Inductive Sense Start Up Block

The inductive sense method allows to determine

the position and the direction of the starting rota-

tion of the motor.

With the rotor at rest, a voltage Vn is applied sub-

sequently to two motor phases, according to this

sequence: UW, VW, VU, WU, WV, UV.

A timer measures the rise time dT to reach the

reference current ISR in each phase.

This reference is fixed on the pin ISR with a resis-

tor divider between the pin BIAS and GND.

Through a comparator is possible to determine

the phase which has the minimum rise time and

so the rotor position is univocally determinated.

The start up is a procedure allowing to start the

motor avoiding any backrotation. This procedure

is realized by a customized logic on chip (no

modification required in the external microproces-

sor software).

For the Motor Connection please refer to the Fig. 4.

Current Limiter

The current limiter aim is to avoid that the current

in the motor winding overides a fixed threshold

value. The voltage input at the pin RF1 is

com-

pared with an internal 0.2V reference.

When the current exceeds the Ilimit value a flip-

flop is reset masking (through a combinational

logic) the signal to the power windings.

Rotor Position Detector

This block is connected to the Hall Sensor Out-

put. A comparator with hysteresis receives the

sinusoidal hall-sensor signal and generates a

squared signal HOUT.

The Zero-Cross signal is generated starting from

the HOUT signal as in fig. 5.

The HOUT signal can be read from the micro-

processor on the output open drain pin HFG.

Frequency multiplier

The Frequency Multiplier generates the memory

scan frequency (Fscan) starting from the Zero-

Cross (ZC) signal from the Rotor Position Detec-

tor block. The scan frequency relates to the rate

of the samples of the input signals.

The number of wave samples in a period T is 36,

so this circuit generates 36 pulses between 2

Zero Crossing.

CURRENT LIMIT

RF1

D98IN882

0.2V

-

+

R

S

TO THE POWER STAGE

SET EVERY

255 CLOCK

CYCLE

INTERNAL

REFERENCE

Figure 3.

HOUT

H+

D98IN883A

-

+

COMPARATOR WITH HYSTERESIS

H-

HOUT

ZC

Figure 5.

T

ZC

Fscan

12345678

35

36

D98IN879

Figure 6.

R1

TIMER

ISR

D98IN881

BIAS

RF1

R2

-

+

Figure 2.

L7203

Bemf coil B

Hall sensor

Bemf coil C

Bemf coil A

MOTOR COIL A

MOTOR COIL B

MOTOR COIL C

U

V

W

H+

H-

H+

H-

MOTOR

D01IN1175

Figure 4. Motor Connections.

L7203

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