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New Project with BQ51050B

Alessandro Giacometti
Prodigy 145 points
Other Parts Discussed in Thread: BQ51050B, BQ51050BEVM-764, BQ24040, BQ24090

Hi all,

I have to design a new medical device with a Wireless Power Recharging.

I would like to use the BQ51050B and this is the schematic that I thought.

2161.Schematic.pdf

The coil that I chose is IWAS-3827EC-50 

1682.iwas3827eceb100j5.pdf

and this is the battery

1401.Battery.pdf

I calculated the value of C1 tot , C2 tot, Rilim (R13 in the schematic) and Rterm (R14 in the schematic ) in this way:

2388.C1tot.docx

Now we come to the questions: everything is correct?

What kind of Wired Charger is best to use for a USB charging in a project with BQ51050B?

I can not understand how to size the R16 and R17 resistor for the Internal Temperature Sense.

The NTC resistor that I chose is ERTJ1VG103JA, the same of the datasheet of BQ51050B, with a  β of 3435.

1106.ERTJ.pdf

In the datasheet of BQ51050B is reporting an incorrect value of β. 

I need to set this thresholds of temperature:

TCOLD = 0°C
THOT = 45°C

From the datasheet of the NTC resistor I found the following values:

Rntc/tcold = 27640

Rntc/thot = 4916

Which values of R16 and R17 have to be set ?

Thanks in advance for all. Best regards

  • 0
    TI__Intellectual 1122 points
    Alessandro,

    Your schematic looks good so far but I see no voltage ratings for your capacitors.
    I would recommend you to use the same voltage ratings as the capacitors we used in the BQ51050BEVM-764 and use a capacitor at the BAT pin.

    IBULK would be 0.926A and ITERM would be 18.8mA with your current resistor values in the schematic.

    For the value of RFOD I would recommend the same value as for the BQ51050BEVM-764. Be aware that RFOD and R1 are used to calculate the charging current. See equation 1 in datasheet.

    Keep in mind, that you usually have to do a FOD calibration with your end equipment to take losses caused by the battery, connectors, etc. into account and stay WPC compliant. For this purpose we plan to release a User Guide and Software this year. FOD calibration also requires use of a third party hardware.

    For the calculation of C1(Cs), be aware to measure Ls´ (Inductance of coil on the transmitter with z-height of end application, see page 25 in the datasheet).

    As a wired charger I would recommend the bq24040 or bq24090. Be aware that you adjust the charging current not to a higher value than the USB source can provide.

    For the NTC calculations I also think, the B value in the datasheet of 4500 is wrong. We are working on a new datasheet version and this will be corrected.
    I will come back to you with a suggestion how to calculate the resistors.

    Also a good way to figure out how the temperature measurement works is to connect a decade box at the TS pin and measure the voltage for different values with a scope.
    Figure 27. in the datasheet shows the TS Pin signal. If you use a default resistor value of 10kΩ at the TS Pin, the voltage of this pulse is about 2.2V (see datasheet for spec VTS for details). TS voltage measured at the high pulse and if you change the resistance the voltage level of this signal will change as a result.
    For example you can adjust the TS voltage to 58.7% and you have the 0°C threshold. Keep in mind that this part has a JEITA compatible TS profile (p.20 in datasheet). This means there are four thresholds instead of two.

    Best Regards,
    Markus
  • 0 in reply to Markus_Fleck
    Prodigy 145 points

    Hi Markus,

    Thanks so much for your reply!!Was very useful!

    I corrected the schematic in this way:

    2465.Schematic.pdf

    I added the capacitor at the BAT pin and added the voltage rating.

    As your suggetion, I modified the value of RFOD like the value on BQ51050BEVM-764 datasheet and recalculated the value of R1 (R13 in my schematic).

    Now I wait your instructions on how to calculate the value of R16 and R17. I reread the datasheet and in my new project are ok the thresholds of JEITA compatible TS profile (p.19-20 in datashhet).

    VT1 = 0°C

    VT2 = 10°C

    VT3 = 45°C

    VT4 = 60°C

  • 0 in reply to Alessandro Giacometti
    TI__Intellectual 1122 points
    Alessandro,

    I will contact you for this topic.

    Best Regards,
    Markus