ISL88731EVAL2Z Intersil, ISL88731EVAL2Z Datasheet - Page 21

• Manufacturer Part Number: ISL88731EVAL2Z
• Description: EVALUATION BOARD FOR ISL88731
• Manufacturer: Intersil

Specifications of ISL88731EVAL2Z

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

frequency pole and a zero at F
information is added to the feedback to create a second zero
F
ISL88731 add a pole at F
divider resistors that set the DC output voltage. For a 3-cell
battery, R
following relate the compensation network’s poles, zeros
and gain to the components in Figure 23. Figure 25 shows
an asymptotic Bode plot of the DC/DC converter’s gain vs.
frequency. It is strongly recommended that F
approximately 30% of F
70% of F
ZERO2
FIGURE 24. FREQUENCY RESPONSE OF THE LC OUTPUT
FIGURE 25. ASYMPTOTIC BODE PLOT OF THE VOLTAGE
-20
-40
-60
60
40
20
0
0.1
. The low pass filter R
LC
3
= 500kΩ and R
.
FILTER
CONTROL LOOP GAIN
R
= 200mΩ
BATTERY
R
= 50mΩ
F
BATTERY
1
ZERO1
Compensator
Modulator
Loop
LC
FREQUENCY (kHz)
FILTER
FREQUENCY
4
and F
= 100kΩ. The equations
21
F2
ZERO1
10
, C
. R
ZERO2
F
ZERO2
F2
3
and R
. Inductor current
between R
F
LC
is approximately
4
100
NO BATTERY
ZERO1
are internal
F
F
ESR
FILTER
F
POLE1
S2
is
and
1000
ISL88731
Compensation Break Frequency Equations
F
F
F
F
F
F
Choose R
from Equation 29.
R
Next, choose C
calculated from Equation 30.
C
PCB Layout Considerations
Power and Signal Layers Placement on the PCB
As a general rule, power layers should be close together,
either on the top or bottom of the board, with signal layers on
the opposite side of the board. As an example, layer
arrangement on a 4-layer board is shown below:
Separate the power voltage and current flowing path from
the control and logic level signal path. The controller IC will
stay on the signal layer, which is isolated by the signal
ground to the power signal traces.
Component Placement
The power MOSFET should be close to the IC so that the
gate drive signal, the LGATE, UGATE, PHASE, and BOOT,
traces can be short.
1. Top Layer: signal lines, or half board for signal lines and
2. Signal Ground
3. Power Layers: Power Ground
4. Bottom Layer: Power MOSFET, Inductors and other
ZERO1
ZERO2
LC
FILTER
POLE1
ESR
VCOMP
VCOMP
the other half board for power lines
Power traces
=
=
-------------------------------
(
2π L C
------------------------------------------- -
(
=
=
=
=
2π C
=
=
VCOMP
--------------------------------------------------- -
(
---------------------------------------------------------------------- -
(
⎛
⎜
⎝
------------------------------------------ -
(
2π R
1
(
2π C
---------------------------------------------- -
2π R
-------------------------------------------------------------------------- -
(
2π R
⋅
0.7 F
0.3 F
⋅
⋅
⋅
o
⋅
⋅
1
R
VCOMP
o
⋅
⋅
⋅
VCOMP
)
SENSE
VCOMP
R
SENSE
F2
1
equal or lower than the value calculated
LC
LC
ESR
1
⋅
)
)
C
⋅
⋅
1
F2
)
(
(
equal or higher than the value
2π C
1
2π R
⋅
⋅
⋅
C
)
C
R
o
⋅
⋅
o
1COMP
)
⎞
⎟
⎠
o
VCOMP
⋅
⎛
⎜
⎝
⋅
-------------------- -
R
R
4
SENSE
R
)
+
4
R
)
3
⎞
⎟
⎠
)
⋅
⎛
⎝
⋅
gm1
----------- -
⎛
⎝
----------- -
gm1
5
5
⎞
⎠
⎞
⎠
⋅
February 8, 2011
⎛
⎜
⎝
R
-------------------- -
3
(EQ. 23)
(EQ. 24)
(EQ. 25)
(EQ. 26)
(EQ. 27)
(EQ. 28)
R
(EQ. 29)
(EQ. 30)
+
FN9258.2
4
R
4
⎞
⎟
⎠