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TPS55340-Q1: TPS55340-Rise Time and Fall Time Details, Queires in SLVA061

Part Number: TPS55340-Q1
Other Parts Discussed in Thread: TPS55340, LM5155

Hi Everyone,

This is Harikrishnan from HCL Technologies. When I look for losses in boost converter I gone through the application note SLVA061. In that application note for power loss in MOSFET equation was provided in

Page No. 26. But the switching loss of MOSFET is wrong I think so. The current should not be squared. Kindly confirm it.

I am using TPS55340-Q1 in my design. Can u provide the rise time and fall time of the integrated N-MOSFET. Currently I am assuming 2% of switching frequency for my analysis. If details not available can I go

ahead with the assumption. If there is any application notes for losses and efficiency calculation in boost converter. Please do share.

Also one more query, in the application note average inductor current is calculated as (IO/1-D). But in TPS55340-Q1 datasheet the avg. current is calculated with some other formula in pg 17.

From the datasheet the estimated efficiency is assumed as 85%. Instead of average current IO/1-D Can I use IM_DC or IL(rms) in equation of application note. Kindly confirm this also.

Regards,

Harikrishnan Thangamani

• Hi Harikrishnan,

Thanks for your interest in TPS55340.

1. Yes, the current square was a typo, and we are going to correct it in the new release. Thank you so much for the note.

2. I will check with our designer about the switching time and get back to you.

3. SLVA061 would be a good reference. You could also look at the app note for LM5155. It is just a controller but the calculation is similar.

4. IO/(1-D) is an ideal formula ignoring the loss. The equation of IM_DC in the datasheet considers the efficiency and would be more accurate. But you need to have an estimation of the efficiency in advance. These are for the average current. For the RMS current, the equation in the datasheet is valid.

Thanks,
Yinsong

• Hi Harikrishnan,

The rise and fall time is parasitic sensitive and related to the layout. For the estimation purpose before you do bench test, you can use 20ns as a reasonable switching time.

Thanks,
Yinsong