ISL97645 Intersil Corporation, ISL97645 Datasheet - Page 9

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

continuous mode (CCM). In continuous current mode,
current flows continuously in the inductor during the entire
switching cycle in steady state operation. The voltage
conversion ratio in continuous current mode is given by:
Where D is the duty cycle of the switching MOSFET.
Figure 11 shows the block diagram of the boost regulator. It
uses a summing amplifier architecture consisting of gm
stages for voltage feedback, current feedback and slope
compensation. A comparator looks at the peak inductor
current cycle by cycle and terminates the PWM cycle if the
current limit is reached.
An external resistor divider is required to divide the output
voltage down to the nominal reference voltage. Current
drawn by the resistor network should be limited to maintain
the overall converter efficiency. The maximum value of the
resistor network is limited by the feedback input bias current
and the potential for noise being coupled into the feedback
pin. A resistor network in the order of 60kΩ is recommended.
The boost converter output voltage is determined by the
following equation:
The current through the MOSFET is limited to 2.6A
V
------------------ -
V
Boost
V
Boost
IN
=
=
V
------------ -
1 D
R
-------------------- -
IN
–
1
1
R
3
3
3
5
5
5
5
3
3
3
5
5
5
5
+
(V)
2
R
2
×
V
FB
9
V
O
12
15
12
15
18
12
15
12
15
18
9
9
9
9
TABLE 2. MAXIMUM OUTPUT CURRENT CALCULATION
(V)
PEAK
.
ISL97645
L (µH)
10
10
10
10
10
10
10
10
10
10
10
10
10
10
This restricts the maximum output current (average) based
on the following equation:
Where ∆I
by:
where f
The Table 2 gives typical values (margins are considered
10%, 3%, 20%, 10% and 15% on V
Capacitor
An input capacitor is used to suppress the voltage ripple
injected into the boost converter. The ceramic capacitor with
capacitance larger than 10µF is recommended. The voltage
rating of input capacitor should be larger than the maximum
input voltage. Some capacitors are recommended in Table 1
for input capacitor.
I
∆I
10µF/16V
10µF/10V
22µF/10V
OMAX
L
TABLE 1. BOOST CONVERTER INPUT CAPACITOR
CAPACITOR
=
V
---------
=
S
L
IN
is the switching frequency (650kHz or 1.2MHz).
L


×
I
is peak to peak inductor ripple current, and is set
LMT
--- -
f
D
RECOMMENDATION
s
F
–
s
∆I
--------
0.65
0.65
0.65
0.65
0.65
0.65
0.65
(MHz)
1.2
1.2
1.2
1.2
1.2
1.2
1.2
2
1206
0805
1210
L
SIZE


×
V
---------
V
IN
O
TDK
Murata
Murata
MFG
C3216X7R1C106M
GRM21BR61A106K
GRB32ER61A226K
IN
, V
O
PART NUMBER
I
, L, f
OMAX
1060
1236
636
419
289
699
482
338
742
525
395
875
658
514
S
(mA)
and I
April 11, 2006
OMAX
FN9263.0
).