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SiP styles for magnetic position sensors in automotive apps

Posted: 10 May 2016 ?? ?Print Version ?Bookmark and Share

Keywords:magnetic position sensor? MPOS? automotive rotary position sensor? PCB? SiP?

In addition, an isolator is required between the cover and the housing. This isolator hinders the use of magnetic position sensors in very harsh environments, where a completely airtight assembly is needed for protection against the ingress of liquids such as oil or water. In this case, an additional seal between the housing and the cover is required to protect the components inside the housing. The application of this extra seal adds cost and complexity to the production process.

By contrast, figure 3 shows how an MPOS realised as a SiP may be accommodated inside a completely overmolded housing: this airtight assembly resists the ingress of liquids, and is suitable for the harshest automotive environments. In addition, failure analysis of an airtight assembly is far quicker and easier.

Facing the challenge of EMC regulations
One potential disadvantage of the PCB-less SiP solution could be that it is more prone to damage by electromagnetic compatibility (EMC) events and high transient voltages. Today's conventional discrete MPOS implementations C with a PCB C commonly use special counter-measures such as multi-layer ground planes or special board layout techniques to increase the circuit's immunity to transients.

Figure 3: The SiP enables the production of a guaranteed airtight housing.

Since a SiP is a complete circuit in a moulded package, it is not possible to add components near the MPOS or change the board layout to eliminate any vulnerability to EMC events. If a SiP is to be used, then, it must be carefully chosen to ensure that it meets system-level EMC requirements.

Supply-chain simplification
The discussion earlier has described the advantages of a SiP implementation in terms of performance. But it also brings advantages to the production engineer as well as the design engineer. This is because a SiP has a smaller, simpler supplier chain than a discrete MPOS design (figures 4, 5).

This is because: there is no requirement for a PCB supplier; and the supply chain for the external components supporting the MPOS (such as capacitors, resistors) is handled by the SiP manufacturer.

This greatly simplifies the automotive supplier's arrangements for quality assurance, purchasing and production.

Figure 4: Minimum supply chain for discrete MPOS solution.

Figure 5: Minimum supply chain for SiP MPOS solution.

How ams implements the MPOS circuit in a SiP
Now ams has integrated the latest MPOS technology together with discrete decoupling components in a single package: this is its AS5171 SiP product (figure 6).

Figure 6: The ams AS5171 SiP magnetic position sensor.

This package has only three external pins: a power supply pin (VDD), a ground pin (GND) and an output pin (OUT). The output supports various communication protocols which may be freely chosen by the system designer. The connection to these three pins may be soldered or welded, for complete flexibility in production (figure 7).

Figure 7: Magnetic position sensor module with a welded terminal.

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