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TPS61088

Joshua Hayes
Prodigy 70 points
Other Parts Discussed in Thread: LM3478, TPS61088

Hello,

I am currently using the LM3478 Switching Regulator Controller for a design that is powered from a single cell Li-Poly battery.   The output voltage ranges from 4.5 to 8.0 volts and is controlled by the DAC on our MCU through the feedback network.  This allows us to deliver at least 14W of power to a load that may be anywhere from 1.0 to 4.5 Ohms.  We have been finding that it has not been as efficient as we thought.  I think it is around 80% efficient (loosing 2-4W as heat).  I am concerned that the MOSFET will and surrounding circuitry will get too hot.

The TPS61088 appears to be more efficient.  It also has an integrated low side N-channel MOSFET and is synchronous.  Is the TPS61088 capable of generating and outputting the following voltages and currents?  Is it advisable to control the output voltage (4.5-8.0v) with an analogue signal from a DAC (DAC output 0.0 - 3.3V) using the feedback network.?

Supply: 3.6 - 4.2V

Output: 4.5V@4.5A to 8.0V@1.8A (14.4W output)

  • 0
    TI__Genius 11085 points
    I will move your question to the forum supporting the LM3478 to get a faster response. -Yang
  • 0
    TI__Mastermind 40080 points

    Dear Sir,

    Yes, TPS61088 can output 4.5V/4.5A very well.

    TPS61088 has PWM working mode and PFM working mode. The maximum input voltage(4.2V) and output voltage 4.5V is very near, if you let it working in the PFM mode, it is oK. If you let it working in the PWM mode, if the operation frequency is higher than a certain value, the output voltage will be higher than the setting value because of the minimum on time limitation. Suggest to set the operation frequency under 500kHz under PWM working mode.

    Yes you can change the output voltageby DAC.

    BR,Helen

  • 0
    TI__Mastermind 40080 points
    One more question: Could you please share the detailed application information for us? Like in what kind of equipment? Thanks!
  • 0 in reply to Helen chen
    Prodigy 70 points

    Thank you for your help. 

    I will use the PWM mode when I require the current.  The output will be applied to the load using a MOSFET.  This MOSFET and the MCU will regulate the power delivered to the load.  We expect that we will be implementing a 1KHz PWM output switch to achieve this.  Is it okay to place the TPS61088 in the PFM mode momentarily when we are not applying power to the load and then switching back to PWM mode when applying power to the load?  We would be changing from PFM mode to PWM mode 1000 times a second.

    I am not at liberty to discuss the project that we are working on.  But it could be a medical product.

    thanks,  Joshua

  • 0 in reply to Joshua Hayes
    TI__Mastermind 40080 points

    Joshua,

    It is oK to place the  TPS61088 in the PFM mode momentarily . But changing from PFM mode to PWM mode 1000 times a second(f=1KHz) maye a little bit too high, could you please make  the changing frequency lower?

    Why set 1000 times a second, to save power or something others?

    For TPS61088: the reference voltage Vref=1.204V under PFM mode and Vref=1.212V under PWM mode, so the output voltatge under these two mode is different. When mode pin transition from PFM mode to PWM mode, the output voltage will drop a little, thus it will release the energy to the input side and cause reverse current.

    BR,

    Helen

  • 0 in reply to Helen chen
    Prodigy 70 points
    Helen,

    Thank you for your quick reply. I will keep the device in PWM mode.

    Joshua