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BQ25798EVM: No power delivered from Solar Panel input

Carl Olen
Expert 1160 points
Part Number: BQ25798EVM
Other Parts Discussed in Thread: BQ25798, , BQSTUDIO, EV2400

I am trying to harvest power from a solar panel into my bq25798 charger. 

I have the solar panel connected to the J1 port of the BQ25798EVM.  With no light the Vin is low and the battery discharges into my 419mA system load.  When I illuminate the panel I get 7.98V at Vin, but no current.  The battery pack continues to discharge into the load. 

Then, when I switch from the Solar Panel to a bench supply at J1, set to 7.9V and current limit to 2.5A, I get the expected results: the power supply feeds the load and also gives a little charge current to the battery pack.  What do I need to do to get my Solar Panel to behave like my power supply?  Is there some setup needed on the BQ25798EVM?

Please let me know.  Thanks,

Carl

  • 0
    TI__Guru**** 169206 points

    Hi Carl,

    I would expect the charging to be functioning in VINDPM.   Can you reply showing me all of the status and fault registers from BQSTUDIO?  I would expect the charging to be functioning in VINDPM.  If the ADC isn't enabled, can you enable and show me the ADC values for VBUS and IBUS?  

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Expert 1160 points

    Jeff, I'll set this up tomorrow and send you the register data.  Thx, Carl

  • 0 in reply to Carl Olen
    Expert 1160 points

    Jeff, here are screen shots of the "Field View" (top and bottom) from my bqstudio session.  Also, I saved the register file as a *.txt and included it, too.

    Fullscreen bqstudioRegisters_16Jun22.txt Download 
    * Created: Thu Jun 16 09:33:36 EDT 2022
*
* Format: Register Name  tab Character,\t  Register Address  tab Character,\t  Hexadecimal register value.
* Device: BQ25798
* BQZ Container: Charger_2_00-bq25798.bqz
*
REG00	12
REG01	0348
REG03	00C8
REG05	51
REG06	0091
REG08	C3
REG09	05
REG0A	63
REG0B	00DC
REG0D	4B
REG0E	3D
REG0F	A2
REG10	85
REG11	40
REG12	00
REG13	61
REG14	16
REG15	AA
REG16	C0
REG17	7A
REG18	54
REG19	0091
REG1B	2B
REG1C	0A
REG1D	01
REG1E	C0
REG1F	00
REG20	00
REG21	00
REG22	EB
REG23	10
REG24	50
REG25	00
REG26	00
REG27	00
REG28	00
REG29	00
REG2A	00
REG2B	00
REG2C	00
REG2D	00
REG2E	30
REG2F	00
REG30	00
REG31	0000
REG33	0000
REG35	2510
REG37	0000
REG37	0000
REG3B	0000
REG3D	0000
REG3F	0000
REG41	0000
REG43	0000
REG45	0000
REG47	00
REG48	18

  • 0 in reply to Carl Olen
    Expert 1160 points

    I replaced the J17 jumper on the EVM.  I now have a green light at D13.  The charge seems to be trickling through from the solar panel now.  But not like would expect.  When I add 100mA of System load, the battery goes straight into discharge.  I want the solar panel to pick up this load but it's not doing so.

    Here is the new register file and screenshot.

    Fullscreen bqstudioRegisters_16Jun22_2.txt Download 
    * Created: Thu Jun 16 10:03:41 EDT 2022
*
* Format: Register Name  tab Character,\t  Register Address  tab Character,\t  Hexadecimal register value.
* BQZ Container: Charger_2_00-bq25798.bqz
*
REG00	00	12
REG01	01	348
REG03	03	C8
REG05	05	49
REG06	06	91
REG08	08	C3
REG09	09	05
REG0A	0A	63
REG0B	0B	DC
REG0D	0D	4B
REG0E	0E	3D
REG0F	0F	A2
REG10	10	85
REG11	11	40
REG12	12	00
REG13	13	61
REG14	14	16
REG15	15	AA
REG16	16	C0
REG17	17	7A
REG18	18	54
REG19	19	91
REG1B	1B	6B
REG1C	1C	6A
REG1D	1D	01
REG1E	1E	C0
REG1F	1F	00
REG20	20	00
REG21	21	00
REG22	22	00
REG23	23	00
REG24	24	00
REG25	25	00
REG26	26	00
REG27	27	00
REG28	28	00
REG29	29	00
REG2A	2A	00
REG2B	2B	00
REG2C	2C	00
REG2D	2D	00
REG2E	2E	30
REG2F	2F	00
REG30	30	00
REG31	31	00
REG33	33	00
REG35	35	2214
REG37	37	00
REG37	39	00
REG3B	3B	00
REG3D	3D	00
REG3F	3F	00
REG41	41	00
REG43	43	00
REG45	45	00
REG47	47	00
REG48	48	18

  • 0 in reply to Carl Olen
    TI__Guru**** 169206 points

    Hi Carl,

    Based on the register below, the charger is trying to charge with VINDPM loop, therefore it is limiting its input current to prevent VBUS from dropping below ABSVINDPM=7.3V (REG0x05).   System load is prioritized over battery charger current.

    If you rerun with ADC enabled, the charger will report the average input current that the panel is providing.  If the panel voltage drops below 7.3V (e.g. due to clouds), the converter essentially stops switching.  Enabling the MPPT bit (REG0x15b0) causes the charger to periodically (as set by REG0x15b4:3) enter HiZ mode and reevaluate the VINDPM threshold = % set in REG0x15b7:5 times the panel's open circuit voltage at VBUS.  MPPT only functions if V(BAT)>VSYSMIN in REG0x00 so I recommend setting that as low as your system load allows.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 1160 points

    How do I make the ADC enabled?  -which register(s)?

    I will reset VSYSMIN to 6300mV or lower (it's currently at 7000mV).

  • 0 in reply to Carl Olen
    TI__Guru**** 169206 points

    Hi Carl,

    REG0x2Eb7 enables the ADC.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 1160 points

    Jeff, I'm sorry I haven't gotten back with you.  I have been traveling on business.

    I changed the order by which I started the system.

    1. I turned the light on illuminating my solar panel. Getting about 8.5Vin
    2. I plugged in the battery pack. Vbatt is about 7.3V
    3. I plugged in the EV2400 USB cable and started bqstudio for the bq25798 charger. Read the registers and got ACK OK message.
    4. Set VSYSMIN to 6250mV.
    5. Removed and replaced the jumper J17. Charger LED is lit.  Charge current to the battery is positive but low (about 30-40mA) with pre-charge current set to 120mA.
    6. Added 100mA load to VSYS. Charger still charging but at a low current level.  Not much current read at Iin, perhaps 10-20mA.
    7. Upped the VSYS load to 200mA. Panel could not keep up.  Charging current hovered around 0mA, but Vbat kept decreasing.
    8. Turned off the VSYS load after about 30 minutes. Charging current increased but only to about 30-40mA.
    9. I upped the Pre charge current setting to 480mA, 620mA, etc. to see the reaction at the charge current measurement. The charge current increased, but not by much.  Only up to about 50-60mA.

    My registers file is attached.  I still need more help getting this working correctly.

    Thanks,

    Carl

    Fullscreen bqstudioRegisters_26Jun22_1.txt Download 
    * Created: Sun Jun 26 17:13:37 EDT 2022
*
* Format: Register Name  tab Character,\t  Register Address  tab Character,\t  Hexadecimal register value.
* BQZ Container: Charger_2_00-bq25798.bqz
*
REG00	00	0F
REG01	01	348
REG03	03	C8
REG05	05	50
REG06	06	91
REG08	08	C3
REG09	09	05
REG0A	0A	63
REG0B	0B	DC
REG0D	0D	4B
REG0E	0E	3D
REG0F	0F	A2
REG10	10	85
REG11	11	40
REG12	12	00
REG13	13	E1
REG14	14	16
REG15	15	AA
REG16	16	C0
REG17	17	7A
REG18	18	54
REG19	19	91
REG1B	1B	0B
REG1C	1C	EA
REG1D	1D	01
REG1E	1E	C0
REG1F	1F	00
REG20	20	00
REG21	21	00
REG22	22	00
REG23	23	00
REG24	24	00
REG25	25	00
REG26	26	00
REG27	27	00
REG28	28	00
REG29	29	00
REG2A	2A	00
REG2B	2B	00
REG2C	2C	00
REG2D	2D	00
REG2E	2E	B0
REG2F	2F	00
REG30	30	00
REG31	31	00
REG33	33	00
REG35	35	24F4
REG37	37	00
REG37	39	00
REG3B	3B	00
REG3D	3D	00
REG3F	3F	00
REG41	41	00
REG43	43	00
REG45	45	00
REG47	47	00
REG48	48	18

  • 0 in reply to Carl Olen
    TI__Guru**** 169206 points

    Hi Carl,

    I am puzzled by your register data.  The registers report charge termination, meaning the battery is a 8.4V.  The ADC is enabled but all of the ADC registers report 00 expect VBUS which reports 9460mV.  I would have expected the charger to be running in VINDPM with the input voltage being regulated to 8V VINDPM threshold but it is not.   

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Expert 1160 points

    So, what is my next move?

  • +1 in reply to Carl Olen
    TI__Guru**** 169206 points

    Hi Carl,

    Can you retry with the ADC?  If the bit is enabled, the registers should report the values. Can you measure the voltage at the BATP pin?  If it is 8.4V, then the charger is correctly terminated.  Do you know the output capability of your panel at the lumens you are providing?  If indoor, the output power is lightly very low.

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Expert 1160 points

    I cannot retry the ADC now.  I was making progress last week.  But now, neither of my EVMs will even connect to the Battery Management Studio.  They were connecting last week, each with a separate instance of the bqstudio.  What happened?

    I feel extremely frustrated, spinning my wheels without results.

    What can I do to get this stuff working?  I don't have enough experience with the Solar Panel, charger, fuel gauge and battery pack as a complete system.  I need help.

    What do I do next?

  • 0 in reply to Carl Olen
    TI__Mastermind 32185 points

    Hi Carl,

    Jeff is out for the week so I will be helping you for now.

    Can you upload a picture of your EVMs so I can check if the jumpers are in the right place?

    When you attach a battery or power supply to the BQ25798 BAT connector, does BAT TP measure the right voltage? Does BAT TP = SYS? After that, can you commincate via I2C?

    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Expert 1160 points

    Ethan, thanks.  I have a number of other things to do before I can get back to my test bench setup.  I'll get back with you as soon as I can.