BQ24780S: BQ24780S 0x39 register

Yes, BQ40Z50 as a Fuel Gauge in battery pack will report temperature to EC by SMBUS.

1, If the system current demand continue to increase after the system current demand exceeds the 0x39 setting values,  the VSYS from battery  will drop heavily which will lead to system shutdown,right?

2, Can I write zero to 0x39 to disable battery discharge to zero if I want to shut off battery discharge action in battery-only mode and LEARN Mode?

Christian Moyer said:

The current will still flow through the body diode of the BATFET. Writing zero will not  stop the battery from discharging. REG0x39 is mainly used for the prochot signal, to indicate to the MCU that the battery is discharging too much current.

You will need an external circuit for to stop battery from discharging.

Can BQ24780S regulate VSRN-VSRP=0V  [so Ibat=(VSRN-VSRP) / Rsr = 0  ] to stop battery from discharging if I write 0x39 to 0A, even though there is body doide in BATFET?

Christian Moyer said:

Zhang Excellent said:

Can BQ24780S regulate VSRN-VSRP=0V  [so Ibat=(VSRN-VSRP) / Rsr = 0  ] to stop battery from discharging if I write 0x39 to 0A, even though there is body doide in BATFET?

No, it will still flow through body diode. There is nothing to prevent it from flowing through body diode .You will need an external circuit for to stop battery from discharging.

So can I say 0x39 Discharge Current Regulation Setting is applicable only to HPB Mode but not applicable to battery-only mode(without adapter present), because only HPB refers to boost operation,right?

Christian Moyer said:

Zhang Excellent said:

So can I say 0x39 Discharge Current Regulation Setting is applicable only to HPB Mode but not applicable to battery-only mode(without adapter present), because only HPB refers to boost operation,right?

Yes, This is correct.

So actually I cannot use 0x39 to limit batter discharge current in battery-only discharge mode according to different temperature because 0x39 is just used for HPB mode(require both adapter and battery present to support HPB),not for battery-only discharge mode(for example, notebook with battery only present but without adapter present) in which the discharge current flows through BATFET only,right?

Christian Moyer said:

Zhang Excellent said:

Can I use EC to write to BQ24780S  Discharge Current Register 0x39 to limit the maximum discharge current by detecting different temperature from battery pack to achieve this discharging current vs. temperature goal?

You can use the EC to write to the device, but you will need some external circuit, like a Fuel Gauge to measure the battery temperature and then feed that information to the EC to determine what charge current to write

1, In this reply to me, you say I can use the EC to write to the device, but you will need some external circuit, like a Fuel Gauge to measure the battery temperature and then feed that information to the EC to determine what charge current to write.

You mean using this way to limit discharge current only in HPB mode,but you do NOT mean using this way in battery-only discharge mode(for example, notebook with battery only present but without adapter present) in which the discharge current flows through BATFET only,right?

2, If I want to limit discharge current to a specific value(such as 5A) in battery-only discharge mode(for example, notebook with battery only present but without adapter present) in which the discharge current flows through BATFET, I must use another way to achieve this goal,instead of using 0x39, right?

3, Can BQ24780S regulate VSRN-VSRP across external Rsr to achieve limiting discharge current to a specific value(such as 5A) in battery-only discharge mode(for example, notebook with battery only present but without adapter present) ?

Christian Moyer said:

How would we be able to regulate this current? We are not able to dynamically change the value of the sense resistor. The power is not flowing through the converter, so we are not able to modify the duty cycle. 

1, Understanding of Discharge Current Regulation and HPB working mechanism by 0x39 setting:

Both SRP and SRN are input pins which can only be used to sense. So both SRP and SRN cannot be used as output pins to regulate the current to be limited directly since only output pins can control something external directly.

It is always BQ24780S boost converter that directly regulates the battery discharge current in HPB mode by sensing actual current through Rsr.

SRP and SRN pins just perform input sensing function and they cannot limit or control discharge current directly as input. In HPB mode, Discharge Current limit and regulation must be executed by boost converter.

2, Understanding of Input Current Regulation,DPM and HPB working mechanism by 0x3F setting:

Similarly, both ACP and ACN are input pins and IDPM and HPB functions use ACP and ACN as input to sense actual input current near to 0x3F setting and then feedback this message internally to regulate the charger buck PWM to decrease battery charge current in DPM mode and regulate boost PWM to increase battery discharge current in HPB mode. In both DPM and HPB mode,  and by such mechanism, input current maintains at 0x3F setting value.

It is always BQ24780S buck or boost converter that regulates the battery discharge current or charge current by sensing actual current through Rac and Rsr. ACP / ACN and SRP/SRN pins cannot do this directly.

3, Anyway,only BQ24780S buck and boost converter can regulate current. The sole executor of Discharge Current Regulation and Input Current Regulation is BQ24780S buck or boost converter. ACP/ACN and SRP/SRN are input pins,only perform sensing function, and so they cannot perform regulation directly!

Are my understanding items above correct?