THS4541: when the temp is -20, the output will oscillate(about 300MHz)

Amelie Zheng

Part Number: THS4541
Other Parts Discussed in Thread: TINA-TI

Hi Team,

Customer now use THS4541 and when the temp is -20, the output will oscillate(about 300MHz), and the output is normal when the temperature is higher than this.

The differential output of this chip does have some capacitive loads (differential mode load 100Ω in parallel with 4pF, positive and negative outputs each have 18pF capacitance to ground), the circuit topology is the usual single-ended input to differential output. The stability margin simulation is as follows:

The phase margin of the Aolβ curve exceeds 90° at 0dB

Aolβ curve amplitude margin when 180° phase shift is -1.21dB

Any advice about this?

over 3 years ago

0 Michael Steffes over 3 years ago

Guru 48395 points

Well Amelia,

That little hump out there in the gain is probably your issue, without the full ckt, no way to proceeed,

The TINA model is a nominal estimate at room temp, if you are starting out with that peak, yes shifting over temp and process could slip over to oscillations. The peak is probably due to the open loop Zol resonance.

Probably will need to eliminate or isolate those 18pF elements.

0 Sima Jalaleddine over 3 years ago

TI__Mastermind 28475 points

Hello Amelie,

Thank you for the simulations, would you also be able to share the Tina-TI File? But, Michael's suggestion is the most probable fix.

Thank you,

Sima

0 Amelie Zheng over 3 years ago in reply to Sima Jalaleddine

TI__Genius 10865 points

Hi Sima and Michael,

Thanks for your reply. I am asking customer to share the file with us.

The open-loop output impedance in the THS4541 model is the structure shown in the figure below

The resistance of the two resistors R15 and R17 is 1.233Ω in the model. What is the average value and standard deviation of the resistance in the actual chip? What is the temperature coefficient? And what is the distribution of wire bonding inductance?

0 Amelie Zheng over 3 years ago in reply to Sima Jalaleddine

TI__Genius 10865 points

Hi Sima and Michael,

FYI.

THS 4541 Stability for TI.TSC

0 kai klaas69 over 3 years ago in reply to Amelie Zheng

Guru 140200 points

Hi Amelie,

what is the purpose of this circuit?

amelie_ths4541_1.TSC

amelie_ths4541.TSC

As you can see, the circuit is instable.

Kai

0 kai klaas69 over 3 years ago in reply to kai klaas69

Guru 140200 points

The introduce of 4R7 isolation resistors could help:

Kai

0 Michael Steffes over 3 years ago in reply to kai klaas69

Guru 48395 points

Why are you putting all those RLC elements inside the output stage path? The model has the internal elements the product the Zol, you don't need those if that is what you are trying to emulate.

Amplifiers

Amplifiers forum

THS4541: when the temp is -20, the output will oscillate(about 300MHz)