el7585il-t7 Intersil Corporation, el7585il-t7 Datasheet - Page 13

• Manufacturer Part Number: el7585il-t7
• Description: Tft-lcd Power Supply
• Manufacturer: Intersil Corporation

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 4mA drive
current, which is sufficient for up to 40mA or more output
current under the low dropout condition (forced beta of 10).
Typical V
to -20V. A fault comparator is also included for monitoring
the output voltage. The undervoltage threshold is set at
200mV above the 0.2V reference level.
The V
within the LCD panel. The DC/DC may be powered directly
from the low voltage input, 3.3V or 5.0V, or it may be
powered through the fault protection switch. The
LDO_LOGIC regulator uses an external PNP transistor as
the pass element. The onboard LDO controller is a wide
band (>10MHz) transconductance amplifier capable of
16mA drive current, which is sufficient for up to 160mA or
more output current under the low dropout condition (forced
beta of 10). Typical V
ranges from +1.3V to V
included for monitoring the output voltage. The undervoltage
threshold is set at 25% below the 1.2V reference.
Set-Up Output Voltage
Refer to the Typical Application Diagram, the output voltages
of V
equations:
V
V
V
Where V
Resistor networks in the order of 250kΩ, 120kΩ and 10kΩ
are recommended for V
Charge Pump
To generate an output voltage higher than V
multiple stages of charge pumps are needed. The number of
stage is determined by the input and output voltage. For
positive charge pump stages:
N
where V
the linear regulator. It ranges from 0.3V to 1V depending on
ON
OFF
LOGIC
POSITIVE
ON
=
LOGIC
=
, V
V
V
CE
=
REF
REF
OFF
OFF
REFN
V
≥
is the dropout voltage of the pass component of
REF
power supply is used to power the logic circuitry
V
------------------------------------------------------------- -
×
= 1.2V, V
, and V
voltage supported by EL7585 ranges from -5V
OUT



+
1
V
×
R
--------- -
R
INPUT
+



22
21
+
R
--------- -
R
1
V
12
11
+
LOGIC
×
LOGIC
CE
R
--------- -
R



REFN
(
DD
–
V
42
41
ON
–
2
REFN



-0.2V. A fault comparator is also
V
×
, V
INPUT
are determined by the following
voltage supported by EL7585
V
= 0.2V.
13
OFF
F
–
V
REF
and V
)
LOGIC
BOOST
, respectively.
, single or
EL7585
the transistor. V
rectifier diode.
The number of negative charge pump stages is given by:
N
To achieve high efficiency and low material cost, the lowest
number of charge pump stages which can meet the above
requirements, is always preferred.
High Charge Pump Output Voltage (>36V)
Applications
In the applications where the charge pump output voltage is
over 36V, an external npn transistor need to be inserted into
between DRVP pin and base of pass transistor Q3 as shown
in Figure 24; or the linear regulator can control only one
stage charge pump and regulate the final charge pump
output as shown in Figure 25.
NEGATIVE
FIGURE 24. CASCODE NPN TRANSISTOR CONFIGURATION
FIGURE 25. THE LINEAR REGULATOR CONTROLS ONE
EL7585
DRVP
EL7585
≥
FBP
------------------------------------------------ -
FOR HIGH CHARGE PUMP OUTPUT VOLTAGE
(>36V)
STAGE OF CHARGE PUMP
V
V
OUTPUT
INPUT
F
0.1µF
is the forward-voltage of the charge pump
DRVP
0.47µF
FBP
7kΩ
–
2
+
OR A
×
TRANSISTOR
V
V
V
CASCODE
CE
Q3
IN
F
VDD
0.1µF
NPN
CHARGE PUMP
7kΩ
0.1µF
OUTPUT
0.1µF
Q3
0.1µF
LX
A
VDD
March 9, 2006
V
ON
FN7345.2
0.22µF
(>36V)
V
ON