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TPS62933: Can TPS62933 be used as inverting converter

Part Number: TPS62933

hi, TI's experts:

     Can TPS62933 be used as an inverter, Vin=5V, Vout=-0.8V to -2.8V, Iout≈-3A.  the output value is adjusted by a DAC.

     

thank you sincerely!

  • Hi, toapex 

    Yes, TPS62933 can be configured as inverting converter. 

    At Vin=5V, 

    When Vout=-2.8V, max Iout can be up to 2.2A. 

    When Vout=0.8V, max Iout can be up to 3A. 

    BTW, 

    Could you let me know what is your application? what is your product? 

    Where 5Vin come from? what is loading? why does it need negative voltage? 

  • thank you, Zhao Ma.

    I have to implement a voltage source which can source 0V to -1.7V and sink continueous -3A. if I use a fixed output negative power, the power dissipation on the PMOS is too high when Vout=0V, so a negative power whose output follows the Vout is needed, and its FB is connected to Vout directly, thus the voltage drop on the PMOS is always a constant 0.8V no matter what Vout is.

    so why does max Iout decrade to 2.2A when Vo=-2.8V? 

    is there any problem in my application block diagram? 

    and I will delete my block diagram one day later,  hope you understand.

  • Hi, toapex 

    1. When buck is configured to inverting buck-boost topology, the output current will be degraded, not equal to 3A. 

    2. I am not familiar with your application, could you explain how MCU regulates Vout? 

  • thank you, Zhao.

    1. Can this degradation be avioded with some methods, e.g enhance the cooling volume?

    2. MCU changes the DAC's output through an SPI interface, and the output is fed to non-inverted input of the error amplifier, meanwhile Vout is fed to the inverted input. the output of the error amplifier controls Vgs of the PMOS, it's a negative feedback system, so the Vout will be equal to DAC's output.

    the error amp. is supplied by a ±10V voltage, In my system, there are many vlotages like +10V, -10V, +2.5V which are not shown in the block diagram.

    at first, the output of TPS62933 may not be negative enough to regulate a precise Vout if I set DAC output to some value, but with the Vgs changing, Vout is gradually changing, and TPS62933's ouput is gradually changing too.

  • Hi, toapex 

    1. the degradation is caused by OC limit, so cooling doesn't work. 

    The max Iout is related with Vin, If you change the Vin to 20V, the max Iout will up to 3.05A. 

    2. I got it, it sounds good.

    You implemented a LDO after TPS62933, right?  

    You didn't draw the inductor for TPS62933 in the diagram. 

  • 1. OK, I see.

    2. Yes, it's a LDO. 

    Yes, I missed the inductor, thanks for kind remind.