THS3470: DIE_TEMP output not working

Andy Bartfay

Part Number: THS3470

I am using a Rev. B chip in a 10 MHz, +/-25V application. So far, it is working well. However, the DIE_TEMP output is not working. With no load, the output is static at ~1.8V, no matter the temperature. VMID and VDD are stable at 0V and 5V, respectively.
Please help.

5 months ago

0 Ignacio Vazquez Lam1 5 months ago

TI__Mastermind 20650 points

Hi Andy,

Just to confirm, when you turn on the device with no output signal or load with a heat sink, does the voltage at this pin remain at 1.8V? Are you using our EVM for your testing or are you implementing your own PCB design?

Best Regards,

Ignacio

0 Andy Bartfay 5 months ago

Prodigy 160 points

Ignacio,

My error.
The DIE_TEMP output stabilized at 1.76V in power-down mode. Had I looked more closely, I would have noticed that it started at ~1.6V and climbed to ~1.85V out of power-down. This is with no heatsink to promote heating (running for a short time to avoid overheating). The final product will have a heatsink.
Sorry for the false alarm.

When do you expect production silicon?

Thanks,
Andy

0 Ignacio Vazquez Lam1 5 months ago in reply to Andy Bartfay

TI__Mastermind 20650 points

Hi Andy,

Thanks for confirming this. As for the official release we expect the full release by the end of the year with the final datasheet.

Best Regards,

Ignacio

0 Andy Bartfay 5 months ago in reply to Andy Bartfay

Prodigy 160 points

Ignacio,

The above numbers are with the DIE_TEMP output unloaded. With the op amp circuit connected (below), the DIE_TEMP output is ~1.3V at ~ 25C and its response seems much less than 5mV/C. In this configuration, DIE_TEMP needs to source only ~50uA. Note that the DIE_TEMP outputs are connected.
Is the op amp circuit inappropriate?

Thanks,
Andy

0 Ignacio Vazquez Lam1 5 months ago in reply to Andy Bartfay

TI__Mastermind 20650 points

Hi Andy,

I can ask our team for the driving capability of this temp pin. I assume this should not be an issue. If you remove R361 and use a multimeter to measure the die temp pin, do you see the voltage at ~1.3V? I am not sure if this is possible with your design but, if possible, could you try this. The die temps being connected should not be an issue.

Best Regards,

Ignacio

0 Andy Bartfay 5 months ago in reply to Ignacio Vazquez Lam1

Prodigy 160 points

Ignacio,

With R361 removed, the DIE_TEMP output works properly. My post above (Oct 23 10:08 AM, "The DIE_TEMP output stabilized at 1.76V in power-down mode...") was with R361 removed.

Thanks,
Andy

0 Ignacio Vazquez Lam1 5 months ago in reply to Andy Bartfay

TI__Mastermind 20650 points

Hi Andy,

That might be making a little more sense. The VMID pin is not meant to drive much and can be causing this weird behavior. Our designer was not available today, but I will try to confirm this next week but now that you are sharing this info, I believe that is what is happening.

Best Regards,

Ignacio

0 Andy Bartfay 5 months ago in reply to Ignacio Vazquez Lam1

Prodigy 160 points

Ignacio,

The DIE_TEMP difference amp does not use VMID. R362 is not installed, but R367 is. I'm using split tracking supplies for the THS3470, so VMID = 0.

Andy

0 Ignacio Vazquez Lam1 5 months ago in reply to Andy Bartfay

TI__Mastermind 20650 points

Hi Andy,

Thanks for clarifying I mixed up the resistors. I will ask and get back to you.

Best Regards,

Ignacio

+1 Ignacio Vazquez Lam1 5 months ago in reply to Andy Bartfay

TI__Mastermind 20650 points

Hi Andy,

I was able to get some clarity on this pin and the best route to take for this device. Internally the device is not buffered so the circuit you have is pulling current and ultimately changing the conversion. We are working on the final version of the datasheet but for these pins we would recommend buffering them. You could try increasing the resistors to 100kohms but ultimately the best option would be using a buffer.

Best Regards,

Ignacio

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THS3470: DIE_TEMP output not working