Connecting from 5V sensor to 3V3 adc channel

[FinFet]

Hello everyone,
I want to make an adc reading using STM32F103C8T6 but I am really confused. first of all, the sensor I will use is the hall effect open loop current sensor ‘L31S300S05FS’ model. this sensor has 4 pins VCC GND VOUT VREF from these pins
VCC= 5V
GND
VREF IN OUT MODE = 2.5V
The VOUT pin gives an output voltage that I do not fully understand. Does it make sense to connect the VREF and VOUT pins at the output of the sensor directly to the ADC pins of the processor or do I need to use an OPAMP? If I need to use an opamp, please help me how to connect the VREF pin. thanks.

[AScha.3]

Hi,

>The VOUT pin gives an output voltage that I do not fully understand.

Its "standard" for DC current sensors : about 2.5V for zero current , +/- xx mV (depending on measured current)

-> at 50A : 2,5 + 0,625 = 3,125 V or at -50A : 2,5 - 0,625 = 1,875 V   VOUT .

>VOUT pins at the output of the sensor directly to the ADC pins of the processor 

Ok, if you stay in the range of the ADC (0..3,3V , at 3v3 VDD i suppose) , you can connect it direct to ADC inputs.

But you can only go up to about 60A + , then VOUT reaches the ADC max. input (3v3).

on other current direction signal will go to lower input voltage, so no problem up to -150A . (the sensors limit)

So: if about -150A ... +60A is ok for you, connect ADC direct. (and get best resolution from adc.)

If you need +/-150A , most simple solution is a divider: 2 x 4k7 , to get 1/2 VOUT to the ADC input.

(But at 6dB loss of ADC resolution .)

[FinFet]

First of all, thank you very much for your reply. Based on the information you have given, does it make sense to connect the VREF pin that the sensor outputs directly to the ADC?

[AScha.3 · Accepted solution]

Yes, if you want to see the "zero ref" (on other ADC channel );

but "usually" the zero signal is just : read in the VOUT (100x or more, to get good average value),

when no current at start.

If you start your program at any time, with current running in sensor, then you need the Vref  as your zero value.

Vref is 2,5V , so no problem to read direct by the ADC.

[FinFet]

Thank you very much for taking the time to reply.