A8902CLBA

更新时间： 2024-02-26 22:47:25

品牌	Logo	应用领域
急速微 - ALLEGRO		驱动器电动机控制电机控制器
页数	文件大小	规格书
12页	157K
描述
3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER WITH BACK-EMF SENSING

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数据手册

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A8902CLBA 数据手册

8902–A

3-PHASE BRUSHLESS DC

MOTOR CONTROLLER/DRIVER

Adaptive Commutation Delay. The

adaptive commutation delay circuit uses the

back-EMF zero-crossing indicator signal

(FCOM) to determine an optimal commuta-

tion time for efficient synchronous operation.

This circuit commutates the outputs, delayed

from the last zero crossing, using two

Blanking and Watchdog Timing Functions. The blanking and

watchdog timing functions are derived from one timing capacitor, C_WD

V_TLx C_WD

where

t_BLANK=

I_CWD

V_THx C_WD

I_CWD

and

t_WD

external timing capacitors, C_D1and C_D2,

The CWD capacitor begins charging at each commutation, initiating

the BLANK signal. BLANK is an internal signal that inhibits the back-

EMF comparators during the commutation transients, preventing errors

due to inductive recovery and voltage settling transients.

FCOM

The watchdog timing function allows time to detect correct motor

position by checking the back-EMF polarity after each commutation. If

the correct polarity is not observed between t_BLANKand t_WD, then the

watchdog timer commutates the outputs to the next state to synchro-

nize the motor. This function is useful in preventing excessive reverse

rotation, and helps in resynchronizing (or starting) with a moving

spindle.

CWD

CD1

CD2

CWD

CD2

BLANK

Dwg. WP-016-2

Dwg. WP-022

to measure the time between crossings.

I_CD(charge)

NORMAL COMMUTATION

where

t_CD= t_FCOMx

I_{CD(discharge)}

C_D1charges up with a fixed current from

its 2.5 V reference while FCOM is high.

When FCOM goes low at the next zero

crossing, C_D1is discharged at approximately

twice the charging current. When CD₁

reaches the CD threshold, a commutation

occurs. C_D2operates similarly except on the

opposite phase of FCOM . Thus the com-

mutations occur approximately halfway

between zero crossings. The actual delay is

slightly less than halfway to compensate for

electrical delays in the motor, which im-

proves efficiency.

CWD

BLANK

Dwg. WP-021

WATCHDOG-TRIGGERED

COMMUTATION

1...4 5 678 9 10...12

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