LM5576: CRamp pin value (shorted or open)

Jason Hansen

Part Number: LM5576

I was curious to know what the effects were on the LM5576 regulator (if any noticeable) if the CRamp pin was either open without a Cramp cap on it or shorted to ground?

over 4 years ago

0 J Arrigo over 4 years ago

TI__Mastermind 28020 points

Hi Jason,

A capacitor is required on the RAMP pin for proper operation.

Are you asking what the are the effects if the RAMP pin is open or shorted to ground?

Thanks, Jason

0 Jason Hansen over 4 years ago in reply to J Arrigo

Prodigy 10 points

Hello,

Yes exactly, I am wondering what the effects are if that RAMP pin is open or shorted to ground.

Any feedback would be appreciated.

Thanks,

Jason

0 J Arrigo over 4 years ago in reply to Jason Hansen

TI__Mastermind 28020 points

Hi Jason,

I will need to check with the design team to see if they have this data. I will let you know what I find out.

Regards, Jason

+1 J Arrigo over 4 years ago in reply to J Arrigo

TI__Mastermind 28020 points

Hi Jason,

The ramp pin FMEA data is shown below for the LM5576. Hope this is what you are looking for. Let me know if you have other questions.

Regards, Jason

Pin
Number	Name	Connection	Damage	Functionality	Comments
9	RAMP	Short to GND	No	No	OUT=1Vpk-pk oscillations around the expected regulation voltage & erratic switching
9	RAMP	Open	No	No	OUT=0, no switching

0 Jason Hansen over 4 years ago in reply to J Arrigo

Prodigy 10 points

Hello Jason,

Thanks for the information. Based off of what you provided I went ahead and setup my circuit to have pin 9 "open" and the regulator output is showing the correct regulated voltage out "unloaded". The information states that the output should be = 0V. Is this worded incorrectly?

For my testing, once I apply 20mA of load, the voltage does drop a bit. I can add another 20mA load and it drops it a bit more. If I increase the load to 500mA it drops the output voltage significantly.

Just curious for some clarification.

Thanks,

Jason

+1 J Arrigo over 4 years ago in reply to Jason Hansen

TI__Mastermind 28020 points

Hi Jason,

Not sure, but this may have been tested at full load. I expect VOUT = 0V if no C_RAMP is added. Can you add a C_RAMP and check the behavior?

Regards, Jason

0 Jason Hansen over 4 years ago in reply to J Arrigo

Prodigy 10 points

Hi Jason,

Yes if we add the capacitor it does function correctly. The question came up on what the effects would be if that capacitor was missing or removed.

Thanks again for the information.

Regards,

Jason

0 J Arrigo over 4 years ago in reply to Jason Hansen

TI__Mastermind 28020 points

Ok, good. Let me know if you have further questions.

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LM5576: CRamp pin value (shorted or open)