MP2770 Max Power

DC-DC Power Converters
1

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?

Thanks for your patience!

Kind regards,
Brian

2

Hello vybz,

This seems to have a recommended operating range with a max of 16V.

What Vsys are you trying to use while charging and providing system power?

3

Hello Eduardo,

Thanks for your reply.

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

  1. Does not allow to physically disconnect the battery via internal switch

  2. 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)

  3. 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.

  4. Because the battery is always connected (no physical disconnect) it will always drain over the SYS rail of the MP2770.

  5. 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.

4

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.

5

the MP2770 will require an external PD controller to negotiate the power levels

Yes I’m aware of this. Thanks for pointing this out! This is a critically design relevant point.

pass-through mode per the datasheet seems to limit the input voltage to 5V

I think this is a misinterpretation. This datasheet section is meant to be an example of the pass-through over voltage protection behavior.

Because VIN_OVP is configurable and will be set by the host, depending on the requirement of the SYS load. The default of VIN_OVP is 16.8 V to enable a max VIN of 16 V (which is VIN_MAX per specs).

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As you can see, VIN_OVP is configurable.
This means, if my application anticipates a VIN of 16 V, i set the VIN_OVP to 16.8 V. If 16 V will be overvoltage in my application, because it only anticipates e.g. 9 V as max VIN, I would lower the over-voltage protection accordingly for proper fail-safe management (error reporting and behavior of the MP227) as in this scenario a VIN of 16 V could indicate a serious damage of the whole system (depending on how VIN is generated).

I believe the device is definitely designed to deliver these outputs of 16 V/3.65 A.
This is what I have found about boosting input too VSYS (VBST):

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These specs (16 V at 3.65 A) couldn’t be achieved if the voltage VIN had been limited to 5 V. This output has to be stable independent of charge modes in order to keep the system load stable.

So I don’t think it is possible to supply that much power into the IC since the max input current is 3.5A.

Could you please verify that the device meets my requirements or recommend an alternative device that can meet them?

Because the Datasheet states that the max input voltage is 16 V, which I thought will allow me to negotiate a PD contract of 16V/3.5 A (USB PD 1.3) or 15 V/3 A (USB PD 3.0), given the max input current of 3.5 A.

This yields a 45 W power budget if a PD contract of 15 V/3 A is negotiated (by an external PD controller) of which I assumed the MP2770 is able to convert to the following internal rails (based on the limits I’ve found in the datasheet specs) using its internal buck converters.

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a) charging rail: 4.2 V at <=6 A ===> ~25 W
b) SYS rail: 4.3 V/3.65 A ===> ~16 W
Total: ~41 W

If you were misinterpreting the configurable over-voltage protection feature, then the MP2770 should be able to output 4.3 V/3.65 A (or theoretically 16V/3.65 A) to SYS.

Do you agree?

7

I missed “host configures” in this section of the datasheet. Based on this I believe the part could work for your use case.

Not sure about providing a lower voltage at system though since datasheet calls out “IN to SYS passthrough path to send input voltage (VIN) to the
system.” You may require a stepdown at sys to achieve desired voltage.

8

Ah, ok. Because the default VIN is 5 v and the SYS is rated at 4.3-16 V I assume the MP2770 is using its internal buck converter to step down (and boost) VIN.

Some datasheets are difficult or ambiguous in some aspects. Additionally, based on the specs a power dissipation of whooping ~85 W (SYS 16 V/3.65 A, CHARGE 4.45 V/6 A) is pretty big for such a small device. That has added some doubt that my understanding is correct.

But based on your last comment I guess the answer to
“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?” is “Yes!”. Because that behavior is covered by the pass-through mode.

Anything that comes in your mind that I need to pay attention to?

9

Based on my last comment Vsys=Vin. This is the behavior the datasheet describes. So it is not directly supported but by using an external buck converter you can drop the Vsys=Vin voltage down to 4.3V.

10

Yes, you are right. I was somewhat biased when interpreting the datsheet as I was using PMICs that integrated one or multiple stable buck regulated outputs. That really helped to compact the layout. Thank you for clarifying this.

The behavior is a bit different than expected but still acceptable. Because I’m using external buck converters and LDOs to generate the system power rails anyways, i think I will still use the MP2770.
It just changes the way power dissipation is distributed. Because the MP2770 is then offloading the full step-down conversion e.g. from 16 V → 4.3 V to the external circuitry. Of course, this removed some complexity when designing the MP2770.

It now looks like VSYS = VIN except when the device is in Boost Mode, that is when VIN is absent (and Boost Mode was explicitly enabled). In this case VSYS = VBST. Additionally ISYS is only 3.65 A max when in Boost Mode (ISYS = IBST). Otherwise ISYS = <=2.9 A. Can you confirm that, please?

Thanks for your patience!

12

Seems like you have forsaken me. Can you please advice me on how to treat FB pin if unused? Should we leave it floating? The datasheet is not specific in terms of functionality and electrical behavior. The datasheet’s typical application design provides a voltage divider for FB. However, the constraints for the FB pin/voltage divider are not explained. Since I’m using the internal DAC I assume it’s safe to a omit that particular circuitry. It appears that floating this pin is fine or even expected. I would be happy if you could advice me on this.

Thanks!

13

Hello vybz,
I am checking to see what the guidance for this would be.

14

Thank you very much! Based on other devices, the FB pin appears to be always connected to the PMID.
I’m also considering to use the MP2760 (which supports the full USB PD profile range) and have posted another related question as the datasheet only mentions the presence of a missing battery detection but does not elaborate on the behavior. May you like to take a look?

15

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If this but is set to 0 the FB pin can be left floating

1 Like
16

Perfect. Thank you so much for your time and support!