BQ25895: BQ25895 NOT charging

Thanks for the response.

  Now I have other question. I have the BQ25895 connected to a Battery. It gives to me 4.2V in VSYS. After I connect the VBUS to 5V, the BQ25895 continues with 4.2V in VSYS. Now if I cut the VBUS before 3 Seconds the VSYS continues with 4.2V, but if I cut the VBUS after 3 seconds when cut VBUS the VSYS go to 1V. Do you know what's happening??

Thanks in advance.

Best Regards

  Yes, but sometimes the bit 5 of REG09 turn off Q4. Now I have too many things that is not working like I want. I will try to describe my project and you tell me if it is posible with the BQ25895. With the Schematic in the first post you will have an idea after describe the functionality.

  I have a hardware running at 5V (Maximum 2 Amps). The voltage I am getting is from VSYS of BQ25895. This VSYS goes to a BOOSTER TPS61235P to get a system always UP running a 5V.

  The BQ25895 have a battery that need to charge and get for a backup if VBUS go out. When the VBUS go out the BQ25895 needs to support the hardware from the battery without any cut in the voltage.


  This system is like a UPS, Is this possible to do with the BQ2595??, if not, Do you have other IC that supports this funcionality??.


Thanks for all of your support.


Best Regards.

The bq25895 should work for your application.  If the part is self turning off Q4, there is a large current spike causing that to happen.  Many boost converters are known to pull large current spikes, especially at startup.  The TPS61235P has an 8-A current limit which means it could try to pull up to 8-A from the charger when the battery is low. This spike could trigger Q4 to turn off.   Is it possible to change to a boost converter will lower current limit?  Can you add more capacitance at SYS to handle this spike? 

Hi Again Jeff.

  Thanks for helping with this. I want to make more question because I do not know why the BQ25895 is not doing the behavior that I expected.

  I make a PCB only with the BQ25895, the battery port, and the VSYS to a PIN to measure the stability of VSYS on oscilloscope, with the VBUS to a power supply for 5V and it can support 100 amperes, and I use robust cables to the VBUS for don't have any problem with the amperes in the input of the BQ25895.

  With the registers that I will post after the paragraph, I can make work the BQ25895 to charge battery (With 500 mA of input current limit) and its only works when turning on Q4 (Forcing BATFET_DIS to 0). With this configuration it supports the lose supply of VBUS. But it only charges the batteries that have 3.9V or 4.0V, with a battery with a 3.8V the BQ25895 is not charging the battery even forcing the BATFET_DIS to 0.

  Other problem is if I change the input current limit from 500 mA to other value higher. If I change to 600 mA, or 900 mA, or 1 A, or 3.25 A, I can not charge any battery. I put a battery with different voltages and it is not charging any of this batteries.

Input Current Limit, HIZ and ILIM pin    08
OTG Temperature thresholds, and Input Voltage DPM Offset    05
ADC controls, OTG Frequency, ICO, DCP, and Input Detection    ED
Battery Load, WDT Reset periods, OTG and Charge Enable, and MINSYS setting    3A
Fast Charge Current Limit settings and MTK Pump enable    20
Pre-charge and Termination Current Limit settings    13
Charge Voltage Regulation Limit, Battery Low Voltage and Recharge threshold    66
Termination Current Enable, STAT pin, WDT, Safety Timer, and JEITA Charge Current    05
IR Compensation and Thermal Regulation thresholds    03
ICO, Extended Safety Timer, BATFET control, MTK Pump Voltage, and JEITA Charge Voltage    00
OTG Regulation Voltage and Current Limit settings    93
Charger VBUS, Charging Mode, PG, USB Input, and System Voltage Regulation status    76
WDT, OTG/VBUS OVP, Thermal Shutdown, Safety Timer, and TS pin faults    00
Input Voltage DPM settings    93
Thermal Regulation Charge Status, and ADC Battery Voltage conversion    5E
ADC System Voltage conversion    5E
ADC TS pin voltage as percentage of REGN conversion    52
VBUS status, and ADC VBUS Voltage conversion    9A
ADC Charge Current conversion    00
DPM status, and Input Current Limit setting    48
Registers reset, Input Current Optimizer status, Device ID, and Temperature Profile    39

  I have the following questions:

  1 - Why with 500 mA of input current limit only charge to batteries with 3.9V or higher??

  2 - Why when I change the Input current limit higher from 500 mA is not charging the batteries??

  3 - Why when the BQ25895 starts the BATFET_DIS is always 1??. In datasheet it says 0 is default, is it for the I2C communication??.

  4 - Can you post me the registers settings for my application?? or the changes from my registers to make works my application?? (Support output of VSYS to 3 Amperes, it can change from VBUS to Battery and to Battery to VBUS with any cut in VSYS and to charge batteries from 3.7V to 4.2V, and charge battery when detected to lower voltage like 3.7V or 3.8 V).

  5 - Why when put ADC Start (CONV_START) to 1 and CONV_RATE to 1 when I read this register (REG02) CONV_START is 0??

  6 - Why if the ADC is activated and the battery is charging the value of REG12 is 0?? I know the battery is charging because the register of charging is marked as Fast charging and for the drain of power supply.

Registers in file:

* Created: Sun Sep 24 13:19:48 CEST 2017
*
* Format: Register Name  tab Character,\t  Hexadecimal register value.
* Device: bq25890
* BQZ Container: Charger_1_00-bq25890_895.bqz
*
Input Current Limit, HIZ and ILIM pin	08
OTG Temperature thresholds, and Input Voltage DPM Offset	05
ADC controls, OTG Frequency, ICO, DCP, and Input Detection	ED
Battery Load, WDT Reset periods, OTG and Charge Enable, and MINSYS setting	3A
Fast Charge Current Limit settings and MTK Pump enable	20
Pre-charge and Termination Current Limit settings	13
Charge Voltage Regulation Limit, Battery Low Voltage and Recharge threshold	66
Termination Current Enable, STAT pin, WDT, Safety Timer, and JEITA Charge Current	05
IR Compensation and Thermal Regulation thresholds	03
ICO, Extended Safety Timer, BATFET control, MTK Pump Voltage, and JEITA Charge Voltage	00
OTG Regulation Voltage and Current Limit settings	93
Charger VBUS, Charging Mode, PG, USB Input, and System Voltage Regulation status	76
WDT, OTG/VBUS OVP, Thermal Shutdown, Safety Timer, and TS pin faults	00
Input Voltage DPM settings	93
Thermal Regulation Charge Status, and ADC Battery Voltage conversion	5E
ADC System Voltage conversion	5E
ADC TS pin voltage as percentage of REGN conversion	52
VBUS status, and ADC VBUS Voltage conversion	9A
ADC Charge Current conversion	00
DPM status, and Input Current Limit setting	48
Registers reset, Input Current Optimizer status, Device ID, and Temperature Profile	39

Based on the ADC, the battery voltage is measuring 4.184V which is close to termination and the charger is reporting that is in IINDPM, meaning that all of the current is going to SYS or PMID.  What is the load on SYS and PMID?

Regarding 1 and 2, What is the current rating of your 1uH?  Can you send oscope pictures of VBUS, VBAT, (both measured close to IC pins) VSW and I(IND) or IBUS when charging and when not charging?

Regarding 3, the bq25895 automatically switches to OTG mode when VBUS is removed.  Do you have a large load on PMID that is causing the BATFET to self protect due to large current spike?

Regarding 4, first we need to figure out why the BATFET is turning off and why you can't charge with lower battery voltages?

Regarding 5, CONV_START returns to 0 once the ADC measurement is complete.

Regarding 6, Is there a load on PMID or SYS that is taking all of the input current?

Hi Jeff.

  My system only have in VSYS a LDO of 250 ma and after de LDO a uC with a 4 mA of drain for controlling the I2C protocoll. In the PMID is not connected only have a pin to measure the output.

  In my tomorrow morning I will attach to you the screenshots of osciloscop and the registers in each moment of this screenshots. Actually my system only consumes the 4 mA of the uC and the charge of battery.

  In the regarding 6 of your response I see do you have a question but it is not ended, it's right?? or the response is only this.

Thanks for all again. And tomorrow I will send you the screenshoots.

Best Regards.

Hi Jeff.

  I was making other tests. I'm going to explain all and show the data in zip files with captures screenshots from osciloscop and the registers in this moment.

  First I need to say the VBUS is attach directly to a external power supply with 100 Amperes and with a good and short cables. I can configure system with 3.25A in the input current, but I need to limit fast charger battery for right operating. I connected the booster from VSYS and connect to the booster a Hardware that consumes 5V 200mA with peaks of maximum 400mA. I only can charge battery when limit the fast charger current to 320mA, for example with 512mA I can't charge battery (The battery supports 2A of charge). For this test I disabled the booster to avoid any consumption from Booster. The external power supply voltaje never falls or limits the current due an overload.

  In the next zip file I attach the system running charging battery with 320mA.

charging320ma.zip

  In the next zip file I attach the system running with not charging battery. The register of fast charge current is limited to 512mA.

notcharging512ma.zip

  In the next zip file I attach the booster running correctly from battery and without any cut, but if I connect the VBUS all stops of running I don't understand why.

runningboosterfrombat.zip

  With VBUS connected the Booster never works, the booster maximum is getting like 600mA from VSYS, and the VSYS supports to 5A. I will be waiting for a reply beacuse I don't know what is happen.

Thanks for your support.

Best Regards.

Thanks for the waveforms. The switching waveform looks normal.  I am still puzzled by this.  Can you provide more than one trace on the same scope plot?  Can you measure current?  Based on the register settings, the IC is in input current limit so the current is going somewhere, either SYS or PMID.  Is it possible to use replace your board with one of the TI EVMs, in other words connect your power source and battery to the EVM and reproduce the same settings?   

Hi Jeff.

  I bought yesterday the BQ25895EVM-664, it will arrive on monday. I test the same conditions on monday or tuesday and put the results here. Before that I want to post you the layout of the board for if you can see any thing in the planes of the BQ25895 in my custom board.

Layout Front:customBoardLayoutFront.pdf

Layout Back: customBoardLayoutBack.pdf

Best Regards.

3021.bq2589xbq2419x_29xlayoutandEMIrecommendation.pdfAre there vias under the IC to the ground plane to provide heat sinking? Attached is the recommended layout, similar to the EVM that you have. Your scope plot did not show any ringing on the switch node, which could be caused by bad part placement.  PMID capacitor is the most critical, needed short, wide traces back to PMID and GND.

Hi Jeff.

  With the PCB in 4 layers the BQ25895 is working that I expected. Thanks for all of your help.

Best Regards.