Instrumenting Boards with Smart Sensors

Document created by David G Dicarlo Employee on May 28, 2019Last modified by David G Dicarlo Employee on May 28, 2019
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Related links:

i.MX Power Profiling System: Smart Current Sensor and Aggregator Shield 

i.MX Power Profiling System: Aggregator Shield Details  

i.MX Power Profiling: Triple-range Smart Current Sensor  

 

Examples of boards instrumented with Smart Sensors. (Some close-ups will be added later.)

 

One rail of the i.MX7ULP SOM is instrumented here. The sensor is immobilized with foam double sticky tape on top of the i.MX7ULP (trying to minimize contact to just that so the tape is more easily removed later). Immobilization is necessary in order to prevent ripping the resistor pads off the target board. The series resistor on the board is removed and the smart sensor is wired into place.

 

Note here that the sensor is shorted so that the SOM will operate while the Smart Sensor being unpowered. The Smart Sensors MUST be powered via the Aggregator in order for the target board to operate. Otherwise, the target board will be starved of power and it will not operate unless all of the Smart Sensors connected to it are powered. An unpowered Smart Sensor presents an open circuit between the input and output terminals.

Here are nine rails instrumented on the i.MX8QM CQC board. One rail Smart Sensor is in the bottom side, the rest are all on top. There is one double sticky taped to the back of the connectors at the back of the photo (the SCU supply, relatively low current, which can tolerate longer wires/series resistance). The rest are connected with 24 gauge wire, no longer than about half an inch long, to keep the series resistance low. The ground wire (center contact) can be a 30 gauge wire-wrap wire, which was used for all the grounds here. Note that the stiff connection wires allow the sensors to stand up in place, which is very helpful since there is no room to double sticky tape the sensors down. This board was not laid out with instrumentation in mind.

Here is an i.MX8QXP CQC board with four rails instrumented. Two of the sensors are on top and two on the the bottom. They are not double sticky taped into place, but they are shielded with heat shrink tubing to prevent any contact with the target board. As above, 24 gauge wires are used for the current in/out lines, 30 gauge wire is used for all the ground contacts. Out of the frame, the four ribbon cables are bundled together to prevent the wires and sensors from moving too much. As above, the heavy wires have been kept as short as possible.

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