MCP8063 datasheet(9/20 Pages) MICROCHIP

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DS20005257B-page 9

MCP8063

4.0

FUNCTIONAL DESCRIPTION

The MCP8063 device generates a full-wave signal to

drive a 3-phase sensorless BLDC motor. High

efficiency and low power consumption are achieved

due to DMOS transistors and synchronous rectification

drive type. The current carrying order of the output is as

follows: OUT1

 OUT2  OUT3.

4.1

Speed Control

The rotational speed of the motor can be controlled

either through the PWM digital input signal or by

varying the power supply (VDD). When the PWM signal

is “High” (or left open), the motor rotates at full speed.

When the PWM signal is “Low”, the motor is stopped

(and the driver outputs are set to high impedance). By

changing the PWM duty cycle, the speed can be

adjusted. Notice that the PWM frequency has no

special meaning for the motor speed and is

asynchronous with the activation of the output

transistors. Thus, the user has maximum freedom to

choose the PWM system frequency within a wide range

(from 20 Hz to 100 kHz), while the output transistor

activation always occurs at a fixed rate, which is

outside the range of audible frequencies. The typical

output frequency of MCP8063 is 23 kHz.

4.2

Frequency Generator Function

The Frequency Generator output is a “Hall-sensor

equivalent” digital output, giving information to an

external controller about the speed and phase of the

motor. The FG pin is an open-drain output, connecting

to a logical voltage level through an external pull-up

resistor. When a lock (or out-of-sync) situation is

detected by the driver, this output is set to high

impedance until the motor is restarted. Leave the pin

open when not used. The FG signal can be used to

compute the motor speed in rotations per minute

(RPM). Typically, for a four-pole BLDC fan (4P/6S), the

speed in RPMs is 30 x FG frequency (Hz).

EQUATION 1-1:

4.3

Lock-Up Protection and Automatic

Restart

If the motor is stopped (blocked) or if it loses

synchronization with the driver, a lock-up protection

circuit detects this situation and ties the outputs to GND

in order to dissipate the remaining energy from the

rotor with a minimum of self heating. After a “waiting

time” (TWAIT), the lock-up protection is released and

normal operation resumes for a given time (TRUN). In

case the motor is still blocked, a new period of waiting

time is started. TWAIT and TRUN timings are fixed

internally, so that no external capacitor is needed.

4.4

Overcurrent Limitation

The motor peak current is limited by the driver to a fixed

value (defined internally), thus limiting the maximum

power dissipation in the coils.

4.5

Thermal Shutdown

The MCP8063 device has a thermal protection function

which detects when the die temperature exceeds

TSD = +170°C. When this temperature is reached, the

circuit enters Thermal Shutdown mode and the outputs

OUT1, OUT2 and OUT3 are tied to GND in order to

dissipate the remaining energy from the rotor with a

minimum

self-heating.

Once

the

junction

temperature (TSD) has dropped below +145°C, the

normal operation resumes (the thermal detection

circuit has +25°C hysteresis function).

FIGURE 4-1:

Thermal Protection

Hysteresis.

4.6

Internal Voltage Regulator

VBIAS voltage is generated internally and is used to

supply internal logical blocks. The VBIAS pin is used to

connect an external decoupling capacitor (1 µF or

higher). Notice that this pin is for IC internal use and is

not designed to supply DC current to external blocks.

4.7

Overvoltage Shutdown

The MCP8063 device has an overvoltage protection

function which detects when the VDD voltage exceeds

VOV = +18.5V. When this temperature is reached, the

circuit enters Thermal Shutdown mode, and outputs

OUT1, OUT2 and OUT3 are disabled (high impedance).

720









-----------------------

Where:

Total number of poles in the motor

Total number of slots in the motor

= Rotor speed RPM

TSD

+145°C

Thermal Shutdown

+170°C

Normal operation

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