BQ24618 Cout, Cin issue

Please see the data sheet toward the end.

It has what caps and a layout section.

The Input Capacitor section of the data sheet toward the end says that "the input decoupling capacitor and should be placed as close as possible to the drain of the high-side MOSFET and source of the low-side MOSFET." Does that mean there should be two input capacitors, one at the drain of the high-side MOSFET and one at the source of the low-side MOSFET? The schematic in Figure 1 does have a 10uF capacitor (C8) connected to the drain of the high-side MOSFET, but nothing connected to the source of the low-side MOSFET. Should both of these capacitors be 10uF? Are C12 and C13 in Figure 1 the output capacitors? 

Thanks for the help,

Andrew

Hello Andrew,

The Drain of the high-side FET is at the SYS rail and the Source of the low-side FET is GND. It is asking that you place C8 from Fig 1 of the datasheet so that the current loop created by the switching elements is as small as possible.

Yes, C12 & C13 are output filter capacitors that that should be places close the Rsense to filter the switching output used to charge the battery.

Let me know if you have any other questions.

Hi Ryan,

Thanks for the response, that does answer my question. One more semi-related question: Does the chip need to be connected to any sort of load before it charges the battery or is it okay to have no load connected? I.e. in Fig.1 on the top right is it okay if there is nothing to the right of C9 where the SYSTEM label is? Thanks,

Andrew

P.S. It says I should "VERIFY" that your response answered my question but I can't seem to figure out how to do that on this forum.

Hello Andrew,

No system load is required to operate this device it is just an optional rail for power path management if the designer desires to use it. Are you creating a dedicated battery charger where the battery is removable so that you do not need the system rail?

To answer your question about "Verifying" the post you would need to have been the original poster of the thread to have the option to verify. I would recommend for future to search to forum first to try and find you answer like to did to find this post and then if it is unanswered create a new post with a properly descriptive heading to help others in their search to help the different teams here at TI with addressing new questions as they are posted.

Hi Ryan,

I will eventually be connecting the circuit to a system, but I had been planning on waiting until I have it successfully charging the battery before connecting the system.

I'll make sure to start a fresh thread next time I have a follow up question. Thanks,

Andrew

Hello Andrew,

Yes, you can use the charger as a stand-alone charger with no system attached but also have a system rail available for when you desire to use it.

No worries about the thread. When you start a new thread it gives you as the original poster more managment options I believe and has higher visibility since it will be a brand new post.

Let me know if any other questions arise.