BQ25720: What‘s the relationship between IinDPM and Two-Level Input Current Limit？

Hello Zhang,

Please refer to section 9.3.20 Two-Level Adapter Current Limit (Peak Power Mode) in the data sheet:

Usually adapter can supply current higher than DC rating for a few milliseconds to tens of milliseconds.The charger employs two-level input current limit, or peak power mode, to fully utilize the overloading capability and minimize battery discharge during system load transient.

Zhang Excellent said:

as the system overload comes to activate the IinDPM action，the ILIM2 in the feature of Two-Level Adapter Input Current Limit will never be hit actually due to the IinDPM operation preventing the input current increasing any more than 1A and hitting the ILIM2 value.

The charger will first apply ILIM2 for TOVLD (PKPWR_TOVLD_DEG register bits), and then ILIM1 for up to TMAX – TOVLD time.

Best Regards,

Christian.

Hello Zhang,

Zhang Excellent said:

1，How can I understand this description since the adapter itself has the capacity of current surge with certain duration which is not given by the charger and is not relevant to the charger？

Zhang Excellent said:

2，Why and how does the charger minimize the discharge of the battery？

If you have a system that requires a load of 16W but the adapter is only able to provide 15W  the device will go into supplement mode and the battery will help the adapter by supplying the remaining 1W of  power to prevent the system from crashing. Most customers do not want to discharge the battery when the adpater is connected, because the battery is supposed to be used as a back up power when adapter is removed. It's also reduces the life cycle of the battery to discharge and recharge the battery.

Usually during system transient loads the system only requires the 16W of power for a short period of time for example 4 milliseconds.

Every adapter has a certain DC rating that it can support, for example 5V/3A(15W). Usally these adapters can go above this value for a short period of time, for examples 5V/3.25A(16.25W) for 5 milliseconds. 

By using the feature of the adapter we can supplly the system load from the adapter without discharging the battery, this helps to increase the life cycle of the battery.

Zhang Excellent said:

1，What does “apply” herein mean？The charger will limit and try to fix the adapter input current to ILIM2  for a duration of TOVLD if it attempts to go high than ILIM2 set in register，right？Or what will charger do if the adapter input current surge increases higher than ILIM2 ？

Yes, This is correct the charger will limit the input current to ILIM2 set in the register

Zhang Excellent said:

2，If the charger will limit and try to fix the adapter input current to ILIM2 for a duration of TOVLD if it attempts to go high than ILIM2，can I leverage the operation mechanism of intel‘s PL1 and PL2 to understand it？

The input current should not be able to go higher than ILIM2.

Zhang Excellent said:

3，If the charger will limit and try to fix the adapter input current to ILIM2 for a duration of TOVLD if it attempts to go high than ILIM2，how does the charger achieve and finish it？

The input current should not be able to go higher than ILIM2.

Best Regards,

Christian.

Hello Zhang,

Zhang Excellent said:

Can the peak-power feature of the adapter terminate the battery supplement mode when the system overload happens?

The peak-power feature happens before the battery enters supplement mode.

Zhang Excellent said:

As I understand, the battery supplement mode itself occurs just after having already experienced the peak-power feature of the adapter which still cannot meet the overload from system ,

Yes, This is correct.

Zhang Excellent said:

so why can you say the battery supplement mode can be avoided if using peak-power feature of the adapter? I'm really confused about the concurrence of supplement mode and the peak-power feature of the adapter.

I don't know how to explain this further. This feature is for a transisent load( a load that rapidly changes, for example 0W to 16W to 0W in only a few milliseconds) The adpater is normally only able to supply 15W, but because we know that most adapter can go above their DC rating for a short period of time, we use this to our advantage.

In most case we can use this to avoid going into supplement mode, but if the system load stays on longer than the programmed ILIM2 limit the charger will go into supplement mode.

I recommend ordering an EVM and testing this on on your own.

Best Regards,

Christian.