EL7520ILZ-T13 查看數據表（PDF） - Intersil

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EL7520ILZ-T13

4-Channel DC/DC Controller

Intersil 

EL7520, EL7520A

FBB

CINT

EN

DRVN

FBN

VREF REFERENCE

GENERATOR

OSCILLATOR

SLOPE

COMPENSATION

OSC

GM

AMPLIFIER

Σ

VOLTAGE

AMPLIFIER

PWM

LOGIC

CONTROLLER

BUFFER

UVLO

COMPARATOR

CURRENT

AMPLIFIER

THERMAL

SHUTDOWN

SHUTDOWN

& STARTUP

CONTROL

CURRENT LIMIT

COMPARATOR

VREF

UVLO

COMPARATOR

BUFFER

SS

+ 0.2V

-

SS

VREF

+

-

CURRENT

LIMIT REF

GENERATOR

SS

+

-

BUFFER

BUFFER

0.4V

UVLO

COMPARATOR

UVLO

COMPARATOR

LX

DRVB

ISIN

ISAD

DRVP

FBP

DRVL

FBL

FIGURE 24. BLOCK DIAGRAM

Boost Converter

The main boost converter is a current mode PWM controller

operating at a fixed frequency. The 1MHz switching

frequency enables the use of low profile inductor and

multilayer ceramic capacitors, which results in a compact,

low-cost power system for LCD panel design.

The boost converter can operate in continuous or

discontinuous inductor current mode. The EL7520 and

EL7520A are designed for continuous current mode, but

they can also operate in discontinuous current mode at light

load. In continuous current mode, current flows continuously

in the inductor during the entire switching cycle in steady

state operation. The voltage conversion ratio in continuous

current mode is given by:

V-----B----O----O-----S----T-

VIN

=

1-----–-1----D---

Where D is the duty cycle of switching MOSFET.

Figure 25 shows the function diagram of the boost controller.

It uses a summing amplifier architecture consisting of GM

stages for voltage feedback, current feedback and slope

compensation. A comparator looks at the peak inductor

current cycle by cycle and terminates the PWM cycle if the

current limit is reached.

An external resistor divider is required to divide the output

voltage down to the nominal reference voltage. Current

drawn by the resistor network should be limited to maintain

the overall converter efficiency. The maximum value of the

resistor network is limited by the feedback input bias current

and the potential for noise being coupled into the feedback

pin. A resistor network in the order of 60kΩ is recommended.

The boost converter output voltage is determined by the

following equation:

VBOOST

=

R-----1----+-----R-----2-

R1

×

VREF

10

FN7318.0

July 12, 2005

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