ISL97642 Intersil Corporation, ISL97642 Datasheet - Page 13

• Manufacturer Part Number: ISL97642
• Description: TFT-LCD DC/DC
• Manufacturer: Intersil Corporation

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The V
of the row driver in the LCD panel. The DC/DC consists of an
external diode-capacitor charge pump powered from the
inductor (LX) of the boost converter, followed by a low
dropout linear regulator (LDO_ON). The LDO_ON regulator
uses an external PNP transistor as the pass element. The
onboard LDO controller is a wide band (>10MHz)
transconductance amplifier capable of 5mA output current,
which is sufficient for up to 50mA or more output current
under the low dropout condition (forced beta of 10). Typical
V
+36V. A fault comparator is also included for monitoring the
output voltage. The undervoltage threshold is set at 25%
below the 1.2V reference.
0.9V
PG_LDON
PG_LDOP
ON
0.4V
voltage supported by ISL97642 ranges from +15V to
FIGURE 19. V
ON
FIGURE 18. V
GMN
power supply is used to power the positive supply
+
GMP
+
-
-
+
+
-
-
CLAMP
ESD
36V
1: Nn
1: Np
OFF
ON
LDO_OFF
CLAMP
LDO_ON
ESD
36V
FUNCTIONAL BLOCK DIAGRAM
FUNCTIONAL BLOCK DIAGRAM
13
700Ω
FBN
DRVN
DRVP
FBP
R
BN
700Ω
R
BP
20kΩ
R
R
N2
N1
20kΩ
V
R
R
V
REF
P1
P2
BOOST
0.1µF
CP (TO 36V)
V
ON
CP (TO -26V)
V
0.1µF
OFF
(TO 35V)
0.1µF
C
ON
(TO -20V)
LX
0.1µF
C
LX
OFF
ISL97642
The V
supply of the row driver in the LCD panel. The DC/DC
consists of an external diode-capacitor charge pump
powered from the inductor (LX) of the boost converter,
followed by a low dropout linear regulator (LDO_OFF). The
LDO_OFF regulator uses an external NPN transistor as the
pass element. The onboard LDO controller is a wide band
(>10MHz) transconductance amplifier capable of 5mA
output current, which is sufficient for up to 50mA or more
output current under the low dropout condition (forced beta
of 10). Typical V
from -5V to -25V. A fault comparator is also included for
monitoring the output voltage. The undervoltage threshold is
set at 200mV above the 0.2V reference level.
Set-up Output Voltage
Refer to the “Typical Application Circuit” on page 18. The
output voltages of V
by Equations 9 and 10:
V
Where V
High Charge Pump Output Voltage (>36V)
Applications
In the applications where the charge pump output voltage is
over 36V, an external NPN transistor needs to be inserted in
between the DRVP pin and the base of pass transistor Q3,
as shown in Figure 20, or the linear regulator can control
only one stage charge pump and regulate the final charge
pump output, as shown in Figure 21.
V
ON
OFF
FIGURE 20. CASCODE NPN TRANSISTOR CONFIGURATION
=
OFF
=
V
V
REF
REF
REFN
ISL97642
power supply is used to power the negative
×
= 1.2V, V
FOR HIGH CHARGE PUMP OUTPUT VOLTAGE
(>36V)
⎛
⎜
⎝
1
+
OFF
+
R
--------- -
R
R
--------- -
R
22
21
DRVP
ON
12
11
voltage supported by ISL97642 ranges
FBP
×
⎞
⎟
⎠
REFN
, V
(
V
OR V
REFN
TRANSISTOR
OFF
CASCODE
V
BOOST
IN
= 0.2V.
NPN
and V
–
700Ω
V
REF
CHARGE PUMP
OUTPUT
LOGIC
)
Q11
are determined
June 18, 2007
V
ON
(EQ. 10)
(EQ. 9)
FN6436.0