Patent ID: 7583105

Claim:
A pull-up circuit, comprising: a pull-up circuit output; logic circuitry to generate an enable signal in response to a battery supply voltage; an active pull-up circuit block that, in response to a first logical value of the enable signal, brings the voltage on the pull-up circuit output to a reference voltage derived from an external voltage supply, the pull-up circuit block including a first input providing the reference voltage; a second input; an operational amplifier, having a reference voltage input connected to the first input thereof and an output, and a first transistor, controlled by the output of the operational amplifier, the first transistor having a first terminal connected to a first supply voltage input and having a second terminal connected to the pull-up circuit output and to the second input of the operational amplifier; and an alternative pull-up circuit block that, in response to a second logical value of the enable signal, brings the voltage on the pull-up circuit output to a reference voltage derived from the battery supply.