Main Site Documentation

Connect an Allegro A1318 Hall Effect sensor to micro ADC


#1

I am planning on connecting an Allegro A1318 Hall Effect sensor to a 12-bit ADC on an NXP LPC1751 micro (datasheet: http://www.kynix.com/uploadfiles/pdf9675/LPC1751FBD80.pdf.)

My application is to compare relative differences in magnetic fields between various magnets. I don’t need to detect a changing magnetic field, so I have no need for a high sample rate. I need to measure up to 60 milliTesla (600 Gauss).

The DC output resistance is low (typically less than 1Ω) due to the internal amp, I believe, and I think that’s a good thing.

The Output load resistance is specified as 4.7 kΩ minimum. I believe this means the load must be this value (or higher) for the output to remain stable. Likewise, the load capacitance should be less than 10nF.

The typical application circuit shows this RLRL, along with a suggested output capacitor of 4.7 nF. A1318 typical application circuit

CiaCia is specified as 15 pF maximum. Does this mean the ADC will “add” 15 pF of capacitance to the line while sampling?

The ADC on the NXP micro is multiplexed between many inputs, but I only need to use a single input. Do I have pay attention to the value of the sampling capacitor inside the micro? (I read through this TI app-note on multiplexed ADCs and I think I don’t have to worry about the sampling capacitor really.)

I think I can connect the sensor, with RLRL = 4.7 kΩ and CLCL = 4.7 nF, directly to the microcontroller ADC without using a buffer. Is this correct?

Follow-up: *I implemented this circuit without any loading resistor and it operated just fine. *


#2

do you think to ask that question at https://community.nxp.com/community/lpc makes more sense ?
i would say yes…