AMC8500 Datasheet, PDF (16/27 Pages) List of Unclassifed Manufacturers – TWO PHASE VARIABLE SPEED FAN MOTOR CONTROLLER

Preliminary Specification
aMC8500
Figure 31- Driving Single Phase Full Wave Motors
12 V
0.1
10
k
10 k
H
SN
M
NS
10
k
0.1
10 k
12
3
4
Under Voltage
Lockout
Hall Amplifier
Non-Overlap
Commutation
16
1
Motor
Drives
Single phase full wave motors can be driven with the addition of two external P-channel MOSFETs. With the gates cross coupled as
shown above, the internal and external MOSFETs can perform as a full bridge driver. Commutation shoot through current is minimized by
the internal non-overlapping delay circuit. The resistor capacitor time constant must be just long enough to prevent pulse width modulation
of the two external PFETs. Current limit protection is maintained since the load is in series with the internal MOSFETs. The motor drive
outputs are limited to a maximum of 36 V.
Figure 32- Current Limit Threshold Programming, Noise Pick Up and Motor Soft Acceleration
Current
Limit
Latch
R
Q
S
Current Limit
Comparator
10 μA
13
Current
Limit
Set
Noise
Pick Up
Elimination
2
110 k
10 nF
Bypass
Capacitor
Current Limit
Threshold Reduction
To V_ref
Single Resistor
Current Source
Biased
Dual Resistor
Reference
Biased
Soft Motor
Acceleration
To V_M
Optional
C_accl
The Current Limit Set input is susceptible to noise pick up and in most applications will require a 10 nF bypass capacitor. The Current
Limit Comparator threshold can be reduced by connecting a single resistor from Pin 2 to ground. This is the most economical
programming method but it is somewhat less accurate than using the dual resistor method shown. This is due to the fact that the
Reference Output is more accurate than the absolute values of the internal current source pull-up and terminating resistor. Motor soft
acceleration during power-up can be accomplished by connecting a capacitor from Pin 2 to ground. During initial device power-up, the
internal current source will charge capacitor C_accl thus gradually increasing the current limit threshold. The diode shown is optional and
may not be required if there is sufficient time for the internal components to discharge the capacitor from when the power source is
removed and then reapplied.
© Andigilog, Inc. 2006
- 16 -
www.andigilog.com
August 2006 - 70A04018