Open drain driver, and a switch comprising the open drain driver

Abstract

An open drain driver ( 7 ) selectively switches a MOSFET switch (MN 1 ) which is passively held in the conducting state into the non-conducting state. The MOSFET switch (MN 1 ) switches an AC analogue input signal on a main input terminal ( 3 ) to a main output terminal ( 4 ) and the gate of the MOSFET switch (MN 1 ) is AC coupled by a capacitor (C 1 ) to the drain thereof. The open drain driver ( 7 ) comprises a first MOSFET (MN 2 ) and a second MOSFET (MN 3 ) through which the gate of the MOSFET switch (MN 1 ) is pulled to ground (Vss). The gate of the first MOSFET (MN 2 ) is coupled to the supply voltage (VDD) for maintaining the first MOSFET (MN 2 ) in the open state. A control signal is applied to the gate of the second MOSFET (MN 3 ) for selectively operating the open drain driver ( 7 ) in the conducting state for operating the MOSFET switch (MN 1 ) in the non-conducting state. When the second MOSFET (MN 3 ) is in the non-conducting state, the first MOSFET (MN 2 ) remains in the conducting state until the voltage on a coupling node ( 9 ) between the first and second MOSFETs (MN 2 ,MN 3 ) equals the difference between its gate voltage and its threshold voltage, at which stage, any over-voltages applied to the gate of the MOSFET switch (MN 1 ) are divided between the first and second MOSFETs (MN 2 ,MN 3 ). A coupling diode (D 1 ) coupling the coupling node ( 9 ) to the supply voltage (VDD) clamps the voltage on the coupling node ( 9 ) at the supply voltage (VDD) plus the conducting voltage of the diode (D 1 ), in the event of the voltage on the coupling node ( 9 ) rising after the first MOSFET (MN 2 ) has gone into the non-conducting state. The coupling node ( 9 ) may be capacitively coupled to the supply voltage (VDD) by a coupling capacitor instead of or as well as the diode (D 1 ) for limiting the voltage on the coupling node ( 9 ).

Description

technical field [0001] The present invention relates to an open drain driver, and a switching circuit comprising a transistor switch operating under the control of the open drain driver. The invention also relates to a method for providing an open-drain driver with improved overvoltage breakdown protection. Background technique [0002] Open drain drivers are known and have many applications. For example, open-drain drivers are commonly used to drive low signals from related circuits onto a common bus to reach distant external circuits. The advantage of using an open-drain driver in this application is that when the open-drain driver is not needed to drive a low signal onto the common bus, the open-drain driver is in a high-impedance state, thereby separating its associated circuitry from the common bus. isolation. In the case where multiple circuits share a bus, the rated power supply voltage of the circuit will vary depending on the type of circuit. Some circuits can o...

AI Technical Summary

Problems solved by technology

However, since AC signals and / or sudden voltage surges capacitively couple through the drain-to-source parasitic capacitance of the first MOSFET to the node coupling the drain of the second MOSFET to the source of the first MOSFET, the first With the MOSFET in a non-conducting state, the voltage at the node coupling the drain of the second MOSFET to the source of the first MOSFET rises to a level that exceeds the breakdown voltage of the second MOSFET

This causes the second MOSFET to fail

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