LM2937: Loop Bandwidth

Hi ACGUY,

We are looking into this. Due to the age of this device, please allow a few days for our response.

Very Respectfully,
Ryan

Hi Ryan,

Thank you for answer. I do like to add a question.
Our customer is using this LDO for Vcc of sensor.
In some individuals, this LDO output has unpredictable voltage fluctuation.

I think that
:The absolute value of the FB resistor is large.
:Ifb is small.
:A heavy LPF is generated at the input of the error amplifier.
-> Therefore, the loop bandwidth decreases and occasionally voltage fluctuation occurs.

Please let me know your opinion.

Regards,
ACGUY

Hi ACGUY,

Could you help me better understand the nature of your voltage fluctuations? Ideally a scopeshot with Vin, Vout, and Iout would help me better understand what is going on in your application.

Very Respectfully,
Ryan

Hi Ryan,

I attached the file. Please see it.

I look forward to reply from you.

Regards,

ACGUY

Reg Out Vol.pdf

Hi ACGUY,

Thanks for the scope shot. These scope shots look like a transient response. This implies that either your input voltage, your output load current, or both are changing to cause the temporary shift in output voltage. Are you able to show a scopeshot with Vin, Vout, and Iout? This would help confirm that your current scope shot is showing a transient response.

Very Respectfully,
Ryan

Hi Ryan,

>> These scope shots look like a transient response.
I think too. However, customer swaped the LDO to other board, they confirmed this fenomenon is to follow up the individual.
When using simple resistannce load, a similar phenomenon occurred.
I think that it is a problem peculiar to some individuals.

Please let mo know your opinion.

Regards,
ACGUY

Hi ACGUY,

Please provide a scope shot with Vin, Vout, and Iout. Without the requested scope shot showing all three, we are not able to continue to debug your application.

Very Respectfully,
Ryan

Hi Ryan,

Please see the attached file.
I got the waveform.
This LDO has voltage dip about Δ1.8mV. The cycle and dipping width are undefined.
Customers use parallel capacitor of aluminum and ceramic for input and output.
I think that ESR is too low, I will suggest delete ceramics to customer.

Please let me know your opinion.

Regards,
ACGUY


LM2937_Voltage dip.pdf

At after that I measured deleted the cera-caps. Situation not changed.

ACGUY