A4964 datasheet(60/92 Pages) ALLEGRO

60 / 92 page

Sensorless Sinusoidal Drive BLDC Controller

A4964

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

READBACK REGISTER

The read-only readback register, register 31, provides access

to six additional measurements plus the Diagnostic register

described above. The measurement to be output on SDO when

shown in Table 6:

Table 6: Read-Back Output Select

RBS

Diagnostic register

Motor speed

Average supply current

Supply voltage

Chip temperature

Demand input

Applied bridge peak duty cycle

Applied phase advance

The first five bits of the readback register are always the most

significant five bits of the Status register. The 10-bit readback

value is the next ten bits followed by a parity bit.

The motor speed measurement is relative to the speed resolution

defined by SR[2:0] and therefore has the same range and resolu-

tion as the speed demand input through register 30. The motor

speed is also available during windmill detection in the forward

direction.

The motor speed, fE,is defined as:

fE = n × fRES (Hz)

where n is a positive integer defined by DO[9:0], fRES is the

speed resolution defined by SR[2:0], and fE is the electrical cycle

frequency of the controller.

The motor speed, ωM, can be calculated from :

()

rpm

�

where ωM is the motor speed in rpm, fE is the electrical cycle

frequency, and NPP is the number of pole-pairs in the rotor.

This range can be extended by a factor of two by using the most

significant bit of the diagnostic register, OSR, as bit 11 of the speed

measurement. That is, when OSR = 1, the speed is defined as:

fE = (n + 1024) × fRES (Hz)

The update period for the motor speed measurement can be cal-

culated from:

()

�

Sf ms

EMF

where fE is the electrical cycle frequency and SEMF is the number

of bemf samples per cycle.

The average supply current measurement is derived from the

average output of the sense amplifier and represents the average

supply current into the motor. The average current value, ISAVG,

is defined as:

()

�

176

SAVG

VSENSE

where n is a positive integer defined by DO[9:0], RSENSE is the

sense resistor value in mΩ, AV is the gain of the sense amplifier

as defined by the SA variable.

The supply voltage measurement is a direct measurement of the

VBRG voltage with a resolution of 53 mV and a range of 54 V.

The supply voltage, VS, is defined as:

VS = n × 0.0528 (V)

where n is a positive integer defined by DO[9:0].

Used together, the average supply current and the supply voltage

measurements can provide a measurement of the average electri-

cal power into the motor.

The chip junction temperature measurement is determined by the

voltage of the internal temperature measurement diodes. The chip

junction temperature, TJ, is defined as:

TJ = 367.7 – (n × 0.451) (°C)

where n is a positive integer defined by DO[9:0].

The temperature measurement result range is –93°C to 367°C,

but the useable measurement range is –50°C to 190°C.

The average supply current, supply voltage, and chip temperature

measurements are updated every 2 ms.

The remaining three selections provide a readback capability for

the variables that can be modified internally by the A4964.

The demand input can be written directly or can be derived from

an input PWM duty cycle. The demand input readback simply

provides the contents of DI[9:0] at the time of readback.

The applied bridge peak duty cycle output provides the peak

value of the duty cycle as determined by the motor control algo-

rithm. The bridge duty cycle, DBR, is defined by:

1023

where n is a positive integer defined by DO[9:0].

A4964 Datasheet(PDF) 60 Page - Allegro MicroSystems

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