MP6505-SINGLE-PHASE BRUSHLESS DC MOTOR DRIVER

MP6505 Rev.1.0

www.MonolithicPower.com

8

3/14/2012

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© 2012 MPS. All Rights Reserved.

FUNCTION DESCRIPTION

Motor Driver

OUT1 and OUT2 pins drive the motor. The

maximum total continuous output current is

400mA at room temperature. The peak output

current value is proportional to the Hall sensor

Frequency Setting

A capacitor at the COSC pin sets the frequency.

For most applications, use a 100pF capacitor for

an oscillator/typical PWM frequency of 30kHz.

Minimum Speed

The voltage on RMI pin sets the minimum PWM

duty cycle, which sets the lowest speed. Connect

to VTH if not used.

Locked-Rotor Detection

The RD pin is the locked-rotor detector, and is

the output of an open collector. It goes low when

the motor rotates and goes into high impendence

if the motor is in a locked-rotor state. Leave it

open if not used.

Speed Detection

The FG pin is the rotational speed detector, and

is the output of an open collector. It outputs a

high or low voltage relative to the Hall

comparator’s output. Higher speeds produce

higher-frequency signals. Leave it open if not

used.

Current Limit and the Hall Signal

An internal amplifier with hysteresis amplifies the

differential Hall signal: The output of this amplifier

serves as the current-limit value. The differential

Hall voltage drops to 0V whenever an opposing

magnet passes the Hall sensor to limit the peak

current during commutation. The Hall sensor is

directly powered by a 1.2V voltage on the HB pin.

Input Over-Voltage Protection

The reverse current generated with every

commutation charges the input capacitor and

causes a periodic voltage spike at the input pin.

The internal input over-voltage protection (OVP)

circuit turns off two HS switches when a spike

exceeds 20V, and recovers from OVP when the

spike is less than 18V.

Working Mode

The driver has operates in one of four modes

under normal conditions, as shown in Figure 2.

The following describes each mode:

 Minimum Speed Mode

This mode runs the motor at the slowest

motor speed. It uses a thermistor to provide

the VTH signal and compares it against RMI

to determine the slowest motor speed.

At low temperatures, VTH exceeds RMI. The

the motor speed. Removing the thermistor

causes VTH and the motor speed to reach

their respective maxima and minima.

 Variable Speed Mode

When the VTH signal falls below RMI, the

the motor speed. In general, VTH controls the

PWM duty cycle, and therefore the motor

speed.

 Full-Speed Mode

the PWM duty is 100% and the motor speed

is at its maximum.

 Locked-Rotor–Protection Mode

capacitor at the CT pin; changing the Hall

comparator’s output provides a reset signal to

drive an internal switch to discharge this

If the motor rotor is locked, the Hall

comparator’s output will not change. Once

driver enters locked-rotor–protection mode

the CT capacitor. During this period, the

PWM duty cycle goes to 0% and the RD pin

is in a high-impedance state. When the

charges the capacitor again. The PWM signal

resumes switching to try to drive motor again.

If the rotor remains locked, the process

repeats.