UCC28070-Q1: Resistor calculation

Mame TINE

Part Number: UCC28070-Q1

Hi,

how can i calculate RIMO and RSYNTH if use a shunt resistor for current sensing instead of a current transform. In datasheet we just formula for CT.

over 7 years ago

0 John Griffin1 over 7 years ago

TI__Mastermind 34465 points

Hello Mame Tine,

You can calculate the RIMO value based on a modification of Equation 17 in the datasheet

The factor Iin(pk)*(Rs/Nct) in this equation is actually the max output voltage of the CT so you can replace this with the peak output voltage of your OPAMP.
Normally you would set this at about 3.6V to get the max range of the CSA,CSB inputs

The value of RSYNTH can be calculated from Equation 12 by noting that Rs/Nct is actually the load resistance seen at the primary side of the CT.
So you can replace Rs/Nct by the value of the current sense resistor (Rs) used on the source of the boost MOSFET.

Regards

John

0 Mame TINE over 7 years ago in reply to John Griffin1

Intellectual 305 points

unit of shunt resistor is ohm or miliohm

0 Mame TINE over 7 years ago in reply to John Griffin1

Intellectual 305 points

Hi,
the unit of shunt resistor is ohm or mili-ohm

Power management

Power management forum

UCC28070-Q1: Resistor calculation