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VOLTAGE REFERENCE START-UP OVERSHOOT PROTECTION

IP.com Disclosure Number: IPCOM000010710D
Publication Date: 2003-Jan-13
Document File: 6 page(s) / 119K

Publishing Venue

The IP.com Prior Art Database

Abstract

The voltage reference is a key element for Power Management Unit (PMU) Circuits. Voltage reference circuits are used as a reference in many circuits, including DC-DC converters, low-drop-out (LDO) regulators, and for battery chargers. The prevention of overshoot has become a mandatory requirement by many customers so as to protect the circuits supplied by PMU circuits, as many voltage regulators deliver an output voltage which is proportional to a reference input voltage. One problem is when there is a substantial overshoot on the reference voltage and the system response time is faster than the overshoot duration, a similar overshoot is produced at the output of the regulator that is harmful to the circuitry supplied by the regulator. To improve overall circuit performance in view of the above problem, designs have become quite complex and expensive, and suffer from poor performance like increased Power Supply Rejection Ratio (PSRR). These complex designs are sensitive to many parameters and so far no easy modification has been found in the prior art to suppress start-up overshoot in all process and environmental conditions. There are many other applications using reference voltages where such an overshoot on the reference voltage may have troublesome effects. Thus, for at least the above reasons, it is desirable to produce a reference input voltage having no overshoot at start-up.

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Voltage reference start-up overshoot protection

Background

The voltage reference is a key element for Power Management Unit (PMU) Circuits.  Voltage reference circuits are used as a reference in many circuits, including DC-DC converters, low-drop-out (LDO) regulators, and for battery chargers.  The prevention of overshoot has become a mandatory requirement by many customers so as to protect the circuits supplied by PMU circuits, as many voltage regulators deliver an output voltage which is proportional to a reference input voltage. 

One problem is when there is a substantial overshoot on the reference voltage and the system response time is faster than the overshoot duration, a similar overshoot is produced at the output of the regulator that is harmful to the circuitry supplied by the regulator.  To improve overall circuit performance in view of the above problem, designs have become quite complex and expensive, and suffer from poor performance like increased Power Supply Rejection Ratio (PSRR).  These complex designs are sensitive to many parameters and so far no easy modification has been found in the prior art to suppress start-up overshoot in all process and environmental conditions.

There are many other applications using reference voltages where such an overshoot on the reference voltage may have troublesome effects.  Thus, for at least the above reasons, it is desirable to produce a reference input voltage having no overshoot at start-up.

DETAILED DESCRIPTION

  In a voltage reference generator there are generally different possible steady states and particularly one in which there is no current at all in the different branches of the generator.  A start-up circuitry is then added to avoid this state and help the generator to settle to the desired steady state with the correct output voltage (refer to Fig. 1).

 This start-up circuitry is active just after powering the reference generator or getting it out of the shut-down mode and forces a biasing current in the branches of the generator.

  Once the generator has begun to start and has reached a given state, the start-up circuitry is switched off so th...