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bq25570 VSTOR supply issue

Other Parts Discussed in Thread: BQ25570, TPS62080

Power Architecture - refer word document

Power Architecture description:

  1. For stand alone testing, BQ25570 solar cell is replaced with 3.3V LDO at 1A rated current.

  2. Internal buck of BQ25570 is configured to source 1.8V to on board components like Sensors, Flash BLE etc. Total current comsumption at 1.8V rail is 20mA

  3. VSTOR (4.2V) is used to source two TPS62080 DC/DC onboard buck regulators 0.6V and 1V. Total current consumption of both buck regulators combined together is 30 to 50mA

  4. Jasmine IC is DNP and therefore both buck regulators are at no load condition.

Output of VSTOR (Solar Harvesting IC) is connected to x2 buck regulators - refer word doc

Voltage Regulator 1 (Currently the buck regulators are at No load condition)

Inductor Isat = 100mA
Iout = No Load condition

Voltage Regulator 2 (Currently the buck regulators are at No load condition)

Inductor Isat = 100mA
Iout = No Load condition

PROBLEM STATEMENT:

  1. With above design, we are facing a random behaviour at VSTOR pin. Initially, boards have 4.2V at VSTOR pin. After many power cycles, the VSTOR voltage drops to 2.5V.

  2. If TPS62080 input bypassed from VSTOR, then VSTOR is restored to 4.2V.

  3. Current consumed by both TPS62080 devices is 34mA at no Load condition. Not sure why buck regulators consume 34mA at not load condition.

  4. Inductor used for TPS62080 has 100mA Isat.

 

 QUERIES:

  1. Is it right method to source external DC/DC buck regulators (TPS62080) from the VSTOR voltage of BQ25570? If yes, then what is the maximum load current it can source?

  2. Why 2A rated current inductor is mandatory for TPS62080 when operated at 10 to 50mA Load?

     

 

  • Hi Folks,

    I am not sure why the word document attachment is not visible. anyways here is my problem statement in short.

    The Board has Solar Harvester (BQ25570) which has a Boost converter as well as buck converter.

    Boost Converter, Output Voltage VSTOR has the load connected as Input Voltage to TPS62080. VSTOR is set to Vout(max) which is 4.2V when no Battery connects to VBAT of BQ25570.

     

    We found that when TPS62080 connects to VSTOR, VSTOR voltage drops to 2.5V from 4.2V, it was due to the high current,20mA drawn by TPS which should be supposed to 70uA.

  • Hello Shankar,

    I just sent a reply to Harmeet from TI who is your local support engineer.

    Please let us know if you have any questions.

    Regards,
    Gautham Ramachandran
    Apps. Engineer- Texas Instruments.