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TPS55340: can we eliminate any passives in this design and reduce the boost inductance?

Kevin Lai
Intellectual 2916 points
Part Number: TPS55340

Hi team,

my customer is printing boards for prototyping now so i need to get this over to them by today.

they are using the TPS55340 in a boost configuration and are leveraging a past schematic. 

their design requirements are as follows:

Input voltage min = 5.5V

Input voltage nom = 9

Input voltage max = 12V

output voltage = 28V

output load current = 0.8A

switching frequency = 630kHz. 

max ambient temp = 60C

they have the following questions.

1. can we reduce the boost inductor (currently 10uH) down to 6.8uH? will the inductor specs provided in the link below suffice? 

https://www.mouser.com/datasheet/2/597/xal4000-270751.pdf

2. can TI help identify if we can eliminate any passives (caps, resistors, inductors) from this design? (space is premium).

3. is the inductor (L405) necessary? it looks to be a pi filter.

Thanks,

Kevin 

  • 0
    TI__Guru 58225 points

    Hello Kevin,

    1. The input current at minimum VIN and maximum load will be in the range of 5A. If you are using as smaller inductance, the ripple current will increase, so with 6.8uH you have a ripple current in the range of 40% or even a little more, so you need an inductor that is at least capable of 6A. If you want to supply the full load at minimum VIN.

    2. If there is not a specific need, I think that the output capacitors with the 1 ohm resistor in series might not be necessary. R418 is useful for measuring stability, but if you want to save space, this could be removed. R414 is giving an opportunity to synchronize the component to a specific frequency, but you could tie the pin SYNC directly to AGND.

    3. L405 is a filter and decoupling capacitor. It is not necessary for the device to operate, but it might help for EMI issues.