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Buck Regulator Architectures Buck Regulator Architectures

Buck Regulator Architectures - PowerPoint Presentation

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Uploaded On 2018-06-29

Buck Regulator Architectures - PPT Presentation

41 Overview BuckSwitching Converters 2 Synchronous NonSynchronous ExternalFET Controllers InternalFET Regulators LM3102 LM22676 LM3489 LM2747 Vin S D L C Vout Io Ic ID: 662660

current mode advantages control mode current control advantages time ton buck synchronous toff voltage side vout dead mosfet diode

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Presentation Transcript

Slide1

Buck Regulator Architectures

4.1 OverviewSlide2

Buck-Switching Converters

2

Synchronous

Non-Synchronous

(External-FET) Controllers

(Internal-FET) Regulators

LM3102

LM22676

LM3489

LM2747Slide3

Vin

S

D

L

C

+

-

Vout

Io

Ic

Id

Is

IL

Δ

I

L, Ton

=

Δ

I

L, Toff

Δ

I

L, Ton

= (Vin – Vout ) * Ton / L

Δ

I

L, Toff

= -Vout * Toff

/ L

Vout = D*Vin

D = Ton / (Toff +Ton)

Non-Synchronous Buck Converters

3Slide4

Buck Topology:

Current and Voltage Waveforms

4

Input current

Low side switch or diode

Output and Inductor

SwitchSlide5

Light-Load Operation:

CCM and DCM

5

t

Inductor current reverses polarity at light loads

t

Inductor current drops to zero before the end of the cycle: “Discontinuous Conduction Mode” (DCM)

Full Synchronous

Mode. Stays in Continuous Conduction Mode (CCM)

Diode or

Diode Emulation

D = V

OUT

/V

IN

D

V

OUT

/V

INSlide6

Cross Conduction with

Synchronous Buck

Direct Connection between V

IN

and GroundHigh – Side and Low – Side must not be in ON state at the same time

A time in which both MOSFET are Turned OFF is required: DEAD - TIME

6Slide7

DEAD – TIME

FIXED DEAD – TIME

Fixed time between Turn-OFF and Turn-ON

No flexibility in MOSFET choice

ADAPTATIVE DEAD – TIMEHigh-Side turns ON only if LS is OFF and vice versaFull flexibility in MOSFET choiceIt is necessary to detect the Turn-OFF of both MOSFET

7Slide8

Control Mode

Voltage Mode Control (VMC)

Current Mode Control (CMC)

Peak Current Mode Control (PCMC)

Valley Current Mode Control (VCMC)Average Current Mode Control (ACMC)Hysteretic Mode Control (HMC)

8Slide9

Voltage Mode Control

Advantages and Disadvantages

Advantages

Stable modulation/less sensitive to noise

Single feedback pathCan work over a wide range of duty cyclesDisadvantagesLoop gain proportional to V

INLC double pole often drives Type III compensationCCM and DCM differences - a compensation challengeSlow response to input voltage changes

Current limiting must be done separately9Slide10

Current Mode Control

Advantages and Disadvantages

Advantages

Power plant gain offers a single-pole roll-off

Line rejectionCycle-by-cycle current limiting protectionCurrent sharingDisadvantages

NoiseMinimum ON-timeSense resistor

10Slide11

Hysteretic Mode Control

Advantages and Disadvantages

Advantages

Ultra fast transient response (preferred to use in power hungry load)

No phase compensation required; In other words, Hysteretic Mode is a kind of large signal controlDisadvantagesNoise Jitter susceptibleVery layout sensitive

Large switching frequency variation; Minimum ripple requirement11Slide12

Thank you!

12