TPS43060: Output Voltage dips at switching load

Himanshu Gupta16

Intellectual 265 points

Part Number: TPS43060
Other Parts Discussed in Thread: , LM5122

I am using EVM TPS43060EVM-199, My Load is switching type ( ON :- 5 ms, OFF :- 5ms, 1.2 Amps MAX)

The Output Voltage dips approx 5 Volts.

Kindly Suggest the solution.

over 5 years ago

0 Himanshu Gupta16 over 5 years ago

Intellectual 265 points

I/P Voltage :- 12V, O/P Voltage :- 50V

0 Garrett Roecker over 5 years ago in reply to Himanshu Gupta16

TI__Mastermind 21720 points

Hi Himanshu,

Please post the schematic and the changes that you made to the EVM. The standard output of the EVM is 40V not 50V.

Take a look at the calculator (linked below) to double check that your component selections is correct.
www.ti.com/.../slvc471

Thanks,

Garrett

0 Himanshu Gupta16 over 5 years ago in reply to Garrett Roecker

Intellectual 265 points

From Original Schematics, R8 Value Changed to 442K to adjust the value to 50V

0 Garrett Roecker over 5 years ago in reply to Himanshu Gupta16

TI__Mastermind 21720 points

Hi Himanshu,

Just to confirm the load transient are you stepping between 0A and 1.5A or is it another condition. Please check and ensure that the inductor current is not limiting.

Also please be aware that the ceramic output capacitor are only rated to 50V. Ceramic capacitors have a DC derating in regards to capacitance. Since the capacitors are at the voltage rating they will have a low effective capacitance and can cause issues during load transients. Please change these to 100V ceramics.

Please provide the waveform of the output transient with VOUT, SW, COMP and VIN on the same scope plot.

Thanks,

Garrett

0 Himanshu Gupta16 over 5 years ago in reply to Garrett Roecker

Intellectual 265 points

Hello,

I have checked it with replacing with 100V rated caps.

How to check weather Inductor is not limiting the current or not ?

I will provide the needed plot shortly.

Thanks

Himanshu

0 Shreenidhi Patil over 5 years ago in reply to Himanshu Gupta16

TI__Expert 3126 points

Hello Garrett ,

as you can see in the attached waveform ,

we are seeing a very high amplitude of output voltage dip and overshoot under transient loading condition .

How can we improve the same.

0 Garrett Roecker over 5 years ago in reply to Shreenidhi Patil

TI__Mastermind 21720 points

Hi Himanshu,

It appears that the control loop should be updated to improve the load transient response. Please use the TPS43060 quick-start calculator to tune the loop. Please try to increase the crossover frequency of the loop as this will help to improve the response. Please also make sure the phase margin is around 60deg.
www.ti.com/.../slvc471

Thanks,

Garrett

0 Shreenidhi Patil over 5 years ago in reply to Garrett Roecker

TI__Expert 3126 points

Hello Garrett ,

We tried the same test condition with the EVM as well .

24V input 40V output with 15mA to 1.6A transient .

However we saw the issue of undervoltage and overvoltage in the EVM as well , much larger than that shown in the user guide of EVM . we are seeing a dip of 1.2V in our EVM vs 0.7V in the user guide .

0 Garrett Roecker over 5 years ago in reply to Shreenidhi Patil

TI__Mastermind 21720 points

The difference between the two is the value of the load transient step. In the user guide the step is 50% to 100% load. In your case the load is 0% to 100% , which will have a worse load transient response. if you want to improve the 0% to 100% load transient a converter that operates in forced pwm mode at light load should be used. This will improve the load transient but increase the no load current. A device that can do this is the LM5122.

Thanks,

Garrett

0 Himanshu Gupta16 over 5 years ago in reply to Garrett Roecker

Intellectual 265 points

Hello,
The EVM operating current is 3 Amps and The test conducted at 1 Amps ( 50E Resistor, 0.8 Amps with 40V)
The Load transient is 0% to 26.6% with 40V O/P.
Is it expected the dip of 1.2V at that much load transient?

0 Garrett Roecker over 5 years ago in reply to Himanshu Gupta16

TI__Mastermind 21720 points

Hello,

The user-guide show a load transient of about 800mA to 2.2A (Figure 6). The ripple voltage is ~700mV.

Since you loading conditions is going from no load to 25% load I would expect the output voltage transient to be larger than the 700mV above. As I mentioned before for your test condition the converter is operating in DCM when the control loop with have a lower band-width.

-Garrett

0 Himanshu Gupta16 over 5 years ago in reply to Garrett Roecker

Intellectual 265 points

Hello,

Is any way to run this device in forced CCM mode? or Is there any other way to reduce the effect of Load transient?

Thanks

Himanshu

0 Garrett Roecker over 5 years ago in reply to Himanshu Gupta16

TI__Mastermind 21720 points

Hi Himanshu,

Not with this device. This is why I mentioned that the LM5122 should be used.

-Garrett

0 Himanshu Gupta16 over 5 years ago in reply to Garrett Roecker

Intellectual 265 points

Hello,

As per App note

"www.ti.com/.../slyt515.pdf"

"However, for some low-noise applications or applications requiring a fast transient response from light loads, it may be preferable to sacrifice improved light-load efficiency to keep CCM operation over the entire load range."

What is its meant for user/ designing point of view?

Thanks

Himanshu

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TPS43060: Output Voltage dips at switching load