ADS1115: Internal Capacitance/Inductance information for explosion-proof

Hi Ryuuichi Machida, 

The ADS1115, TLA2021 and TLA2022 do not have simple, fixed internal capacitance and inductance values.

These are dynamic and change based on the specific measurement and the device configuration. The devices have a high input impedance which draws little current and have a minimal effect on the circuit being measured. The input sampling capacitors are well below 10pF.

When totaling the PCD total capacitance for directives such as the ATEX, the filtering capacitors on the analog inputs be full magnitudes larger than any internal capacitance of these devices.

The IBIS models for each device are linked below, this can give further insight to the inductance and capacitance for each pin. 

ADS1115

TLA202x 

Regards, 

Andrew

Hi,

Thank you for your reply.
I calculated internal Capacitance and inductance value by using IBIS.
Here is case of ADS1115 as example.



And also added sampling capacitor of DeltaSigma ADC (This is made by quoting your comment.)



As you know, IBIS model only show I/O information.
I understand that it's difficult to provide actual value, but I will try to provide as much information as possible.
Is there any information which you can disclose ?

Best Regards,

Hi Ryuuichi, 

The internal sampling capacitor of the Delta-Sigma ADC is well below 10pF, but an over estimation would be fine for calculations. We don't have the exact information for the total capacitance and inductance of the devices.

However, it is important to note that in a typical application of the ADS1115, TLA2021, and TLA2022 requires the use of a power supply decoupling capacitor. These capacitors are the uF capacitance range which nearly negates the pF capacitance of the device itself. 

From datasheet: "VDD must be decoupled with at least a 0.1µF capacitor" this capacitor converted to pF would be 100,000pF.

Regards, 

Andrew

Hi,

Thank you for your reply.
>These capacitors are the uF capacitance range which nearly negates the pF capacitance of the device itself. 
Do you mean that internal total capacitor should be amount of "pF"?

What do you think about "total internal inductance" ?

Best Regards,

HI Ryuuichi, 

After a short discussion with the design team here's what information I have:

A good estimation for the total device capacitance is 100pf. This includes both the analog and digital loads. 

The IBIS numbers are good for inductance since it measures the inductance on the bond wire. The only inductance is on the bond wires. 

The total device capacitance will be significantly smaller than the system capacitance when you account for the analog filtering capacitors and the power supply decoupling capacitors.  

Please note that this information is not guaranteed by the datasheet and is used at your own risk.

Regards, 

Andrew 

Hi,

Thank you for discussing about this on your team.
I understood way of thinking for ADS1115.

>A good estimation for the total device capacitance is 100pf. This includes both the analog and digital loads. 

>The IBIS numbers are good for inductance since it measures the inductance on the bond wire. The only inductance is on the bond wires. 
Can we say same thing for TLA2021 and TLA2022 as well ?
If internal total capacitance / inductance are different from ADS1115, please inform this as well.

Best Regards,