Methods and systems for generating interim voltage supplies
View Patent ↗Methods and systems for protecting integrated circuits (“ICs”) from power-on sequencing problems provide an interim voltage during power-on sequences in order to prevent over-voltage conditions across IC terminals. Voltages at first and second terminals of a circuit are monitored and an interim voltage to the second terminal is provided when the voltage at the first terminal exceeds a first threshold and a voltage at the second terminal is below a second threshold. The interim voltage protects the circuit from excessive voltage differences across the first and second terminals during power-on sequences, and is deactivated during normal operation so as not to draw excessive current. The method/system helps to insure that multi-supply dependent logic and/or other circuitry does not receive inappropriate voltage levels, and thus helps to insure that lower voltage level based circuitry is not damaged during power-up, transients, and/or glitches.
1. An interim voltage generator for protecting a circuit from excessive voltage differences across first and second voltage inputs of the circuit when a first voltage amplitude is applied to the first voltage input before a second voltage amplitude is applied to the second voltage input, comprising:
first and second terminals coupled to the first and second voltage inputs of the circuit, respectively;
an interim voltage supply coupled to the first terminal; and
a PMOS transistor having a gate terminal selectively coupled to the second terminal, a drain terminal coupled to the second terminal, and a source terminal coupled to the interim voltage supply;
wherein the PMOS transistor is selectively biased to couple the interim voltage supply to the second terminal when the first voltage amplitude exceeds a first threshold and the second voltage amplitude is below a second threshold.
2. The interim voltage generator of claim 1 wherein the interim voltage supply provides an interim voltage that is below the second threshold.
3. The interim voltage generator of claim 1 wherein the interim voltage supply comprises a series of diode-connected transistors coupled between the first terminal and the source terminal of the PMOS transistor.
4. An interim voltage generator, for providing an interim voltage during voltage transients at a first voltage input of a circuit, comprising:
first and second terminals coupled to first and second voltage inputs of the circuit, respectively;
third terminal coupled to a bias mid power supply;
a voltage sensor coupled to the first, second and third terminals;
a switch having a first contact coupled to the second terminal and a control input coupled to an output of the voltage sensor; and
an interim voltage supply coupled to a second contact of the switch, the interim voltage supply providing an interim voltage amplitude;
wherein the voltage sensor senses over-voltage transients at the first terminal and controls the switch to couple the interim voltage supply to the second terminal.
5. The interim voltage generator of claim 4 further comprising means for limiting DC leakage current between the first and second terminals.