LT8491 not exiting Stage 0 charging

We have developed a custom MPPT based on the DC2703A-A-KIT and we are now in the phase of programming it. For that we are using the Simple LT8491 User Interface software. We have successfully been able to configure it but for some reason the MPPT doesn't exits Stage 0 charging. 

Could you please check the configuration bellow to check if you spot any errors in it?

CFG Register Read

Reading RAW Bytes for CFG_XX Registers (0x28 to 0x5B):
0x258 0x1838 0x4B0 0x7FFF 0x5654 0x137E 0x250 0x135 0x532 0x1001 0x8E8F 0x8C96 0x32EC 0x0 0x0 0x7 0x104 0x2008 0xB 0xFB03 0xB779 0xA2F0 0x3AAF 0xB22D 0xBE1D 0x0 

(0x28) CFG_RSENSE1: 0x258 ==>> 6,00 mOhm
(0x2A) CFG_RIMON_OUT: 0x1838 ==>> 62,00 K
(0x2C) CFG_RSENSE2: 0x4B0 ==>> 12,00 mOhm
(0x2E) CFG_RDACO: 0x7FFF ==>> 327,67 K
(0x30) CFG_RFBOUT1: 0x5654 ==>> 2210,00 K
(0x32) CFG_RFBOUT2: 0x137E ==>> 49,90 K
(0x34) CFG_RDACI: 0x250 ==>> 5,92 K
(0x36) CFG_RFBIN2: 0x135 ==>> 3,09 K
(0x38) CFG_RFBIN1: 0x532 ==>> 133,00 K
(0x3A) CFG_INIT_CHRG_EN: 0x1 ==>> 00000001
(0x3B) CFG_VS3_25C: 0x10 ==>> 86,60 %
(0x3C) CFG_UV_S0: 0x8F ==>> 71,50 %
(0x3D) CFG_VS3_25C: 0x8E ==>> 71,00 %
(0x3E) CFG_S0_S1: 0x96 ==>> 75,00 %
(0x3F) CFG_S1_S0: 0x8C ==>> 70,00 %
(0x40) CFG_TBAT_MIN: 0xEC ==>> -20 degC
(0x41) CFG_TBAT_MAX: 0x32 ==>> 50 degC
(0x42) CFG_TMR_S0: 0x0 ==>> 0,00 Min
(0x43) CFG_TMR_S1: 0x0 ==>> 0,00 Min
(0x44) CFG_TMR_S2: 0x0 ==>> 0,00 Min
(0x45) CFG_TMR_S3: 0x0 ==>> 0,00 Min
(0x46) CFG_RSTRT_IN_FLT: 0x7 (00000111)
CFG_RSTRT_IN_FLT -> RSTRT_ON_TMR_FLT_HRS bits[7:4]: 0000 ==>> 0,00 Hrs
CFG_RSTRT_IN_FLT -> NO_RSTRT_ON_VOLTS bit[3]: 0
CFG_RSTRT_IN_FLT -> NO_RSTRT_ON_DISCON_FLT bit[2]: 1
CFG_RSTRT_IN_FLT -> NO_RSTRT_ON_BATLOW_FLT bit[1]: 1
CFG_RSTRT_IN_FLT -> NO_RESUME_ON_TBAT_FLT bit[0]: 1
(0x47) CFG_RSTRT_IN_DONEA: 0x0 (00000000)
CFG_RSTRT_IN_DONEA -> RSTRT_IN_DONE_ON_VOLTS bit[7]: 0
CFG_RSTRT_IN_DONEA -> RSTRT_IN_DONE_SET_VOLTS bits[6:0]: 0 %
(0x48) CFG_RSTRT_IN_DONEB: 0x4 (00000100)
CFG_RSTRT_IN_DONEB -> Reserved bits[7:6]: 00
CFG_RSTRT_IN_DONEB -> RSTRT_IN_DONE_HRS bits[5:0]: 2 Hrs

(0x49) CFG_RSTRT_IN_S3: 0x1 (00000001)
CFG_RSTRT_IN_S3 -> Reserved bits[7:1]: 00
CFG_RSTRT_IN_S3->RSTRT_S3_C5_VS3[0]: 1
(0x4A) CFG_TERMINATE: 0x8 (00001000)
CFG_TERMINATE -> Reserved bits[7:6]:00
CFG_TERMINATE -> PS_S2_C10_TERM_EN bit[5]: 0
CFG_TERMINATE -> SOLAR_S2_C10_TERM_EN bit[4]: 0
CFG_TERMINATE -> S3_TMR_TERM_EN bit[3]: 1
CFG_TERMINATE -> S2_TMR_TERM_EN bit[2]: 0
CFG_TERMINATE -> S1_TMR_TERM_EN bit[1]: 0
CFG_TERMINATE -> S0_TMR_TERM_EN bit[0]: 0
(0x4B) CFG_SCAN_RATE_LP: 0x20 ==>> 533,12 Sec
(0x4C) CFG_SCAN_RATE: 0xB ==>> 183,26 Sec
(0x4D) CFG_CHRG_MISC: 0x0 (00000000)
CFG_CHRG_MISC -> Reserved bits[7:5]: 000
CFG_CHRG_MISC -> USE_VS3_IN_STAGE2 bit[4]: 0
CFG_CHRG_MISC -> LPMODE_EN[3]: 0
CFG_CHRG_MISC -> PS_S3_ENABLE bit[2]: 0
CFG_CHRG_MISC -> SOLAR_S3_ENABLE bit[1]: 0
CFG_CHRG_MISC -> TC_ENABLE bit[0]: 0
(0x4E) CFG_TC3: 0x03FB79B7 ==>> -1,490E-005 
(0x52) CFG_TC2: 0xF0A2AF3A ==>> 1,340E-003 
(0x56) CFG_TC1: 0x2DB21DBE ==>> -1,540E-001 
(0x5A) CFG_USER_CODE: 0x0000

******************************************************************

Bellow is also the schematic of the PCB.

PDF

  • 0
    •  Analog Employees 
    on May 26, 2021 1:33 PM

    Ensure the source can support the Stage 1 charging rate. Ensure load is greater than 75% of VS2 setting. Ensure battery thermistor is between -20C and 50C. Ensure resistor configuration matches schematic and actual populated resistors.

  • Hi Charlie,

    The source at the moment is a Delta Elektroinka power supply that has a function to simulate solar panels. And it is capable of proving way more current than the one that the board is pulling. The board is only pulling 0.1 A @ 42 V.

    I didn't understood the part in which you said to ensure that the load is greater than 75% of VS2 setting. VS2 is a voltage specification and load is current. Can you elaborate on that?

    Also what is the maximum value for register 0x2E? When setting the register as 0x8656 the GUI decodes it as a negative value. I think it is a decode problem on the GUI since the data sheet states that this value is an unsigned integer.

  • 0
    •  Analog Employees 
    on Jun 8, 2021 2:24 PM in reply to tsb

    The transition from Stage 0 to Stage 1 has the following requirements:

    - Input voltage stays in range in Stage 0 and when the algorithm tries to go to Stage 1 and draws more current.

    - (VBAT > Vso_s1) -> [VBAT > (VS2 * 75%)] per configuration provided.

    - Stage 0 limit timer has not expired. Disabled per configuration provided.

    - Thermistor reading above -20C and below 50C per configuration provided.

    I don't see CFG_SO_UV setting. See page 47 of datasheet.

    Note:  Simulated supplies and simulated loads are the most common cause of unexpected behavior. Please check these carefully.

    Regarding the register 0x2E: 

    Found the issue.  It’s in the diagnostics “Read Configuration” function.  It’s a (signed integer vs unsigned integer problem).  If you go to the configuration tab and then go to tool and select read configuration, the appropriate value is calculated.

    I’d suggest using the configuration tab instead of the diagnostics tab.  So what I did…

    1. Under diagnostics tab, type in 0x2E 0x8656 for the “write word” button.
    2. Under diagnostics tab, type in 0x2E and then click “read word” button.  I get back 0x8656.  So I know the raw value is getting there.
    3. Under diagnostics tab, clock “Read Configuration”  I see the negative value…  -311.46k
    4. Under configuration tab, I then select from the “tools” from the tools strip menu and select “read configuration”, the value displayed for CFG_RDACO shows 343.9

     

    The diagnostics tab was really built for the demo board group to test the demo boards.  It wasn’t wildly tested.  I would suggest users to use the configuration tab the and the “tools” menu to change values.  It has been tested thoroughly. Maximum value is going to be 0hFFFF -> 0d65535  -> 655.35kOhm

  • We have checked and all the conditions are satisfied. Battery voltage was around 48 V. CFG_SO_UV is register 0x3D but has the wrong name (another bug in the software), it is set to 71%.

    Is there any other thing in our configuration that can be causing this behaviour? We have already tested with a real Solar Panel and a real battery but without much success.

  • 0
    •  Analog Employees 
    on Jun 11, 2021 1:24 PM in reply to tsb

    Please verify the resistor values entered match the schematic AND match what was placed on the PCB. I also recommend checking the input voltages at the IC pins with a scope to ensure they are what you expect and are correct.