TDA5146T 查看數據表（PDF） - Philips Electronics

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TDA5146T

Brushless DC motor drive circuit

Philips Electronics 

Philips Semiconductors

Brushless DC motor drive circuit

Product specification

TDA5146T

The system will only function when the EMF voltage from the motor is present. Therefore, a start oscillator is provided that will generate

commutation pulses when no zero–crossings in the motor voltage are available.

A timing function is incorporated into the device for internal timing and for timing of the reverse rotation detection.

The TDA5146T is designed for systems with low current consumption: use of I2 L logic, adaptive base drive for the output transistors (patent

pending).

Adjustments

The system has been designed in such a way that the tolerances of the application components are not critical. However, the approximate

values of the following components must still be determined:

• The start capacitor; this determines the frequency of the start oscillator

• The two capacitors in the adaptive commutation delay circuit. These are important in determining the optimum moment for commutation,

depending on the type and loading of the motor

• The timing capacitor; this provides the system with its timing signals

• Three external, damping RC–combinations that can be used to reduce BF interference and acoustic noise from the motor

The Start Capacitors (CAP–ST)

This capacitor determines the frequency of the start oscillator. It is charged and discharged, with a current of 2 mA, from 0.05 V to 2.2 V and

back to 0.05 V. The time taken to complete one cycle is given by:

tstart = (2.15  C)s

(with C in mF)

The start oscillator is reset by a commutation pulse and so is only active when the system is in the start–up mode. A pulse from the start

oscillator will cause the outputs to change to the next state (torque in the motor). If the movement of the motor generates enough EMF the

TDA5146T will run the motor. If the amount of EMF generated is insufficient, then the motor will move one step only and will oscillate in its new

position. The amplitude of the oscillation must decrease sufficiently before the arrival of the next start pulse, to prevent the pulse arriving during

the wrong phase of the oscillation. The oscillation of the motor is given by:

fOSC + (0.5ńp) (Kt I pńJ)1ń2

where:

Kt = torque constant (N.m/A)

I = current (A)

p = number of magnetic pole–pairs

J = inertia J (kg/m2)

Example: J = 72  10–6 kg/M2, K = 25  10– 3 N.m/A, p = 6 and I = 0.5 A; this gives fosc = 5 Hz. If the damping is high then a start frequency of

2 Hz can be chosen or t = 500 ms, thus C = 0.5/2 = 0.25 mF, (choose 220 nF).

The Adaptive Commutation Delay (CAP–CDM and CAP–CDS)

In this circuit capacitor CAP–CDM is charged during one commutation period, with an interruption of the charging current during the diode pulse.

During the next commutation period this capacitor (CAP–CDM) is discharged at twice the charging current. The charging current is 8.1 mA and

the discharging current 16.2 mA ; the voltage range is from 0.9 to 2.2V. The voltage must stay within this range at the lowest commutation

frequency of interest, fc1:

C=8.1–6 / f  1.3=6231/fC1

(C in nF)

If the frequency is lower, then a constant commutation delay after the zero–crossing is generated by the discharge from 2.2 to 0.9V at 16.2 mA.

maximum delay = (0.076 x C) ms

(with C in nF)

Example: nominal commutation frequency = 900 Hz and the lowest usable frequency = 400 Hz, so:

CAP–CDM = 6231 / 400 = 15.6

(choose 18 nF)

The other capacitor, CAP–CDS, is used to repeat the same delay by charging and discharging with 20 mA. The same value can be chosen as

for CAP–CDM. Figure 8 illustrates typical voltage waveforms.

1994 May 18

12

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