TPSF12C1-Q1: Questions about the quickstart calculator

Jacob Wyrick

Expert 8365 points

Part Number: TPSF12C1-Q1

Hi team,

Questions about the TPSF12C1-Q1 Quickstart calculator. Can you advise?

Grid Source Impedance
1. How do we estimate or measure L_GRID and R_GRID? (Let’s assume we use 5uH LISN)
2. Is L_GRID1= L_GRID2 = L_GRID ?
3. With the information of source/grid impedance, are we (Quickstart calculator) trying to match or mismatch the EMI filter input impedance ?
Regulator CM Noise Source Impedance (parasitic)
1. How do we estimate C_SRC^,R_SRCand L_SRC ?
2. Is Regulator CM noise source the same as the Regulator Input Impedance ? (If not, how do we account for Middlebrook’s Stability Criteria ?)

Thanks,

Jacob

over 1 year ago

0 Timothy Hegarty over 1 year ago

TI__Guru 73742 points

Hi Jacob,

1. You can assume that the CM grid inuductance contribution is < 10uH. It doesn't really make an impact, as there is a high cap value to the left of the LISN's 5uH. In general, the grid source impedance does not have a significant impact on stability, as the grid-side choke (to the left of the AEF circuit) provides an impedance buffer.

2. In terms of the regulator noise source impedance, the important parameter here is the switch-node parasitic capcaitnace to GND, as this sets the amplitude of CM noise current into the filter. Icm = Vsw/Zsw, where Zsw is effectively the impedance of Csw. You can measure the CM current to get an estimate of this.

I attached the latest quickstart file here, where it takes Vsw (switch-node voltage amplitude) and Csw, and derives the consequent voltage swing on INJ, which is important to check to avoid amplifier voltage saturation for a given VDD. This particular file has the values applicable to our single-phase filter EVM.

For more detail, see the FAQs here: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1257197/faq-tpsf12c1-and-tpsf12c3-power-supply-filter-ic-faqs

TPSF12C1EVM-FILTER quickstart calculator A8.xlsm

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TPSF12C1-Q1: Questions about the quickstart calculator