L6208PD software, I managed to overheat and damage the L6208PD. I used
a standard soldering iron to disengage
each of the L6208PD’s 36 pins and the
high-wattage soldering iron to break
the solder bond between the PCB
heatsink area and the L6208PD heatsink
lug. The L6208PD removal operation
took less than 10 minutes to perform.
The L6208PD pin layout is very well
thought out. All of the L6208PD ground
connections lie on the four corner pins
of the device. The L6208PD heatsink lug
is also attached internally to the device’s
grounding system. Thus, all we have to
do is pull our combination ground/
heatsink pad through the center line of
the L6208PD pads, attaching the four corner L6208PD ground pins in the process.
The L6208PD datasheet recommends that a star ground point be
placed at the intersection of the
ground return point of the H-bridge
sense resistors and the bulk power
supply ground entry point. A 100 μF
bulk filter capacitor (C3 in the schematic) is also located at this star ground
point. The star ground point serves as
the single-point connector area for the
signal and power grounds, as well.
Large pad areas are used to
connect the H-bridge current sense
resistors (R9 and R10) between the
L6208PD SENSEA/SENSEB pins and the
star ground return point. Take another
look at Screenshot 1 and you will see
that the same large pad area design
point is also applied to the bulk
power (VSD, GND) and motor winding
terminations (1A, 2A, 1B, 2B).
A pair of 0.041 inch pads with
0.020” holes are used to interface the
L6208PD’s H-bridge output pins to their
termination points. The thru hole pads
provide a high-current path from the
L6208PD H-bridge pins on the top side of
the PCB to the H-bridge termination pins
that are fed from large pad areas on the
bottom side of the PCB. Note also that
the incoming bulk supply voltage is distributed to the L6208PD power pins using
a large bottom side pad and 0.031 inch
thru holes to the L6208PD power pins.
I really like using screw terminals for
motor project boards. However, it can be
a pain in the rotor to screw and unscrew
motor leads and power leads when you
need to fix or make changes to
the board’s electronic components.
The ideal solution is to design in
removable screw terminations.
For this project, I used 5 mm
pitch PCB mounted terminal block
headers. The terminal block headers accept 5 mm removable screw
terminal blocks. The removable
screw terminal blocks I used come
as an assembly of two screw
terminations on a removable block.
The terminal block pairs can be
coupled to other terminal blocks to
form a single integrated terminal
block of screw terminals that can be
removed and mounted as a single entity.
The 5 mm terminal block headers
and their matching 5 mm screw terminal
block assemblies can be had from
Digi-Key. The 24-pin breakable 5 mm
terminal block part number is ED1682-
ND. The two-position 5 mm terminal
block plug assembly can be ordered from
Digi-Key as part number ED1613-ND.
Since you can’t see the 5 mm terminal block assemblies completely when
they are mounted, I’ve provided a shot of
the terminal block headers and the terminal block plug-in assemblies I used in this
project in Photo 1. You can also get the
terminal block plugs with 3, 4, 5, 6, 7,
10, or 12 screw terminals per assembly.
Now that the foundation of the
L6208PD Motor Driver Board is in
PHOTO 1. Isn’t it funny? Here we are designing
a device around a piece of high-tech silicon
and the least complex piece of the puzzle — a
screw terminal — demands our attention.
place, let’s flesh out the supporting
hardware. All of the L6208PD’s
companion componentry is laid down
on our driver board in Screenshot 2.
My L6208PD application requires a
bulk voltage between 12 and 24 volts.
Thus, the voltage rating for C3, in my
case, can be safely set at 35 volts. The
L6208PD can accept bulk voltages up
to 52 volts. So, choose your working
voltage for C3 accordingly.
C1, C2, and C9 are all rated for
100V. C1 and C2 are standard ceramic
chip capacitors in a 1206 SMT package. It
is recommended that C9 be a higher quality type of capacitor. My C9 is a thru hole
mounted 0.22 μF metalized polyester film
capacitor (Digi-Key BC1647-ND).
H-bridge sense resistors R9 and R10
should be non-inductive, which eliminates
SCREENSHOT 2. Things are starting to shape up and make sense. With the L6208PD
supporting hardware in place on the printed circuit board, all we have to do is run
some traces to put the capacitors and resistors to work for us.
SERVO 03.2008 51