MP2760 power on without battery

DC-DC Power Converters
1

Hi,
I have a questions regarding the startup behavior of the MP2760 and need to ensure that the device can perform up to the requirements.

Requirement

System implements multiple behaviors that transition between power states.
In one particular state

  • System must be completely powered off
  • USB C reconnect is the only wakeup event to exit that state

Strategy

  1. Disconnect battery by disabling BATFET (forced turn off by setting BGATE_ CTRL in the configuration register REG10h to1).
    If V IN is absent, the MP2760 is no longer able to generate its VCC and is completely powered off ==> system is dead.
  2. On USB C reconnect, MP2760 can generate VCC from VIN and boots and generates VSYS which then causes the other system components to boot ==> system is alive.

Question

  1. When BATFET was forced off via I²C, will the MP2760 reset the BGATE_ CTRL flag to 0 after a reset to reconnect the battery or will it sense a missing battery and fail to restart as BGATE_ CTRL is persisted across resets? (I expect all registers to be set to default after a power cycle reset)

  2. Regarding the “Missing battery detection” feature: will the MP2670 halt or continue to operate and feed SYS with VIN when battery is not present?
    From the datasheet:

    Battery Missing Detection
    The MP2760 counts how often charging
    terminates every 10s. If charging terminates
    more than three times in 10s, the MP2760
    reports that the battery is missing in the status
    register and initiates an INT signal.

    Based on my interpretation that means that the MP2760 infinitely loops through 10s cycles trying to detect the battery where within each cycle the battery presence is asserted >3 times. And in addition, after every 10s cycle the INT signal is issued. Then cycling stops once the battery was detected.

    However, whether VSYS is populated during the absence of a battery is not clear.
    Also whether MP2760 continuous charging after connecting a battery is not clear. There are sources that state that similar MP devices don’t tolerate a battery connect event after startup.
    Furthermore, will disabling BATFET (and therefore disconnect the battery) also trigger the “missing battery” detection? I assume the MP2760 senses the BATT pin, which should have a valid VBATT independent from the state of BATFET?
    Will connecting a battery also raise INT?

This is the only uncertainity I have and that I like to sort out before ordering the part for further evaluation.
Thanks for your time!

2

Hi,
I am currently working with the MPS team. I will get back to you shortly.
Thanks for your patience.

3

Thanks! I will wait.

Meanwhile, I also have another question regarding battery temperature monitoring (maybe someone can share his experience).
Could you please do me the favor and check the temperature monitoring behavior too, please?

Because common temperature thresholds for Li-Ion batteries are 45 °C for charging and 60 °C for discharging.

Now, the datasheet mainly focuses on the charging mode. It states that we can use REG0Ch(datasheet, page 42) to configure a JEITA action when VNTC < VWarm (which is a temperature > 45 °C by default). I can use this configuration to throttle charging to an extend that the battery is allowed to cool down.

However, it’s not apparent (to me) whether this REG0Ch register will be evaluated during standby and source mode?
In source mode, the temperature thresholds appear to be restricted to VCold and VHot, which means the REG0Ch register will be ignored. That’s an assumption made on the very vague paragraph on page 33:

The MP2760 also monitors the battery
temperature in source mode. If the NTC
function is enabled, an interrupt (INT) is
asserted if the battery temperature is below
VHOT or above VCOLD.

Based on this sparse information this I can only assume that the REG0Ch register is ignored, although this is not explicitly mentioned somewhere.

Does this behavior also apply to the standby mode? Based on the common temperature ranges of charging vs discharging I would expect that in standby mode (and source mode) the REG0Ch will be ignored as well as this would be the only chance to allow battery temperature to rise up to 60 °C (otherwise the 45 °C limit would apply).

Can you confirm this, please? I don’t find anything about it in the datasheet (although I can’t rule out that I have overlooked or misinterpreted something).

Thanks again, and thanks for being patient with me.

4

Hi,

To answer your initial question:

When BGATE is forced off using BGATE_CTRL, BATFET will turn off and charging will be disabled. Once BGATE is disabled, the MP2760 will act as a typical DC/DC buck-boost converter using the input voltage to power the system.

You are correct. Power cycling the device will cause the BGATE_CTRL bit to reset back to its default, 0, which will not force BGATE off.

As far as the Missing Battery Detection feature- If there is no battery, an interrupt (INT) signal will be sent to the device letting the device know that the battery is missing. The device will continue to power the system with the input voltage as a typical DC/DC buck-boost converter.

Let me know if you need any more clarification here.

For the temperature monitoring, are you looking for an interrupt that will notify the system if the temperature is too hot/too cold in standby? Thanks!

5

Thank you very much. That was very helpful. Thanks for taking your time to help.

I assume another INT signal is issued when battery is detected after flagging its absence? Thanks!

It really depends on the behavior.
My point is that the datasheet is mainly explaining behavior in charge mode. Here it states that the action for the temperature range between TWarm ≥ 45 °C and THot ≥ 60 ° C can be configured (using the REG0Ch register). This makes perfect sense as for charging the max tolerable temperature for a Li-Ion cell is 45 °C.

Now, during discharging (standby mode) the battery has a different characteristic. The 45 °C threshold doesn’t apply. Whille 45 °C is the common max temperature during charging, the threshold for discharging is usually 60 °C.

This means, to protect the battery during charging, the charging voltage must be cut off (or heavily throttled) and current limited when 45 °C is reached to allow the battery to cool down.

But this behavior must not apply during discharging. Cutting off current (or reducing voltage) prematurely (at TWarm = 45 °C) would negatively impact the system’s performance, since we can discharge the battery up to THot = 60 °C.

But there is only a single register to confugre the behavior between TWarm and THot.

If the MP2760 is not ignoring the REG0Ch register during discharge (or standby mode) I would have to manually stop the MP2760 from taking premature action at TWarm by disabling the configured behavior in the REG0Ch register. But to to this, I need to know when the MP2760 is charging and when discharging. Only if the MP2760 is not ignoring REG0Ch during discharge I need a notification that I can monitor. And whether or not the register is ignored during discharge is not mentioned in the datasheet.

The datasheet only addresses source mode, where the register appears to be ignored. I say “appears” because it only mentiones the INT signal which is only issued if temperature crosses TCold or THot. We can only guess that this means that the TWarm logic defined by REG0Ch is ignored. Standby mode is never mentioned.

That’s why I’m asking about the temperature monitoring behavior in context of TWarm and the associated REG0Ch register.

Please let me know if I have to explain it better. I don’t want the charging action at TWarm = 45 °C (defined in REG0Ch) to be executed durinng discharge, where this limit is not relevant and only the THot = 60 °C threshold matters.

Thanks for being patient with me. I really try my best to explain it. I hope you don’t feel like I’m wasting your time. Thanks again.

6

Hi,

Yes, your explanation makes sense. REG0Dh configures the threshold values (COLD, COOL, WARM, HOT). REG0Ch configures the charging behavior when these threshold values are met. In source mode, only the HOT and COLD temperature thresholds are taken into account when deciding when to assert an interrupt. You should not have to worry about changing the behavior when the battery is discharging.

The BATT_MISS_STAT in REG16h is the indicator for a missing battery. An INT is sent only when it is asserted. This function is to guarantee safe operation.

Thanks!

1 Like
7

Thank you so much for your time and help! This answeres my questions.

I wish you a great day!

8

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