MTD6501G datasheet(9/24 Pages) MICROCHIP

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 2010-2012 Microchip Technology Inc.

DS22263B-page 9

MTD6501C/D/G

3.0

FUNCTIONAL DESCRIPTION

The MTD6501C/D/G devices generate a full-wave sig-

nal 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.

3.1

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 (VCC). 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 IC 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 of the range of audible frequencies. The

MTD6501C and MTD6501D typical output frequency is

20 kHz. The MTD6501G output frequency is 23 kHz.

3.2

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-imped-

ance 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). Typi-

cally, for a four pole BLDC fan, the speed in RPMs is 30

FG frequency (Hz).

3.3

Lockup 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 disables the driver (by

setting its outputs to high-impedance) in order 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). 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.

3.4

Overcurrent Protection and Short

Circuit Detection

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

value (defined internally), thus limiting the maximum

power dissipation in the coils. The detection of a short-

circuit situation immediately sets the driver outputs to

high-impedance, in order to avoid permanent damage

to the IC.

3.5

Thermal Shutdown

The MTD6501C/D/G have 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 disabled

(high-impedance), avoiding IC destruction and allowing

the circuit to cool down. Once the junction temperature

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

resumes (thermal detection circuit has +25°C

hysteresis function).

FIGURE 3-1:

Thermal Protection

Hysteresis.

3.6

Internal Voltage Regulator

VDD voltage is generated internally and is used to

supply internal logical blocks. The VDD 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.

TSD

+145°C

Thermal Shutdown

+170°C

Normal operation

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