Electrostatic Breakdown Protection Circuit for Open-Drain Transistors
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Solution Overview
Problem
Conventional semiconductor integrated circuit devices with open-drain output transistors are vulnerable to electrostatic breakdown, as they fail to prevent the transistor from erroneously turning on due to electrostatic pulses, especially in power-off states, and existing protection methods only reduce overcurrent without fundamentally preventing breakdown.
Innovation Solution
An electrostatic breakdown protection circuit comprising a diode, resistor, and a PNP or P-channel transistor connected to the output transistor, along with a clamp element and Darlington configuration of NPN transistors, which prevents the gate potential from rising during electrostatic pulses without requiring power, thereby protecting the open-drain output transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current-limiting resistor is provided between the drain of the output transistor and an output terminal, then overcurrent is reduced, but the output transistor still erroneously turns on due to electrostatic pulses
Solution Approach 1:
The protection circuit applies preliminary anti-action by preemptively counteracting the harmful effect of electrostatic pulses before they can cause breakdown. The circuit includes a protection transistor (Qp) whose base is connected to the output terminal and whose emitter is connected to the gate of the output transistor. When an electrostatic pulse is detected at the output terminal, the protection transistor turns on and clamps the gate potential of the output transistor, preventing it from rising to the threshold voltage required for turn-on. This preliminary protective action occurs before the electrostatic pulse can cause harmful overcurrent, thereby resolving the contradiction by providing robust electrostatic protection without requiring complex additional circuitry.
2Reliability
If conventional protection methods are used, then overcurrent is reduced in power-on state, but no protection is provided in power-off state
Solution Approach 1:
The protection circuit achieves universality by designing a configuration that provides electrostatic protection in both power-on and power-off states using the same circuit elements. The protection transistor (Qp) is configured with its base connected to the output terminal and its emitter connected to the gate of the output transistor, allowing it to function independently of the power supply state. Additionally, a diode (D1) with its cathode connected to the output terminal and anode connected to the base of the protection transistor ensures that the protection mechanism remains active regardless of whether power is supplied to the circuit. This multi-functional design resolves the contradiction by providing consistent protection across different operational states without increasing circuit complexity.
3Reliability
If the gate potential is allowed to rise during electrostatic pulses, then the output transistor turns on to conduct current, but this causes breakdown of the output transistor
Solution Approach 1:
The protection circuit introduces an intermediary mechanism to mediate between the electrostatic pulse and the output transistor gate. The protection transistor (Qp) serves as this intermediary: its base receives the electrostatic pulse at the output terminal, and its emitter connects to the gate of the output transistor. When the electrostatic pulse raises the potential at the output terminal, the protection transistor turns on and acts as a voltage clamp, preventing the gate potential from rising to the threshold level required for erroneous turn-on. This intermediary action effectively decouples the harmful electrostatic pulse from the output transistor gate, resolving the contradiction by preventing erroneous turn-on while maintaining immunity to electrostatic pulses.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively prevents open-drain output transistors from erroneously turning on due to electrostatic pulses, enhancing the reliability and handling of semiconductor integrated circuit devices by providing robust protection against electrostatic breakdown in both power-on and power-off states.
Implementation Method 1
a diode having an anode thereof connected to a signal input terminal leading to the output transistor and a cathode thereof connected to the gate of the output transistor
Implementation Method 2
a PNP bipolar transistor or a P-channel field effect transistor having an emitter or a source, a base or a gate and a collector or a drain connected to the gate of the output transistor
Implementation Method 3
a clamp element connected in parallel to the output transistor, the trigger voltage of the clamp element being set lower than the design withstand voltage of the output transistor
Data Source
AI summary
A protection circuit according to the present invention includes: a diode (D1) having an anode thereof connected to a gate signal input terminal and a cathode thereof connected to the gate of an output transistor (N1); a resistor (R1) having one end thereof connected to the gate signal input terminal and the other end thereof connected to ground; a PNP bipolar transistor (Qp1) having the emitter, base and collector thereof connected to the gate of the output transistor (N1), the one end of the resistor (R1) and ground, respectively. With this configuration, it is possible to prevent, without the need for electric power, an open-drain output transistor from erroneously turning on as a result of an electrostatic pulse or the like being applied thereto, and thus to protect the output transistor from electrostatic breakdown.