TI 控制模式快速参考指南说明书

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2024年3月22日发(作者：)

Analog Design Journal

Control-mode quick reference guide

Overview

TI is active in the development of leading-edge control

circuits to help engineers address specific design

challenges. Since no control mode is optimal for every

application, various control modes for non-isolated step-

down controllers and converters are referenced with their

advantages and how to learn more about each mode.

The TI portfolio contains 15 types of control architectures

for non-isolated TPS- and LM-series switching DC/DC

converters and controllers.

Internally-

Direct connection to

Voltage mode

compensated

advanced current

the output capacitor

mode (ACM)

(D-CAP™)

Voltage mode with

Hysteretic control

D-CAP+

™

control

voltage feed-forward

mode

mode

Peak current modeConstant on-time

D-CAP2™ control

mode

Average current

Constant on-time

D-CAP3™ control

mode

with emulated ripple

mode

mode

DCS-Control™:

Emulated current

Direct control with

seamless transition

D-CAP4

™

control

mode

into power-save

mode

mode

Voltage mode

Pulse-width modulation (latch output) is accomplished

by comparing a voltage error signal (V

E

) from the output

voltage and reference voltage to a constant saw-tooth-

ramp waveform. The ramp is initiated by a clock signal

from an oscillator. Good noise-margin performance is

attained with a fixed ramp amplitude (V

R

). Voltage

regulation is independent of the output current. Voltage

mode uses type-3 compensation addressing a double-

pole power stage to support a wide range of output

filter

combinations for externally compensated devices.

When to use: When a fixed, predictable switching

frequency is desired. Also useful when wide output-load

variations are possible.

Control-mode quick reference guide

Popular devices: TPS54610, TPS40040, LM22670

Learn more: Switching Power Supply Topology Voltage Mode vs.

Current Mode

CLOCK

V

E

V

R

LATCH

OUTPUT

Voltage mode with voltage feed-forward

Similar to voltage mode, but ramp generator varies the

PWM ramp slope with the input voltage at a constant

ramp magnitude and delivers an instantaneous response

to input voltage variations. The PWM does not have to

wait for loop delays to change the duty cycle.

When to use: When a fixed, predictable switching

frequency is desired. Also useful when wide variations

of input voltage and output load are possible.

Popular devices: TPS40057, TPS40170, TPS56121

Learn more: Effect of Programmable UVLO on Maximum Duty

Cycle Achievable With the TPS4005x and TPS4006x Family of

Synchronous Buck Controllers

V

SW

V

COMP

RAMP

V

t

t

t

t

D=

t

t

t>tand D

>D

Peak current mode

Pulse-width modulation (latch output) is accomplished

by comparing a voltage error signal (V

E

) and a ramp

waveform (V

S

) derived from the output current. The ramp

is initiated by the clock signal. This mode offers fast

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Analog Design Journal

response to output current changes. However, it can be

susceptible to noise sensitivity at low duty cycles due to

leading-edge current spike. It uses type-2 compensation

addressing a single-pole power stage for externally

compensated devices.

When to use: When a fixed, predictable switching

frequency is needed with a lower parts count than

the externally-compensated, double-pole voltage mode.

Peak current mode uses a single zero compensator,

which is easier to design than voltage mode’s double-

zero compensator.

Popular devices: TPS54620, TPS62913, LM5140-Q1

Learn more: Understanding and Applying Current-Mode Control

Theory

CLOCK

V

E

V

S

LATCH

OUTPUT

Average current mode

Average current mode addresses noise immunity issues,

peak-to-average current errors, and slope compensation

needs of peak current mode. Average current mode

introduces a high gain integrating current error amplifier

into the current loop. The voltage across a current

sense resistor represents the actual inductor current. The

difference, or current error, is amplified and compared

to a large amplitude saw-tooth (oscillator ramp) at

the PWM comparator inputs. The gain of the current

loop effectively sets the slope compensation without

restricting the minimum on-time or minimum-off time.

Current sensing is usually inside the regulator, but can

be external.

When to use: Effectively control currents other than

inductor current, allowing a much broader range of

topological application.

Control-mode quick reference guide

Popular devices: TPS546D24S, TPS546B24S

Learn more: Average Current Mode Control of Switching Power

Supplies

V

R

Control and Gate Drive

L

V

C

+±

Current Error AmplifierINA240

±

+

±

+

±

PWM Generation

+

Reference Voltage

Voltage Error Amplifier

Emulated current mode

Similar to current mode, but employs a gated sample

and hold circuit to capture current information emulated

by measuring inductor voltage to estimate the ramp

current. Eliminates the leading-edge spike issue of

the traditional peak-current mode by allowing smaller

duty cycles. Provides a clean current waveform when

operating near the minimum on-time.

When to use: When low duty cycle is needed

versus traditional current mode, without current noise

susceptibility.

Popular devices: LM5116, LM5119

Learn more: Emulated Current Mode Control for Buck Regulators

Using Sample and Hold Technique

Internally-compensated advanced current

mode (ACM)

Internally-compensated ACM is a ripple-based, peak-

current-mode control scheme that uses an internally

generated ramp to represent the inductor current.

This control mode provides a balance between the

fast transient response of non-linear control modes (D-

CAP™, constant on-time, and so forth) and the broad

capacitor stability of other externally-compensated,

fixed-frequency control modes (voltage mode, current

mode). Internally-compensated advanced current mode

provides a fixed, predictable frequency and a simplified

compensation selection to reduce external components.

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