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TPS61288: TPS61288 design

Chang Cao
Intellectual 520 points
Part Number: TPS61288
Other Parts Discussed in Thread: MC33063A-Q1

Hi, I need help for below questions:

1. What's the difference between TPS61288L and TPS61288?

2. we have a LCD backlight power supply project. The Vin is battery (8V~15V), The Vout connects to the backlight drive circuit. backlight norm parameter is 12V 1A. When the battery is at low end (8V~12VI), the booster step up to 12V. My original idea is when the battery is at high end (12V~15V), the battery voltage goes directly to the Vout. However I see TPS61288 internal has an extra MOSFET connecting between SW pin and VOUT pin (TPS61288 datasheet page 1). When the Vin is larger than Vout setting 12V, what the Vout voltage?

3. The backlight drive has an inrush current 5A at its input side, that mean an 5A inrush on TPS61288 output side. I set the TPS61288 maximum output current 3A, Please teach me how to deal with the 5A inrush current, I don't want to change TPS61288 current setting to 5A because of cost consideration.

Thanks.

Best Regards.

Chang Cao

  • 0
    TI__Genius 16225 points

    Hi Chang Cao,

    Thank you for reaching out.

    for the questions,

    1. TPS61288 and TPS61288L have different production process, TPS61288L is for thermal improvement, but they are same package.

    2. when Vin is larger than the target, the switching will stop switching and the body diode of inner mos will turn on and flow through current.

     The output ripple will become quite large when you add loads if Vin is close to 12V.

    the situation is as below:

    when Vout is higher than 12V, the switching stops and current flow through diode, 

    then voltage drops below 12V and switch start to turn on. Due to minimum turn-on time limitation, the output voltage will climb quickly.

    switch stops again when Vout is above 12V.

    This process continues and we will see large output voltage ripple.

    So, it is recommended to shut down the device when Vin is close to 12V at heavy load. Otherwise, please estimate the large output ripple.

    when Vin is much higher than 12V, like 15V, the voltage will not drop below 12V even current flow through diode.

    The voltage drop between Vin and Vout will be about 0.7V.

    3. The maximum output current of the device is related to its input and output voltage.

    TPS61288's current is 15A, for input 8V and output 12V 5A, the peak current will be about 10A, it will be enough for the inrush.

    Best Regards

    Fergus

  • 0
    Intellectual 520 points

    ,Hi, Fergus:

    Thank you for your help and fast response.

    Chang

  • 0
    Intellectual 520 points

    Hi, Fergus:

    Thank you for your help and fast response.

    Chang

  • 0 in reply to Chang Cao
    Intellectual 520 points

    Hi, Fergus:

    I order TPS61288 sample, it's too small. I can't use breadboard to build prototype for verification. I prefer SOIC or small pitch SOC (I can solder wires to the pins and use copper foil for heat dissipating). I search TI website, only find MC33063A-Q1 is SOIC8 package. Would you please teach me how can I search chip in the SOC category?

    THanks.

    Chang

  • +1 in reply to Chang Cao
    TI__Genius 16225 points

    Hi Chang,

    In the web, Step-up (boost) regulators product selection | TI.com

    you can use filter to package type select all the SOC like package, like SOIC,SOP,SOT23, etc.

    Best Regards

    Fergus