TPS61021A: TPS61021ADSGR Output Voltage Drops Under Load

Hello Nivethitha,

Please check the input voltage when you step to 300mA. It is possible that the voltage on the VIN pin of the device is dropping below the minimum supply voltage.

Best regards,
Brigitte

Hi Brigitte,

The input voltage is fixed 1.5V , but when load of 300mA is given, the output drops to zero. why does this happen?

Hello Nivethitha,

Can you please check the input voltage with an oscilloscope on the IC VIN pin?

Best regards,
Brigitte

Yes brigitte, I can check and share the scope screenshots. But, Could you confirm that if we can use the same converter with AAA battery as input as 3.3V/3V output under 500mA load, with affecting the output voltage?

Hi Brigitte,

Please find the below scope shot.

Below is the schematic we implemented, the load is given across C10 , D12 is DNP (to neglect the forward voltage drop - used for testing purposes only)

Hi Nivethitha,

I tried the same condition with 350mA load and did not see any problem. Please zoom in the VOUT-drop part to 10us/div. And add SW pin waveform.

Hi Brigitte,

Thank you for your help on this case.

Best Regards,

Travis

Hi Travis,

Please find the below image, Could you mention which part of Vout you wanted to be zoomed in?

This waveform is taken using TPS61021A-PWR723 Evaluation Module under 350mA load

Could you confirm that if we can use the same converter with AAA battery as input(Voltage from 1V to 1.5V) as 3.3V/3V output under 500mA load, with affecting the output voltage?

Also, please note when 2.5v is given as input the output voltage drops to 2.9v(which is expected to be 3.3v)

Hi Nivethitha,

From the waveform, we can see that the VIN drops before VOUT. So I think the input rail has large internal resistance or low current limit and cannot support  that output power.

Best Regards,

Travis

Yes, Vin drops immediately after the load, but the evaluation module is supplied from 3A,DC power supply. 

Vout delay in drop can be of output capacitor?

How will it behave with battery as input, wont it be able to deliver required load current for eg.(350mA atleast)?

Hi Nivethitha,

Maybe the 3A DC power supply have terrible transient performance. Please apply bulk capacitor over 200uF on the input side and see whether the VIN still drops.

The 22uFx2 output capacitor cannot hold Vout for over 600us.

About battery input, this depends on your internal resistance. If the battery has terrible internal resistance, it'll still encounter such Vin_drop -> device_reset problem. You can calculate the maximum output power of battery by (Vbat_open)^2/(4*Rin) 

Best Regards,

Travis

We have conducted tests using the AAA Duracell battery, as well as two different power supplies, and we observed that the output voltage sometimes drops to zero. In other cases, we noticed a gradual decrease in the output voltage under increased load. Specifically, with a 3.3V output, the voltage drops progressively from 3.3V to 3.1V, 2.9V, 2.7V, 2.5V, and so on, depending on the load conditions.

Additionally, we used a 100µF capacitor in parallel with the existing 150µF capacitor that is already integrated into the evaluation board. However, this did not fully resolve the voltage drop issue.

Could you please share your test results and setup when applying the same 350mA load current with a 1.5V input? It would help us compare performance and identify potential solutions to improve transient performance.

Our requirement is,

Input voltage - 0.9V to 1.5V (from AAA Battery)

Output voltage - 3.3V

Output current - 500mA

with lower quiescent current(in uA)

Please do suggest any boost converter that suits the application?

Hi Nivethitha,

This picture is captured under below condition:

Vin1V Vout3.3V Iout 0A->500mA->0A

CH1: VIN

CH2:SW

CH3: VOUT

CH8:Iout

I think TPS61021 suits this application well. If the VIN drop rapidly when load is applied, then other IC cannot work normally as well.

Best Regards,

Travis