EL7586 INTERSIL [Intersil Corporation], EL7586 Datasheet - Page 15

• Manufacturer Part Number: EL7586
• Description: TFT-LCD Power Supply
• Manufacturer: INTERSIL [Intersil Corporation]

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 31; or the linear regulator can control only one
stage charge pump and regulate the final charge pump
output as shown in Figure 32.
NEGATIVE
FIGURE 31. CASCODE NPN TRANSISTOR CONFIGURATION
EL7586A
EL7586
≥
------------------------------------------------ -
FOR HIGH CHARGE PUMP OUTPUT VOLTAGE
(>36V)
V
V
OUTPUT
F
INPUT
is the forward-voltage of the charge pump
DRVP
FBP
–
2
OR A
+
×
TRANSISTOR
V
V
CASCODE
V
CE
IN
F
VDD
15
NPN
CHARGE PUMP
7kΩ
OUTPUT
Q3
V
EL7586, EL7586A
ON
Discontinuous/Continuous Boost Operation and
it's Effect on the Charge Pumps
The EL7586 and EL7586A V
LX switching edges to drive diode charge pumps from which
LDO regulators generate the V
be 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.
The following equation gives the boundary between
discontinuous and continuous boost operation. For
continuous operation (LX switching every clock cycle) we
require that:
I(A
where the duty cycle, D = (A
For example, with V
12V we find continuous operation of the boost converter can
be guaranteed for:
L = 10µH and I(A
L = 6.8µH and I(A
L = 3.3µH and I(A
OUT
FIGURE 32. THE LINEAR REGULATOR CONTROLS ONE
VDD
EL7586A
EL7586
, switching frequency and the A
_load) > D*(1-D)*V
DRVP
FBP
STAGE OF CHARGE PUMP
ON
0.1µF
/V
VDD
VDD
VDD
VDD
OFF
IN
0.47µF
) > 61mA
7kΩ
) > 89mA
) > 184mA
= 5V, F
regulation, the boundary of
boost load currents, then this may
IN
ON
Q3
/(2*L*F
VDD
ON
0.1µF
OSC
ON
and V
and V
- V
0.1µF
and V
= 1.0MHz and A
OSC
IN
0.1µF
OFF
VDD
OFF
)/A
)
OFF
VDD
regulation -
current loading, to
architecture uses
supplies. It can
0.1µF
LX
A
VDD
October 7, 2005
VDD
FN9210.1
IN
0.22µF
=
(>36V)
,
V
ON