ISL97645 Intersil Corporation, ISL97645 Datasheet - Page 10

• Manufacturer Part Number: ISL97645
• Description: Boost VON Slice VCOM
• Manufacturer: Intersil Corporation

Inductor
The boost inductor is a critical part which influences the
output voltage ripple, transient response, and efficiency.
Values of 3.3µH to 10µH are used to match the internal
slope compensation. The inductor must be able to handle
the following average and peak current:
Some inductors are recommended in Table 3.
Rectifier Diode
A high-speed diode is necessary due to the high switching
frequency. Schottky diodes are recommended because of
their fast recovery time and low forward voltage. The reverse
voltage rating of this diode should be higher than the
maximum output voltage. The rectifier diode must meet the
output current and peak inductor current requirements. The
following table is some recommendations for boost converter
diode.
Output Capacitor
The output capacitor supplies the load directly and reduces
the ripple voltage at the output. Output ripple voltage
consists of two components: the voltage drop due to the
inductor ripple current flowing through the ESR of output
capacitor, and the charging and discharging of the output
capacitor.
I
I
V
6.8µH/3A
10µH/4A
5.2µH/4.55A
SS23
MBRS340
SL23
LAVG
LPK
RIPPLE
TABLE 4. BOOST CONVERTER RECTIFIER DIODE
DIODE
INDUCTOR
=
TABLE 3. BOOST INDUCTOR RECOMMENDATION
=
I
LAVG
PEAK
PEAK
------------ -
1 D
=
I
–
O
I
PEAK
LPK
RECOMMENDATION
+
V
R
∆I
--------
2
/I
×
7.3x6.8x3.2
8.3x8.3x4.5
10x10.1x3.8
DIMENSIONS
L
AVG
30V/2A
40V/3A
30V/2A
ESR
(mm)
RATING
+
V
----------------------- -
O
V
–
O
10
V
TDK
Sumida
Cooper
Bussmann
IN
PACKAGE
MFG
×
--------------- -
C
SMB
SMC
SMB
OUT
I
O
RLF7030T-6R8N3R0
CDR8D43-100NC
CD1-5R2
×
--- -
f
1
PART NUMBER
s
Fairchild
Semiconductor
International
Rectifier
Vishay
Semiconductor
MFG
ISL97645
For low ESR ceramic capacitors, the output ripple is
dominated by the charging and discharging of the output
capacitor. The voltage rating of the output capacitor should
be greater than the maximum output voltage.
Note: Capacitors have a voltage coefficient that makes their
effective capacitance drop as the voltage across then
increases. C
effective value of the capacitor at a particular voltage and not
the manufacturer’s stated value, measured at zero volts.
The following table shows some selections of output
capacitors.
Compensation
The boost converter of ISL97645 can be compensated by a
RC network connected from CM1 pin to ground. 4.7nF and
10k RC network is used in the demo board. The larger value
resistor and lower value capacitor can lower the transient
overshoot, however, at the expense of stability of the loop.
Cascaded MOSFET Application
An 20V N-channel MOSFET is integrated in the boost
regulator. For the applications where the output voltage is
greater than 20V, an external cascaded MOSFET is needed
as shown in Figure 13. The voltage rating of the external
MOSFET should be greater than A
10µF/25V
10µF/25V
TABLE 5. BOOST OUTPUT CAPACITOR RECOMMENDATION
CAPACITOR
FIGURE 13. CASCADED MOSFET TOPOLOGY FOR HIGH
V
IN
OUT
OUTPUT VOLTAGE APPLICATIONS
1210
1210
ISL97645
SIZE
Intersil
in the equation above assumes the
TDK
Murata
MFG
LX
FB
C3225X7R1E106M
GRM32DR61E106K
VDD
.
PART NUMBER
April 11, 2006
FN9263.0
A
VDD