EL7640, EL7641, EL7642
The V
OFF
power supply is used to power the negative
V
BOOST
LX
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
0.1µF
LDO_ON
0.9V
PG_LDOP
CP (TO 36V)
0.1µF
+
-
36V
ESD
CLAMP
R
BP
700Ω
DRVP
FBP
V
(TO 35V)
ON
of 10). Typical V
voltage supported by EL7640, EL7641
R
OFF
P1
P2
C
ON
and EL7642 ranges from -5V to -25V. A fault comparator is
also included for monitoring the output voltage. The under-
voltage threshold is set at 200mV above the 0.2V reference
level.
R
+
-
20kΩ
GMP
1: Np
Set-up Output Voltage
Refer to Typical Application Diagram, the output voltages of
ON OFF
equations:
FIGURE 19. V
FUNCTIONAL BLOCK DIAGRAM
ON
V
, V
and V
are determined by the following
LOGIC
R
12
LX
---------
V
= V
×
REF
1 +
ON
R
11
0.1µF
R
22
---------
V
= V
+
× (V
– V
)
REF
OFF
REFN
REFN
R
21
CP (TO -26V)
Where V
= 1.2V, V = 0.2V.
REFN
LDO_OFF
REF
V
REF
0.1µF
PG_LDON
0.4V
-
+
High Charge Pump Output Voltage (>36V)
Applications
R
N2
20kΩ
FBN
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 21, or the linear regulator can control only
one stage charge pump and regulate the final charge pump
output as shown in Figure 22.
1: Nn
R
N1
V
(TO -20V)
OFF
-
DRVN
+
C
OFF
GMN
R
BN
700Ω
36V
ESD
CLAMP
V
IN
CHARGE PUMP
OUTPUT
OR V
BOOST
700Ω
FIGURE 20. V
FUNCTIONAL BLOCK DIAGRAM
OFF
Q11
DRVP
FBP
The V
ON
power supply is used to power the positive supply
NPN
CASCODE
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)
ON
TRANSISTOR
EL764X
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
FIGURE 21. CASCODE NPN TRANSISTOR CONFIGURATION
FOR HIGH CHARGE PUMP OUTPUT VOLTAGE
(>36V)
V
voltage supported by EL7640, EL7641 and EL7642
ON
ranges from +15V to +36V. A fault comparator is also
included for monitoring the output voltage. The under-
voltage threshold is set at 25% below the 1.2V reference.
FN7415.1
13
September 26, 2005
INTERSIL [ Intersil ]
