# US 2017/0288397 A1 · Electrostatic discharge protection > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0288397 A1 - Document ID: US20170288397A1 - Status: Published application - Kind: A1 - Application number: 15/083,699 - Filed: 2016-03-29 - Published: 2017-10-05 - Earliest claimed: 2016-03-29 - Assignees: NXP B.V. - Applicants: NXP B.V. - Inventors: Ge Wang - Web page: https://patentgrep.com/patent/US20170288397A1 ## CPC - H02H 9/046: {responsive to excess voltage appearing at terminals of integrated circuits} - H02H 11/006: {in case of too high or too low voltage} - H10D 89/811: {using FETs as protective elements} - H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H) - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES ## Abstract Circuits and methods concerning voltage surge protection are disclosed. In an example embodiment, an apparatus includes a switching circuit configured to enable a current path between a first node and a second node in a first mode and disable the current path in a second mode. A biasing circuit configured to, in the surge protection mode, prevent a voltage surge at the first node from enabling the current path to the second node by biasing a voltage of the control node. ## Claims ### Claim 1 An apparatus, comprising: a switching circuit configured and arranged to enable a current path between a first node and a second node in a first mode and disable the current path in a second mode; and a biasing circuit configured to, in a second mode, prevent a voltage surge at the first node from enabling the current path to the second node by biasing a voltage of a control node. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the switching circuit is configured to operate in the first mode in response to a voltage of a control node relative to a voltage of the first node exceeding a threshold voltage, and operate in the second mode in response to the voltage of the control node relative to the voltage of the first node being less than the threshold voltage, wherein in the second mode the switching circuit is configured and arranged to disable the current path; and the biasing circuit configured to, in the second mode, prevent a negative surge at the first node from enabling the current path to the second node by biasing the control node to reduce the voltage of the control node. ### Claim 3 (depends on 2) The apparatus of claim 2, wherein the switching circuit includes a transistor having a source and a drain electrically connected in the current path and a gate electrically connected to the control node; the transistor is configured to enable the current path in response to a gate-source voltage exceeding the threshold voltage and disable the current path in response to the gate-source voltage being less than the threshold voltage; and the biasing circuit is configured to reduce the voltage of the gate, in response to the first node having a voltage below an operating voltage range of the switching circuit, by an amount sufficient to prevent the gate-source voltage from exceeding the threshold voltage. ### Claim 4 (depends on 3) The apparatus of claim 3, wherein the biasing circuit includes an n-type transistor having a drain electrically connected to the control node, a source electrically connected to the first node, and a gate electrically connected to a ground voltage. ### Claim 5 (depends on 4) The apparatus of claim 4, further comprising a driver circuit configured to drive the control node with a mode selection circuit. ### Claim 6 (depends on 5) The apparatus of claim 5, wherein the biasing circuit further includes a first resistor having a first end connected to the drain of the n-type transistor and a second end connected to an output of the driver circuit; and a second resistor having a first end connected to the source of the n-type transistor and a second end connected to the first node. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the switching circuit includes a first transistor and a second transistor connected together in series. ### Claim 8 (depends on 7) The apparatus of claim 7, wherein the first and second transistors are configured to exhibit a leakage current via the current path that is less than 0.1 mA. ### Claim 9 (depends on 1) The apparatus of claim 1, wherein the switching circuit includes three of more transistors connected together in series. ### Claim 10 (depends on 1) The apparatus of claim 1, wherein in the second mode the switching circuit is configured and arranged to prevent negative voltage surges of up to 20V at the first node from reaching the second node. ### Claim 11 (depends on 1) The apparatus of claim 1, further comprising a surge protection circuit including the switching and biasing circuits. ### Claim 12 (depends on 11) A mobile device, comprising: a USB port having a power pin connected to the first node; a battery coupled to the second node; and a circuit protection circuit of claim 11. ### Claim 13 A method, comprising: in a first mode, enabling a current path between a first node and a second node by setting a control node of a switching circuit electrically connected in the current path to a first voltage; and in a second mode, disabling the current path between the first node by setting the control node to a second voltage; and in response to a voltage surge at the first node, preventing the switching circuit from enabling the current path by biasing the voltage of the control node. ### Claim 14 (depends on 13) The method of claim 13, wherein the switching circuit includes at least one n-type transistor having a source and a drain electrically connected in the current path and a gate electrically connected to the control node, the n-type transistor being configured to enable the current path in response to a gate-source voltage exceeding a threshold voltage and disable the current path in response to the gate-source voltage falling below the threshold voltage; and the biasing of the voltage of the control node includes reducing the voltage of the control node by an amount sufficient to prevent a gate-source voltage from exceeding the threshold voltage. ### Claim 15 (depends on 13) The method of claim 13, wherein the biasing of the voltage is performed using an n-type transistor having a drain electrically connected to the control node, a source electrically connected to the first node, and a gate electrically connected to a ground voltage. ### Claim 16 (depends on 13) The method of claim 13, further comprising, operating in the second mode in response to a device including the switching circuit being powered on; and in response to detecting connection of a power supply to the first node determining whether voltage surge is present at the first node, and operating in the first mode after determining that voltage surge is not present at the first node. ### Claim 17 (depends on 16) The method of claim 16, further comprising, while operating in the first mode, charging a battery connected to the second node by providing current from the first node to the second node via the current path. ### Claim 18 (depends on 16) The method of claim 16, further comprising, operating in the second mode in response to detecting a voltage surge while operating in the first mode. ### Claim 19 (depends on 16) The method of claim 16, further comprising, while operating in the first mode, communicating data between the first node and the second node. ### Claim 20 (depends on 16) The method of claim 16, wherein the switching circuit includes a first transistor and a second transistor coupled together in series in the current path; and the first and second transistors are configured to exhibit a leakage current via the current path that is less than 0.1 mA.