BQ24650EVM-639: BQ24650EVM-639:

Dave Whitaker

Part Number: BQ24650EVM-639
Other Parts Discussed in Thread: BQ24650

I have a few more questions about the EVM schematic for the BQ24650.

1) Please tell me why the following components are included on the EVM Board for Part Number BQ24650 and also what purpose they perform. I have noticed that, with the exception of C15 - 22Pf they are not included on the data sheet schematic.

R11 - 100 Ohms, C17 - 22pf, C15 - 22pF, C1 - 10uF, C11- 0.1uF.

2) C13, C9 and R8 are designated as open (not populated). Are these NOT included due to a board EC or do they offer some sort option if require ? If so, can you explain?

3) I would have thought that R6 (sense resistor) would have been place after the output caps C7 and C8 and not before. Was there a reason for this – maybe not much of a difference?

4) Page 9, part 5 of the BQ24650 EVM guide refers to the "capacitors for the BAT". What capacitors are being refereed to here in the schematic on page 17.

5) From what I can tell, there is no reverse protection circuitry on the board or in the IC to protect against a battery being hooked up with reverse polarity. Is that correct?

Thanks
Dave

over 6 years ago

0 Jeff F over 6 years ago

TI__Guru**** 166996 points

Hi Dave,

Regarding 1:

R11 - current limit resistor for TS pin transient

C17 - optional high frequency noise filtering; Likely not needed if 0.01uF<C3<1.0uF if used; should not exceed 100pF to prevent interference with MPPSET feedback loop

C1 - Additional capacitance to handle up to 8A charge current, compared to 2A design in datasheet

C11 - switching noise decoupling capacitor

Regarding 2,

C13 - optional noise filtering on TS pin

C9 and R8 - form a RC snubber on the SW node to reduce high frequency switching noise that produces EMI if component placement on PCB is not ideal and/or C3 not used.

Regarding 3, with low enough ripple current (i.e. inductor sized to give <=40% ripple current) and C11, C12 and C14 filter caps, the current sensing circuit can accurately measure current even without a bulk capacitor before the resistor. Some customers add an additional bulk capacitor before the resistor. Placing the resistor and therefore SRN pin after a bulk resistor would make the current limit circuit inaccurate during a load transients.

Regarding 4, page 9 part 5 is referring to C8 and C11.

Regarding 5, you are correct. There is no reverse polarity circuity on this EVM. The simplest reverse polarity circuit is a FET in the battery current path as explained here

Regards,

Jeff

0 Dave Whitaker over 6 years ago in reply to Jeff F

Prodigy 190 points

Thanks Jeff,

Much appreciated, but I was not able to open the file you posted - I got the following error below. Can you send me the file in an alternate format ? maybe Jpeg or screen shot to the following address ? davewhitaker3@gmail.com

Unfortunately, the page you've requested no longer exists. Please use the search form above to locate the information you're interested in.

Regards

Dave