TPS7H5005-SEP: Duty cycle variation in every switching cycle.

Dinesh Murugan

Part Number: TPS7H5005-SEP

Tool/software:

Dear team.

We are using TPS7H5005-SEP for our forward converter application.We have given the OUTA pulse to primary FET through gate driver.Duty From the Controller IC is changing for Every switching cycle(400Khz).Both Input and output voltage and current are in stable condition.Current sense is within the threshold,Kindly provide solution for this problem.Refer Image for OUTA from Controller IC.

9 months ago

0 Daniel Hartung 9 months ago

TI__Mastermind 28915 points

Hey Dinesh,

The most common causes for this behavior are:

1. Incorrect slope compensation

2. Incorrect loop compensation

3. Noise

Please review your schematic that these values were done correctly.
You can provide it here if you would like us to look it over.

Thanks,
Daniel

0 Dinesh Murugan 9 months ago in reply to Daniel Hartung

Prodigy 50 points

Dear Daniel ,

We have verified the gate pulse at open loop and found its is constantly providing 50% Duty at 400Khz. while we check for the closed loop one 40% Duty pulse and one 15% Duty pulse observed at OUTA. And also we have verified the Slope and loop compensation values as per the formulae given in the data sheet. Current sense is within the limit of COMP/2 but Still duty is changing for every consecutive pulses.I'll share Slope and loop compensation values and kindly provide the solution for this problem.

Slope compensation resistor value.

RSC = 499Kohm ( Vout = 7V ,L = 8.2uH , Ns = 7 ,Np = 7 , NCSP = 1 , NCSS = 100 & R= 11ohm)

RComp value = 3.6Kohm , Ccomp = 0.1uF & CHF = 47pF.

Also provide any possibility that we can use this IC in Voltage control mode.

Channel 1 : COMP PIN

Channel 2 : CS ILIM PIN

..........................

Channel 1 : CS ILIM PIN

Channel 2 : OUTA

0 Daniel Hartung 9 months ago in reply to Dinesh Murugan

TI__Mastermind 28915 points

Hey Dinesh,

The equations in the datasheet are meant for a push-pull converter and not a forward converter.
I will work on reviewing your compensation.

Thanks,
Daniel

0 Daniel Hartung 9 months ago in reply to Daniel Hartung

TI__Mastermind 28915 points

Hey Dinesh,

What are you using for the feedback loop for the forward?
Is there an isolated feedback path?

Thanks,
Daniel

0 Dinesh Murugan 9 months ago in reply to Daniel Hartung

Prodigy 50 points

What are you using for the feedback loop for the forward?

We have used controller IC in the secondary side and the primary FET is driven through isolated gate driver.

No isolated feedback path.Resistor divider network is used which is connected to Vsense

Regards,

Dinesh.

0 Daniel Hartung 9 months ago in reply to Dinesh Murugan

TI__Mastermind 28915 points

Hey Dinesh,

Are you able to provide a schematic?
I need all the values listed here to find what the recommended compensation would be:

I will use power stage designer to find the recommended values which you can go through as well: