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nPM1300: Suitability for dual USB Solar charging

JordanYates

I am looking to evaluate whether the nPM1300 is suitable for use in a dual charge source setup.
Given the device is designed for USB charging, I have no doubts it is works as designed when charging over USB.
The question is therefore how the device behaves when the CC pins are floating (USB cable unplugged) and a variable strength voltage source is supplied to VBUS.

I have determined the following from the datasheet (please correct me if I'm wrong):

* Using any solar panel with an open-circuit voltage over 5.5V will immediately trigger the over voltage protection, regardless of the voltage it would be under load.
* The VBUS current limit is set to 100mA
* The VBUS current limit can not be updated by the MCU, because a device is never detected via the CC pins.

As a result, it would seem that the maximum charge current that could be provided by the solar panel is 100mA.

Section 6.2.10 of the datasheet (Dynamic power-path management) talks about CHARGER entering supplement mode to provide current.
The basic situation I am trying to understand is this:

If a 5V 30mA solar panel is connected to VBUS and is in full sun, how does the nPM1300 behave when the battery is low and the system load (ignoring charging) is 20mA vs 40mA.
In the first instance, will 20mA from the panel be used for the regulators, with the remaining 10mA going to the battery?
In the second, will all 30mA from the panel be used for the regulators, with the remaining 10mA being supplied from the battery?

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  • +1

    I've been able to acquire some new information.

    Using any solar panel with an open-circuit voltage over 5.5V will immediately trigger the over voltage protection, regardless of the voltage it would be under load.

    This is correct. The overvoltage protection will be triggered when the open-circuit voltage exceeds 5.5 V.

    The VBUS current limit is set to 100mA

    The default VBUS current limit is set to 100 mA.

    The VBUS current limit can not be updated by the MCU, because a device is never detected via the CC pins.

    The VBUS current limit may be changed by the host (MCU), regardless of the CC pins being used for port detection or not. Port detection via CC does not automatically update the VBUS current limit, as this has to be read by the host first and then later be updated. Hence, it's always the host that will configure the VBUS current limit.

    The CC pins are used to ensure compatibility with the USB host, which is out of scope for this case, as you're not powering the nPM1300 by USB.

    If a 5V 30mA solar panel is connected to VBUS and is in full sun, how does the nPM1300 behave when the battery is low and the system load (ignoring charging) is 20mA vs 40mA.
    In the first instance, will 20mA from the panel be used for the regulators, with the remaining 10mA going to the battery?
    In the second, will all 30mA from the panel be used for the regulators, with the remaining 10mA being supplied from the battery?

    Unfortunately, we can not guarantee that it will behave the way you're describing. The setup may work if VBUS is kept above the minimum voltage of 4 V when the system is loaded. However, there is a chance of VBUS dropping below 4 V when the system is under load, leading to failure. You can perform tests and see how it works but we can not guarantee that the nPM1300 will function as intended.

    If you want to implement charging by using solar panels, our advice is to use a circuit that supports this and which is able to supply the correct voltage to VBUS (4.0 - 5.5 V).

    Best regards,
    Mathias

Reply
  • +1

    I've been able to acquire some new information.

    Using any solar panel with an open-circuit voltage over 5.5V will immediately trigger the over voltage protection, regardless of the voltage it would be under load.

    This is correct. The overvoltage protection will be triggered when the open-circuit voltage exceeds 5.5 V.

    The VBUS current limit is set to 100mA

    The default VBUS current limit is set to 100 mA.

    The VBUS current limit can not be updated by the MCU, because a device is never detected via the CC pins.

    The VBUS current limit may be changed by the host (MCU), regardless of the CC pins being used for port detection or not. Port detection via CC does not automatically update the VBUS current limit, as this has to be read by the host first and then later be updated. Hence, it's always the host that will configure the VBUS current limit.

    The CC pins are used to ensure compatibility with the USB host, which is out of scope for this case, as you're not powering the nPM1300 by USB.

    If a 5V 30mA solar panel is connected to VBUS and is in full sun, how does the nPM1300 behave when the battery is low and the system load (ignoring charging) is 20mA vs 40mA.
    In the first instance, will 20mA from the panel be used for the regulators, with the remaining 10mA going to the battery?
    In the second, will all 30mA from the panel be used for the regulators, with the remaining 10mA being supplied from the battery?

    Unfortunately, we can not guarantee that it will behave the way you're describing. The setup may work if VBUS is kept above the minimum voltage of 4 V when the system is loaded. However, there is a chance of VBUS dropping below 4 V when the system is under load, leading to failure. You can perform tests and see how it works but we can not guarantee that the nPM1300 will function as intended.

    If you want to implement charging by using solar panels, our advice is to use a circuit that supports this and which is able to supply the correct voltage to VBUS (4.0 - 5.5 V).

    Best regards,
    Mathias

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