EL7641ILTZ datasheet(13/19 Pages) INTERSIL

13 / 19 page

FN7415.1

September 26, 2005

FIGURE 19. VON FUNCTIONAL BLOCK DIAGRAM

FIGURE 20. VOFF FUNCTIONAL BLOCK DIAGRAM

The VON power supply is used to power the positive 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_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

VON voltage supported by EL7640, EL7641 and EL7642

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.

The VOFF power supply is used to power the negative

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 VOFF voltage supported by EL7640, EL7641

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.

Set-up Output Voltage

Refer to Typical Application Diagram, the output voltages of

VON, VOFF and VLOGIC are determined by the following

equations:

Where VREF = 1.2V, VREFN = 0.2V.

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.

36V

ESD

CLAMP

GMP

LDO_ON

PG_LDOP

1: Np

FBP

DRVP

700

Ω

RBP

VBOOST

0.1µF

CP (TO 36V)

20k

Ω

RP2

RP1

CON

VON (TO 35V)

0.9V

36V

ESD

CLAMP

GMN

LDO_OFF

1: Nn

FBN

DRVN

0.1µF

CP (TO -26V)

RBN

COFF

VOFF (TO -20V)

RN1

RN2

20k

Ω

VREF

PG_LDON

0.4V

700

Ω

REF

----------







OFF

REFN

----------

REFN

REF

–

()

VIN

OR VBOOST

CHARGE PUMP

OUTPUT

700

Ω

Q11

FBP

DRVP

NPN

CASCODE

TRANSISTOR

EL764X

VON

FIGURE 21. CASCODE NPN TRANSISTOR CONFIGURATION

FOR HIGH CHARGE PUMP OUTPUT VOLTAGE

(>36V)

EL7640, EL7641, EL7642

EL7641ILTZ Datasheet(PDF) 13 Page - Intersil Corporation

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