Electricity: electrical systems and devices – Safety and protection of systems and devices – Voltage regulator protective circuits
Reexamination Certificate
2001-05-04
2004-08-10
Sircus, Brian (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Voltage regulator protective circuits
C361S111000
Reexamination Certificate
active
06775112
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electronic circuits that utilize shunt regulators. In particular, the present invention relates to a method and apparatus that provides for enhanced protection from electrostatic discharge (ESD) in shunt regulators.
BACKGROUND OF THE INVENTION
Static electricity has been an industrial problem for centuries including such examples as paper and grain mills. The age of electronics brought with it new problems associated with static electricity and electrostatic discharge. Additionally, as electronic devices have become faster and smaller, their sensitivity to electrostatic discharge (ESD) has increased. Today, ESD impacts productivity and product reliability in virtually every aspect of the electronic environment. Despite a great deal of effort during the past decade, ESD still affects production yields, manufacturing costs, product quality, product reliability, and profitability. The costs of damaged devices can range from only a few cents for a simple diode device to several hundred dollars for complex hybrid microelectronic circuits.
An example of an ESD test circuit (
100
) for an electronic circuit is shown in FIG.
1
. ESD test circuit
100
includes an ESD tester (
110
) and test a device (
120
). The ESD tester (
110
) includes a voltage supply (V
1
), a circuit ground potential (GND), a capacitor (C
1
), two resistors (R
10
and R
11
), an inductor (L
1
), and a switch (SW
1
).
The voltage supply (V
1
) includes a ground terminal that is connected to the circuit ground potential (GND) and a power terminal that is connected to node N
10
. Resistor R
10
is connected between nodes N
10
and N
11
. Capacitor C
1
is connected between node N
11
and the circuit ground potential (GND). Resistor R
11
is connected between nodes N
11
and N
12
. Inductor L
1
is connected between nodes N
12
and N
13
. Switch SW
1
is connected between nodes N
13
and N
14
. A test control signal (TCTL) is in communication with switch SW
1
. Test device (
120
) includes a test pin (P
1
) that is connected to node N
14
and a ground pin (P
2
) that is connected to the circuit ground potential (GND).
Electrostatic discharge is the direct transfer of electrostatic charge through a significant series resistor from the human body or from a charged material to the electrostatic discharge sensitive (ESDS) device. The model used to simulate this event is the Human Body Model (HBM). The Human Body Model is the oldest and most commonly used model for classifying device sensitivity to ESD. The HBM testing model represents the discharge from the fingertip of a standing individual delivered to the device. In one example, the HMB is modeled by a 100 pF capacitor(C
1
), a 1.5 k&OHgr; series resistor (R
11
), a 100 M&OHgr; resistor (R
10
), and a 4 uH inductor (L
1
). In operation, at a first time, switch SW
1
is in an open position allowing capacitor C
1
to charge to the full potential of the voltage supply (V
1
). At a subsequent time, switch SW
1
is closed by the test control signal TCTL causing the capacitor (C
1
) to discharge through the series combination of resistor (R
11
), inductor (L
1
), switch SW
1
, and into the test device (
120
) through test pin P
1
. If the test device does not have sufficient ESD protection, it will be damaged during this test.
SUMMARY OF THE INVENTION
The present invention is directed to a method and an apparatus that improves electrostatic discharge protection in a shunt regulator. An improved shunt regulator includes an “on-chip” Miller capacitance circuit that is coupled between the drain and gate terminals of a field effect transistor (FET) shunt device. The Miller capacitance circuit provides a fast transient signal path that activates the FET to prevent damage.
Briefly stated, voltage regulators are exposed to extreme amounts of voltage over short periods of time during an electrostatic discharge (ESD) event. Shunt regulators include one or more devices that require protection from ESD events. ESD events inherently introduce extreme voltages into the shunt regulator. Capacitors are passive devices that may be used to couple high frequency signals. By providing a capacitance circuit between the gate and drain of the shunt device (or devices) in combination with a resistor circuit, a voltage can be applied to the gate of the shunt device(s) that activates the shunt device(s) in response to a fast-transient ESD event. The applied gate voltage causes the shunt device(s) to “turn on”, thereby providing a path for the excess voltage from the ESD event to discharge through so as to avoid catastrophic failures. A master-slave ESD protection device may be supplemented to the improved shunt regulator to further protect the shunt regulator from longer lasting ESD events.
In one aspect, the present invention is directed toward an apparatus for improving fast transient protection in a shunt circuit that includes a control terminal. The apparatus includes a protection circuit that is arranged to couple a fast transient signal to the control terminal in response to a fast transient event such that the shunt circuit is activated in response to the fast transient signal and the shunt circuit is protected from the fast transient event.
In another aspect, the present invention is directed toward an apparatus for improving electrostatic discharge protection in a shunt regulator. The apparatus includes an error amplifier circuit that is arranged to produce a control signal at a control terminal in response to a reference potential and a potential at a power supply terminal. The error amplifier has an associated amplifier response time. A capacitance circuit is arranged to couple a fast transient signal to the control terminal in response to a fast transient ESD event that occurs at the power supply terminal. A resistance circuit is arranged to produce another control signal at the control terminal in response to the fast transient signal. A shunt circuit is arranged to selectively couple power from the power supply terminal to a circuit ground terminal when activated. The shunt circuit is activated by the control signal during normal operation and the shunt circuit is activated by the other control signal during the fast transient ESD event. Excess energy from the fast transient ESD event is shunted from the power supply terminal to the circuit ground terminal by providing the other control signal to the control terminal in a time interval that is shorter than the amplifier response time.
In yet another aspect, the present invention is directed toward another apparatus for improving electrostatic discharge protection in a shunt regulator. The apparatus includes a means for amplifying that is arranged to produce a control signal at a control terminal in response to a reference potential and a regulation potential. The regulation potential is associated with a power supply terminal. A means for coupling is arranged to couple a fast transient signal to the control terminal in response to a fast transient ESD event that occurs at the power supply terminal. A means for producing is arranged to produce another control signal at the control terminal in response to the fast transient signal. A means for shunting is arranged to selectively couple power from the power supply terminal to a circuit ground terminal when activated. The shunt circuit is activated by the control signal during normal operation and the shunt circuit is activated by the other control signal during the fast transient ESD event. Excess energy from the fast transient ESD event is shunted from the power supply terminal to the circuit ground terminal by providing the other control signal to the control terminal in a time interval that is shorter than the amplifier response time.
In a further aspect, the present invention is directed toward a method of protecting a shunt device in a shunt circuit regulator from a fast ESD event on a power terminal. The method includes detecting the fast ESD event with a capacitance circuit, providing a current through the capacitance cir
Archer Donald
Oglesbee John Wendell
Smith Gregory J.
Hertzberg Brett A.
Merchant & Gould P.C.
National Semiconductor Corporation
Nguyen Danny
Sircus Brian
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