ISL78022 Intersil Corporation, ISL78022 Datasheet - Page 13

• Manufacturer Part Number: ISL78022
• Description: (ISL78020 / ISL78022) Automotive Grade 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
on-board 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 +15V to +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 ISL78020 and ISL78022 ranges
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)
ISL78020, ISL78022
0.1µF
C
ON
(TO -20V)
LX
0.1µF
C
LX
OFF
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 on-board 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
ISL78022 ranges 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 “Typical Application Circuit” on page 18, the output
voltages of V
Equations 10 and 11:
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 Q
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
ISL7802x
power supply is used to power the negative
ON
×
FOR HIGH CHARGE PUMP OUTPUT VOLTAGE
(>36V)
= 1.2V, V
⎛
⎜
⎝
1
+
, V
OFF
+
R
--------- -
R
OFF
R
--------- -
R
22
21
DRVP
12
11
voltage supported by ISL78020 and
FBP
×
⎞
⎟
⎠
(
REFN
and V
V
OR V
REFN
TRANSISTOR
CASCODE
V
BOOST
IN
NPN
= 0.2V.
LOGIC
–
700Ω
V
REF
CHARGE PUMP
OUTPUT
are determined by
)
Q11
December 6, 2007
V
ON
(EQ. 10)
(EQ. 11)
FN6386.2
3
as