A4941GLPTR-A-T PDF 데이터시트 ( Data )

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A4941GLPTR-A-T 기능

기능

Three-Phase Sensorless Fan Driver

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Allegro Micro Systems

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A4941

Three-Phase Sensorless Fan Driver

Features and Benefits

• Sensorless (no Hall sensors required)

• Soft switching for reduced audible noise

• Minimal external components

• PWM speed input

• FG speed output

• Low power standby mode

• Lock detection

• Optional overcurrent protection

• Variant A automotive qualified to AEC-Q100 Grade 2

Package: 16-pin TSSOP with exposed

thermal pad (suffix LP)

Description

The A4941 three-phase motor driver incorporates BEMF

sensing to eliminate the requirement for Hall sensors in fan

applications.

A pulse wave modulated (PWM) input is provided to control

motor speed, allowing system cost savings by eliminating

external variable power supply. PWM input can also be used

as an on/off switch to disable motor operation and place the

IC into a low power standby mode.

The A4941 is provided in a 16-pin TSSOP package (suffix LP)

with an exposed thermal pad. It is lead (Pb) free, with 100%

matte tin leadframe plating.

Not to scale

12 V

10 μF

VBB

SLEW

PWM

25 kHz

VBB

O/C FC

TEST

10 kΩ

Functional Block Diagram

VCP

0.1 μF

CP1

0.1 μF

CP2

+VINT

Soft

Switch

Control

Logic

Charge

Pump

3-Phase

Half Bridges

OUTA

OUTB

OUTC

OSC

Timers

Startup

OSC

Sequencer

(Direction)

CDCOM

Adaptive

Commutation

Delay

FCOM

OCP

SENSE

0.167 Ω

GND

OUTA

OUTB

OUTC

CTAP

GND

BEMF Comparator

A4941-DS, Rev. 4

A4941

Three-Phase Sensorless Fan Driver

Functional Description

The driver system is a three-phase, BEMF sensing motor control-

ler and driver. Commutation is controlled by a proprietary BEMF

sensing technique.

The motor drive system consists of three half bridge NMOS

outputs, BEMF sensing circuits, adaptive commutation control,

and state sequencer. The sequencer determines which output

devices are active. The BEMF sensing circuits and adaptive com-

mutation circuits determine when the state sequencer advances to

the next state.

A complete self-contained BEMF sensing commutation scheme is

provided. The three half-bridge outputs are controlled by a state

machine with six possible states, shown in figure 1. Motor BEMF

is sensed at the tri-stated output for each state.

BEMF sensing motor commutation relies on the accurate com-

parison of the voltage on the tri-stated output to the voltage at the

center tap of the motor. The BEMF zero crossing, the point where

the tri-stated motor winding voltage crosses the center tap volt-

age, is used as a positional reference. The zero crossing occurs

roughly halfway through one commutation cycle.

Adaptive commutation circuitry and programmable timers

determine the optimal commutation points with minimal

external components. The major blocks within this system are:

the BEMF zero crossing detector, Commutation Delay timer, and

the Blank timer.

BEMF Zero Cross Detection

BEMF zero crossings are detected by comparing the voltage at

the tri-stated motor winding to the voltage at the motor center

tap. Zero crossings are indicated by the FCOM signal, which

goes high at each valid zero crossing and low at the beginning

of the next commutation. In each state, the BEMF detector looks

for the first correct polarity zero crossing and latches it until the

next state. This latching action, along with precise comparator

hysteresis, makes for a robust sensing system. At the beginning

of each commutation event, the BEMF detectors are inhibited for

a period of time set by the Blank timer. This is done so that com-

mutation transients do not disturb the BEMF sensing system.

Commutation Event

See figure 1 for timing relationships. The commutation sequence

is started by a CDCOM pulse or a valid XCOM at startup. After

Output

State

AB CD EF AB CD EF

OUTA

OUTB

OUTC

FCOM

CDCOM

Figure 1. Motor Terminal Output States

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

4페이지

A4941

Three-Phase Sensorless Fan Driver

Application Information

VBB C2

VBB

1 OUTC

2 CP1

3 CP2

4 VCP

5 GND

6 SLEW

7 PWM

8 FG

CTAP

A4941

OUTB 16

OUTA 15

SENSE 14

PAD

VBB 13

CTAP

GND

12 C1

11 CTAP

FC 10

TEST 9

VBB

Typical Application Circuit; speed adjusted via VBB

Name

C2,C3

Typical Value

10 μF / 25 V

0.1 μF / 25 V

10 kΩ

>1.5 A rated

15 V

0.167 Ω

Description

VBB supply capacitor, minimum 10 μF,

electrolytic can be used

Charge pump ceramic capacitors

FG pull-up resistor, can be pulled-up to

VBB if required

Optional blocking diode for supply reverse

polarity protection

Transient voltage suppressor (TVS)

Current limiting sense resistor, required for

low resistance motors

Startup Oscillator Setting (FC)

Typically, the 50 ms setting is optimum for motors appropriate

for use with the A4941. If the motor does not produce a proper

BEMF signal at startup when power is applied, a longer setting

may be required.

SLEW Setting

Connect SLEW to ground to enable the soft switching func-

tion. For some motors, soft switching may reduce audible noise.

Enabling the soft switching function can result in motor stall for

some motors, specifically motors with large inductance that run at

higher speeds. For this situation, there are two potential solutions:

• Limit the motor speed by lowering the maximum demand, by

reducing either Vmotor(max) or the PWM duty applied.

• Disable soft switching by leaving SLEW pin open circuit.

Current Limiting

Use of the current limit circuit is not required. If motor resistance

(phase-to-phase) will limit the current below the rating in the

Absolute Maximum table, then simply connect the SENSE pin to

ground. That is:

• If (VBB(max) / Rmotor ) < 1.25 A, eliminate RS.

• If (VBB(max) / Rmotor ) > IOUT (max), the choice of RS deter-

mines the current limit setting; recommended range is

167 mΩ < RS < 250 mΩ.

Note: For some motor types, use of the current limit circuit may

prevent proper startup due to the effect of the chopping on the

BEMF voltage appearing on the tri-stated winding.

Layout Notes

• Connect GND pins (5,11) to exposed pad ground area under

package.

• Add thermal vias from exposed pad to bottom side ground

plane.

• Place VBB decoupling capacitor as close to the IC as possible.

• Place sense resistor, (if used), as close to the IC as possible.

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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Allegro Micro Systems에서 제조한 전자 부품 A4941GLPTR-A-T은 전자 산업 및 응용 분야에서
광범위하게 사용되는 반도체 소자입니다.

A4941GLPTR-A-T의 기능 및 특징 중 하나는 "Three-Phase Sensorless Fan Driver" 입니다.

일반적으로, Allegro Micro Systems에서 제조되는 전자부품들은 우수한 성능과
품질에 대한 신뢰성을 갖추고 있습니다.

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A4941GLPTR-A-T	Three-Phase Sensorless Fan Driver	Allegro Micro Systems