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Original question:

BQ51050B: Would it also charge LiFePo4 ?

BQ51013B: Combining it with BQ25185

gustavo zarba
Expert 1110 points
Part Number: BQ51013B
Other Parts Discussed in Thread: BQ25185, BQ24072, BQ51050B

Hi Bill, (I hope this reaches you, since we had already talked about)

Following your suggestion, I am modifying the charger system, using now a BQ51013B and a BQ25185 together, to charge a 1 Cell LiFePO4 Battery.

Here are the key-specs of the batt:

- Nominal Capacity 600mAh At 0,2C CC discharge

- Minimal capacity 600mAh

- Nominal Voltage 3.2V

- Charge voltage 3.65V Max. 3.8V

- Standard Charging

0.5C Standard 2.5 hour nominal

1C max. 1.5 hour rapid

- Cell internal impedance ≤102Ohm Measured at 1khz after 50% Charge

- Charging temperature 15 – 25°C Maximum 0 - 45°C

-Standart Charge

Charging cell initially with constant current at 0.5C to 3.65V,

then with constant voltage at 3.65V

till charge current is below 0.02C

-----------------------

And here a preliminary circuit:

The questions I have are:

- Could you please check, if the circuit is ok like this?

and for the BQ25185:

- I cannot find a way to ILIMt to be 600 mA by having VBATREG 3.65V

The table on P.16 of the data sheet has several values for RILIM/VSET, where ILIM changes between 500 and 1100 mA.

How do I get something in between? And how is VBATREG set?

- The last question refers to the SYS Voltage.
The data sheet says, the voltage is regulated to 4.5V
I only need 2.4V here, since I have an LDO afterwards to regulate the voltages I need in the Load.
Internally pulling the battery voltage high, only to pull it down externally again does not seem to be wise in terms of power dissipation to me.
I cannot find any mention to noise in the data sheet. I suppose, the process is generating some ripple...?

Sorry, too many questions...

Best regards and anticipated thanks for the help,

Gustavo

PS: I changed the circuit image. I had attached an older version.

  • 0
    TI__Guru* 75556 points

    Hi Gustavo

    BQ51013B -- Need to take a closer look at the AD and AD-EN connections.  Typically AD is grounded and AD-EN is floating.

    BQ25185 -- Let me get back to you on this one.

  • 0 in reply to Bill Johns
    Expert 1110 points

    Hi Bill,

    thanks for the reply.

    For the AD and AD-EN connections, I followed the design I already had with the BQ51050B and BQ24072, since the pins seem to behave the same.

    The data sheet of the BQ51050B says about this on P32:

    ---------------

    "bq51050B Wireless Power Receiver and Wired Charger

    9.2.2.1 Design Requirements

    The requirements for this solution are identical to the first application so all common components are identical. This solution adds a wired charger and a blocking back-back FET (Q1).

    The addition of a wired charger is simply enabled. The AD pin on the bq5105x is tied to the input of the DC supply. When the bq5105x senses a voltage greater than VAD-Pres on the AD pin, the BAT pin will be disabled (high impedance). Once the BAT pin is disabled, the AD_EN pin will transition and enable Q1. If wireless power is not present, the functionality of AD and AD_EN remains and wired charging can take place."

    -------------

    However is this: "When the bq5105x senses a voltage greater than VAD-Pres on the AD pin, the BAT pin will be disabled (high impedance)", not clear on the data sheet of the BQ51013B. But I hope it will be the same, since on P37:

    9.2.3 Wireless and Direct Charging of a Li-Ion Battery at 800 mA shows in Figure 9-11: BQ51013B Used as a Wireless Power Supply With Adapter Multiplexing for a Linear Charger

    using the same procedure as by the bq51050B Wireless Power Receiver and Wired Charger

    Could you confirm, that OUT will be disabled (high impedance)?

    Best regards,

    Gustavo

  • 0 in reply to gustavo zarba
    TI__Guru* 75556 points

    Hi Gustavo

    Update on the BQ25185 - The schematic looks good, only the typical SYS capacitance should be 10 uF.

  • +1 in reply to Bill Johns
    TI__Guru* 75556 points

    Hi Gustavo

    Bill Johns said:
    BQ51013B -- Need to take a closer look at the AD and AD-EN connections.  Typically AD is grounded and AD-EN is floating.

    Bill J -- Connecting the AD pin to OUT without the switch circuit will be a problem.  When OUT goes o 5V AD will signal for the wireless power to turn off.

  • 0 in reply to Bill Johns
    Expert 1110 points

    Hi Bill,

    yes, you are wright, I did not see this "detail".
    By the bq51050B the output is BAT and charges the battery, but since the BQ51013B is not a charger, the combination with the BQ25185 does not seem to be possible in this way. Now I understand.

    I think, we can close this now. I will have to think about another solution (always and only with Ti devices, of course! Blush

    Thanks again and best regards,

    Gustavo