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TPS63020 getting hot

Vitalij König
Prodigy 60 points
Other Parts Discussed in Thread: TPS63020, TPS630250, TPS63000

Hello,

I am using the TPS63020 Buck-Boost-Converter for powering LEDs which are controlled with FAN5624 constant current LED-Driver.

Power source is Li+ battery so Vin is 2,6-4,2 V and Vout is 3,3V.

When the Li+ battery is fully chargend 4,2V then the current is 1,6A and the IC TPS63020 is round about 45°C.

But if the battery drops down to 3,6 V current is going up to 1,8 A and IC is getting hotter 55°C this continue until 2,8V 2,2A IC is now 90°C hot and Vout is switching but is still near 3,3V. When I cool down the IC with ICE-Spray Vout is 3,3V and there is no switching.

Why is the IC getting that hot?

Why is the current rising when the Li+ Voltage drops and the IC is operating in Step-Up?

What can I do to avoid that high Temperature?

   

  • 0
    TI__Guru**** 151520 points
    With a constant output power, the input current must increase if the input voltage is lowered. This is the conservation of power.

    As shown in the D/S figure 11, efficiency drops with decreasing input voltage. Thus, the temp goes up.

    You are operating the device very near its maximum power level. I recommend the newer TPS630250 which is more efficient and a little bit higher power.
  • 0 in reply to Chris Glaser
    Prodigy 60 points

    Thank you for your reply!

    I compared the datasheet of TPS63020 to TPS630250 and as you said TPS630250 is more efficient especially at lower voltage.

    In my case TPS630250 Vin 2,5V Vout 3,3V / 2A near 85% efficiency (Figure 11) in comparison TPS63020 with same specification has only 70% efficiency (Figure 6).

    How can I calculate the power dissipation and the temperature of the TPS63020/TPS630250?

    Also is it possible to get the heat away of the TPS Buck/Boost-Converter with 2-layer board or is it necessary to have a 4-layer design?

    Could you please recommend a better Buck/Boost-Convert for my specification Vin 2,8-4,2V Vout 3,3V / 2A with near the same package an periphery stuff?

    Another problem which I do have with using BQ29700DSET as cut off guard for the Li+ battery voltage at 2,8V is that there are to scenarios which are unacceptable for my circuit:

    1. When the Li+ battery has low charge e.g. 3V the inrush current at power on is that high that Voltage of Li+ battery drop for a small period of time under 2,8V (I saw it on scope it goes down to 0.9V) and

    the BQ29700DSET switches off. Because of that I can't use the whole capacity of the Li+ battery. What can I do? I thought a about an extended soft-start could these be a right solution and if yes how I can add it to TPS630250 or TPS63020?

    2. When the Li+ battery reaches the threshold voltage 2,8V of BQ29700DSET it switches off as aspected but then the battery voltage recovers without load above 2,8V and I can switch on the device again these I can repeat endlessly.

      But my goal is that once the battery reach 2,8V BQ29700DSET switch off an only switch on again when the battery was charging about 2,8V and not because of voltage rising with no load.

      Is there any possibility to do that with BQ29700DSET?

    thanks a lot for your advice!

  • 0 in reply to Vitalij König
    TI__Guru**** 151520 points
    The power dissipation is calculated from the efficiency graphs which are at a certain output power. The difference is the loss. This is mainly in the IC and inductor. Webench has some tools for estimating these types of things, but it is highly application dependent. I recommend the TPS630250.

    You need to post in the battery charging forum for the battery charger questions.
  • 0 in reply to Chris Glaser
    Prodigy 60 points

    TPS63020 which I currently using does have a integrated soft start but at lower voltage like 2,8-3V the inrush current is that hight that the Li+ battery voltage drops a lot so I can't start my circuit.

    What about TPS630250 is the integrated soft start function better then TPS63020 or do I need to extend it like in the application note SLVA307A?

    Is SLVA307A usable for all TPS6xxxxx devices?

    Also I would like to know what max current TPS630250 is able to give at Vin 2,8V and Vout 3,3V or better 3,5V.

    And how hot it is getting when it draws 2,5A @ Vin 2,8V Vout 3,5V.

    The effeciency graphs end at 2A is it able to give more then 2 A by a worse effeciency and if yes how is the graph goes on ?

    Is effeciency then near 85%?

    Also in the datasheet of TPS63020 it is recommenden that R2 in the FB voltage divider should be in the range of 200K is my FB voltage divider at schematic R13 1M , R14 178K for 3,3 Vout okay or should I calculate it again?

    Also what about the feedforward capacitor like the TPS63000 is using do I need it also for TPS630250 or TPS63020?

    thanks a lot

     

  • 0 in reply to Vitalij König
    TI__Guru**** 151520 points
    Wow, that sure is a smattering of questions.

    Each D/S is for an individual device. So, don't necessarily use recommendations from one D/S on a different device. They key thing is to follow the guidelines in the D/S of the device you are interested in.

    The TPS630250 D/S has calculations for the maximum output current.

    SLVA307 is a general type of circuit which can be used on many converters.

    The thermal questions were addressed before.

    Your best bet is to order the EVM and take some performance data in your system.