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• Resolved

TPS61046: Operation Below 4 V Output Voltage

Part Number: TPS61046

Hi there!

I would like to have your opinions on using the TPS61046 slightly out of specification.

The input voltage is between 3.0 V and 3.3 V, the output voltage is set to 3.71 V. The load is made up of 8 LEDs, which are simultaneously switched on and off at around 2 kHz.

In the datasheet, it is mentioned that "The TPS61046 starts to limit the output current whenever the output voltage drops below 4 V." I only need 45 mA of current when all LEDs are continuously lit, so I figured it is worth the try and got the evaluation kit. I loaded the output with a 68 Ohm resistor and found that the TPS61046 will not start up when powered. However, if I leave the load unconnected while powering the TPS61046, it will start up and power the 68 Ohm load when connected.

I have read in other topics that it is better to start the TPS61046 in light load conditions, which is feasible in the design, as can be seen in the schematic of the LEDs below:

For improved efficiency, I would like to power the TPS61046 directly from the system voltage rather than from the VCC rail. The system voltage varies from 3.0 - 4.33 V. I noticed that when the input voltage rises above the output voltage, the TPS61046 stops switching at some point and the output voltage will rise some 50 mV over the programmed output voltage at 4.33 V input voltage. This would be acceptable in the product.

Q1) Is drawing 45 mA at an output voltage of 3.71 V feasible at an input voltage of 3.0 V - 3.3 V if we guarantee that the TPS61046 can start up with no load connected?

Q2) If the answer to Q1 would be affirmative, would it be possible to use an input voltage range of 3.0 V - 4.33 V ?

I'm looking forward to your feedback!

Cheers,

Casper

• Hi Casper:

May I know what's the status of your project? For Vin, Vout below 5.5V cases, I'll recommend TPS61099 or TPS61023 for you.

Best Regards

Minqiu

• In reply to Minqiu Xie:

Hi Casper:

As long time no hear from you, I assume you have solved the issue. If not, just reply below. Thank you!

Best Regards

Minqiu

• In reply to Minqiu Xie:

Hi Minqiu,

I want to use this specific part because of BoM consolidation, as it is used more often on this PCBA and for higher output voltages.

I would like to hear expert opinions on operating the TPS61046 in the regions I described in my previous message.

Cheers,
Casper

• In reply to Casper van Doorne:

Hi Casper:

The TPS61046 is designed for higher output voltage. To prevent the inrush current and other functions, TPS61046 has limited current capability when Vout is low, like below 4V.

That's why I recommend TPS61099 and TPS61023 for you.

Best Regards

Minqiu

• In reply to Minqiu Xie:

Hi Minqiu,

I understand your recommendations and, obviously I will use a different part if the TPS61046 cannot do the job. I am still looking for an answer to my original two questions though:

Q1) Is drawing 45 mA at an output voltage of 3.71 V feasible at an input voltage of 3.0 V - 3.3 V if we guarantee that the TPS61046 can start up with no load connected?

Q2) If the answer to Q1 would be affirmative, would it be possible to use an input voltage range of 3.0 V - 4.33 V ?

Best regards,
Casper

• In reply to Casper van Doorne:

Hi Casper:

I did several test in our lab and the converter can supply such case in room temperature. But it should be noted that we can't guarantee every part has such capability.

Best Regards

Minqiu

• In reply to Minqiu Xie:

Hi Minqiu,

I accidentally pressed the "This resolved my issue" button, sorry about that.

It is good to see that you were able to replicate the results that I had in my lab with the evaluation kit.

Now, if we know a bit more about the design of the part, we could be able to definitely say if it will be able to supply the required 45 mA, even though it is beyond the scope of the regular specification of the device.

Please go the extra mile, since we will be using this part a lot and we are keen to optimize from a cost perspective.

Best regards,
Casper

• In reply to Casper van Doorne:

Hi Casper:

In my test, the inductance peak current limit is larger than 300mA for Vin=2.5V, Vo=3.7V.

As it's not one of standard test item during production, it's hard to give you a certain answer.

Best Regards

Minqiu

• In reply to Minqiu Xie:

Hi Minqiu,

I have calculated the peak inductor current to be 156 mA worst case.
I am still inclined to give this idea a try.
Once we have a prototype batch we can see how much margin there is over the entire performance range.