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TPS7H1101A-SP: Input & output capacitance

Itai Eden
Intellectual 310 points

Part Number: TPS7H1101A-SP
Other Parts Discussed in Thread: TPS7H1101-SP

Hi,

The datasheet recommends using Tantalum capacitor (10uF-220uF) with the ESR range of 10 mΩ to 2 Ω along with 0.1uF ceramic capacitor. 

please advise on the following:

1. Is there a recommendation regarding the capacitance with respect to the load current? For a low load current  (0.2A for example) what input/output capacitance is recommended?

2. For a large load current, I intend to use a 220uF tantalum capacitor. However, the one that I have available has an ESR of 6mOhm. Should I add a 20-30mOhm resistor in series with the capacitor?

3. For a small load current, (0.2A or 0.8A), in case I can use a smaller capacitor, is it OK to use ceramic capacitors (2-3X22uF) with a 20-30mOhm series resistor (in order to comply with the ESR needed for stability)?

Best regards,

Itai

  • 0
    TI__Guru 62930 points
    Itai,
    All of our engineers that support this device are out of the office until next Wednesday for the Holidays.
    One of them will address your question on their return. I apologize for the delay.
    Regards,
    Wade
  • 0
    TI__Expert 4420 points

    Hi Itai, thanks for your inquiry. As you know, the TPS7H1101-SP is a space rated linear regulator. As a result, we intend to replicate the conditions in which our customers will use this device in real life applications. Even though all the components in the EVM (apart from the regulator) are commercial components, not space rated, the input and output capacitors used are tantalum since that is what is available for space applications for large capacitance values. Typically, ceramic capacitor for space applications are of much smaller value. Therefore, we decided to use a 220uF tantalum capacitor in the EVM to emulate this situation. This particular capaitor has an ESR of 35mΩ. You can find the exact part number for the capacitor in the EVM user's guide located in the product folder.

    In addition, we perform radiation testing of our devices using the EVMs we release. As a result, the TPS7H1101-SP was tested under heavy ions using this capacitor. This information can be found at the SEU report for this device located at ti.com/radiation.

    Finally, derating is a common practice in space applications due to aging and other factors. As a result, customers tend to use much larger output capacitance values than the ones that would be required just from the electrical point of view (load current for example). Therefore, for your smaller load application yes, you could probably use a smaller output capacitor from the electrical point of view but other factors, such as a output tolerance requirements, mission duration and orbit, need to be considered.

    Please let me know if you have any further questions. Thanks,

    JV

  • 0 in reply to Javier Valle
    Intellectual 310 points

    Hi Javier,

    Thank you for the detailed answer.

    One thing I would like you to address is regarding using a capacitor with a low ESR (5mohm).

    Should I connect a 20mOhm resistor in series with the capacitor (for stability purposes).

    Regards,

    Itai

  • 0 in reply to Itai Eden
    TI__Expert 4420 points
    Hi Itai, there is no issue with using a low ESR capacitor. As described in the compensation section of the datasheet, the TPS7H1101-SP is designed to minimize the effect of the ESR of the output capacitor.

    Thanks,

    JV