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Compact DC Voltage and Current Sense PCB with Analog Output
Features
•
New! Three Ideals ranges for small robotics applications:
o
New 50 V / 180 Amps
o
50 V / 90 Amps
1
o
New 13.6 V / 45 Amps
Low zero current offset and high sensitivity
Analog output scaled for 3.3V ADC
Self powered
Compact thin design (4 x 15 x 19mm)
Analog Voltage Outputs for Sensed Parameters:
o
50V/180A = 63.69mV / Volt 18.30mV / Amp
o
50V/90A = 63.69mV / Volt 36.60mV / Amp
o
13.6V/45A = 242.3mV / Volt 73.20mV / Amp
New! Re-designed to accept direct solder connection with
Deans Ultra connectors
Description
A small voltage and current sense
PCB. DC current is determined by
measuring voltage drop across a
shunt resistors then converted to
analog voltage output by the
Texas
Instruments
INA-169.
Voltage sense is accomplished by
scaling to 3.3V ADC range by a
precision resistor divider.
The current limit coincides with
maximum power rating of the
shunt resistors.
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•
•
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Assembly
The PCB is supplied without leads or connectors. Care must be exercised in soldering,
though the pad sizes are large enough to accommodate 12 gauge heavy duty leads (see
photograph below). Smaller gauge leads may be easier to solder without creating shorts.
The sensed current path is from “In+” to “Out+”. It is important to completely flood this
connection path through shunt resistors with solder,
on both sides
of the PCB. As-supplied,
the PCB has some solder flooding in this area, but it is up to you to ensure this is maintained
after attachment of leads. The shunt resistors each have four terminals in a Kelvin
configuration. Two terminals carry the shunt current load, and the other two terminals are
used for the voltage drop monitor INA-169.
It is important that both shunt resistors carry equal current load for sensor accuracy. To
ensure equal current load, the solder pads have a large via holes through which the leads
must pass through then be flooded with solder. Pass the “In+” and “Out+” leads through the
large via holes and solder flooded on top and bottom of the PCB. The “GND” pads also have
a large via hole however large current does not flow through the PCB from the GND leads;
the PCB “GND” pad is merely a small current common GND connection. The large current
flow in GND is from one lead to the other through the pad and solder-flooded via hole itself.
Photo Tips for Soldering
AttoPilot International LLC, 2011
1
180 Amp Sensor – Recommended Lead Arrangement
For the 180 Amp sensor, it is recommended to use doubled pairs of 12 gauge wire, as shown
above.
AttoPilot International LLC, 2011
Figure 1 Schematic
2
Connection to ADC and Use
There are three 0.1” spaced plated through holes labeled “GND”, “V” and “I”.
V
is the analog output
for voltage sensing, and
I
is analog output for current sensing.
V
and
I
are both relative to
GND.
You
may use this sensor directly with a 5V ADC, however some resolution will be lost relative to a 3.3V
12 bit ADC unless a higher bit ADC is used. For scaling factors refer to “Features” table at the top of
page 1 of this document.
The
I
analog output contains a 0.1uF bypass capacitor, but no series resistor. To complete an RC
filter into the ADC inputs, you may place a low value resistor between the ADC inputs and
I
output.
The
V
output has a resistance of 14.7kΩ between the sensed drain and analog output with 0.1 uF
bypass capacitor for an approximate bandwidth of 108 Hz, via the equation 1/(2
π
RC)
The shunt resistors typically need no cooling airflow as the copper leads provide a facile pathway
for heat loss. Power dissipation by the shunt resistors is:
Dissipated Power = I
2
x R
For the “90A” device R = 5x10
-4
Ohms, power in Watts, and current in Amperes. The upper power
limit of each shunt is 2 Watts for a total of 4 Watts in their parallel configuration. The upper current
limit is computed by solving the equation above for I with R = 0.0005 Ohms and Power = 4 Watts. I
= (4 Watts / 0.0005 Ohms)
0.5
= 89.44 Amps. Max amps for “45A” “180A” parts below.
Absolute Maximum Ratings
Operating Temperature………………....-55 to +125 Centigrade
Voltage with 3.3V ADC…………….......-0.3V to 51.8V (upper limit set to not exceed 3.3V output)
Voltage with 5V ADC…………………..-0.3V to 60V (upper limit set to not exceed INA169 limit)
Current……………………………….….44.7
/
89.4
/
178.8 Amps (upper limit set by shunt resistor)
AttoPilot International LLC, 2011
3
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