BQ76930: 推荐电路相关问题

cooo lin

Prodigy 40 points

Part Number: BQ76930
Other Parts Discussed in Thread: BQ76920

问题1：D6在此处的作用应该是短路时防止AFE供电不稳定，R3和C3的作用看起来是和D6的作用重复了，请问是否可以去掉D6或者R3和C3?

问题2：请问Q33和D42的作用是？

问题3：一般快放电路没有Q36，请问增加Q36的作用是？

1 年多前

0 Star Xu 1 年多前

TI__Guru*** 130456 points

您好，正在查询，稍后回复。

0 cooo lin 1 年多前回复 Star Xu

Prodigy 40 points

你好，请问该问题有在跟进吗？

0 Star Xu 1 年多前回复 cooo lin

TI__Guru*** 130456 points

您好，请参考下面内容

1- R3 and C3 are part of the recommended filter components for the supply pins. See below for D6. More info can be found in this video

2- The purpose of Q33 is to add a voltage drop along with D41 to lower the voltage at the gates of Q38, Q40, and Q42 (this is explained in the Design guide). I would assume D42 is for the same purpose, to lower the gate voltage for Q39, Q41, Q43.

3， The purpose of Q36 is to expedite to extract and exhaust the charges on the gate of Q39 so that the cut off speed of Q39 can be desired for actual application, adjusting the value of R91 can change the FET cut off speed.

0 cooo lin 1 年多前回复 Star Xu

Prodigy 40 points

1-视频上说76920不需要D6，76930/40需要，但是并没有说原因，请问原因是？

2-我认为D44和D41的作用是一样的，但是D42我觉得应该不是。

3-我可以不要Q36，直接用Q35的3管脚接PACK-吗？

0 Star Xu 1 年多前回复 cooo lin

TI__Guru*** 130456 points

您好

1, D6 is a flyback diode as described in page 27 of the EVM user guide www.ti.com/.../slvu924d.pdf
If the discharge FET turns off quickly with high current and with a large inductive load on the pack terminals, the inductance may create a high voltage on the PACK- terminal. D6 will limit the voltage to near the PACK- terminal. D6 may not be needed, without D6 the discharge FET may handle such a voltage surge with its avalanche rating.
While the bq76920 has a non-zero pull down resistance which will avoid an instant turn off of the discharge FET, the EVM has the R16 resistor to the gate as 0. Resistance can be added at the R16 location to slow switching to avoid the fast dI/dt which can cause the transient. The designer should select a turn off which will not cause the FET to overheat during switching.

3, 建议使用推荐的电路, 推荐的电路是工程师反复验证过的.

0 cooo lin 1 年多前回复 Star Xu

Prodigy 40 points

Star Xu 说：
D6 will limit the voltage to near the PACK- terminal.

how D6 limit the voltage to near the PACK- terminal?

Star Xu 说：
3, 建议使用推荐的电路, 推荐的电路是工程师反复验证过的.

我知道推荐的电路没问题，我只是想搞清楚该设计的原因是什么而已？

0 Star Xu 1 年多前回复 cooo lin

TI__Guru*** 130456 points

您好，正在查询，稍后回复。

0 Star Xu 1 年多前回复 Star Xu

TI__Guru*** 130456 points

您好，请参考下面内容：

D6 will be forward biased when the discharge FET is turned off as the current would continue to flow from Pack- to Pack+ via D6, since it is forward biased, the Pack- voltage is clamped to Pack+, this is how Pack- voltage is limited.

I haven't tried with direct connecting Pin3 of Q35 to GND, suggest to make a simulation to check the result

0 cooo lin 1 年多前回复 Star Xu

Prodigy 40 points

Star Xu 说：
D6 will be forward biased when the discharge FET is turned off as the current would continue to flow from Pack- to Pack+ via D6, since it is forward biased, the Pack- voltage is clamped to Pack+, this is how Pack- voltage is limited.

i did a short test, the BMS with D6, but the P- voltage was not clamped to BAT(i think it should be BAT instead of PACK+). the volatage of P- is double than BAT. could you tell me why?

0 Star Xu 1 年多前回复 cooo lin

TI__Guru*** 130456 points

您好， Do you have the plot of short test, in the schematic of P29, Pack- shall be clamped to BATT+ when the discharge path is cut off, due to respond delay of D6, a brief high pulse on PACK- may be observed, but it should be quickly clamped by D6, D6 should be selected with appropriate forward clamping respond speed so that the brief pulse won't damage other components in the circuit.