Charging of a bootstrap capacitance through an LDMOS
First Claim
1. A charging circuit for a bootstrap capacitance having a circuit for charging the bootstrap capacitor including an integrated LDMOS transistor;
- and a circuital device for preventing the turning on of a parasitic transistor of the LDMOS structure during transients comprising;
a predetermined number of p-n junction diodes positioned between a source node and a body node of the LDMOS transistor;
at least a current generator connected to the ground potential of the circuit and functionally connected between said body node and a ground node, at least one switch connected between said source node and a first junction of said predetermined number of p-n junction diodes, a limiting resistance connected between said body node and said current generator, and switch controlling means connected to said at least one switch for opening said at least one switch during a charging phase of said bootstrap capacitance and for closing said at least one switch when a charge voltage of the bootstrap capacitance reaches a predetermined threshold.
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Accused Products
Abstract
A charging circuit for a bootstrap capacitance employing an integrated LDMOS transistor and including a circuital device for preventing the turning on a parasitic transistors of the integrated LDMOS structure during transients that comprises a plurality of directly biased junctions (D1, D2, . . . , Dn) connected in series between a source and a body of the LDMOS transistor structure and at least a current generator, tied to ground potential, coupled between said body and ground, has at least one switch (INT1) between said source and a first junction (D1) of said plurality of junctions and a limiting resistance (R) connected between the body and the current generator (GEN). The switch (INT1) is kept open during a charging phase of the bootstrap capacitance (Cboot) and is closed when the charge voltage (Vboot) of the bootstrap capacitance reaches a preset threshold. Moreover, the body voltage (VB) is prevented from exceeding the source voltage (VS) plus a Vbe, by controlling a discharge path (T2) with a control stage (T1, R1) in response to a drop of the voltage on the limiting resistance (R). This body voltage control circuit is enabled by a second switch (INT2) driven in phase with the first switch (INT1).
28 Citations
15 Claims
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1. A charging circuit for a bootstrap capacitance having a circuit for charging the bootstrap capacitor including an integrated LDMOS transistor;
- and a circuital device for preventing the turning on of a parasitic transistor of the LDMOS structure during transients comprising;
a predetermined number of p-n junction diodes positioned between a source node and a body node of the LDMOS transistor;
at least a current generator connected to the ground potential of the circuit and functionally connected between said body node and a ground node, at least one switch connected between said source node and a first junction of said predetermined number of p-n junction diodes, a limiting resistance connected between said body node and said current generator, and switch controlling means connected to said at least one switch for opening said at least one switch during a charging phase of said bootstrap capacitance and for closing said at least one switch when a charge voltage of the bootstrap capacitance reaches a predetermined threshold. - View Dependent Claims (2, 3, 4, 5, 6, 7)
- and a circuital device for preventing the turning on of a parasitic transistor of the LDMOS structure during transients comprising;
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8. An integrated circuit, comprising:
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a bootstrap capacitor; an LDMOS transistor connected to said bootstrap capacitor, said LDMOS transistor having a body node, a source node, a parasitic PNP transistor, and a parasitic NPN transistor; a plurality of diodes located between said source node and said body node; a current generator connected to at least one of said plurality of diodes and a ground potential and also connected between said body node and the ground potential; a resistor connected to said body node and said current generator; a switch located between said source node and one of said plurality of diodes; and control circuitry connected to open said switch when charging said bootstrap capacitor, and close said switch when the voltage of said bootstrap capacitor reaches a predetermined threshold; wherein the voltage of said body node increases when said switch is closed, without turning on either of said parasitic transistors.
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9. An integrated circuit, comprising:
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a bootstrap capacitor; an LDMOS transistor connected to said bootstrap capacitor, said LDMOS transistor having a body node, a source node, a parasitic PNP transistor, and a parasitic NPN transistor, a plurality of diodes located between said source node and said body node; a current generator connected to at least one of said plurality of diodes and a ground potential and also connected between said body node and the ground potential; a resistor connected to said body node and to one of said plurality of diodes; a switch located between said source node and one of said plurality of diodes; and control circuitry connected to open said switch when charging said bootstrap capacitor, and close said switch when the voltage of said bootstrap capacitor reaches a predetermined threshold; wherein the voltage of said body node rises when said switch is closed, without turning on either of said parasitic transistors; whereby said resistor functions as a current limiter when said switch prematurely closes.
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10. An integrated circuit, comprising:
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a bootstrap capacitor; an LDMOS transistor connected to said bootstrap capacitor, said LDMOS transistor having a body node, a source node;
a parasitic PNP transistor, and a parasitic NPN transistor;a plurality of diodes located between said source node and said body node; a current generator connected to at least one of said plurality of diodes and a ground potential and also connected between said body node and the ground potential; a resistor connected to said body node and to one of said plurality of diodes; a driving stage connected to said bootstrap capacitor, wherein said bootstrap capacitor biases said driving stage when said driving stage is driven in a turn-on mode; a switch located between said source node and one of said plurality of diodes; and control circuitry connected to open said switch when charging said bootstrap capacitor, and close said switch when the voltage of said bootstrap capacitor reaches a predetermined threshold; wherein a voltage of said body node rises when said switch is closed, without turning on either of said parasitic transistors; whereby a supply of said driving stage is ensured by said bootstrap capacitor. - View Dependent Claims (11)
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12. An integrated circuit, comprising:
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a bootstrap capacitor; an LDMOS transistor connected to said bootstrap capacitor, said LDMOS transistor having a body node, a source node, a parasitic PNP transistor, and a parasitic NPN transistor; a plurality of forward biased diodes located between said source node and said body node; a current generator connected to at least one of said plurality of diodes and a ground potential and also connected between said body node and the ground potential; a first resistor connected to said body node and one of said plurality of forward biased diodes; a first switch located between said source node and one of said plurality of forward biased diodes; discharge circuitry comprising a discharge path of said body node through a first transistor, and a driving stage, said discharge path being controlled by said driving stage, said driving stage being connected in response to the voltage drop across said resistor; a second switch driven in phase with said first switch, said discharge circuitry being enabled by said second switch; and
control circuitry connected to open said first and second switches when charging said bootstrap capacitor and to close said first and second switches when a voltage of said bootstrap capacitor reaches a predetermined threshold;wherein a voltage of said body node rises when said first switch is closed, without turning on either of said parasitic transistors; wherein said second switch enables said driving stage when the capacitance of said bootstrap capacitor reaches a desired charge; whereby said second switch functions as a current limiter when said first switch prematurely closes. - View Dependent Claims (13, 14)
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15. A method for charging a bootstrap capacitor, comprising the steps of:
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providing an LDMOS transistor connected to said bootstrap capacitor, said LDMOS transistor having a body node, a source node, a parasitic PNP transistor, and a parasitic NPN transistor; providing a current generator connected to said body node of said LDMOS and a ground potential; connecting a plurality of diodes between said source node and said body node; connecting a resistor between said body node and at least one of said plurality of diodes; providing a switch located between said source node and one of said plurality of diodes; opening said switch when charging said bootstrap capacitor; and closing said switch when the voltage of said bootstrap capacitor reaches a predetermined threshold; wherein a voltage of said body node rises when said switch is closed, without turning on either of said parasitic transistors.
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Specification