Controlled linear start-up in a linear regulator

Details Controlled linear start-up in a linear regulator Controlled linear start-up in a linear regulator

1999-09-04

2001-01-16

Riley, Shawn (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C323S901000, C323S281000

Reexamination Certificate

active

06175223

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Cross reference is made to the following patent applications, each assigned to the same assignee, the teachings of which are incorporated herein by reference:
Patent No.
Serial No.
Filing Date
Inventor
Title
TBD
09/389,811
09/04/99
Grant
Integration of
Synchronous Rectifier
Restoration of Boot
Capacitor into
Charge-Pump
TBD
09/389,691
09/04/99
Grant
Charge-Pump Closely
Coupled to Switching
Converter to Improve
Area Efficiency
TBD
09/389,809
09/04/99
Grant,
Charge Pump Device
et al
And Method of
Sequencing Charge-
Pump Switches
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to a linear regulator, and more specifically to a low drop-out linear regulator that is used in an integrated circuit (IC), and that implements a method of dynamically controlling the voltage supplied to a device, such as a digital signal processor (DSP).
BACKGROUND OF THE INVENTION
As integrated circuit (IC) devices and IC circuits (collectively, IC circuitry—such as digital signal processors (DSPs) and mixed signal analog circuits, for example) continue to shrink in size and increase in complexity, more precise control of input voltages and input currents to IC circuitry is required. To control input voltages, modem IC circuitry utilize voltage regulators to insure that a relatively constant input voltage is maintained on the input to the IC circuitry. However, the miniaturization of IC circuitry has progressed to the point where constant input voltage regulation alone is not sufficient to insure the integrity and performance of the IC circuitry.
For example, when an IC circuitry starts-up, if the operational (steady-state) input voltage of the IC circuitry is immediately placed on the IC circuitry input, the IC circuitry may experience an excessive input current. This excessive input current may bum out transistors (called high in-rush current and may cause “over-voltage condition”), place undesired biases in the IC circuitry, and inject free electrons into the substrate of the IC circuitry. To limit the problems caused by an excessive input current, and to control other damaging effects of start-up operation, some regulators use two different regulation states (these are known as dual-mode voltage regulators). For example, one dual-mode voltage regulator uses current sources to place one fixed voltage on the input to the IC circuitry for a brief period of time, called a start-up phase. Then, after the start-up phase is complete, the dual-mode voltage regulator places a second fixed voltage (the operational voltage of the IC circuitry) on the input to the IC circuitry.
Unfortunately, the performance of prior-art voltage regulators, including dual-mode voltage regulators, is unsatisfactory and suffers from numerous disadvantages. For example, even small sudden changes in the input voltage can inject noise into the IC circuitry. In addition, though dual-mode voltage regulators reduce the damage caused by placing an operational voltage source directly on an IC circuitry, over-voltage conditions may still occur, free electrons may still be injected into the substrate, and the forwarding of back diodes can still occur. Also, the addition of the start-up phase in dual-mode voltage regulators increases the time it takes for an IC circuitry to become operational, which decreases the performance of the IC circuitry. Furthermore, dual-mode voltage regulators occupy a relatively large amount of IC wafer space. All of these factors contribute to reducing the performance and efficiency of the IC circuitry.
Therefore it is desired to have a voltage regulator circuit and a method for implementing a voltage regulator that provides safe start-up operations, increases start-up speeds, increases IC circuitry efficiency, prevents over-voltage conditions, and reduces the likelihood of noise injection in the IC circuitry, and electron injection into the substrate. The present invention provides such a device and method.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a linear voltage regulator (sometimes called a low drop-out linear regulator, or LDO) and a method of operating a linear voltage regulator. The method ramps-up a voltage from zero volts to a target voltage during the start-up operation of an IC circuitry, and then provide a constant output voltage for the steady-state operation of the IC circuitry. The linear voltage regulator provides advantages over voltage regulators that are designed to simply maintain one constant output voltage, as well as regulators that use one fixed output voltage during the start-up operation of the IC circuitry, and then a second fixed output voltage during the steady-state operation of the IC circuitry. Accordingly, the disclosed linear voltage regulator provides the advantages of preventing high in-rush currents, over-voltage conditions, eliminating the forward-biasing of back-diodes, reduces electron injection into the substrate, reduces the likelihood of noise injection, provides faster start-up speeds, and increases IC circuitry efficiency.
The invention provides a method of operating a linear voltage regulator. The method begins with the step of generating a ramping voltage and applying the ramping voltage to a load via a load connection. The ramping voltage begins at ground voltage and increases linearly until a target voltage is reached. The time it takes to achieve the target voltage is controlled via a slow-start voltage generator. Next, the method proceeds to generate an operating voltage and applies the operating voltage to the load via the load connection.
The step of generating the ramping voltage is selected when a slow-start voltage of a control circuit is determined to be less than a reference voltage of the control circuit. Likewise, the step of generating the operating voltage is selected when a slow-start voltage of the control circuit determined to be is greater than or equal to an input voltage of the control circuit.
The present invention also provides a linear voltage regulator configuration. The linear voltage regulator has a control circuit and a regulation circuit coupled to the control circuit.
The control circuit includes a first switch coupled between a reference voltage input and an error amplifier node, and a second switch coupled between a slow-start voltage generator and the error amplifier node. The switches are implemented as PMOS transistors. The control circuit also provides a comparator for comparing the reference voltage to the slow-start voltage. The comparator has an output that is connected to the first switch to control said first switch. In addition, the control circuit has an inverter coupled to the output of the comparator. An output of the inverter is connected to the second switch to control said second switch. Furthermore, the control circuit includes an error amplifier for comparing an output voltage of the regulation circuit with the voltage on the error amplifier node, and also includes an output voltage driver for converting the output of the error amplifier to the appropriate input for the regulation circuit.
The regulation circuit includes an input node, an output node, and a variable resistance device (implemented as an NMOS transistor) coupled between the input node and the output node. A first capacitor coupled between the input node and a connection to ground, and a second capacitor coupled between the output node and the connection to ground are provided in the regulation circuit to provide a stiff-voltage. The variable resistance device is in communication with the control circuit to animate the linear voltage regulator.


REFERENCES:
patent: 4731574 (1988-03-01), Melbert
patent: 5079497 (1992-01-01), Barbu et al.
patent: 5532576 (1996-07-01), MacRobbie et al.

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