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TPS62136: from 5Vin to -12Vout violate the recommended operating range

Stefano Alfredo La Spina
Prodigy 220 points
Part Number: TPS62136
Other Parts Discussed in Thread: DAC8734, TIDA-01423, , LMR33640, TPS62933

Hi TI experts.

I need to design from a 5V input a -12V output to be fed to the negative rail of the TI DAC8734.

So I have taken as a starting point the TIDA-01423 3-V to 4.5-V Input, 400-mA, –12-V Inverting Buck-Boost Reference Design

it helps me, being in a hurry for the design as a good starting point for generating from a 5V the negative rail.

however using the TPS62136 that has a 3V to 17V input range the design says:

" The output voltage range is the same as when configured as a buck converter, but negative. The output voltage for the inverting buck-boost topology must be set between –0.8 V and –12 V. The output voltage is set in the same way as the buck configuration, with two resistors connected to the FB pin. The TIDA-01423 design sets the output voltage at –12 V, which gives an input voltage range of 3 V to 5 V. However, TI does not recommend to use a 5-V input voltage because voltage tolerances on the input supply can violate the recommended operating range of TPS62136."

could you please point me out some alternative for this chip? I have spent many days trying to navigate through without effort.

Best regards and thanks.

 

  • 0
    TI__Expert 7860 points

    Hi Stefano,

    If you haven't already read this APP note: Working with Inverting Buck-Boost Converters (Rev. B), it provides guidelines for creating an inverting BB design that may be beneficial.

    My recommendation would be to use a buck IC that has a wider input and output voltage range to accommodate your operating condition.

    The App note uses the LMR33640 which has plenty of input and output margin for your design. A newer device to look at is the TPS62933, which has better internal FETs.

    Is there anything specific you are trying to optimize the design for? Or any other design requirements like max output current? 

    Thanks,

    Joseph

  • 0 in reply to Joseph Conrad
    Prodigy 220 points

    Thank You Joseph for the reply.

    The main goal is to design a quite voltage rail that, together with the +24V has to feed the DAC voltage rail. So while output current may not be a concern, a low output ripple and reduced EMI should be the main two targets.

    How can I decide which device or topology is the best for this task?

    Best regards and Thanks

  • 0 in reply to Stefano Alfredo La Spina
    TI__Expert 7860 points

    Hi Stefano,

    You will want to look for a device that supports an inverting buck-boost converter, or another standard inverting DC/DC topology. Most standard buck ICs are able to also be used as an inverting buck-boost by modifying the schematic as talked about in the application note I linked above. 

    The TPS62933 uses current mode control and has the spread spectrum feature that will help to reduce peak EMI at certain frequencies. If you'd like I can verify your desired operating conditions on an EVM?

    Thanks,

    Joseph