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Datasheet: https://eu.mouser.com/datasheet/2/821/MMC5883MA-RevC-1219541.pdf

Here is their answer and my question:

Hello,

May I know whether or not I can do away without the 10 uF set/reset coil's capacitor ?

The datasheet mentions something about a charge pump: In the device status register, bit #3:

"Pump On Indicates the charge pump status."

Does the 10 uF capacitor on the CAP pin have anything to do with this charge pump ? If yes, what voltage swings are expected on the CAP pin ?

I do not intend to ever use the set/reset coil. Datasheet says:

"The SET/RESET function can be performed for each measurement, periodically, or when the temperature changes by a predetermined amount as the specific application requires. In addition, the SET/RESET function clears the sensors of any residual magnetic polarization resulting from exposure to strong external magnets."

I have no need for these functions above. So, will the MMC5883MA run fine without that 10 uF cap ?

Thank you

Hi

10uF is a must for MMC5883MA, and no need to use the charge pump.

Please let us konw your application and company, then we can provide better support. Thanks.

No further answers from them. I have tried taking out the 10 uf cap for testing; it seemed to work fine without it. Since they say I need it I shall leave it there. But I still wonder why it is needed...

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    \$\begingroup\$ SET/RESET operation is required to restore proper sensor operation in case of disturbing fields. If you don't put the 10 uF cap then you would see unwanted behavior in your IC. \$\endgroup\$
    – user115094
    Oct 19, 2020 at 19:43
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    \$\begingroup\$ Not only does the SET/RESET pulses restore operation from disturbing fields as @Blue_Electronx mentions, but it also allows AMR bridge offset voltage to be calibrated out. Only if you don't need good data should you consider not pulsing. Considerable pulse current during SET/RESET requires that big capacitor. Without it, pulse current can't saturate the AMR bridge sensor. At some point, I'd consider a SET and/or RESET pulse mandatory - you don't know what happened during shipping/storage. \$\endgroup\$
    – glen_geek
    Oct 19, 2020 at 20:40

1 Answer 1

Reset to default
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Capacitors charge over the course of time and thus are often used for filters. In this case, the capacitor acts as a buffer on the input to prevent the noise from influencing the pin.

If your ground signal becomes subject to noise, what happens when the set/reset pin sees that noise? It is a very decisive signal that changes the state of operation of the device. Per the datasheet:

the SET/RESET function clears the sensors of any residual magnetic polarization resulting from exposure to strong external magnets

This is something that changes the operation of your device and it may be difficult to return to your prior operating state if the set/reset pin receives an erroneous or undesired signal.

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