EL7585AILZ(2005) Просмотр технического описания (PDF) - Intersil

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Компоненты Описание

производитель

EL7585AILZ
(Rev.:2005)

TFT-LCD Power Supply

Intersil 

EL7585A

LX

0.1µF

PG_LDON -

+

0.4V

LDO_OFF

VREF

FBN

RN2

20kΩ

1: Nn

-

+

GMN

36V

ESD

CLAMP

RN1

DRVN

Q2

RBN

3kΩ

CP (TO -26V)

0.1µF

VOFF (TO -20V)

COFF

FIGURE 24. VOFF FUNCTIONAL BLOCK DIAGRAM

0.9V

PG_LDOL +

-

LDO_LOG

VIN OR VPROT

(3V TO 6V)

RBL

500Ω

DRVL

FBL

Q5 VLOGIC

(1.3V TO 3.6V)

CLOG

RL1

10µF

-

+

GML

1: N1

RL2

20kΩ

FIGURE 25. VLOGIC 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 4mA drive current,

which is sufficient for up to 40mA or more output current

under the low dropout condition (forced beta of 10). Typical

VON voltage supported by EL7585A 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 4mA drive

current, which is sufficient for up to 40mA or more output

current under the low dropout condition (forced beta of 10).

Typical VOFF voltage supported by EL7585A ranges from

-5V 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 VLOGIC power supply is used to power the logic circuitry

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 VLOGIC voltage supported by EL7585A

ranges from +1.3V to VDD-0.2V. A fault comparator is also

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 VON, VOFF, and VLOGIC are determined by the following

equations:

VON

=

VR

EF

×



1



+

R-----1---2-

R11

VOFF

=

VRE

F

N

+

R-----2---2-

R21

×

(

VREF

N

–

VR

E

F)

VLOGIC

=

VR

E

F

×



1



+

R-----4---2-

R41

Where VREF = 1.2V, VREFN = 0.2V.

Resistor networks in the order of 250kΩ, 120kΩ and 10kΩ

are recommended for VON, VOFF and VLOGIC, respectively.

Charge Pump

To generate an output voltage higher than VBOOST, single or

multiple stages of charge pumps are needed. The number of

stage is determined by the input and output voltage. For

positive charge pump stages:

NPOSITIVE ≥ -V----O----VU----IT--N---+--P---VU----C-T---E-–----–-2----V-×---I-V-N----FP----U----T--

where VCE is the dropout voltage of the pass component of

the linear regulator. It ranges from 0.3V to 1V depending on

12

FN7523.2

September 21, 2005

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