Hi. We've placed these items in a temperature- and magnetic-controlled chamber for 2 weeks, cycling 5C to 38C:
1) 2 each EVM modules from TI
2) Custom boards with DRV425's (not Q1) using non-magnetic materials and conforming to the recommended datasheet circuit
3) Laboratory grade magnetometers to nullify the magnetic field
Each time the temperature returned to 25 C, the EVM modules showed no more than 50 nT offset. However, the custom boards showed more than 500 nT offset. We have 3 theories:
1) Our soldering technique required touch-ups with a hand iron, which may have heated the devices,
2) The devices vary in performance depending on the particular day the silicon was made,
3) The EVM circuit is different than the recommended circuit in the datasheet (shouldn't matter, but....),
Do you have any thoughts on what might be causing our boards (which use the same passive components as the EVM, but the recommended circuit in the datasheet) to perform differently than the EVM? Also, do you believe the automotive quality part would have lower drift over time and temperature? Thanks.