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BQ25792EVM: fail to startup

Jim Yan
Prodigy 150 points
Part Number: BQ25792EVM
Other Parts Discussed in Thread: BQ25792

Hi, 

My customer are  testing the BQ25792EVM OTG mode to drive a fan as follow show. But it has a startup problem. 

Test condition: 

VBAT connect a 7.5v DC power, VIN1 connect a fan. OTG reg voltage:5-13V

Test problem:

Disable EN OTG MODE and then enable EN OTG MODE by change  REG12 register, when the OTG reg voltage less than 10V, it can startup, but when the OTG reg voltage set to larger than 10V, it can not startup. I test the VBAT voltage when OTG reg voltage set as 13V, test result as follow, the moment the REG12 register is written, there a voltage drop in VBAT, and the fan cannot start up and VIN has no voltage. Can you tell me why BQ25792 cannot startup when OTG reg voltage set to larger than 10V? Thank you!

  • 0
    TI__Prodigy 150 points

    When it startup with OTG voltage that less than 10V and increase OTG voltage to 13V after it started-up, there are no problem.

  • 0 in reply to Jim Yan
    TI__Mastermind 40365 points

    Hello,

    Can you please describe your setup more? I enabled OTG from 7.5 BAT, attached 10 Ohm load, then enabled ACDRV1 and the converter started outputting 13.94 V at 1.37 A. I am not seeing the issue with the battery. Please provide more information.

    Thanks,

    Mike Emmanuel

    Please click "Resolved" if this answered your question.

  • 0 in reply to Michael Emanuel35
    TI__Prodigy 150 points

    Hi Mike,

    The register configuration is set as follow, I use electronic load to test. Can it still start-up when CC mode 1.5A or CR mode 7 Ω is attached ？Or if register configuration has some errors?  

    Fullscreen 7455.register.txt Download 
    * Created: Fri Jun 04 13:12:57 CST 2021
*
* Format: Register Name  tab Character,\t  Register Address  tab Character,\t  Hexadecimal register value.
* BQZ Container: Charger_2_00-BQ25790_92.bqz
*
REG00	00	12
REG01	01	348
REG03	03	12C
REG05	05	24
REG06	06	12C
REG08	08	C6
REG09	09	05
REG0A	0A	63
REG0B	0B	3FC
REG0D	0D	4B
REG0E	0E	3D
REG0F	0F	82
REG10	10	80
REG11	11	40
REG12	12	40
REG13	13	41
REG14	14	96
REG15	15	AA
REG16	16	C0
REG17	17	7A
REG18	18	64
REG19	19	32
REG1B	1B	00
REG1C	1C	00
REG1D	1D	01
REG1E	1E	C0
REG1F	1F	00
REG20	20	00
REG21	21	00
REG22	22	C3
REG23	23	12
REG24	24	00
REG25	25	10
REG26	26	80
REG27	27	10
REG28	28	00
REG29	29	00
REG2A	2A	00
REG2B	2B	00
REG2C	2C	00
REG2D	2D	00
REG2E	2E	38
REG2F	2F	00
REG30	30	00
REG31	31	00
REG33	33	00
REG35	35	00
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	00

  • 0 in reply to Jim Yan
    TI__Mastermind 40365 points

    Hello,

    I am thinking the inductive load of the fan is causing the OTG UVP to happen. You need to make sure the input is regulating to the OTG voltage before you attach the fan. Is there any way you can turn the fan on after the input is regulating the desired OTG voltage?

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.

  • 0 in reply to Michael Emanuel35
    TI__Prodigy 150 points

    Hi Mike,

    Actually, the customer has a prototype that use BQ25792 as charger and can start-up when fan is inserted. But they are not know why. Customer want the function is that press the button (enable OTG mode) and than the fan spins instead of inserting the fan and then the fan spins. I am wonder if it can realize by add a extra hardware circuit or other method?

  • 0 in reply to Jim Yan
    TI__Mastermind 40365 points

    Hello,

    You could use a microcontroller to recognize when the fan is inserted and the button pushed to send an I2C command to enable OTG.

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answers your question.

  • 0 in reply to Michael Emanuel35
    TI__Prodigy 150 points

    Hi Mike,

    I am sorry that I am not describe the question clearly. I mean that customer requirement is the fan is inserted and then enable OTG to drive fan. However, as you answer above, the fan may as a inductive load, so it may have star-up problem. But now, the customer has a prototype that use BQ25792 as charger and the prototype can start-up when fan is inserted. He didn't know why the prototype can solve the star-up problem, if we have method to solve the start-up problem? add a extra hardware circuit or other method can solve the inductive effect? Thanks.

  • 0 in reply to Jim Yan
    TI__Mastermind 40365 points

    Hello,

    I want to make sure I am on the same page. The BQ25792 EVM doesn't let you start up, but your prototype does? Please fully describe the differences between the prototype and the EVM as well as all the operating conditions, such as battery voltage etc. I need to see the differences to help explain the behavior.

    Thanks,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    TI__Prodigy 150 points

    Hi Mike,

    The prototype customer has is sent by his EC that is for test only, so unfortunately the customer do not have the schematic in this time,  the test condition is same when use BQ25792EVM or prototype that VBAT connect a 7.5v DC power, VIN1 connect a fan. OTG reg voltage:13V. I also wonder why it can be different, but I am sure the start-up problem described above is solved in prototype.  So I am wonder if you have some idea about the start-up problem when use BQ25792EVM? 

    or if you don't have the fan, the start-up problem of BQ25792EVM also occur when  an e-load is attached (VBAT connect a 7.5v DC power, VIN1 connect a CC mode 1.5A or CR mode 7 Ω e-load. OTG reg voltage set as13V. and the current didn't exceed the limit), if there is method can solve the start-up  problem when use  BQ25792EVM+e-load?

  • 0 in reply to Jim Yan
    TI__Mastermind 40365 points

    In order to better answer your question, I am going to need to see the prototype schematics and how they differ from the BQ25792EVM. I observed in the lab that I could not start up OTG if I applied the 1.5 A CC load before OTG was enabled. I had to enable OTG then apply the load.

    Thanks,

    Mike Emanuel