OF CONVERTER GAIN
ISL6532A
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