LM3481-Q1: LM3481-Q1 Ton time specification

Aparna Vashishtha

Part Number: LM3481-Q1

Tool/software:

In my application, input is 5V to 18V, my output is 11.64V, my duty cycle when Vin>8V is 34% & below, so Ton time =below 377ns when switching frequency is 917KHz, so what is the behavior of the output when it is below the minimum on time specification.?

2 months ago

0 Mounika Girish 2 months ago

TI__Intellectual 2426 points

Hi Aparna,

Are you using it as pre boost solution as stated in the attached e2e link? or a SEPIC

Best regards,

Mounika

0 Aparna Vashishtha 2 months ago

Prodigy 30 points

as pre boost solution.

0 Aparna Vashishtha 2 months ago in reply to Aparna Vashishtha

Prodigy 30 points

any update???

0 Mounika Girish 2 months ago in reply to Aparna Vashishtha

TI__Intellectual 2426 points

Hi Aparna,

The output voltage will overshoot (cause it stays on too long), and then at some point start to skip.. then overshoot again..

Best regards,

Mounika

0 Aparna Vashishtha 2 months ago in reply to Mounika Girish

Prodigy 30 points

hi,

yes its understood, overshoot will be there at the output but I did not understand '" because it stays on too long".

In our application (Vin>8V), on time is < minimum on time specs in datasheet.

Do you have any data or formula to estimate the overshoot voltage for the output capacitor around 100uF?

0 Mounika Girish 2 months ago in reply to Aparna Vashishtha

TI__Intellectual 2426 points

Hi Aparna,

Please allow me sometime to look into this.

Best regards,

Mounika

0 Mounika Girish 2 months ago in reply to Mounika Girish

TI__Intellectual 2426 points

Hi Aparna,

The min Ton of this device is 363ns which translates into min Duty cycle at 34% at 917kHz

This means for Vin> 8V the Duty cycle cannot be decreased by the device ( It has to stay on 363ns)

Which means the Duty cycle will remain at the same level even when the Input voltage is increased and the increase in the Vout would depends on this formula -> Vout = (1/1-D) * Vin

==> According to your specifications, Vout = 1.53* Vin.Because of which we see the output voltage rising to more than 11.64V and it goes into Over voltage protection when VFB+ Vovp is at 1.36V at Vin ~ 8.2V.

Best regards,

Mounika

Power management

Power management forum

LM3481-Q1: LM3481-Q1 Ton time specification