low negative voltage PSU for precision ADC

We are looking for a design which would give us -1V or -2V with low noise. This is the negative rail for our op-amps.

The ADCs are 16 and 18 bit so a very clean power supply would be required.

Looking at the ADP1621 CUK design tool we are getting a circuit with 28 components.

Could anyone suggest another possible solution with a lower component count?    

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  • 0
    •  Analog Employees 
    on Sep 7, 2011 3:24 AM

    Jimmy,

    powering op-amps (or ADCs) with dual supplies is a common requirement. There are multiple ways of solving this problem depending on what voltages are already available to you.

    For example, if you have a positive voltage and need to generate a negative one a Cuk topology (like the one you found with the ADP1621) is an option. The same can be implemented with a ADP1613 requiring less components, although a cuk topology typically needs more components it is the least noisy option unless you want to follow it with a negative LDO.

    Another handy topology is the inverting buck boost. This can be implemented with a buck regulator such as the ADP2300 (or many other more integrated parts). Here is AN-1083 describing how to do it.

    Powering op-amps often leads to the need of a positive and a negative rail that are equal in voltage but of reversed polarity. In this case a coupled Sepic-Cuk could be handy, especially because the op-amp current requirements are balanced between the positive and negative rail.

    This topology is covered as part of the ADIsimPower tool set by downloading one of the SEPIC_Cuk tool.

    Here is the link for the ADP1613 tool.

    http://download.analog.com/PMP/ADP161x_SEPIC_Cuk_Designer.zip

    Another option is to start with an inverting charge pump such as the ADM8860 or ADP3506 followed by either a negative LDO or a LC filter.

    In power the options are many and often are dictated by what's already available on the board or what else you are trying to power.

    AnalogXPRT

Reply
  • 0
    •  Analog Employees 
    on Sep 7, 2011 3:24 AM

    Jimmy,

    powering op-amps (or ADCs) with dual supplies is a common requirement. There are multiple ways of solving this problem depending on what voltages are already available to you.

    For example, if you have a positive voltage and need to generate a negative one a Cuk topology (like the one you found with the ADP1621) is an option. The same can be implemented with a ADP1613 requiring less components, although a cuk topology typically needs more components it is the least noisy option unless you want to follow it with a negative LDO.

    Another handy topology is the inverting buck boost. This can be implemented with a buck regulator such as the ADP2300 (or many other more integrated parts). Here is AN-1083 describing how to do it.

    Powering op-amps often leads to the need of a positive and a negative rail that are equal in voltage but of reversed polarity. In this case a coupled Sepic-Cuk could be handy, especially because the op-amp current requirements are balanced between the positive and negative rail.

    This topology is covered as part of the ADIsimPower tool set by downloading one of the SEPIC_Cuk tool.

    Here is the link for the ADP1613 tool.

    http://download.analog.com/PMP/ADP161x_SEPIC_Cuk_Designer.zip

    Another option is to start with an inverting charge pump such as the ADM8860 or ADP3506 followed by either a negative LDO or a LC filter.

    In power the options are many and often are dictated by what's already available on the board or what else you are trying to power.

    AnalogXPRT

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