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TPS7H4010-SEP: Negative Voltage Generation

Shibin Varghese
Prodigy 185 points
Part Number: TPS7H4010-SEP
Other Parts Discussed in Thread: LM25088, , TPS50601A-SP, LMZM23600, LMZ34002, LMZM33602, LMZM33606, LMZ14202H

Hi Team,
We are using TPS7H4010MRNPTSEP in one of our projects.
The input voltage is +20V and the required output voltage is -16V.
We realized negative voltage generation is not practical in this chip from a brief reading of the datasheet.
But when I search for some designs in WEBENCH power designer for negative voltage generation within my constraints, I found that some switching regulators like LM25088 can generate negative voltage even if the negative voltage creation is not specified in the datasheet.
So, can we generate negative voltage using TPS7H4010-SEP?

  • +1
    TI__Expert 7025 points

    Hi,

     

    Unfortunately, it looks like this device would not work for your design. There are a few special considerations that apply when using a Buck in an Inverting Buck-Boost configuration. One major requirement is that the input-to-output differential does not exceed the recommended differential between the PVIN and PGND pins of the device stated in the datasheet. In this case, that condition is not met: 20V + 16V > 32V.

    I have highlighted a few of the other main considerations that would apply when using a Buck in an Inverting Buck-Boost configuration in this E2E post: TPS7H4010-SEP: Output voltage clarifications. There is also a link in my post to an Application Report that contains more in-depth examples and design guidelines for working with Inverting Buck-Boost converters.

    Another option you might consider is using one of our controllers (like the UC1843B-SP) in a Flyback topology.

     

    Thanks,

    Sarah

  • +1 in reply to Sarah Koch
    Prodigy 185 points

    Hi Sarah,
    Thank you for your reply.
    If the input-output differential voltage is satisfied that is my required output voltage is less than -12V for the same input voltage of +20V, can I use a similar circuit as in the case of LM25088 for my TPS7H4010MRNPTSEP regulator to generate a negative voltage.

  • +1 in reply to Shibin Varghese
    TI__Expert 7025 points

    Hi Shibin,

    Yes, using a smaller output voltage would satisfy the input-to-output differential voltage requirement. There are a few more considerations you would also want to review. They are explained in detail, along with examples, in this application report (Working with Inverting Buck-Boost Converters).

    The TPS7H4010-SEP should theoretically be suitable for use in an inverting buck-boost configuration like you described, but we have not specifically tested or characterized how the device behaves in this configuration so it will be important for you to thoroughly review your design. We have tested one of the other Bucks we offer (TPS50601A-SP) in this configuration and it had issues with the frequency response and drawing larger current than expected. That doesn't necessarily mean that the TPS7H4010-SEP would also have these issues, but since we have not tested it we cannot guarantee how it will behave. 

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    Prodigy 185 points

    Hi Sarah,
    Thank you for your reply.
    I think LMZM2360 will work fine for me because its input-to-output voltage is 36V and I think -15.5V is not an issue with a +20V supply.
    The negative voltage thus generated is used as the negative power supply for an op-amp and of course, I'll need a positive voltage of +15.5V in the same circuit to drive the positive rail of the op-amp. I hope I can use LMZM2360  to generate a +15.5V for the same.
    My doubts are,
    1) Both the positive and negative voltage as well as the entire system in the design is referred to the same ground. Will that create any problem?. 
    2) Will LMZM2360 works fine for me for the design?.
    3) 

  • 0 in reply to Shibin Varghese
    TI__Expert 7025 points

    Hi Shibin,

    Can you clarify if you mean the LMZM23600? I want to make sure we are talking about the same device. 

    If that is correct, I can ask the engineers who are familiar with the LMZM23600 to review your question and provide any details that might be specific to that device. 

    But first, there is something else I want to check with you. The TPS7H4010-SEP is a space-grade device that is radiation-hardened and intended for space applications, such as satellites. The LMZM23600 is not a space-grade device and is not radiation-hardened. If your design is meant for use in space, this would be an issue.

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    Prodigy 185 points

    Hi Sarah,

    Thank you for your reply.

    LMZM23600 36-V, 0.5-A Step-Down DC/DC Power Module in 3.8-mm × 3-mm Package is the thing I'm refering to.

    I think LMZM2360 will work fine for me because its input-to-output voltage is 36V and I think -15.5V is not an issue with a +20V supply.
    The negative voltage thus generated is used as the negative power supply for an op-amp and of course, I'll need a positive voltage of +15.5V in the same circuit to drive the positive rail of the op-amp. I hope I can use LMZM2360  to generate a +15.5V for the same.
    My doubts are,
    1) Both the positive and negative voltage as well as the entire system in the design is referred to the same ground. Will that create any problem?. 
    2) Will LMZM2360 works fine for me for the design?.

  • 0 in reply to Shibin Varghese
    TI__Expert 7025 points

    Hi Shibin,

    Is your design intended to operate in a space environment? I need to know this in order to make sure your question is answered correctly.

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    Prodigy 185 points

    Hi Sarah,

    This is only a test board. Not for space applications

  • 0 in reply to Shibin Varghese
    TI__Expert 7025 points

    Thanks for confirming Shibin, I will ask the engineers who are familiar with the LMZM23600 to review your questions and see if there are any details specific to that device that you should be aware of.

    Best Regards,

    Sarah

  • 0 in reply to Shibin Varghese
    TI__Expert 8130 points

    Hello Shibin,

    The LMZM23600 will not work with your application requirements. This device is recommended to operate within 1.2V to 15V output. I would not recommend to use this device as you will be in corner conditions.
    I would like to make sure I understand your requirements correctly for me to suggest the best device suitable for your application. So, can you please clarify the following?

    1. If I understood correctly, two devices will be used to power on an op-amp. One device will be configured as an inverting and the other device configured as a buck (standard). Correct?
    2. What is your output current requirement?

    Thanks,
    Alejandro

  • 0 in reply to iAlejandro
    Prodigy 185 points

    Hi,

    Thank you for your reply.

    Yes you're correct. I'll require to devices to power the op amp and related circuitry. One of which is  configured as inverting buck boost.

    The maximum output current required would be 1A.

    It'll be very helpful if you suggest a chip.

    Also, I've some more doubts when configured as IBB.

    1) Both the positive and negative voltage as well as the entire system in the design is referred to the same ground. Will that create any problem?. 

  • +1 in reply to Shibin Varghese
    TI__Expert 8130 points

    Understood. Thanks for the clarification. With that noted, I would recommend LMZ34002 for negative output and the LMZM33602 for the positive output (standard buck). The LMZ34002 is a negative output power module. So, no need to configure the device to IBB.

    Configuring a Buck into IBB has some consequences to the device, not necessarily the entire system. For instance, the max output current and input voltage are reduced, higher power loss (efficiency drops), and a level-shifting circuitry might be needed to alleviate any problems associated with the offset voltages. Take a look at the following Application Report which goes into details when Working With Inverting Buck-Boost Converters.

    Thanks,
    Alejandro

  • 0 in reply to iAlejandro
    Prodigy 185 points

    Hi @ iAlejandro
    I have a doubt.
    The recommended working voltage of LMZM23600 is 36V (absolute maximum is 40V) and in my case, it'll be 20+15.5 = 35.5V<36V.
    I've seen some devices with a maximum recommended Vin 36V in Webench power designer to be used as IBB for -15.5V rail.
    Like, LMZM33606. But its Vout is in the range of 1-20V.
    Why is that?.
    Also, can you suggest some ICs for negative voltage with input +20V and output -15.5V?
    It would be great if it is a leaded package (SMD)

  • +1 in reply to Shibin Varghese
    TI__Expert 8130 points

    Hi Shibin,

    As stated previously, LMZM23600 will not work with your application. The device has a recommended output range of 1.2V to 15V (below your 15.5V requirement). LMZM33606 has an output range of 1-V to 20-V, hence why it is capable of generating a -15.5V rail when in IBB configuration. Below are two recommend modules for your specific application conditions:

    • LMZ34002
    • LMZ14202H

    Regards,
    Alejandro

  • 0
    TI__Prodigy 195 points

    (Update June 2023) - Just wanted to post here for the benefit of anyone considering the TPS7H4010-SEP for negative voltage generation in space applications.  TI has released an application note detailing the design and testing of an inverting-buck-boost converter using this device to generate a number of different negative voltage rails from different input voltages. 

    For more details, see Radiation Tolerant Inverting Buck-Boost Converter with TPS7H4010-SEP