MTD6505 datasheet(9/20 Pages) MICROCHIP

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 2011 Microchip Technology Inc.

DS22281A-page 9

MTD6505

4.0

FUNCTIONAL DESCRIPTION

The MTD6505 generates a full-wave signal to drive a

3-phase BLDC motor. High efficiency and low-power

consumption are achieved due to CMOS transistors

and synchronous rectification drive type.

4.1

Speed Control

The rotational speed of the motor can be controlled

either through the PWM digital input signal or by acting

directly on 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 IC outputs are

set to high-impedance and the motor is stopped.

By changing the PWM duty cycle, the speed can be

adjusted. Thus, the user has maximum freedom to

choose the PWM system frequency within a wide range

(from 1kHz to 100kHz).

Since the PWM pin has an internal pull-up resistor

connected to VDD, it is recommended to drive it

between 0V and High-Z. The PWM driver must be able

to support the pull-up resistor current, in order to drive

the pin. See “PWM Internal Pull-Up Resistor” in

Section 1.0, Electrical Characteristics.

The output transistor activation always occurs at a fixed

rate of 30 kHz, which is outside of the range of audible

frequencies.

4.2

Motor Rotation Direction

The current-carrying order of the outputs depends on

the DIR pin state (“Rotation Direction”) and is described

in Table 4-1. The DIR pin is not designed for dynamic

direction change during operation.

4.3

Frequency Generator Function

The Frequency Generator output (FG) is a “Hall-effect

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 an 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 it is not used.

4.4

Lockup Protection and Automatic

Restart

If the motor is blocked and cannot rotate freely, a lock-

up protection circuit detects it and disables the driver by

setting its outputs to high-impedance to prevent the

motor coil from burnout. After a “waiting time” (TWAIT),

the lock-up protection is released and normal operation

resumes for a given time (TRUN). If the motor is still

blocked, a new period of waiting time is started. TWAIT

and TRUN timings are fixed internally, so that no exter-

nal capacitor is required.

4.5

Overcurrent Protection

The motor peak current is limited by the driver to

750 mA (standard value), thus limiting the maximum

power dissipation in the coils.

4.6

Thermal Shutdown

The MTD6505 device has a thermal protection function

which detects when the die temperature exceeds

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

circuit enters the Thermal Shutdown mode, and the

outputs OUT1, OUT2 and OUT3 are disabled (high-

impedance), avoiding the IC destruction and allowing

the circuit to cool down. When the junction temperature

(TJ) drops below +145°C, normal operation resumes.

The thermal detection circuit has +25°C hysteresis.

FIGURE 4-1:

Thermal Protection

Hysteresis.

Note 1: The PWM frequency has no direct affect

on the motor speed and is asynchronous

with

the

activation

the

output

transistors.

Note 2: The standard output frequency is 30 kHz.

A 20 kHz output frequency option is

available upon request.

TABLE 4-1:

MOTOR ROTATION

DIRECTION OPTIONS

(DIR PIN)

DIR Pin State

Rotation

Direction

Outputs Activation

Sequence

Connected

to GND

or Floating

Forward

OUT1

 OUT2  OUT3

Connected

to VBIAS

Reverse

OUT3

 OUT2  OUT1

+145°

Thermal shutdown

+170°

Normal

operation

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