EL7562 查看數據表（PDF） - Renesas Electronics

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EL7562

Monolithic 2Amp DC-DC Step-Down Regulator

Renesas Electronics 

EL7562

Block Diagram

0.1µF

270pF

VREF

COSC

Junction

Temperature

Voltage

Reference

Oscillator

Controller

Supply

39

VDD

5V

0.1µF

EN

PWM

Controlle

Drivers

Power

FET

Power

FET

SGND

FB

Current

Sense

VDRV

VHI

VIN

0.1µF

4.7µH

PGND

100µF

2370

VOUT

1k

Applications Information

Circuit Description

General

The EL7562 is a fixed frequency, current mode controlled DC-

DC converter with integrated N-channel power MOSFETs and

a high precision reference. The device incorporates all the

active circuitry required to implement a cost effective, user-

programmable 2A synchronous step-down regulator suitable

for use in DSP core power supplies.

Theory of Operation

The EL7562 is composed of 5 major blocks:

1. PWM Controller

2. NMOS Power FETs and Drive Circuitry

3. Bandgap Reference

4. Oscillator

5. Thermal Shut-down

PWM Controller

The EL7562 regulates output voltage through the use of

current-mode controlled pulse width modulation. The three

main elements in a PWM controller are the feedback loop and

reference, a pulse width modulator whose duty cycle is

controlled by the feedback error signal, and a filter which

averages the logic level modulator output. In a step-down

FN7295 Rev 1.00

May 1, 2006

(buck) converter, the feedback loop forces the time-averaged

output of the modulator to equal the desired output voltage.

Unlike pure voltage-mode control systems, current-mode

control utilizes dual feedback loops to provide both output

voltage and inductor current information to the controller. The

voltage loop minimizes DC and transient errors in the output

voltage by adjusting the PWM duty-cycle in response to

changes in line or load conditions. Since the output voltage is

equal to the time-averaged of the modulator output, the

relatively large LC time constant found in power supply

applications generally results in low bandwidth and poor

transient response. By directly monitoring changes in inductor

current via a series sense resistor the controller's response

time is not entirely limited by the output LC filter and can react

more quickly to changes in line and load conditions. This feed-

forward characteristic also simplifies AC loop compensation

since it adds a zero to the overall loop response. Through

proper selection of the current-feedback to voltage-feedback

ratio the overall loop response will approach a one-pole

system. The resulting system offers several advantages over

traditional voltage control systems, including simpler loop

compensation, pulse by pulse current limiting, rapid response

to line variation and good load step response.

The heart of the controller is an input direct summing

comparator which sum voltage feedback, current feedback,

slope compensation ramp and power tracking signals together.

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