Witam

Projektuę obecnie płytkę dla A3977 na elementach dyskretnych przewlekanych.
W dziale FAQ dla A3977 znalazłem kilka zaleceń producenta odnośnie projektu
płytki jak i mocy rozpraszanej, pozwolę sobie je zapreazntować (tylko wybrane):

Q10 - Are there any layout concerns I should be aware of?
Yes. The sense resistor, Rs, should be connected as close as possible to the device.
The ground side of Rs should return on a separate trace to the ground pin(s) of the
device. The ground traces at the device should be as large as physically possible.
A 47 µF or larger electrolytic decoupling capacitor should be placed between the
load supply pins and ground and be placed as close as physically possible to the device.

Q12 - What is the recommended minimum copper ground plane area for reducing
power dissipation at high currents?
A ground plane area at least two times larger than the package outline is a good place to
start. For further layout considerations, please refer to the following on the Allegro website:
"Package Thermal Characteristics" at
http://www.allegromicro.com/techpub2/th ... rmlchr.pdf

Q13 - Are there special techniques to reduce the package power dissipation when
running at high currents?
Use of external Schottky diodes with low Vforward, to clamp the outputs to VBB and
ground, will help to reduce the power dissipation in the A3977. Heat sinks are also a
possibility, but not as efficient. Note: When using external diodes, synchronous rectification
should be disabled to achieve maximum results. For additional information, please refer to
the following on the Allegro website: "Power Drive Circuits" at
http://www.allegromicro.com/techpub2/te ... werics.pdf

Q14 - Is there an application note on the use of external diodes?
There is no application note about using external diodes for the A3977. Each of the outputs
should have one Schottky diode connected to VBB (cathode to VBB). Each output should
also have one Schottky diode connected to ground (anode to ground, not to the sense pins).
When full-step mode is used, or if PFD is set to slow decay only, then use only the four
Schottky diodes between the outputs and ground. The four Schottky diodes from the
outputs to VBB will not help improve thermal performance in slow decay mode.

Tu można znaleźć wszystkie FAQ odnoścnie A3977:
A3977 FAQ

W związku z tym mam pytanie do kolegi wojtekl, czy mógłbyś sprawdzić
jak układ zachowuje się z dołożonymi clamp diodes, czy faktycznie zmniejszy się
grzanie układu A3977? Wg. producenta powinno to dać lepsze efekty niż radiator.

Ski Man