I need to drive this Delta Sigma ADC, for current sensing, from a 50mV shunt. The common mode voltage can occasionally goto +6 or -6V.

The absolute maximum ratings specify
Input voltage of VDD+0.3 Max, and AGND-1.6V Min.
Continuous Current to the pin is +10mA or -10mA.

Will it be alright with a series resistors of 5k on the positive & negative inputs to drive this ADC? I can add a diode to VDD for positive side protection, but cannot do so for the negative side, as this ADC generates the negative supply internally with a charge pump and the negative supply pin is not available outside!

I would appreciate any suggestion for any other method of protection.
Thank You for your time.

Rama D

 

Part number of ADC ?

Regards, Dana.

 

I need to drive this Delta Sigma ADC, for current sensing, from a 50mV shunt. The common mode voltage can occasionally goto +6 or -6V.

The absolute maximum ratings specify
Input voltage of VDD+0.3 Max, and AGND-1.6V Min.
Continuous Current to the pin is +10mA or -10mA.

Will it be alright with a series resistors of 5k on the positive & negative inputs to drive this ADC? I can add a diode to VDD for positive side protection, but cannot do so for the negative side, as this ADC generates the negative supply internally with a charge pump and the negative supply pin is not available outside!

I would appreciate any suggestion for any other method of protection.
Thank You for your time.

Rama D

A 5K resistor would limit current to <10mA. Unfortunately, the only guidance the datasheet gives re input voltage is to not exceed the PS/Gnd voltages by more than a few tenths of a volt. In my opinion that is not sufficient information. We do not know what input voltage would be produced by your 6V/5K limiting, despite that it meets the input current limit. To be safe, at a minimum, add Schottky diodes from the inputs to ground and power, in addition to the 5K resistors OR otherwise limit the input voltages to keep them from exceeding the gnd-to-Vdd range. The internal negative voltage is irrelevant. The specs are relative to ground and Vdd, and both of those are available to you.

 

The input Z is of concern -



To maintain 16 bit accuracy you need to account for this.


Regards, Dana.

 

Part number of ADC ?

Regards, Dana.

It's TI ADS131M04.

 

A 5K resistor would limit current to <10mA. Unfortunately, the only guidance the datasheet gives re input voltage is to not exceed the PS/Gnd voltages by more than a few tenths of a volt. In my opinion that is not sufficient information. We do not know what input voltage would be produced by your 6V/5K limiting, despite that it meets the input current limit. To be safe, at a minimum, add Schottky diodes from the inputs to ground and power, in addition to the 5K resistors OR otherwise limit the input voltages to keep them from exceeding the gnd-to-Vdd range. The internal negative voltage is irrelevant. The specs are relative to ground and Vdd, and both of those are available to you.

Thanks for the response.
That was my concern too. But the Vin negative limit is GND-1.6V, and GND-1.2V is usable too. That's where I am stuck.

 

Thanks for the response.
That was my concern too. But the Vin negative limit is GND-1.6V, and GND-1.2V is usable too. That's where I am stuck.

It would be helpful if you would post your schematic so we can see how and why a +/-6V common-mode voltage is necessary, and what steps might be taken to better interface to the ADC.

 

The input Z is of concern -

View attachment 197582

To maintain 16 bit accuracy you need to account for this.


Regards, Dana.

Thank you Dana.
I was thinking of calibration to manage the drop in the input resistor due to lower input impedance. Will that be alright?

 

It would be helpful if you would post your schematic so we can see how and why a +/-6V common-mode voltage is necessary, and what steps might be taken to better interface to the ADC.

Sure. I'm out of town and would post it as soon as I reach office tomorrow.

 

W

Thank you Dana.
I was thinking of calibration to manage the drop in the input resistor due to lower input impedance. Will that be alright?

What G are you using in A/D settings, the input amp internal to part ?

Regards, Dana.