AMC8500 Datasheet, PDF (12/27 Pages) List of Unclassifed Manufacturers – TWO PHASE VARIABLE SPEED FAN MOTOR CONTROLLER

Preliminary Specification
aMC8500
Motor Drives
The aMC8500 contains two 0.5 Ω N-channel power MOSFETs that are designed to directly drive the motor coils from the
Phase 1 and Phase 2 outputs. The drive characteristics are shown in Figures 9 and 10. Each output contains a 36 V zener
with a series diode that connects from the drain to the gate. This configuration provides active clamp protection for the
MOSFETs when switching off the inductive motor load. In applications that demand driving higher current or higher voltage
motors, external MOSFET power transistors can be used. Two examples are shown in Figures 29 and 30. Although this
device is designed to drive two phase half wave motors, a method for driving single phase full wave motors is shown in
Figure 31.
Due to the inherent winding coupling that is present in two phase motors, the drain voltage of the off phase will be driven
negative and current will be sourced from that output. This current will cause additional device heating and may affect
operation of high current motors at elevated ambient temperatures. A simple solution is to place the cathode of a low forward
drop Schottky diode from each drive output to ground. Likewise if the motor windings are highly inductive, the internal active
clamp will be required to dissipate this energy which will also result in additional heating. This too can be eliminated with the
addition of an external zener diode connected from each drain to ground. The zener breakdown voltage should be in the
range of 30 V to 34 V.
Under Voltage Lockout and Auto Power Down
An Under Voltage Lockout circuit has been incorporated to prevent erratic device operation under low power supply
conditions. This circuit enables the Motor Drives when V_DD rises above 4.7 V to guarantee full IC functionality, and disables
the drives when V_DD falls below 4.2 V. The UVLO circuit has 500 mV of hysteresis to prevent oscillations as the thresholds
are crossed during power-up and power-down. The IC is designed to directly drive 9.0 V and 12 V motors.
As previously discussed, the device features a selectable auto Power Down mode. This mode is automatically entered
when the voltage applied to the Speed Control Input commands zero or less than zero percent on-time. When entered, the
power supply current is reduced from 1.6 mA to 130 μA. Refer to Figures 1, 2, and 14.
Thermal Shutdown
Internal Thermal Shutdown circuitry is provided to protect the device in the event that the maximum junction temperature is
exceeded. When activated, typically at 140°C, the Motor Drive outputs are disabled to reduce device power dissipation. This
feature is intended to prevent catastrophic device failures in the event of accidental overheating. Although it is possible to
operate the device above the specified maximum junction temperature of 125°C, this protection feature is not intended to be
used as a substitute for proper thermal system design. When the junction temperature falls below 120°C, normal device
operation resumes. Refer to Figure 19.
Figure 19- Thermal Shutdown Operation
Thermal
Shut Down
Deactivated
Motor
Drives
Enabled
T_J(max)
Thermal
Shut Down
Activated
Motor
Drives
Disabled
80
100
120
140
160
T_J, Junction Temperature (°C)
SYSTEM APPLICATIONS
The following section shows numerous device circuit configurations and several complete fan control solutions with a brief
description. For clarity, many of the circuits show only the internal functional blocks that are of interest with the associated
pin numbers.
© Andigilog, Inc. 2006
- 12 -
www.andigilog.com
August 2006 - 70A04018