BQ24610: Snubber at the switching node

Jason Hu27

Part Number: BQ24610

Dear experts, I want to add a snubber circuit at the switching node of bq24610. External DC adapter power source is 24V, battery is 4-serial Li-iron battery(16V). How to choice the footprint of resistor and capacitor(0603 or 0402)? In other words, could I use the 0402 size components on snubber circuit(for example, 2 ohm resistor and 2.2nF capacitor). Regards.

over 7 years ago

0 Kedar Manishankar over 7 years ago

TI__Mastermind 24075 points

Hello Jason,
Just to clarify, are you looking for any advantages and tradeoffs in using different footprints, or specific resistor and capacitor values for the snubber circuit?

0 Jason Hu27 over 7 years ago in reply to Kedar Manishankar

Intellectual 910 points

Dear Kedar, please refer to below figure. The waveform of PH pin on bq24610 has ring on rising and falling edge. I want to add the snubber circuit at the switching node of bq24610. External DC adapter power source is 24V, battery is 4-serial Li-iron battery(16V). Because my PCB is very small, I do not have enough space to put the large size components(such as resistor and capacitor). So, could I use the snubber components with 0402 footprint? Or, can you suggest the suitable compponents' size? Regars.

0 Kedar Manishankar over 7 years ago in reply to Jason Hu27

TI__Mastermind 24075 points

Hello Jason,
Yes 0402 and 0603 are both viable footprints for snubber circuits. You can use 0402 for your application. This should attenuate the ringing you observe.

0 Jason Hu27 over 7 years ago in reply to Kedar Manishankar

Intellectual 910 points

Dear Kedar, my external DC adapter power source is 24V, battery is 4-serial Li-iron battery(16V). Charging current is 1.8A. I will use 2-Ohm resistor and 2200pF capacitor. Can I use the 0402 footprint snubber components? Because I see some documents that suggest use the resistor with 0805 size. But 0805 size is too big on my PCB. Does 0402 footprint be safe for my application?

0 Kedar Manishankar over 7 years ago in reply to Jason Hu27

TI__Mastermind 24075 points

Hello Jason,
Yes you may use the 0402 for your application. This is not high voltage circuit so 0402 can be safe.

0 Jason Hu27 over 7 years ago in reply to Kedar Manishankar

Intellectual 910 points

Dear Kedar, thanks for your help. I have a puzzle, could you give me a hand? I get a equation from FAIRCHILD. It discuss how to design a snubber circuit on DC BUCK application. You can refer to below equation. The TI bq24610 switching frequency is 600KHz.(fSW). If I use 3300pF capacitor(Csn) and DC power source is 24V(Vsw). The power dissipated in the resistor is about 1.14W. The resistor size must choice 2512 footprint. Maybe I misunderstand below equation. Could you give me some suggestions? Thanks.

0 Kedar Manishankar over 7 years ago in reply to Jason Hu27

TI__Mastermind 24075 points

Hello Jason,
Yes you are correct, the power dissipation is quite high and 0402 for resistor would not be good, however could you give me more information on how you calculate the snubber capacitance required? It might be possible to reduce the capacitance required, and thereby the power dissipation. You can still use 0402 for the capacitor element.

0 Jason Hu27 over 7 years ago in reply to Kedar Manishankar

Intellectual 910 points

Dear Kedar, I just refer to the capacitance on most popular documents. Or, you have some suggetions on capacitance?

0 Kedar Manishankar over 7 years ago in reply to Jason Hu27

TI__Mastermind 24075 points

Hello Jason,
If size is your biggest constraint, you can make some tradeoffs with ringing and power consumption to decrease footprint of resistor. This blog post helps to determine the capacitance you actually need based on your circuit. e2e.ti.com/.../calculate-an-r-c-snubber-in-seven-steps

0 Jason Hu27 over 7 years ago in reply to Kedar Manishankar

Intellectual 910 points

Dear Kedar, thanks for your reply. I try to add the resistor at the Gate of Low side MOS of bq246410 and snubber circuit at Low side MOS. It can improve the rising edge ringing, but falling edge ringing still exist. Do you have solution to improve the falling edge ringing ? Best regards.

0 Kedar Manishankar over 7 years ago in reply to Jason Hu27

TI__Mastermind 24075 points

Board layout design is crucial to reducing overshoot and ringing. Place decoupling input capacitor close to IC to decrease overshoot and ringing. You can also add a series resistor to the bootstrap circuit to slow down turn on of high-side FET and reduce overshoot. The snubber circuit should also reduce any voltage or overshoot you experience on the falling edge of PH. Adding the snubber circuit however, will decrease your efficiency.

Power management

Power management forum

BQ24610: Snubber at the switching node