TLV61048: 2.7VIN - 12VOUT Boost Converter - Vout not reaching 12V at 3VIN and no load condition

Some more details:

IC is set to work at 600kHz, but I have tested with 1MHz and it behaves the same way.

Cin is 22uF

Cout is 330uF, low ESR

Hello Rai,

Could you share some waveforms of VIN, VOUT, SW and inductor current? We would like to see some details. Thanks.

Hi Zack,

Please see the waveforms below.

Key is CH1 (Yellow) = 12V Out rail / CH2 (Purple) = 2.7-3.3V in DC rail / CH3 (Blue) = SW Node voltage / CH4 (Green) = Input Current to Boost Converter from Vin

STARTUP WAVEFORM - VIN = 2.7VDC

STARTUP WAVEFORM - VIN = 3V DC

STARTUP WAVEFORM - VIN = 3.3V DC

==============================================

NORMAL OPERATION - VIN = 2.7V DC / NO LOAD ON VOUT RAIL

NORMAL OPERATION - VIN = 3.0V DC / NO LOAD ON VOUT RAIL

NORMAL OPERATION - VIN = 3.3V DC / NO LOAD ON VOUT RAIL

As you can see from the waveforms above, the IC is switching at 2.7VIN to 3.3VIN range, but it is drawing very less current at 2.7VIN and when the voltage is increased to 3.3VIN, it draws more current from the bench supply to reach the 12V target output.

Can you advise why it would not be able to boost the 2.7VIN to 12V with no load? Is there some internal mechanism in the IC that is not being met or tripping to prevent it from working to get to 12V dc?

Please let me know if you need more waveforms or information.

Hi Zack,

Some more waveforms if they are helpful. I was able to measure the current through the inductor too so have attached waveforms below.

Key is CH1 (Yellow) = 12V Out rail / CH2 (Purple) = 2.7-3.3V in DC rail / CH3 (Blue) = SW Node voltage / CH4 (Green) = Inductor Current (10x for TA018 100mV/Amp setting)

VIN = 2.7Vdc

============================================================

VIN = 3V DC

=============================================================

VIN = 3.3V DC

===================================================

VIN = 3.6VDC

=========================================================

With VIN at 3.6Vdc, the Vout > 12V dc does happen and the converter goes into the PFM mode as per the waveforms I am seeing. Another interesting observation is that when the Vout > 12Vdc and the converter is in PFM mode, then if I drop the VIN to 3.3V or 3V dc, it keeps the voltage at 12Vdc correctly.

Hi Rai,

It's quite strange that when Vin is 2.7V, 3V that output voltage is less than setting 12V. When FB pin is less than reference voltage, the device should have switching to transfer energy from VIN to VOUT.

Could you also share the schematic and layout?

Hi Zack,

Please find the requested information below. It is quite strange that the device goes into the PFM type waveform mode when Vout < 12V at the 2.7V and 3V indeed. It does work correctly at > 3.6V which indicates that the circuit is fundamentally working, just not at the lower voltages for some reason.

Schematic is as below.

DC-DC Boost - TLV61048.pdf
...
PCB Layout Screenshot with the relevant components highlighted as below:Bottom Layer (Blue) is Ground plane.

Hello Rai,

Please remove the capacitor C24. It will affect the normal regulation.

Let me know if the problem still exists.

In the meanwhile, I suggest you update your layout in next version PCB. The Cout should be placed close to diode and IC GND.

Hi Zak,

I have removed the 100nF C24 part and the issue is still present in the behaviour. It doesn't drive to 12V DC and it is still showing the PFM type of behaviour at the 2.7-3V DC input levels.

Hi Rai,

I'll check it on EVM. Due to tight resource, please wait a while.

Hi Zack,

Will wait for your feedback but if you can expedite this, it would be appreciated as I need to resolve this issue asap with the converter design.

Is there anything about the converter IC in the Errata or internal design documentation that suggests that it would not work below 3V dc? It seems weird that it works fine at 3.3Vdc at VIN almost like that it is some sort of internal threshold to start working properly and below 3.3Vdc doesn't work reliably at all.

Below 3V VIN doesn't work at all in this design which is not as per the datasheet.