Motor Output
60
Juno Step Motor Control IC User Guide
10
Figure 10-1:
PWM High/Low
Encoding
In PWM High/Low mode two output pins are used per motor or per motor phase, allowing separate high-side/low-
side control of each bridge switch. In this scheme, as
shows, the high side output and the low side output
are never active at the same time, and there is generally a period of time when neither output is active. This period of
time is called the dead time, and provides a shoot through protection function for MOSFET or IGBT switches.
Figure 10-2:
PWM High/Low
Signal
Generation
The dead time is specified in
nSecs. The correct value can generally be determined from the MOSFET or IGBT IC
manufacturer’s data sheet, or you can call PMD Corp. technical support if you have questions.
In addition to dead time, some high side switch drive circuitry requires a minimum amount of off time to allow the
charge pump circuitry to refresh. This parameter specifies this refresh time and has units of nSecs. The related
parameter of refresh time period, which is the time interval between these off time refreshes has units of current loop
cycles.
It is also possible to control the maximum allowed PWM duty cycle. This may be useful to limit the effective voltage
presented to the motor windings, or to provide some other needed off-time for the switching amplifier circuitry.
0 / 1024
(100% negative
command)
1
0
1
0
1
0
1
0
1
0
1024 / 1024
(100% positive
command)
1023 / 1024
(large positive
command)
512 / 1024
(zero command)
1 / 1024
(large negative
command)
The Juno step motor control IC default values for dead time, refresh time, and refresh period are set to be max-
imally safe but are not appropriate to drive typical switching hardware. For proper amplifier function these values
must be set with values appropriate for the connected switching circuitry.
PWM High-Side
Drive
1
0
PWM Low-Side
Drive
1
0
Dead Time
Dead Time
