ISL6526EVAL1 Intersil, ISL6526EVAL1 Datasheet - Page 10

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ISL6526EVAL1

Manufacturer Part Number
ISL6526EVAL1
Description
EVALUATION BOARD SOIC ISL6526
Manufacturer
Intersil
Datasheet

Specifications of ISL6526EVAL1

Main Purpose
DC/DC, Step Down
Outputs And Type
1, Non-Isolated
Voltage - Output
2.5V
Current - Output
5A
Voltage - Input
3.3 ~ 5V
Regulator Topology
Buck
Frequency - Switching
300kHz
Board Type
Fully Populated
Utilized Ic / Part
ISL6526
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Power - Output
-
the PHASE node. The PWM wave is smoothed by the output
filter (L
The modulator transfer function is the small-signal transfer
function of V
Gain and the output filter (L
break frequency at f
the modulator is simply the input voltage (V
peak-to-peak oscillator voltage ΔV
Modulator Break Frequency Equations
f
The compensation network consists of the error amplifier
(internal to the ISL6526, ISL6526A) and the impedance
networks Z
network is to provide a closed loop transfer function with the
highest 0dB crossing frequency (f
margin. Phase margin is the difference between the closed
loop phase at f
the compensation network’s poles, zeros and gain to the
components (R
these guidelines for locating the poles and zeros of the
compensation network:
ESR
1. Pick gain (R
f
ΔV
LC
FIGURE 5. VOLTAGE-MODE BUCK CONVERTER
OSC
=
=
----------------------------------------- -
2π x
O
------------------------------------------ -
2π x ESR x C
and C
OSC
IN
OUT
L
1
COMPARATOR
1
COMPENSATION DESIGN
O
and Z
O
0dB
ERROR
AMP
1
DETAILED COMPENSATION COMPONENTS
V
ISL6526, ISL6526A
x C
2
).
, R
/V
E/A
/R
PWM
E/A
and 180°. Equations 6, 7, 8 and 9 relate
O
FB
2
1
Z
+
LC
O
-
) for desired converter bandwidth.
, R
FB
-
+
COMP
. The goal of the compensation
. This function is dominated by a DC
C
and a zero at f
REFERENCE
3
2
REFERENCE
, C
C
+
O
-
1
1
10
DRIVER
, C
DRIVER
R
and C
Z
2
IN
2
, and C
0dB
OSC
FB
O
Z
), with a double pole
) and adequate phase
ESR
FB
.
PHASE
(PARASITIC)
3
V
C
) in Figure 5. Use
. The DC Gain of
IN
3
IN
L
Z
R
) divided by the
IN
O
1
R
ESR
3
C
O
V
OUT
ISL6526, ISL6526A
(EQ. 4)
(EQ. 5)
V
OUT
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 previously mentioned 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
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
loop. A stable control loop has a gain crossing with
-20dB/decade slope and a phase margin greater than
45°. Include worst case component variations when
determining phase margin.
f
f
f
f
P1
2. Place first zero below filter’s double pole (~75% f
3. Place second zero at filter’s double pole.
4. Place first pole at the ESR zero.
5. Place second pole at half the switching frequency.
6. Check gain against error amplifier’s open-loop gain.
7. Estimate phase margin - repeat if necessary.
FIGURE 6. ASYMPTOTIC BODE PLOT OF CONVERTER GAIN
Z1
Z2
P2
FB
100
-20
-40
-60
80
60
40
20
=
=
=
=
and Z
0
-------------------------------------------------------- -
2π x R
--------------------------------- -
------------------------------------------------------ -
2π x R
----------------------------------- -
2π x R
10
MODULATOR
20
×
IN
log
R
(
GAIN
1
1
2
2
to provide a stable, high bandwidth (BW) overall
3
1
×
100
x
x C
R2
------- -
R1
1
+
1
f
C
Z1
R
2
C
--------------------- -
C
3
3
1
1
) x C
x C
+
f
C
LC
1k
2
2
3
f
Z2
FREQUENCY (Hz)
f
ESR
10k
f
P1
100k
f
P2
P2
with the capabilities
1M
ERROR AMP GAIN
COMPENSATION
November 24, 2008
20
OPEN LOOP
LOOP GAIN
log
10M
LC
GAIN
----------------- -
V OSC
FN9055.10
(EQ. 6)
(EQ. 7)
(EQ. 8)
(EQ. 9)
).
V
IN

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