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LM22671: Select a part used as current source

Vincent Li00
Intellectual 2035 points
Part Number: LM22671

Hi Guys

Our customer want to use Buck convert as a current source. Input 7-15V; Output: 100mA current source; Vout is about 3.6V. They use it to charge a three series batteries(Ni-MH).  Their battery vendors don't suggest that they use BQ charger to charge the Ni-MH battery. They need the constant current source to do this to protect battery. Maybe OVP and OCP are needed here.

So do you any suggestion about this application? Any proper Part to do it? It is better if we have converter integrated high side and low side drivers.

Any feedback are appreciated.

-Vincent

  • 0
    TI__Mastermind 25590 points

    Vincent,

    This is a good part for your application. You can use the current limit feature to charge at a constant current, then it will naturally go to constant voltage when the load decreases (battery is almost fully charged). The part will fold back frequency in overcurrent situations which takes care of your OCP. OVP in VIN can be taken care of by a TVS or other protection. OVP on the output will be taken care of by FB (or additional circuitry if necessary).

    The only issue would be pre-bias conditions. If the battery is charged on the output and there is no supply on VIN, the internal FET body diode will conduct which will place VOUT (minus a bit) on VIN. This may cause undesired behavior if the IC tries to turn on. The way to remedy this is to have UVLO using a resistor divider from VIN to EN. Set it up so the highest VOUT placed on VIN will not turn the IC on.

    We do have some TI designs if they do end up wanting a BQ part.

    -Sam

  • 0 in reply to Samuel Jaffe
    TI__Intellectual 2035 points
    Hi Sam
    Do we have more proper prat for the current source design? Maybe more efficiency, more easy to use...
    -Vincent
  • 0 in reply to Vincent Li00
    TI__Mastermind 25590 points

    Vincent,

    I may have made a mistake. I think I was looking at the wrong datasheet - at a part with adjustable current limit. So this part does not have adjustable current limit.

    You can search through our parts with the feature, "Adjustable Current Limit" to find a list of applicable parts. Use your knowledge of the end equipment and customer requirements to pick the best one for you.

    -Sam