isl97652 Intersil Corporation, isl97652 Datasheet - Page 15

• Manufacturer Part Number: isl97652
• Description: 4-channel Integrated Lcd Supply With Dual Vcom Amplifiers
• Manufacturer: Intersil Corporation

than the maximum input voltage. The peak current rating is 2A,
and the average current should be as the following equation,
Where I
following table shows some diode recommended.
Output Capacitor (Buck Converter)
Four 10µF or two 22µF ceramic capacitors are recommended
for this part. The overshoot and undershoot will be reduced
with more capacitance, but the recovery time will be longer.
PI Loop Compensation (Buck Converter)
The buck converter of ISL97652 can be compensated by a
RC network connected from VCB pin to ground. C
and R
larger value resistor can lower the transient overshoot,
however, at the expense of stability of the loop.
The stability can be optimized in a similar manner to that
described in the section on "PI Loop Compensation (Boost
Converter)”.
Bootstrap Capacitor (C
This capacitor is used to provide the supply to the high driver
circuitry for the buck MOSFET. The bootstrap supply is
formed by an internal diode and capacitor combination. A
470nF is recommended for ISL97652. A low value capacitor
can lead to overcharging and in turn damage the part.
If the load is too light, the on-time of the low side diode may
be insufficient to replenish the bootstrap capacitor voltage.
In this case, if V
pull-up device may be unable to turn-on until V
Hence, there is a minimum load requirement in this case.
The minimum load can be adjusted by the feedback
resistors to FBB.
I
AVG
CAPACITOR
TABLE 9. BUCK OUTPUT CAPACITOR RECOMMENDATION
PMEG2020EJ
100µF/6.3V
10µF/6.3V
10µF/6.3V
22µF/6.3V
TABLE 8. BUCK RECTIFIER DIODE RECOMMENDATION
DIODE
=
SS22
CB
(
o
1 D
= 10k RC network is used in the demo board. The
is the output current of buck converter. The
–
)*I
o
IN
-V
V
RATING
SIZE
0805
0805
1210
1206
20V/2A
20V/2A
R
BUCK
/I
AVG
<1.5V, the internal MOSFET
B
TDK
Murata
TDK
Murata
15
VENDOR
)
PACKAGE
SOD323F
SMB
C2012X5R0J106M
GRM21BR60J106K
C3216X5R0J226M
GRM31CR60J107M
Philips
Semiconductors
Fairchild
Semiconductor
PART NUMBER
VENDOR
LOGIC
CB
= 4.7nF
(EQ. 13)
falls.
ISL97652
Regulated Charge Pump Controllers (V
V
The ISL97652 includes 2 independent charge pumps (see
charge pump block and connection diagram). The negative
charge pump inverters the V
regulated negative output voltage. The positive charge pump
doubles or triples the V
positive output voltage. The regulation of both the negative
and positive charge pumps is generated by internal
comparator that senses the output voltage and compares it
with the internal reference.
The pumps use pulse width modulation to adjust the pump
period, depending on the load present. The pumps can
provide 30mA for V
Positive Charge Pump Design Consideration
The positive charge pump can drive multiple stages for 2X/
3X step up ratios, or higher. Internal switches (M1 and M2)
drive external steering diodes via the pump capacitor CP.
Figure 18A shows 2X configuration and Figure 18B shows
3X configuration. The output voltage is divided by feedback
resistors R7 and R8, which is then compared to the internal
reference via comparator A1. The maximum V
pump current can be estimated from the following equations
assuming a 50% switching duty:
I
2 V
---------------------------------------------------------------------------------------------------------------------- 0.95A
I
3 V
---------------------------------------------------------------------------------------------------------------------- 0.95A
MAX
MAX
OFF
•
•
SUP
SUP
(
(
2x
3x
)
)
)
–
–
∼
∼
(
2
4
min of 50mA or
min of 50mA or
2
4
•
•
•
•
V
V
(
(
DIODE
R
DIODE
R
ONH
ONH
OFF
+
(
(
+
2 I
2 I
SUP
R
R
•
and 20mA for V
•
ONL
ONL
MAX
MAX
voltage and provided a regulated
SUP
)
)
)
) V V
) V V
–
–
voltage and provides a
(
(
ON
ON
)
)
ON
•
•
.
ON
ON
November 2, 2007
charge
and
(EQ. 14)
FN9287.1