BQ76200: BQ76200: Schematic check requirement

Hello Gary,

Biggest thing I notice is that there are no gate resistors for the Q2 and Q5 FETs. Switching could have issues with no resistances, we recommend to have at least a few hundred Ohms for these FETs. We talk and explain this in Table 1. DSG Turn On Current Flow of our BQ76200 Beyond the Simple Application Schematic application note. See also Table 3. External Component Description from this application note.

Since PCHG is not being used, they should ground the PCHG_EN pin. PCHG can be left floating. Same with CP_EN, this should be to Vss or connected to DSG or CHG (See Table 1. CHG and DSG with Respect to CP_EN, CHG_EN, and DSG_EN in the datasheet), it should not be left floating.

Could they specify more about in how many boards they've seen this issue? Are both FETs OFF in these cases? Are there some boards with no issues whatsoever? 

In what test conditions do they see the FETs not working?

Best Regards,

Luis Hernandez Salomon

Hi Luis,

Thanks for your help.

There is a problem that CHG and DSG are not always on. But we have already turn both CHG_EN and DSG_EN on.

And you can see as below, the VDDCP is normal and the value is 32.8V when the BAT is about 22.8V. So I think the charge pump is working well.

Question is that do you know other control can cause the open for a while and close for a while to BQ76200.

Hello Gary,

Could you try increasing the VDDCP capacitor to 1-uF? The behavior of the CHG/DSG pins is similar to that when the charge-pump is overloaded. As seen in Section 2.1 Charge Pump of the  BQ76200 Beyond the Simple Application Schematic application note.

Best Regards,

Luis Hernandez Salomon

Hi Luis,

Thanks for your help.

Customer have already change VDDCP to 1uF. And the phenomenon still exists. When the voltage between VDDCP and BAT is below 8.7V, the output of CHG and DSG will down to low as picture show. is there a UVLO of 9V in this part?

Hello Gary,

Yes you are correct, there is a UVLO of 9-V for the charge-pump. This is described in Section 2.1 Charge Pump of the Beyond the Simple Application Schematic application note. This is also mentioned in Section 7.3.1 Charge Pump Control of the datasheet.

Does this condition happen sometimes? Or always? If it happens sometimes, do you know what test conditions they are using to replicate the issue?

Best Regards,

Luis Hernandez Salomon

Hi Luis,

If the chip is damaged, this phenomenon will always exist.