7 Replies Latest reply on Feb 2, 2016 12:21 PM by Vincenze

    LiPo charger circuit documentation bug


      I'm running an Edison with the Mini Breakout board and it looks to me like the documentation for the board has a mistake. The doc says:


      "When you attach a rechargeable lithium-ion battery, the breakout board will recharge the battery whenever power is applied via J21 or J22, or via J3 (when the board is attached to a USB host)."



      Which claims the battery is charged by plugging in J3 (the console port). In reality, the behavior I'm observing is, the charging happens while plugging power to J16 (the OTG port). Can someone from Intel confirm what the expected behavior is? I'd also love additional documentation regarding the J2 lipo / li-ion battery behavior - what's the expected thermistor resistance / what's the max output to the battery when charging? The feature seems mostly undocumented.

        • 1. Re: LiPo charger circuit documentation bug

          Hello sulka,


          I've checked the documentation and you're right. It should be J16 instead of J3. You can power the Mini-Breakout Board though J21 (or J22), or though the USB OTG port which is J16. I'll inform about this detail so the team in charge of the documentation can check it and make the corrections required.


          Regarding the documentation about J2, I recommend you to check the datasheet of the BQ24074. It's the IC used for the charging circuit. You can check the circuit in the Mini-Breakout Board schematic: Intel® Edison Breakout Board Schematic for Boards and Kits. The datasheet of the IC BQ24074 can be checked in the following link: http://www.ti.com/lit/ds/symlink/bq24079.pdf




          • 2. Re: LiPo charger circuit documentation bug

            Hey related - the overall charge behavior and how the LEDs reflect the charge status is also undocumented.


            The behavior I'm observing is, when a LiPo is connected AND I connect a charger to J16, both LEDs on the board light up for some time, after which the USB charge indicator (?) LED turns off. Subsequently the Edison runs for some time and then just turns off.


            1) Is the USB indicator LED a sign of the LiPo charging?

            2) Is the USB indicator LED turning off a sign of the IC thinking the LiPo is fully charged?

            3) Is it expected behavior, that if a LiPo AND J16 are connected, the board eventually powers down (after first charging and then discharging the LiPo)?

            • 3. Re: LiPo charger circuit documentation bug

              1) The Charging LED is connected to the CHG pin. It should light up only during charging.

              "Open-Drain Charging Status Indication Output. CHG pulls to VSS(ground) when the battery is charging. CHG is high impedance when charging is complete and when charger is disabled."

              3) That is a more complicated question. The Edison breakout is connected to both a USB port and a battery.

              If the Edison consumes more milliamperes than the USB port can provide, then it also uses the battery.


              A USB port can provide 100mA, 500mA or more. The Edison with an active Wi-Fi transfer can consume 150mA or more.

              The breakout power circuit assumes that a USB port can provide 190mA. However, a device that wants to draw more than 100mA must negotiate with a host via a process called "enumeration", and the circuit misses this part.


              all USB power ports, when active (i.e., "not suspended," in USB parlance), were classified as either "Low Power" (100mA) or "High Power" (500mA). Any port could also be "suspended," which means nearly off but still able to supply 2.5mA. For the most part, ports on PCs, laptops, and powered hubs (A powered hub is a USB breakout box with its own wall wart for bus power.) are "High Power," while ports on hubs that receive no power other than what is supplied by the upstream USB host are considered "Low Power." Once plugged in, a device is allowed initially to draw up to 100mA while enumerating and negotiating its current budget with the host. Subsequently it might be allowed to raise its drain to 500mA, or it might be held at 100mA.

              • 4. Re: LiPo charger circuit documentation bug

                Another missing piece in the documentation: when a Li-Ion is connected to J2 and a USB power source is connected to J16, there's three possible states for LED DS3: on, off and blinking. The blink is not documented; any details on what it means?

                • 5. Re: LiPo charger circuit documentation bug

                  Hi sulka,


                  I've checked the Mini-Breakout Board Hardware Guide (Intel® Edison Breakout Board Hardware Guide for Boards and Kits) but I couldn't find the information about the blinking status, actually there is no mention about those possible three states you said. On the other hand, if you check page 12, section 2.6 you will see that the DS3 LED will turn on when the battery is being charged, otherwise it remains off. There isn't a third state (blinking).

                  DS3 is the charging LED. (See Figure 2 for location.) It will turn on when the BQ24074 is charging an attached battery.


                  Let me know where you saw the information about the blinking state to check it.




                  • 6. Re: LiPo charger circuit documentation bug



                    The questions is based on observing how the board behaves and finding undocumented behavior. The blinking happens when I have a Li-Ion batter connected to J2 and a USB charger is connected to J16. After some time of charging (takes up to a few hours), the LED starts to blink, and does not stop blinking until the Edison is powered down. I've replicated this several times, so the behavior is consistent, which made me wonder what is going on.

                    • 7. Re: LiPo charger circuit documentation bug

                      The charging chip has a timer.


                      If the pre charge timer expires before the battery voltage reaches VLOWV, the bq2407x indicates a fault condition.

                      The CHG output flashes at approximately 2Hz to indicate a fault condition.

                      After 6.5 hours(set by the TMR resistor) of charging, the LED starts to blink. If the charging current is 190mA, then 6.5x190=1200mAh. You can't use a battery with a capacity more than 1200mAh.


                      You need to change this TMR resistor if you want to use a bigger battery. It's super tiny.


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