TLV9064: capacitive load

Hi Ivy,

That's a difficult question to answer as it really depends on a set of other conditions such as:

• system's acceptable stability level (phase margin)
• gain configuration
• feedback network
• Inclusion of a isolation resistor
• Inclusion of the dual feedback topology
• Any resistive load in the network

May I ask a few questions:

• Is 10nF the maximum capacitive load?
• Are you expecting the load to vary quite a bit in capacitance? 
• Would you be interesting in using an isolation resistor or other topology that improves stability? 
• Is there a particular gain you need this op amp to be in? 

The more information you provide the better we can support this! 

Best Regards,

Robert Clifton 

Hi Robert,

Thanks for your reply!

Below is customer's schematic.

In customer applications, when a 10nF capacitive load is connected to the output of the TLV9064, the output can sometimes be stabilized at 2.5V, and sometimes the output will oscillate randomly as shown in the figure below.(Vref=Vout=2.5V，Vout(p-p) 500mV)

The customer has no specific requirements for gain and phase margin, but expects the output to be stable.

Could you please help give your suggestions about the issue, or whether the TLV9064 can not support 10nF capacitive load?

Regards,

Ivy

Hi Ivy,

Thank you for sharing! 

I put this in TINA-TI to see if there's any instability issues. I made some changes to the circuit to make it easier. I changed the supplies to dual supply configuration with 0V on the Vref rather than the single 5V supply and Vref = 2.5V.  

Looking at the second stage. It's labeled as the LMV3544, I'm assuming this was also to be a TLV9064. I also assumed that the 10nF capacitor was located on Vout. Please correct me if I'm wrong on that. 

As you can see, the phase margin is 10.91 degrees aka this circuit is unstable. For reference, we recommend having 45 degrees of phase margin to have what's considered a stable circuit. 

Is the customer able to make adjustments to their circuit design to add an Riso resistor? 

Best Regards, 

Robert Clifton

Hi Robert,

Highly appreciate your help! It's helpful, thanks!

Regards,

Ivy