el7585a Intersil Corporation, el7585a Datasheet - Page 13

• Manufacturer Part Number: el7585a
• Description: Tft-lcd Power Supply
• Manufacturer: Intersil Corporation

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
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.
ON
OFF
LOGIC
POSITIVE
NEGATIVE
ON
=
=
, V
V
V
CE
=
REF
REF
OFF
REFN
V
≥
is the dropout voltage of the pass component of
≥
REF
V
------------------------------------------------------------- -
×
= 1.2V, V
------------------------------------------------ -
, and V
V
OUT
V



+
OUTPUT
1
V
F
INPUT
×
R
--------- -
R
INPUT
+
is the forward-voltage of the charge pump



22
21
+
R
--------- -
R
1
V
12
11
+
LOGIC
×
LOGIC
CE
–
R
--------- -
R



REFN
(
DD
–
2
V
42
41
ON
+
–
2
REFN
×



V
-0.2V. A fault comparator is also
V
×
, V
V
CE
INPUT
are determined by the following
voltage supported by EL7585A
V
F
= 0.2V.
13
OFF
F
–
V
REF
and V
)
LOGIC
BOOST
, respectively.
, single or
EL7585A
Discontinuous/Continuous Boost Operation and
its Effect on the Charge Pumps
The EL7585A V
edges to drive diode charge pumps from which LDO
regulators generate the V
appreciated that should a regular supply of LX switching
edges be interrupted, for example during discontinuous
operation at light A
affect the performance of V
depending on their exact loading conditions at the time.
To optimize V
discontinuous/continuous operation of the boost converter
can be adjusted, by suitable choice of inductor given V
V
be in continuous operation.
EL7585A
OUT
FIGURE 24. CASCODE NPN TRANSISTOR CONFIGURATION
FIGURE 25. THE LINEAR REGULATOR CONTROLS ONE
, switching frequency and the A
EL7585A
DRVP
FBP
FOR HIGH CHARGE PUMP OUTPUT VOLTAGE
(>36V)
STAGE OF CHARGE PUMP
ON
ON
0.1µF
/V
VDD
OFF
DRVP
and V
0.47µF
FBP
7kΩ
regulation, the boundary of
boost load currents, then this may
OR A
OFF
TRANSISTOR
ON
V
CASCODE
ON
Q3
IN
VDD
0.1µF
NPN
and V
architecture uses LX switching
and V
CHARGE PUMP
7kΩ
0.1µF
OUTPUT
OFF
0.1µF
OFF
VDD
Q3
supplies. It can be
regulation -
current loading, to
0.1µF
LX
A
VDD
March 9, 2006
V
ON
FN7523.3
IN
0.22µF
(>36V)
,
V
ON