Buck boost regulator ripple affecting magnetometer accuracy...

[vinodstanur]

Hi,
I am using tsp6120 buck boost regulator to provide 3.3v from a lipo battery. But magnetometer heading calculation results in +- 4 degree error!
But when I connected it directly to battery, it is working fine...
I am using LSM303DLHC magnetometer+accelerometer chip...
Tried to reduce the ripple using capacitors etc, but still magnetometer heading is showing +- 4 degree error....
Any suggestions?

 

[BradtheRad]

Yes, this seems to be a mystery...

Until we remember...

The coil creates a magnetic field. It will throw off any magnetic sensor nearby.

Could that be the cause?

 

[crutschow]

Can you move the regulator in relation to the magnetometer to see if that changes your error?

 

[vinodstanur]

I am keeping the magnetometer far from the regulator.

- - - Updated - - -

I can see 150mv ripple but I cannot use a high value capacitor because my pcb is very small and total expected pcb height is also very less, say 2.5mm...

 

[crutschow]

Post the schematic of the regulator circuit you are using. (I couldn't find any reference to the tsp6120. Is that the correct number?). Does the regulator layout follow the data sheet recommendations?

If you can squeeze in a small inductor in front of the output capacitor, that may help significantly.

 

[HTA]

The LSM303DLHC needs typical 150uA. If the magnetic field is the problem then maybe a Buck/Boost Charge Pump gives better result. If the ripple on the supply line it the problem then a LDO might an option. The layout could also cause a problem if the switching current is flowing through the LSM303DLHC ground line.

Enjoy your trouble shooting design work!