Circuit and method for detecting short circuit failure of a switching transistor

{
  "publication_number": "US9658276B2",
  "country": "US",
  "kind": "B2",
  "title": "Circuit and method for detecting short circuit failure of a switching transistor",
  "abstract": "A circuit and method are provided detecting a persistent short circuit in a power MOSFET for the purpose of protecting a load from over-current.",
  "claims": [
    "1. A method of determining a fault condition in a circuit, comprising: comparing a voltage at a current sense element with a reference voltage; and if the voltage at the current sense element exceeds the reference voltage, turning off a switch comprising a gate and a first terminal and a second terminal, the first terminal coupled to a load and the second terminal coupled to the current sense element; and after a predetermined period of time after the turning off of the switch, if the voltage at the current sense element exceeds the reference voltage, asserting a signal indicating a fault.",
    "2. The method of claim 1, wherein the fault condition is a short circuit failure of the switch.",
    "3. A protection circuit, comprising: a switching transistor having a first terminal, a second terminal, and a gate; a current sense element coupled to the switching transistor; a comparator with a first input terminal, a second input terminal, and an output, the first input terminal coupled the current sense element and the second input terminal coupled to a reference voltage, wherein the output indicates whether the voltage of the current sense element exceeds the reference voltage; a gate driver with an input coupled to the output of the comparator and with an output coupled to the gate of the transistor, wherein the output of the gate driver turns on the transistor during normal operation and turns off the transistor during a mode to determine whether a fault exists in the transistor; a blanking circuit for generating a blanking delay of a predetermined time period, the blanking circuit having an input coupled to the output of the comparator and an output; and a logic gate for receiving the output of the blanking circuit and the output of the gate driver, wherein the logic gate outputs a signal indicating a fault condition in the transistor.",
    "4. The circuit of claim 3, wherein the fault condition is a short circuit failure of the transistor.",
    "5. The protection circuit of claim 3, wherein the logic gate is an AND gate comprising: an inverting input for receiving the output of the gate driver; and a non-inverting input for receiving the output of the blanking circuit.",
    "6. The protection circuit of claim 4, wherein the logic gate is an AND gate comprising: an inverting input for receiving the output of the gate driver; and a non-inverting input for receiving the output of the blanking circuit.",
    "7. A protection circuit, comprising: a switching transistor having a first terminal, a second terminal, and a gate; a current sense element coupled to the switching transistor; a blanking circuit for generating a blanking delay of a predetermined time period, the blanking circuit having an input coupled to the current sense element and an output; a comparator with a first input terminal, a second input terminal, and an output, the first input terminal coupled to the output of the blanking circuit and the second input terminal coupled to a reference voltage, wherein the output indicates whether the voltage of the output of the blanking circuit exceeds the reference voltage; a gate driver with an input coupled to the output of the comparator and with an output coupled to a gate of the transistor, wherein the output of the gate driver turns on the transistor during normal operation and turns off the transistor during a mode to determine whether a fault exists in the transistor; and a logic gate for receiving the output of the comparator and the output of the gate driver, wherein the logic gate outputs a signal indicating a fault condition in the transistor.",
    "8. The circuit of claim 7, wherein the fault condition is a short circuit failure of the transistor.",
    "9. The protection circuit of claim 7, wherein the logic gate is an AND gate comprising: an inverting input for receiving the output of the gate driver; and a non-inverting input for receiving the output of the comparator.",
    "10. The protection circuit of claim 8, wherein the logic gate is an AND gate comprising: an inverting input for receiving the output of the gate driver; and a non-inverting input for receiving the output of the comparator."
  ],
  "description_excerpt": "A circuit and method are provided detecting a persistent short circuit in a power MOSFET for the purpose of protecting a load from over-current.\n\nFIG. 1 depicts a prior art protection circuit 100 for protecting a load 110 from over-current stress due to a short- circuit failure 199 of a transistor 102, the protection circuit 100 comprising a current sense resistor 103 and a circuit breaker 106. The load 110 receives power from an input source of voltage 101 through the transistor 102 biased into conduction by a driver 105. In operation, when a voltage threshold is exceeded across the sense resistor 103, the circuit breaker 106 disconnects the load 110 from the input voltage source 103.\n\nThe prior art protection circuit 100 suffers high cost of components and is not well suited for integration in a monolithic die with the driver 105. In addition, circuit breaker 106 does not provide adequate protection in a system with low headroom voltage.\n\nWhat is needed is an improved circuit and method for performing direct detection of the transistor failure.\n\nThe present invention proposes a method and circuit for detecting a short circuit failure of a switching transistor adapted for connecting a load to an input source of voltage, the method comprising: a step of detecting an over-current condition at the load; a step of biasing the switching transistor non-conductive when the over-current condition is detected; a step of a blanking delay to allow the over-current condition to clear; a step of reporting a fault status in the case of the over-current condition persisting past the blanking delay.",
  "cpc": [
    "G01R 31/2621",
    "G01R 31/025",
    "G01R 31/52",
    "H02H 3/04",
    "H02H 3/044",
    "H02H 3/08",
    "H02H 3/093"
  ],
  "ipc": [
    "G01R 31/02",
    "G01R 31/26",
    "H02H 3/04",
    "H02H 3/08",
    "H02H 3/093"
  ],
  "assignees": [
    "Microchip Technology Inc"
  ],
  "inventors": [
    "Alexander Mednik",
    "Rohit Tirumala",
    "Marc Tan",
    "Simon Krugly"
  ],
  "filing_date": "2015-06-18",
  "publication_date": "2017-05-23",
  "grant_date": "2017-05-23",
  "priority_date": "2014-06-23",
  "application_number": "US-201514743945-A",
  "family_id": "54869416",
  "cited_by_count": 1,
  "citations": [
    "US5917292A",
    "US6185082B1",
    "US20140077782A1",
    "US20150372678A1"
  ]
}