Hello, we want to use t he MP2770 but we need to assert that it can perform as expected.
To my understanding the MP2770 does not allow the 20 V at 5 A PD contract per USB PD 3.0 specs. This means the max I can accept is 20 V at 3 A, is that correct?
Furthermore, when charging a battery at 5-6 A can the system rail still deliver the 3.65 A ISYS at e.g. 3.7 V?
And lastly, how will the MP2770 behave when it sees an input current of e.g. 500 mA which would be to low to power the system which depends on 3.5 A? Will it disconnect the SYS path and use the 500 mA to charge and then enable the SYS path again once the battery has charged?
Sorry for wasting your time by missing some crucial context information. I will try to give you a more detailed context.
Please, I would be extremely happy if you could verify my understanding of the device’s capabilities, as reading through the support forum has introduced confusion.
Goal
My goal is to implement fast charging by supporting USB Type C, USB PD and USB BC1.2 for a mobile application.
I originally opted to support VIN of 20 V at 5 A (per USB PD 3.0 or greater).
But it turned out that the MP2770 only supports 3 A input. I can accept that as 20V at 3 A still yields a 60 W power budget which is ok (especially when considering the thermal implications).
The system rail would preferably provide 4.3 V at 3.65 A (max current).
Battery charging with up to 5.5 A (design is for 6 A).
Guarantee the 4.3 V at 3.65 A for the SYS rail while charging at 6 A (==> 40.895 W total MP2770 power).
The battery is a 10 Ah Li-Ion cell (1S) and allows a charge/discharge <=1C (<=10 A).
Please confirm the folowing behavior of the MP2770
Does not allow to physically disconnect the battery via internal switch
Supports explcit/manual charger stop via registers which stops charging but always keeps the e.g. 4.3 V at 3.65 A SYS rail active (especially when the charger is stopped)
In order to maintain the battery cell and ensure that the cell’s capacity remains within the e.g. 60-70% range, manual duty cycling of the charger is required i.e. there is no autonomous battery maintenence behavior.
Because the battery is always connected (no physical disconnect) it will always drain over the SYS rail of the MP2770.
The current NTC temperature (ADC readings) are stored in the 17h register.
5.1. The values are scaled to a 0-1.28 V range (raw voltage drop over NTC pull-up).
5.2. There is no chance to get converted temperature (e.g. in Celsius) or a voltage scaled to a normalized 0-4.2 V range.
Questions
A) Is the MP2770 designed to provide 6 A to the charging path and 4.3V/3.65 A to the SYS path at the same time (40.895 W) when VIN is at e.g. 15-20 Vat 3 A (45-60 W)?
B) A member of the support team wrote:
All load power goes through the battery boost path. The MP2770 doesn’t support direct source to load passthrough or prioritization.
Does this mean the MP2770 can not manage the power budget and allocate/distribute this budget for the SYS and CHARGE path autonomously? I would expect that it e.g. prioritizes the SYS rail over the CHARGE rail, still ensuring that the battery sees some charging current.
In that context: B1) could you please explain the behavior of the MP2770 if it configured with the mentioned limits (4.3 V/3.65 A and 4.2 V/6 A) but only sees an input of e.g. 5 V/0.5 A?
B2) can you explain how the MP2770 behaves if the charger is disabled? Will it still convert VIN to 4.3 V at 3.65 A?
C) If the MP2770 is the wrong device for the task, can you please recommend a more suitable device(s)?
I know this is a lot I’m asking of you. But I start to believe that the MP2770 is the wrong device for the task. The forum couldn’t cease my concerns and the datasheet is either missing a detail or is ambiguous in some aspects.
Just to clear a few things up the MP2770 will require an external PD controller to negotiate the power levels you described.
However, pass-through mode per the datasheet seems to limit the input voltage to 5V. Setting over voltage to 6.4V. So I don’t think it is possible to supply that much power into the IC since the max input current is 3.5A.