Rev. 1.00
134
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Rev. 1.00
135
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HT66FM5440
Brushless DC Motor A/D Flash MCU
HT66FM5440
Brushless DC Motor A/D Flash MCU
Current Protection Function
T
he device contains a
n
internal OPA0, a high speed (2
µs
)
1
2-bit A/D Converter, an 8-bit D/A
Converter and a comparator to measure the motor current and to detect excessive current values。If
an over current situation should occur, then the external drive circuit can be shut down immediately
to prevent motor damage. More details are provided in the Over Current Detection chapter.
As the motor driver PCB will have rather large amounts of noise, and as this noise will be amplified
by the OPA0, this can easily lead to false triggering. For this reason the Fault Mode must be used.
The PROTECTOC mechanism provides a more immediate current protection. Ensure that the ISHE
bit has been set to select the hardware over current protection before setting the OCPSE bit high.
After this the over current compare interrupt int_Is can be used to directly switch off the drive
signals. Since Int_Is is a pulse signal, a latch component must be used to latch the over current
trigger source. When the PROTECTOC signal is logic high, the drive signals at the polarity stage
will be ignored and the over current protection logics in the OCPS register are used to immediately
switch off drive signals to protect the power MOS. To remove the PROTECTOC over current
protection mechanism, set the OCPSE bit from low to high to trigger the software reset function
thus pulling the PROTECTOC signal to low, after which the normal polarity drive signals will be
recovered.
For the MOS current limiting mechanism Int_AHL_Li, when AHLHE=0 then the hardware mode
is disabled, and when AHLHE=1 the hardware is enabled. The current limiting circuit is a hardware
circuit, for which the A/D converter channel must select one of th
e
operational amplifier outputs if it
is to be effective.
AHLPS=0 → The protection ciruit will allow the PWM output to immediately restart once the Int_
AHL_Lim interrupt has been reset.
AHLPS=1 → The protection circuit will only allow the PWM output to restart on the next PWM
period once the Int_AHL_Lim interrupt has been reset.
For the MOS over current mechanism Int_Is, when ISHE=0 the hardware mode is disabled. When
ISHE=1 the hardware mode is enabled and the protect signals are generated according to the
CMP0_EG[1:0] bits in the OPOMS register. It should be noted that only when CMP0_EG[1:0]=11 a
interrupt will be generated, but no protection is activated. When ISPS=0, the Fault Mode is selected,
when ISPS=1, the Pause Mode is selected.