el7641a Intersil Corporation, el7641a Datasheet - Page 13

• Manufacturer Part Number: el7641a
• Description: Tft-lcd Dc/dc With Integrated Amplifiers
• Manufacturer: Intersil Corporation

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
EL7642A 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.
0.9V
PG_LDON
PG_LDOP
ON
0.4V
voltage supported by EL7640A, EL7641A and
FIGURE 20. V
ON
FIGURE 19. 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
EL7640A, EL7641A, EL7642A
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
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
EL7641A and EL7642A 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.
Set-up Output Voltage
Refer to Typical Application Diagram, the output voltages of
V
equations:
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 21, or the linear regulator can control only
one stage charge pump and regulate the final charge pump
output as shown in Figure 22.
V
ON
ON
OFF
FIGURE 21. CASCODE NPN TRANSISTOR CONFIGURATION
, V
=
OFF
=
OFF
V
V
REF
REF
REFN
EL764X
power supply is used to power the negative
and V
×
= 1.2V, V
FOR HIGH CHARGE PUMP OUTPUT VOLTAGE
(>36V)
⎛
⎜
⎝
1
+
OFF
+
R
--------- -
R
LOGIC
R
--------- -
R
22
21
DRVP
12
11
voltage supported by EL7640A,
FBP
×
⎞
⎟
⎠
REFN
(
V
OR V
are determined by the following
REFN
TRANSISTOR
CASCODE
V
BOOST
IN
= 0.2V.
NPN
–
700Ω
V
REF
CHARGE PUMP
OUTPUT
)
Q11
V
May 15, 2006
ON
FN6270.0