TMC5160 DATASHEET (Rev. 1.08 / 2018-NOV-19)
21
BRIDGE OPTIMIZATION EXAMPLE
A stepper driver for 6A of motor current has been designed using the MOSFET AOD4126 in the
standard schematic.
The MOSFETs have a low gate capacitance and offer roughly 50ns slope time at the lowest driver
strength setting. At lowest driver strength setting, switching quality is best (Figure 3.6), but still
shows a lot of ringing. Low side gate resistors have been added to slightly increase switching slope
time following high-side bulk diode conduction by increasing the effect of Gate-Drain (Miller) charge.
High side gate resistors have been added for symmetry. Tests showed, that 1nF output capacitors
dramatically reduce ringing of the power bridge following bulk diode conduction (Figure 3.7). Figure
3.8 shows the actual components and values after optimization.
+VM
470n
CA2
HA2
4.7µF
HS
HS
CA1
4x AOD4126
470n
HA1
10R
10R
10R
10R
BMA1
Coil
out
BMA2
LA1
LS
LS
1n,
100V
1n,
100V
LA2
SRAH
47R
47R
50m,
2512
SRAL
Figure 3.8 Example for bridge with tuned components (see scope shots)
BRIDGE LAYOUT CONSIDERATIONS
-
-
Tune the bridge layout for minimum loop inductivity. A compact layout is best.
Keep MOSFET gate connections short and straight and avoid loop inductivity between BM and
corresponding HS driver pin. Loop inductance is minimized with parallel traces, or adjacent traces
on adjacent layers. A wider trace reduces inductivity (don’t use minimum trace width).
Minimize the length of the sense resistor connection to low-side MOSFET source, and place the
TMC5160 near the sense resistor’s GND connection, with its GND connections directly connected to
the same GND plane.
-
-
-
Optimize switching behavior by tuning gate current setting and gate resistors. Add MOSFET bridge
output capacitors (470pF to a few nF) to reduce ringing.
Measure the performance of the bridge by probing BM pins directly at the bridge or at the
TMC5160 using a short GND tip on the scope probe rather than a GND cable, if available.
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
