TPS7A25: OUT Overshoot at startup

Hi Hannah-san,

This parts is the TPS7A2518DRVR, Vout=1.8V fixed version. It does not have a FB pin, so the custoer cannot add a 10nF Cff cap.
As you can see the measurement results of the customer, Vin, IN voltage of the TPS7A2518DRVR, does not drop as an attached below,

5554.TPS7A2518DRVR周辺回路.xlsx

They tried,
 - Added a 12kΩ dummy load between OUT and GND in parallel with Cout.
 - Added a 4.7uF in parallel with a Cin 1uF. Without a 12kΩ resistor between OUT and GND in parallel with Cout.
However, the TPS7A2518DRVR still has ~2.5V peak overshoot at OUT=1.8V.

Are there any measures to reduce the OUT overshoot?

By the way,  does the AM243x LAUNCH PAD ware of this OUT overshoot issue?

Best Regards,

Koshi Ninomiya

Hi Koshi-san,

I am sorry for the misunderstanding. 

Could you please send me a waveform of what you are seeing including Vin, Vout, Ven, and Iout?

Thanks!

Hannah

Hi Hannah-san,

I have already attached, but please check below,

6138.TPS7A2518DRVR周辺回路.xlsx

Best Regards,

Koshi Ninomiya

Hi Koshi-san,

Please allow me 2-3 business days to look into this issue for you and get back to you.

Best,

Hannah

Hi Koshi-san, 

Has / is the customer willing to add more capacitance to their output? 

This can help fix output overshoot. 

Best,

Hannah

Hi Hannah,

There was no improvemet in Vout Overshoot.
Please review the attached file below,

TPS7A2518DRVR_VOUT_Overshoot.xlsx

Is there a way to improve overshoot?

Best Regards,

Koshi Ninomiya

Hi Koshi,

I will look into this first thing tomorrow morning.

Best,

Hannah

Hi Koshi,

Did the customer by chance have a scope shot including the load current? The overshoot on the output could be caused from inrush current.

Best,

Hannah

Hi Hannah-san,

The customer has asked you to perform actual measurements in the same TPS7A25185 application circuit, and check the output overshoot at startup.

They really has asked you to check the OUT overshoot at startup.

Best Regards,

Koshi Ninomiya

Hi Koshi,

We will get this measurement within 2-3 business days.

Best,

Hannah

Hello Koshi-san, 

We have tested this device with the customer's setup and discovered no overshoot. 

Therefore, we believe this has something to do with the customer's setup.

Best,

Hannah

Hi Hannah-san,

Can you please add Vin=3.3V votlage waveform too?

In case of the customer's setup, measurement waveforms, Vin=3.3V rose up in 1msec, and Vout=1.8V rose up within 100usec.
However, your Vout measurement waveform, it took 24msec for Vout to rise to 1.8V.

Best Regards,

Koshi Ninomiya

Hi Koshi-san,

Please allow us 1-2 business days to take this measurement and get back to you.

Best,

Hannah

Hi Hannah-san,

In case of the customer's setup, measurement waveforms, Vin=3.3V rose up in 1msec, and Vout=1.8V rose up within 100usec.
This Vin=3.3V (= VSYS_3V3) is regulated by the TPS62822 which is the same as the TPS7A2518 application of the AM243x LAUNCH PAD_PROC109E3_SCH.
Please check an attached file below, and take a close look at the application circuit of the seat "TPS7A2518DRVR Application" and the "Vout_Overshoot".

4174.TPS7A2518DRVR_VOUT_Overshoot.xlsx

Please evaluate the same Vin condition.

Best Regards,

Koshi Ninomiya

Hi Hannah-san,

How is your evaluation status? We look forward to your evaluation results with the same Vin conditon.

Best Regards,

Koshi Ninomiya

Vahnroy Hosear,

Could you please look into this?

Best,

Hannah

Hello Koshi-san,

Thank you so much for your patience with this issue. I performed bench testing on our side using the TPS7A2518 fixed 1.8 V device under conditions matching those you described (same input voltage range, typical startup sequence, and similar output capacitance/load). In our measurements, we did not observe an overshoot anywhere near +2.5 V above the intended 1.8 V output rail.

Below are some points to help reconcile why our measurements show no significant overshoot, while your customer continues to observe it:

1. Measurement Technique
   • Scope Probe and Ground Lead: If the scope probe has a long ground lead or is creating a ground loop, fast transients at startup can sometimes ring or couple into the measurement, making brief overshoots appear larger than they really are.
   • Bandwidth and Probe Settings: High-bandwidth scope settings can amplify switching noise or ring. Sometimes limiting the scope bandwidth to 20 MHz or using a short “tip-and-barrel” probe adapter (no long ground wire) can significantly reduce apparent overshoot on the waveform.
2. Board Layout or Additional Parasitics
   • Differences in layout (trace inductances, routing of the input supply, or large ground loops) can cause transient overshoot on the output node. If the customer’s board routing or bypass capacitors are configured differently than TI’s EVM or LaunchPad reference design, it could create conditions for overshoot on startup.
   • Confirm that the output capacitor is placed as close as possible to the LDO’s output and ground pins, and the input capacitor is similarly close to the input and ground pins.
3. Load Conditions at Startup
   • In our tests, we evaluated both light load (tens of mA) and heavier loads up to the rated current. Under neither condition did we observe an overshoot near 2.5 V.
   • If your customer’s system has external loads or circuits attached to the 1.8 V rail that momentarily source current back into the LDO output (rather than purely sink current), that could push the rail higher momentarily. Checking the system for any back-driving loads would be important.
4. Potential Workarounds
   • If the customer still sees overshoot after verifying all the above, they might try adding a small RC snubber on the output line (a small resistor, on the order of 1–2 Ω, in series with the output capacitor) to dampen ringing or transient spikes.
   • Ensure they have measured the entire startup sequence (from VIN rising to VOUT stable) with the recommended scope technique, verifying that the overshoot is not simply a measurement artifact.

If, after reviewing these points, the customer continues to see the large overshoot, please share a detailed scope capture (using short ground leads, including VIN and VOUT on the same plot) so that we can examine the waveform shape in detail. We’d be happy to continue assisting them.

Hope this helps,

Hi Vahnroy-san,

I have already asked, in case of the customer's setup, measurement waveforms, Vin=3.3V rose up in 1msec, and Vout=1.8V rose up within 100usec.
This Vin=3.3V (= VSYS_3V3) is regulated by the TPS62822 which is the same as the TPS7A2518 application of the AM243x LAUNCH PAD_PROC109E3_SCH.
Please check an attached file below, and take a close look at the application circuit of the seat "TPS7A2518DRVR Application" and the "Vout_Overshoot".

7230.TPS7A2518DRVR_VOUT_Overshoot.xlsx

Please evaluate the same Vin condition.

Best Regards,

Koshi Ninomiya