TPS552882-Q1: Schematic Review - 12V Output buck boost

Hi Matthew,

Thanks for reaching out. 

1. May I know what is the product type and application here?

2. Does the device need to operate at 36Vin? Because the max recommended operation voltage is 36V for this device.

3. What is the part number of the output capacitors? The ESR and effective capacitance is needed to calculate the compensation. You can also use the calculation tool on product page for that.

4. The input and output capacitors are decided by the voltage ripple and undershoot/overshoot voltage during transient. Is the VOUT of LTC4368 far away from TPS552882 input side? If so, recommend to populate the aluminum capacitors at the input side.

BRs,

Bryce

Hi Bryce

1. This is for an automotive grade BMS to modify the 6-36V input to a solid 36V output.
   
   
2. It does need to operate at 36V but I expect it never will be operated that high in reality. The VIN to this will be shut off at 36.5V
   
   
3. C20: 12101C475K4T2A C21: EEE-FK1J221AV C72-C74: GCM32EC71E226KE36K C69-C71: EEHZA1E560V
   
   
4. The next 2 pictures will show the layout so far and the voltage path. LTC is labelled as 1 and TPS is labelled as 2:
   
   
   

Thank you!

Hello,

1. Yep sorry, was meant to say 12v output!
2. That's ok, 36 is the limit on my board, any more is a fault cause and therefore this will be protected upstream
3. Ok so 4 x 10uF overall? Or go to more than 4?
4. Where would you put this? between the Sw pin and pin 2 of the capacitor shown in the schematic?
5. Ok, thank you
6. Ok, will do
7. I have current limit elsewhere, I was planning on skipping this?
8. I have the following layout at the moment. I started with the layout guide and it is only the output that goes off in a different angle, does this look ok?
   
9. What is a MOS? is that refering to a MOSFET? If so, which one should I change? These were the TI suggested ones on webench.

Thank you for the help, much appreciated!

Hi Matthew,

Please see my follow up comments below.

1. Ok so 4 x 10uF overall? Or go to more than 4?

-> I think 4pcs is ok.

2. Where would you put this? between the Sw pin and pin 2 of the capacitor shown in the schematic?

-> See below for example.

3. I have current limit elsewhere, I was planning on skipping this?

-> It's ok.

4. I have the following layout at the moment. I started with the layout guide and it is only the output that goes off in a different angle, does this look ok?

-> The output capacitor is very important for Boost mode, can you share the pictures for each layer?

5. What is a MOS? is that refering to a MOSFET? If so, which one should I change? These were the TI suggested ones on webench.

-> It refers to Buck side MOSFETs, it's ok but would be better if you have better choice with smaller tr/toff.

BRs,

Bryce

Hi Bryce,

1. Ok, will change, thank you.
2. Ok will add. I assume I still use the 16V rated caps like webench uses for the outout? On that note, shouldn't all the caps connected to VOUT be 25V rated caps to be double to voltage?
3. Ok will ignore, thanks
4. Here is the transparent view and an individual view of all 4 layers. Just the serperated AGND on L3 and MOSFET gate, VIN for pin 3 and output to LED on L4. GND on L2.
   
   
   
   
   
5. Would this choice be better: changing both MOSFET to the same PN and going for IAUC41N06S5L100? Should they be different as I saw on yours that they are the same?

Thank you!

Hi Bryce,

Thank you for all the help. I think I have implemented everything you have saidf but there are still a couple of confusions on my part. I will attach the new layout and schematic below to help show you what I have done.

1. The 2 extra ceramic caps on VIN, I have just made them 10uF like the other input caps should these be 0.1uF instead?
2. The Infineon MOSFET can replace both MOSFET's? I have swapped both for now, please let me know if this is not ok!
3. I am confused about the PGND and AGND loop tbh! The link you sent has them connected at the IC in 1 image and then seperated with a via on another so I am really not sure what this AGND loop should look like!
4. Does having this close to my MCU present an issues? It is this far away:

Here are my design files, I have all 4 layers, transparent view, 3D view and schematics. Thanks agains for the help! I think we are nearlly there!

3D

Tranp

Top Layer

L2 - GND

L3 - Contains AGND

Bottom layer

Schematic

Hi Bryce,

Great, thanks!

I have made the few changes you just suggested.

Just to check, this means having 7 input caps overall (6x10uF and 1x 0.1uF) is that right? is there a downside to this many caps?

Also, is there anyway you could show me layer 3 of that AGND image? So I can see what is on your AGND path and how it's layed out please?

Lastly, how can I change my schematic to be able to control the output of this with a MCU digital signal?

Many thanks for the help!

Hi Matthew,

1. I think the downside is the cost increases with more caps. From my point of view, 4*10uF+1*0.1uF is ok here. Keep C67, C68, C65, C66 which is close to the FETs.

2. I can send you the file via personal message, please send the friendship request to me.

3. You can choose I2C version TPS55288 to control the output voltage. The package is same, just pin5 and pin6 are different.

BRs,

Bryce

Hi Bryce,

Great, I have removed 2 of the 10uF capacitors and sent you a friend request.

The TPS55288 does not appear to be automotive grade, unfortunately this is a requirement of mine. Is it not possible to have an enable on the TPS552882? Maybe an example of this:

Thanks!

Hi Matthew,

Please check the file which I sent to you.

TPS55288 has automotive version which is TPS55288-Q1. Sorry I thought you mean program the output voltage to different values. If you mean turn on or shutdown the device, this TPS552882-Q1 also has EN pin which I saw you connect to Vin through the resistor divider.

BRs,

Bryce

Hi Bryce,

Yes I mean enabling and shutting down the device from the uC. So would putting a MOSFET in the middle of my voltage divider shown above work? Output off when mosfet is open and 12v on when mosfet is closed? 

Can I confirm that the device current will be in the uA range when shutdown? 

Thank you