Q.
How do you determine the Vin range for an adjustable output regulator?
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A.
Most data sheets specify the operating range of the LDO. If this is not available, look for the Absolute Maximum Rating of the device. Use the Maximum Vin rating as guidance. It is not to be exceeded at anytime.
The minimum input is simply the Vout + Vdropout. All LDO has the Vdropout specified in the electrical table. The Vdropout is also referred to as the (Vin-Vout).