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LTC6242 voltage follower output saturation voltage

Peck
on Sep 21, 2018

I used LTC6242 as a voltage follower configuration: - power to IC is 4.2V

- measured V+ to IC is 3.8V

- V- is feedback to Vout, measured about 3.6V

- output is set at high impedance for testing

(Note that I wanted output to be 3.8V)

When the power is at 4.2V, output seems to be saturated at 3.6V even I increased the V+ voltage higher.

Has anyone tested the saturation level of this op amp?

Other than increasing the power supply, any other method?

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  • +1
    •  Analog Employees 
    on Sep 23, 2018 6:47 AM over 2 years ago

    Hi,

    Please be mindful of the input common voltage range of this opamp.  You are using a slightly lower supply voltage of 4.2V, the closest specified supply voltage in the datasheet could be referenced at Vsy=5V to ground. At Vsy=5V, the max input voltage range is 3.5V, which could mean that at Vsy=4.2V to ground, the max input range can be safe to assume to be lower. So, in the part of your circuit where you want to output 3.8V from a supply of 4.2V, your input due to voltage divider is 3.8V which is greater than the max input voltage of 3.5V or less. You must always operate the opamps in its specified supply, input, output voltage range limits. This tutorial can help you to further understand these concepts.

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  • +1
    •  Analog Employees 
    on Sep 23, 2018 6:47 AM over 2 years ago

    Hi,

    Please be mindful of the input common voltage range of this opamp.  You are using a slightly lower supply voltage of 4.2V, the closest specified supply voltage in the datasheet could be referenced at Vsy=5V to ground. At Vsy=5V, the max input voltage range is 3.5V, which could mean that at Vsy=4.2V to ground, the max input range can be safe to assume to be lower. So, in the part of your circuit where you want to output 3.8V from a supply of 4.2V, your input due to voltage divider is 3.8V which is greater than the max input voltage of 3.5V or less. You must always operate the opamps in its specified supply, input, output voltage range limits. This tutorial can help you to further understand these concepts.

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