Datasheet

TMC603 DATA SHEET (V. 1.05 / 11. Mar. 2009) 39
Copyright © 2008 TRINAMIC Motion Control GmbH & Co. KG
where
I
MOTOR
is the motor current, e.g. 10A
R
DSON
is the on-resistance of the MOSFETs at a gate voltage of about 10V, e.g. 20m
t
DUTY
is the actual duty cycle of the chopper, e.g. 80% = 0.8
V
VM
is the motor supply voltage, e.g. 24V or 48V
f
CHOP
is the chopper frequency, e.g. 20kHz
t
SLOPE
is the slope (transition) time, e.g. 300ns
Example:
With the example data for a 10A motor at 24V, we get the following power dissipation:
P
STAT
= 3.2W
P
DYN24
= 2.88W
For comparison: The motor output power is 10A*24V*0.8=192W
The dynamic and static dissipation here are in a good ratio, thus the choice of a 20m
MOSFET is good.
At 48V, the dynamic power dissipation doubles:
P
DYN48
=5.76W
Here, the dynamic losses are higher than the static losses. Thus, we should reduce the slope time.
Given that the gate capacity would not allow for faster slopes than 300ns, we could go for a 30m
MOSFET, which has a lower gate charge and thus allows faster slopes, e.g. 200ns. With these
modifications we get a static loss of 4.8W and a dynamic loss of 3.84W. This in sum is 8.64W, which is
slightly less than the 8.96W before. At the same time, system cost has decreased due to lower cost
MOSFETs. The loss is still low when compared to a motor power of 384W.