XTR111: Maximum current output for integrated Regulator

Hi Stephan,

user4991603 said:

can the integrated regulator source more than 5mA of current?

The integrated regulator 5mA_min is a typo. It seems that it can source high current, but the output will droop, so 5mA_max should be the limit per the REGF specification. 

user4991603 said:

I would really like to avoid the suggested external solution from figure 45c as space is very limited in my design.

Will you be able to do this? Use OPA189 or similar op amp to obtain a voltage with higher current driving capability. Some op amp comes with small package, and is capable to drive up to 40mA or more in current. 

user4991603 said:

I just tried to set up a simulation with the XTR111 in Pspice but there doesn't seem to be a simulation model for the XTR111.

We do not have PSpice model for XTR111. In Tina-TI, we only have the pseudo simulation model, see the attached file. 

XTR111_0-5V_to_0-20mA 08152023.TSC

If you have other questions, please let us know. 

Best,

Raymond

Hello Raymond,

I mean we could also use the same supply the XTR111 is using but the board will work in high temperature environments and we want to avoid temperature related drift of the OPA189 as much as possible.

It probably won't be better to shift the heat to the XTR111 but it isn't bad to have a cleaner supply for the OPA in TIA configuration that works with currents in the 100nA range.

We also want to be able to switch opamps and alot of the precision opamps out there don't have such a high supply range like the OPA189 has.

Using the spice simulation model of the OPA189 in LTspice led to a suspiciously low noise density at the output of the circuit.

Thanks for your suggestion but instead of using a separate opamp to generate the supply of an opamp with REGF as reference I would rather use an external LDO with a better tolerance or implement the suggested circuit in figure 45c with a prebiased transistor like this for example:

https://www.digikey.de/de/products/detail/diodes-incorporated/DDTD113EC-7-F/1934746

Best regards,

Stephan

Hi Stephan,

OPA189 will have an ultra low temperature drift and it should work well in elevated temperature. The XTR111's datasheet is only specified up to 85C, though it may go up to 125C, but the performance specification may change. 

user4991603 said:

but it isn't bad to have a cleaner supply for the OPA in TIA configuration that works with currents in the 100nA range.

We normally do not recommend to use chopper amplifier (OPA189) for TIA application. Due to the large feedback resistor in TIA, it may generate additional voltage spikes near the chopper frequency. What is the TIA application?

Enclosed is a TIA application note for your reference, and we have many others as well.  

https://www.ti.com/lit/ug/tidu535/tidu535.pdf?ts=1692072987429

user4991603 said:

Using the spice simulation model of the OPA189 in LTspice led to a suspiciously low noise density at the output of the circuit.

The OPA189 should have very low noise density, see the image below. I am unable to use LTSpice due to license agreement, but we can verify it via Tina-TI. 

user4991603 said:

I would rather use an external LDO with a better tolerance or implement the suggested circuit in figure 45c with a prebiased transistor like this for example

As long as the Vref is stable, OPA189 based voltage reference will out perform LDO at any time, especially at higher temperature. LDO's regulation is in 1% or better range. OPA189 or op amp based voltage reference can be multiple magnitude better than 1%. BTW, the linked LDO is not temperature compensated.  

If the application requires higher current, then LDO will be the choice. Also, op amp does not like drive capacitive load, which it needs some kind of compensation for the loop stability. 

If you have other questions, please let us know. 

Best,

Raymond 

Hi Raymond,

it is going to be a TIA for a photodiode. The gain of the circuit currently is 11.000.000 V/A.

A photo current of 91nA leads to an output amplitude of 1V but I will probably double the gain.

The photodiode capacitance is pretty low compared to other photodiodes.

I have simulated the circuit again in LTspice and the output noise density now looks more realistic than it looked before.

now: 72uV / sqrt(Hz) VS before: 22nV / sqrt(Hz)  

i will probably switch to a JFET Input opamp. 

Do you know the chopper frequency of the OPA189? It is not stated in the datasheet.

Can you suggest a diffferent opamp for a photodiode TIA? 

Regarding your circuit example from before: you are using the REGF output of the XTR111 for the opamp reference voltage but I think that I read that the REGF output has a tolerance of 5%.

Best regards,

Stephan

Hi Stephan,

user4991603 said:

i will probably switch to a JFET Input opamp. 

user4991603 said:

Can you suggest a diffferent opamp for a photodiode TIA? 

The PRAMPS TIA op amp is designed up to 50MHz. If the op amp's BW is higher than 50MHz, then you have to look into HSAMPS products. I think that OPA320, OPA328 and OPA3S328 has low noise spectrum density that you may be interested in. JFET type may be in OPA827, OPA828, OPA140 in the link below (You can sort these based on the key performance parameters in your design by selecting filter options in the front columns with two fields).  My guess is that the application needs the op amp's BW near 20MHz range. 

https://www.ti.com/amplifier-circuit/op-amps/precision/products.html#480=1&3247max=0.02%3B1&sort=7typ;asc&

https://www.ti.com/amplifier-circuit/op-amps/precision/products.html#480=1&3247max=1%3B10&sort=7typ;asc&

HS op amp TIA products: 

https://www.ti.com/amplifier-circuit/special-function/transimpedance/products.html

user4991603 said:

Do you know the chopper frequency of the OPA189?

I believe that the chopping frequency is near 125kHz range, see the plot below. 

user4991603 said:

Regarding your circuit example from before: you are using the REGF output of the XTR111 for the opamp reference voltage but I think that I read that the REGF output has a tolerance of 5%.

I mentioned if the input Vref does not change, the Vout from op amp will be very precise, which is better than LDO. Yes, XTR111's voltage reference has ±5% tolerance, If the application requires a precision reference voltage, you may have to go with bandgap or voltage reference with low temperature drift part in ppm/C.

If you have other questions, please let us know. 

Best,

Raymond 

Hello Raymond,

thanks for your help so far.

Is it possible that we switch to private message or email for further application advice?

Best regards,

Stephan

Hi Stephan,

Raymond is traveling at the moment, I'll reach out and connect and we can discuss over email.

Regards,
Mike

Hello Mike,

thanks and I'm looking forward talking to you.

Best regards,

Stephan