MP6505-SINGLE-PHASE BRUSHLESS DC MOTOR DRIVER
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
output voltage of (V
IN+
–V
IN-
).
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
device compares V
COSC
against RMI to
generate a PWM signal, PWM
-RMI
, to control
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
device compares V
COSC
against VTH to
generate a PWM signal of PWM
-VTH
to control
the motor speed. In general, VTH controls the
PWM duty cycle, and therefore the motor
speed.
Full-Speed Mode
When the VTH signal is less than V
COSC(MIN)
,
the PWM duty is 100% and the motor speed
is at its maximum.
Locked-Rotor–Protection Mode
An internal current source, I
CT1
, charges the
capacitor at the CT pin; changing the Hall
comparator’s output provides a reset signal to
drive an internal switch to discharge this
capacitor to V
CTL
.
If the motor rotor is locked, the Hall
comparator’s output will not change. Once
the voltage on the capacitor goes to V
CTH
, the
driver enters locked-rotor–protection mode
and another current source, I
CT2
, discharges
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
voltage on the capacitor drops to 0V, I
CT1
charges the capacitor again. The PWM signal
resumes switching to try to drive motor again.
If the rotor remains locked, the process
repeats.
MP6505 Rev.1.0
3/14/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
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