Interfacing BQ24392 with BQ24075

Hello Claus,

I suggest the following:

• EN2: CHG_DET
• EN1: AND(NOT CHG_DET, NOT SW_OPEN).  Or you can also: NOR(CHG_DET, SW_OPEN))
• Also in typical applications CHG_AL_N is tied to VBUS.  This ensures that the charger does not start charging until the detection sequence has completed. 

This logic combination for EN1 and EN2 will allow you to use high current charging for every possible high current charger attachment.

Regards,

Andrew

Dear Andrew,

thanks a lot for your answer, I don't quite catch it though. I'll copy the logic tables I have used. From BQ24075 we have for En1, En2

On the other hand, from BQ24392 I get

I have associated the corresponding USB devices in the last columns. Now if I apply your logic:

USB-dev columns are not sound. However, when applying my logic I get:

(this is how I arrived at the circuit) What am I missing here?

Kind regards, Claus

Hello Claus,

I think you have the EN pins for the BQ24075 mixed up in the above.  Here is the table from the datasheet:

Explanation of my implementation for your design: 

If you tie EN2 to CHG_DET it will mirror the BQ24075 logic table.  For both 100 mA and 500 mA charging case it will be low and for 1.5 A it will be high (I view Standby as don’t care because the charger will be disabled by CHG_AL_N in this case).  Also a CDP can be up to 5A according to BC1.2 specifications and a SDP can be up to 500 mA.

Now we need to create the logic to mimic the BQ24075 EN1 logic.

I have come up with the table below. To get 500 mA from an SDP I believe you need to negotiate with the host for it per USB spec so the SW_OPEN pin must be active to do this communication(i.e. low or 0 in this case). Then if you want to utilize a CDP as a high current charger the SW_OPEN output can be high-z or low depending on GOOD_BAT.

Using a EN1 = !( CHG_DET or SWOPEN) will yield the following table which matches the above:

Does this make sense?  Of course you can choose not to use the CDP as a high current charger in which case your implementation will work perfectly.

Regards,

Andrew

Dear Andrew,

thanks for your detailed answer! I think I understand that it is better to have CDP mapped to 1.5A,so both CDP and DCP can use the high current charger. With my logic CDP would charge only with 500mA.

However, in the case of SDP, one should start with 100mA and then negotiate, i.e. in this case  I would expect CHG_DET=0 and SW_OPEN=0 from the BQ24392 side. One would then have to set EN1 depending on the negotiation, but CHG_DET and SW_OPEN should stay low, shouldn't they? How could SW_OPEN be 1 for SDP (low) and 0 for SDP (high)??

This would certainly be interesting for an AN, it is not so easy to derive...

Kind regards, Claus

Hello Claus,

My thoughts on this were that if GOOD_BAT is low during an SDP attach(and stayed low) then SW_OPEN will be high-z and the USB switches open.  Then you couldn't negotiate for the higher current 500 mA.  If GOOD_BAT is high then the SW_OPEN pin will be low, the switches closed, and you can negotiate for the 500 mA.

I am not 100% sure how your system is handling this but this was my assumption. 

Regards,

Andrew

OK, so you had in mind the battery failure case. So let me summarize, if I finally have got it.

EN2=CHG_DET.

GOOD_BAT=HIGH:

EN1=0 (only set EN1=1 if 500mA negotiaition succesfull)

because with a working battery we would have SW_OPEN=0, EN1=0 in the SDP case for 100mA. This would actually mean to set EN1=0 all the time, with the exception of the case of a sucessful 500mA negotioation, which would set EN1=HIGH (for CHG_DET=1 no negotiation woud be initiated and can thus not be sucessfull).

Or did I miss something again? Thanx for your patience, Andrew!