Hi Abhiram,

Thanks for reaching out.

1. May I know how is this Buck-boost is used here? Do you have any block diagram about this?

2. In automotive applications, FPWM mode is usually selected due to fixed switching frequency and is easier to pass EMI. May I know the reason to choose PFM?

3. What is the part number of the inductor?

4. What is ESR value and part number of the output capacitance? Then we can check COMP parameters.

BRs,

Bryce

Dear Bryce, 

Thanks for your suggestion.

1. This buck boost is used to power one of our gateway IC and further 5V LDO's.

2. We had selected APFM as our BMS is going to use on different power levels in i.e., sleep and standby. As per you suggest we can switch to FPWM.

3. SRN8040TA-5R6MCT-ND (5.6uH inductor we are going to use). It is of Bourns.

4. EDH226M050S9GAA is the 22uF Electrolytic capacitor.

Thanks 

Hi Abhiram,

Thanks for feedback. Please find my replies below.

1. If BMS is used on sleep and standby applications, is the efficiency important for the system? Because the efficiency at light load with FPWM would be lower than PFM mode. Or it is suggested to modify the MODE pin as below to leave the options to select PFM or FPWM according to the real final test results..

2. Check the effective capacitance of VCC cap is higher than 2uF at 5.2V dc bias voltage. And recommend to add one 0.1uF/0402 close to VCC pin.

3. Recommend to change Fsw to 400kHz to pass the EMI test easily according to the EMI test standard.

4. If fsw=400kHz is selected, the inductor value can choose 4.7uH with saturation current>4A.

5. Recommend to change the output current sense resistor to 20ohm to set 2.5A output current limit since 2A is the max output current.

6. Recommend to add two 10uF ceramic capacitors at the output side to decrease the output voltage ripple. 

7. Recommend to add RC snubbers (2.2ohm---1206 package)+2.2nF at both SW1 and SW2 node for EMI consideration, you can leave them floating first and populate them according to the EMI test results.

8. For the COMP parameters, I don't find the ESR value of EDH226M050S9GAA on the official website, can you share the value with me? And the ESR value at -40C is also important because we saw some capacitors have very large ESR at low temp and would cause the system unstable.

BRs,

Bryce

Hi Bryce,

Thanks for your suggestions, 

We will follow the same.

We are going with 10uF+10uF+2.2uF Ceramic capacitors in the output Capacitor. Could you please let us know the maximum ESR we can keep in that.

We also have one doubt that you have mentioned 20ohms sense resistor. Is it 20 mOhms because the calculated value is coming in the range of 25 mOhms.

Rest of the circuit would be according to attached calculation sheet right

...

Thanks & Regards

Abhiram

Hi Bryce,

Thanks for your suggestions, 

We will follow the same.

We are going with 10uF+10uF+2.2uF Ceramic capacitors in the output Capacitor. Could you please let us know the maximum ESR we can keep in that.

We also have one doubt that you have mentioned 20ohms sense resistor. Is it 20 mOhms because the calculated value is coming in the range of 25 mOhms.

Rest of the circuit would be according to attached calculation sheet right

...

Thanks & Regards

Abhiram

Hi Abhiram,

1. Do you mean the output capacitors will change to only 2*0.1uF+1uF+2.2uF+2*10uF and all are ceramic capacitors? Can you share the screenshot with us and share the part number of the output capacitors with us? For ceramic capacitors, the ESR is very small compared with aluminum capacitors, the ESR is not critical.

2. Since you mentioned the max output current will be 2A, it is recommend to select higher output current limit value to leave some margin.

BRs,

Bryce

Hi Bryce,

PFA sent for your reference.

IC part number - TPS552872-Q1

TPS552872-Q1

Also, kindly clear a doubt that you have mentioned 20ohms sense resistor. Is it 20 mOhms because the calculated value is coming in the range of 25 mOhms.

Thanks & Regards,

Abhiram

Dear Bryce,

Greetings!!

1.We have placed CRF1206-FZ-R020ELF 20mOHM (1206 package) Resistor as recommended.

2. 0.1uF cap is placed near VCC along with 4.7uF.

3. We have placed 4.7uhH inductor with ISAT of 5.9A (SPM5030VT-4R7M-D).

4. Changes has been done according to your recommendation on 'Comp' pin. (Please refer the attached schematic)

5. We have updated the voltage rating of the snubber caps to 50V for SW1 & SW2.

6. We have added 100nF and 10nF MLCC (50V) in the output although in further circuits we have added significant input capacitors to improve the performance in load transient.

Please find attached schematics for your review:

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Best Regards,

Abhiram Tiwary,

Hardware Design Engineer

Dear Bryce,

One more thing we need to confirm that is it essential to separate AGND & PGND with a ferrite bead

Best Regards

Abhiram