UCC28950: OUTPUT INDUCTANCE CALCULTAION

SAMRAT PUJARI

Part Number: UCC28950

Hello

IN SLUA560 at Lout calculation why Vo term is used? Inductance value should depend upon the voltage across it and not output voltage? (1-Dtyp) I guess signifies the off period ie when inductor current is falling.

is it not?

Dtyp =0.65

so voltage at the input terminal is 24/0.66=33.36

so voltage across inductor comes out to be 33.06-24=12.36 is this not the value that should be used for LOUT calculation?

where i am making mistake?

please guide me through.

thanks

samrat

over 6 years ago

0 Benjamin Lough over 6 years ago

TI__Mastermind 26225 points

Hi Samrat,

Thanks for your interest in UCC28950. Let me look into your question and get back to you when I am in the office on Monday.

Best Regards,

Ben Lough

0 Benjamin Lough over 6 years ago in reply to Benjamin Lough

TI__Mastermind 26225 points

Hi Samrat,

Equation 44 is sizing the ripple current to be 20% of the total output current and is using Pout/Vout to get the total output current.

In Equation 45, the voltage across the output inductor during the off time is the output voltage.

Equation 46 is calculating the root mean square of the output current. So you have Pout/Vout to give the output current and delta-Iout/sqrt(3) to calculate the root mean square of the ripple current.

You might find power stage designer helpful. It is able to suggest values for components in popular power topologies such as phase shifted full bridge:

Best Regards,

Ben Lough.

0 SAMRAT PUJARI over 6 years ago in reply to Benjamin Lough

Intellectual 730 points

hello Ben

thank you for recommending the power designer.

but still i find huge inconsistency in recommenced values of transformer magnetizing inductance shim inductance and output inductance.

why is that so?

I put design values given SLUA560 in power designer and got this but the values recommended by SLUC222C tool are Transformer inductance=2.76mH

Secondary inductance=2.02 uH (approx consistent) and shim inductance=26.06 uH.

POWER DESIGNER calculations are based on sluc222 tool only. only thing that synchronous rectification is not der in power designer circuit but that cannot make this much change in values?

whats change?

thanks

samrat.

0 Benjamin Lough over 6 years ago in reply to SAMRAT PUJARI

TI__Mastermind 26225 points

Hi Samrat,

Could you send me a copy of SLUC222C with your inputs filled in?

Best Regards,
Ben Lough

0 SAMRAT PUJARI over 6 years ago in reply to Benjamin Lough

Intellectual 730 points

UCC28950 Excel Design Tool_SLUC222C.xlsHello Ben

its nothing but the original design tool values. here i am attaching.

please check

thanks

samrat

0 Benjamin Lough over 6 years ago in reply to SAMRAT PUJARI

TI__Mastermind 26225 points

Hi Samrat,

I am seeing the recommended primary magnetizing inductance as 5.51mH, shim inductance of 26.06uH and output inductance of 4.04uH. These values are close to the values derived from power stage designer. Please keep in mind that these two sources are using two different methods to arrive at the same answer so there will be a little bit of variation among calculator tools. Using values from either source should be fine.

Best Regards,
Ben Lough

0 SAMRAT PUJARI over 6 years ago in reply to Benjamin Lough

Intellectual 730 points

hello Ben

can you please send me your sluc222c excel design tool where your are getting those values?
I am not getting what mistake i am making.

thanks
samrat

0 Benjamin Lough over 6 years ago in reply to SAMRAT PUJARI

TI__Mastermind 26225 points

UCC28950 Excel Design Tool_SLUC222C for Samrat.xls

Hi Samrat,

I had to change the switching frequency to 100kHz in SLUC222C to match the inputs you have in power stage designer.

Best Regards,

Ben Lough

0 SAMRAT PUJARI over 6 years ago in reply to Benjamin Lough

Intellectual 730 points

hello Ben

Power designer uses FET frequency which is half of Lout frequency. so for 100kHz In power designer we have to keep 200kHZ in sluc222c is it not? which recommends same values i listed in previous comments and its not consistent.

Even in file you sent the Lout frequency 100 KHz the LOUT recommended is 4.04 which is almost double?! I understood that Ls is dependent on Coss avg but recommended values i do not see consistent(nearby) for same turns ratio. Actually turns ratio recommended is consistant in both.

5226.UCC28950 Excel Design Tool_SLUC222C.xls

please guide me through.

thanks

samrat

Power management

Power management forum

UCC28950: OUTPUT INDUCTANCE CALCULTAION