TPS61040-Q1: Uncertain behavior with higher temperature

Hi Tobias,

Could you help on the following measurements for further debug:

• Monitor the Vin, Vout, SW and Iout;
• Same the above waveforms at different temperatures, for example, 25C, 50C, 70C, 75C, 80C, 85C.

I'd like to know what happened to the IC around 80.5°C.

Thank you.

Regards

Lei

Hi Tobias,

If available, could you share the application?

Regards

Lei

Hi Lei,

here are the requested measurements:

Note: At the right-hand end of the illustrations, where the temperature decreases rapidly, you can see the shutdown of our product.

Figure 1 (above) shows:

• the temperature curve of the regulator, measured at the surface of the housing (blue)
• the input voltage (red)
• the input current (green)

Figure 2 (above) shows:

• the temperature curve of the regulator, measured at the surface of the housing (blue)
• the output voltage (red)
• the output current (green)

The following figures show the SW signal measured with an oscilloscope.
Note: The large overshoots on the rising edge of the SW signal are due to the measurement setup. In order to carry out the measurements, the measurement signal had to be routed out of the temperature chamber via long cables.

SW @ 50°C

SW @ 70°C

SW @ 75°C

SW @ 80°C

SW @ 85 °C

SW @ 87°C

TPS61040 circuitry:

Inductor: VLS3012ET-100M 10 µH

Input Capacitor: 4.7 µF; 6.3 V; X5R; 0402

Output Capacitor: 1 µF; 50 V; X5R; 0805

Thanks for the support

Regards

Tobias

Hi Tobias,

Thanks for providing the detailed information.

I'll check and give you the feedback today.

Regards

Lei

Hi Tobias,

I measured the efficiency on TPS61040EVM, here are the data for your reference.

We can see that as the temperature is below 95C, the efficiency is quite stable. As the temperature increases more, the input current increases and the efficiency drops to 56.15% at 125C. This is normal because the IQ and Rdson increases as the temperature increases.

On my measurement, the input current is 51mA even the TA is 125C. But in you circuits, the input current jumps to around 200mA when TA is around 85C, which is abnormal.

I don't think the TPS61040 internally consumed current will have such a big jump around 85C, could you help check again that where the test point is when your measure the Iout? Are there any possible load changes from next stage at the TPS61040 Vout?

Is there a feedforward Cff used in your application? If yes, will it have a big leakage when the temperature increases above 85C?

If you try a fresh TPS61040 in your application, will the same behavior be generated?

Thank you.

Regards

Lei

Hi Lei,

the current was measured at a 1 Ohm resistor at Vin.
There is no load change at the output. We repeated the measurement with a 5k (Iout=5mA) resistor to rule this out.

Cff is 10pF.

The problem currently occurs in all assemblies in which the TPS61040 is installed.

Can you show me your circuit (and layout)?

Thanks.

Regards

Isabell 

Hi Tobias,

The basic schematic and layout can be downloaded here. Since I only have this official EVM at hands.

I just make a little adjustment to configure the TPS61040 as normal boost circuit, shown below.

Here is the picture of the EVM which I used to test.

Could you send me the part number of Cff? And also the layout?

Thank you.

Regards

Lei

Hi Tobias,

Could you send me your schematic and layout?

And if available, could you also ship two boards to me so I can check in our lab?

Thank you.

Regards

Lei