ESD Discharge Circuit to Distinguish Pulses From Hot-Swap Events
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Solution Overview
Problem
Existing ESD protection circuits face challenges in distinguishing between ESD pulses and hot-swap power supply signals, leading to conflicting requirements for the bias resistor value, which can result in inadequate protection against overvoltage and excessive heat damage.
Innovation Solution
The introduction of an auxiliary ESD protection device with a discharge resistor and transistor connected in series between voltage rails, along with a diode and coupling capacitor, allows for controlled turn-on and turn-off times, enabling effective discharge of ESD pulses while preventing damage from hot-swap power supplies by extending the on-time of the auxiliary device beyond the primary ESD protection device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a small bias resistor value is used to enable fast turn-off of the main transistor, then the turn-off speed is improved, but the ESD rail cannot be fully discharged before consecutive ESD pulses, leading to voltage accumulation and circuit damage
Solution Approach 1:
The patent divides the ESD protection function into two separate discharge paths: a first discharge path with the main transistor M0 and bias resistor R0 for fast response, and a second discharge path with the auxiliary transistor M2 and auxiliary bias resistor R2 for sustained discharge. This segmentation allows each path to be optimized for its specific function without compromise.
Solution Approach 2:
The auxiliary transistor M2 acts as an intermediary element that extends the discharge function beyond the main transistor's operational window. It remains active after M0 turns off to complete the discharge of the ESD rail, ensuring full voltage dissipation before the next ESD pulse arrives.
2Reliability
If a large bias resistor value is used to fully discharge the ESD rail before consecutive ESD pulses, then the protection reliability is improved, but the turn-off time is delayed causing excessive current flow and heat damage
Solution Approach 1:
The discharge function is segmented into two phases: the first phase handled by M0 with small R0 for rapid initial discharge and fast turn-off, and the second phase handled by M2 with larger R2 for sustained discharge without excessive current. This eliminates the need to choose between conflicting resistor values.
Solution Approach 2:
The auxiliary discharge path provides partial discharge action that supplements the main discharge path. M2 performs the remaining discharge task after M0 completes its primary function, ensuring complete voltage dissipation without requiring the main transistor to operate beyond its optimal current handling capacity.
3Measurement precision
If the ESD protection circuit is designed to respond to rapid voltage changes, then ESD pulse detection is improved, but hot-swap power supply signals are mistakenly triggered causing false protection activation
Solution Approach 1:
The patent implements dynamic control of the auxiliary transistor M2 through the coupling capacitor C1 and resistor R1 network. This circuit responds to the rate of voltage change (dV/dt) by generating a transient current that activates M2 only during rapid ESD pulses, while the slower hot-swap voltage transitions do not generate sufficient transient current to trigger false activation.
Solution Approach 2:
The coupling capacitor C1 provides feedback that detects the rate of change of the ESD rail voltage. During ESD pulses, the rapid voltage change generates a strong feedback signal through C1 that turns on M2. During hot-swap events, the slower voltage change produces insufficient feedback signal to activate M2, thereby distinguishing between the two conditions.
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
This solution ensures reliable protection against continuous ESD pulses and prevents damage from hot-swap power supplies by allowing the auxiliary ESD discharge path to fully discharge the ESD rail before the next pulse, reducing the risk of circuit damage and overheating.
Implementation Method 1
The coupling capacitor C0 functions as a differentiating circuit. The coupling capacitor C0, as a differentiating circuit, is used to detect a sudden change of the voltage on the ESD rail. When the voltage on the ESD rail suddenly rises in response to an ESD pulse, the coupling capacitor C0 is able to convert the rate of the voltage change of the ESD pulse into a current flowing through R1.
Implementation Method 2
A diode D1 and a first bias resistor R2 are connected in series between the ESD rail and the gate of the transistor M2. The diode D1 is configured to block a current from flowing from the gate of the transistor M2 to the ESD rail.
Data Source
AI summary
An ESD protection apparatus includes a discharge resistor and a transistor connected in series between a first voltage rail and a second voltage rail, a first coupling capacitor, a diode and a first bias resistor connected in series between the first voltage rail and the second voltage rail, wherein a common node of the diode and the first bias resistor is connected to a gate of the transistor, and an ESD protection device connected between the first voltage rail and the second voltage rail.