A4941 데이터 시트보기 (PDF) - Allegro MicroSystems

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A4941

Three-Phase Sensorless Fan Driver

Allegro MicroSystems 

A4941

Three-Phase Sensorless Fan Driver

Application Information

VBB C2

C3

VBB

R2

1 OUTC

2 CP1

3 CP2

4 VCP

5 GND

6 SLEW

7 PWM

8 FG

M

CTAP

A4941

PAD

OUTB 16

OUTA 15

SENSE 14

R1

VBB 13

CTAP 12

C1

GND 11 CTAP

D1

D2

FC 10

TEST 9

VBB

Typical Application Circuit; speed adjusted via VBB

Name

C1

C2,C3

R2

D1

D2

R1

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

7

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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