Patent Description:
High-side switching elements (or "switches") are increasingly being used to drive loads, such as actuators, in automotive applications including engine control, passenger comfort electronics and chassis control.

High-side switches can be realized using power n-channel metal-oxide semiconductor field-effect transistors or "N-channel MOSFETs" (often referred to simply as "nMOS transistors). nMOS transistors tend to be preferred over pMOS transistors due to having a lower ON-resistance and being cheaper. However, nMOS transistors require a high source-gate voltage to switch it ON and so a suitable circuit for supplying a higher voltage is required.

Referring to <FIG>, one such suitable circuit is a bootstrap circuit which includes a bootstrap capacitor Cbs and an auxiliary voltage source stacked above a supply voltage source, which in this case is a battery. The battery supplies a voltage Vbat to the nMOS transistor drain. A load Zload is connected between an nMOS transistor source node and ground GND. To turn the nMOS transistor ON, a pre-driver circuit is supplied with a higher voltage VCP using the auxiliary voltage source, where VCP > Vbat.

Many applications have a complex load with significant inductive component. Consequently, turning the nMOS transistor causes the load Zload to drive the transistor source node VS negative. The negative voltage can be either clamped using a suitable element, such as a Zener diode (not shown), or be controlled an integrated pre-driver power control circuit supplied with a voltage VCP from the auxiliary voltage source and with a stabilized voltage V<NUM> from a stable voltage source.

The nMOS transistor is often a discrete element, while the pre-driver and its power supply control circuit are provided in an integrated circuit, such as an application specific integrated circuit (ASIC).

A challenge facing pre-driver integrated circuits (which are typically based on a BiCMOS process) is to how to deal with negative voltages at the transistor source node and, thus, the pre-driver negative supply level. The pre-driver should ensure not only that the nMOS transistor is switched ON in the ON state, but also that the transistor is switched OFF in the OFF state. Moreover, the speed (i.e., slew rate) of the negative source node drop in both transitions should not lead to big transient currents into or out of the bootstrap capacitor Cbs and so avoid circuit destruction and/or reverse current to the stabilized base supply V<NUM>. This is made more challenging since the slew rate of clamping events can have a value lying in a wide range, for example, from -<NUM> mVµs-<NUM> to -<NUM> Vµs-<NUM>.

<CIT> describes a power semiconductor device which comprises high-side and low-side switching elements. The device comprises a high-side drive circuit that drives the high-side switching element and a low-side drive circuit that drives the low side switching element. The device comprises a bootstrap capacitor having first and second terminals and supplying a drive voltage to the high-side drive circuit, the first terminal connected to a connection point between the high-side switching element and the low-side switching element. The second terminal is connected to a power supply terminal of the high-side drive circuit. The device comprises a bootstrap diode having an anode connected to a power supply and a cathode connected to the second terminal of the bootstrap capacitor and supplying a current from the power supply to the second terminal of the bootstrap capacitor. The device comprises a floating power supply using the high voltage side potential as a reference potential and a bootstrap compensation circuit supplying a current from the floating power supply to the second terminal of the bootstrap capacitor, when the high side drive circuit turns ON the high side switching element and the low-side drive circuit turns OFF the low-side switching element.

<CIT> describes a voltage-dividing resistor circuit.

According to a first aspect of the present invention there is provided a monolithic integrated circuit for controlling a high-side switching element (such as an nMOS) for a load using a bootstrap capacitor. The integrated circuit comprises a first supply voltage input for receiving a first input supply voltage, a second supply voltage input for receiving a second, current-limited input supply voltage, a voltage-sensing input for receiving a source voltage, a first output for providing a drive signal to the switching element, a second output for providing a charging signal to the bootstrap capacitor, a pre-driver for generating the drive signal, the pre-driver having a voltage input and an output which is coupled to the first output, and a power supply control section comprising first and second switches. The first and second switches are arranged in series between the first input and the second output, the second input is coupled to a node between the first and second switches, and the second node is coupled to a voltage input of the pre-driver. The first and second switches are selectively operable following switching of the switching element from an ON state to an OFF state:in response to a determination that the source voltage is below a predetermined level, to decouple the second output; and, thereafter, in response to determination that the source voltage is above the predetermined level, to couple the second output to first input.

The first and second switches may be selectively operable, in the ON state, to decouple the first input from the node. The first and second switches may be selectively operable following switching from the ON state to the OFF state to couple the first input to the node.

The monolithic integrated circuit may further comprise first and second comparators arranged to control the first and second switches respectively, wherein the first comparator has an input coupled to the second output, and the second comparator has an input coupled to voltage-sensing input.

The voltage input of the pre-driver is may be a first voltage input and the pre-driver may have a second voltage input which is coupled to the voltage-sensing input.

According to a second aspect of the present invention there is provided apparatus comprising the monolithic integrated circuit of the first aspect of the invention, with the bootstrap capacitor coupled between the second output and the voltage-sensing input.

The apparatus may further comprise a high-side switch having a control node coupled to the first output, a load coupled to the high-side switch, a battery coupled to the high-side switch, a first input supply voltage source coupled to the first supply voltage input and a second input supply voltage source coupled to the second supply voltage input.

The load may be a coil, such as, for example, a coil of a solenoid or a stator coil of a motor.

The integrated circuit may be an application-specific integrated circuit (ASIC).

The apparatus may further comprise a controller (such as a microcontroller) in communication with the integrated circuit.

According to a third aspect of the present invention there is provided a motor vehicle comprising the integrated circuit of first aspect or the apparatus of the second aspect of the invention.

The motor vehicle may be a motorcycle, an automobile (sometimes referred to as a "car"), a minibus, a bus, a truck or lorry. The motor vehicle may be powered by an internal combustion engine and/or one or more electric motors.

Certain embodiments of the present invention will now be described, by way of example, with reference to <FIG> of the accompanying drawings, in which:.

Referring to <FIG>, a pre-driver integrated circuit (IC) <NUM> for driving an external, high-side discrete nMOS field-effect transistor <NUM> for switching a complex load <NUM> powered by a supply voltage VBAT from a battery <NUM> via a supply voltage node <NUM> is shown. The nMOS transistor <NUM> and load <NUM> are connected in series, via a source node <NUM>, interposed between the battery supply node <NUM> and ground GND.

The pre-driver IC <NUM> includes first and second power-supply pins <NUM>, <NUM> (or "inputs") for receiving a first, stabilized supply voltage V<NUM> from a first power supply <NUM> and a second, low-current supply voltage VCP from a second, low-current (or "weak") auxiliary power supply <NUM>, for example, in the form of a charge pump. The pre-driver integrated circuit <NUM> also includes an analogue ground pin <NUM> for connection to ground GND.

The pre-driver IC <NUM> includes one or more control input pins (not shown) for receiving one or more control signals (not shown) from a controller <NUM> (<FIG>) for example, in the form of a microcontroller or system-on-a-chip (SoC).

The pre-driver IC <NUM> includes a source level sensing pin <NUM> (or "source node input") for connection to the source node <NUM>.

The pre-driver IC <NUM> includes a gate drive pin <NUM> (or "gate drive output") for connection to the gate G of the nMOS transistor <NUM> for applying a gate voltage VG and a bootstrap capacitor charging pin <NUM> (or "bootstrap capacitor charging output") for applying a bootstrap capacitor voltage Vbs across a bootstrap capacitor <NUM>.

The bootstrap capacitor <NUM> is connected between the source node pin <NUM> and the bootstrap capacitor pin <NUM>. The bootstrap capacitor <NUM>, for example, may have a value of <NUM> nF.

The pre-driver IC <NUM> includes a pre-driver <NUM> (or "gate driver") which includes a control signal input <NUM> for receiving a driver ON/OFF signal, first and second voltage inputs <NUM>, <NUM>, and an output <NUM> which is coupled to the gate drive pin <NUM>. The pre-driver <NUM> comprises first and second switches <NUM>, <NUM>. The first switch <NUM> is used to control turn ON (i.e., gate charge) of the external FET <NUM>, while the second switch <NUM> is used to control turn OFF control (i.e., gate discharge). Both switches <NUM>, <NUM> may include a current limitation for slew rate control of the external FET <NUM>.

The pre-driver IC <NUM> includes a power supply control section <NUM> (herein also referred to as "supply management section") which includes first and second comparators <NUM>, <NUM> having respective outputs which control first and second supply control switches <NUM>, <NUM> respectively, first and second voltage sources <NUM>, <NUM> and a current source <NUM>.

The first power-supply pin <NUM> is connected to a first internal node <NUM>. The first voltage source <NUM> is connected between the first internal node <NUM> and the non-inverting input of the first comparator <NUM>. The first switch <NUM> is connected between the first internal node <NUM> and a second internal node <NUM> and the second switch <NUM> is connected between the second internal node <NUM> and a third internal node <NUM> which is connected to the bootstrap capacitor charging pin <NUM>. The third internal node <NUM> is connected directly to the inverting input of the first comparator <NUM>. The second voltage source <NUM> is connected between the non-inverting input of the second comparator <NUM> and a fourth internal node <NUM> between the second current input <NUM> and the source node pin <NUM>. The inverting input of the second comparator <NUM> is connected to ground. The current source <NUM> is connected between the second power-supply pin <NUM> and first voltage input <NUM> of the pre-driver <NUM>.

The charge pump <NUM> has a limited current capability, for example, of <NUM> mA. Moreover, charge pump <NUM> may need to supply n pre-drivers, where n ≥ <NUM> (e.g., n = <NUM>). Thus, an individual charge pump current supplied to the pre-driver <NUM> may be further limited, for example, to <NUM> mA/<NUM> = <NUM>µA). The individual charge pump current (e.g., <NUM>µA) represents the budget for the pre-driver <NUM> for all internal switch controls and also (static) gate control. Thus, the pre-driver current consumption is arranged so as not to exceed the individual charge pump current budget, in other words, iAmp1stat <! iCP_lim.

As will be explained in more detail hereinafter, the supply control section <NUM> selectively controls which power sources <NUM>, <NUM> are coupled to the bootstrap capacitor <NUM> and to the pre-driver <NUM>, especially when the source level VS is negative.

By splitting supply management into different phases, a clean pre-driver supply can be achieved without significant charging and discharging of the bootstrap capacitor <NUM>. As a result, ripple noise and overload at the stabilized source <NUM> can be avoided and, furthermore, the pre-driver supply voltage can be kept clean (i.e., ripple-free) for its intended function, i.e., gate control.

Referring also to <FIG>, integrated pre-driver supply control is split into four different operational phases.

During phase I, the first and second supply control switches <NUM>, <NUM> are ON (i.e., closed). Accordingly, the first voltage supply <NUM> supplies the first voltage V<NUM> to the pre-driver <NUM> and charges the bootstrap capacitor <NUM>. The second, current-limited voltage supply <NUM> (which has a current limit ICP_lim) has minimal effect.

During phase II, the load voltage Vload (which is equal to the source node level VS) rises to about VBAT. During the transition into the ON state, the bootstrap supply VBS exceeds the first voltage V<NUM> and so the first comparator <NUM> turns the first switch OFF (i.e., opens the first switch). Static current consumption of the pre-driver <NUM> is compensated by the current-limited voltage supply <NUM>. Meanwhile, the second switch <NUM> remains ON (i.e., remains closed).

During a negative transition, the supply control can operate in two sub-phases:
First, if VBS drops below the first voltage V<NUM>, then the first switch <NUM> turns ON, while the the second switch <NUM> remains ON. This sub-phase occurs in case the dynamic gate control had discharged the bootstrap capacitor <NUM>.

Secondly, if the load voltage Vload (which is equal to the source node level VS) becomes negative, then the first switch <NUM> remains ON and the second switch <NUM> quickly turns OFF. The second switch <NUM> is controlled by the second comparator <NUM> in response to detecting a negative load voltage. An offset Voff2 may apply. Thus, the bootstrap capacitor <NUM> will not charge up with a big transient current and the pre-driver <NUM> still operates with a positive supply at around V<NUM>.

When the load inductive energy is consumed, the load voltage recovers from negative level back to around oV. The second comparator <NUM> enables the second switch <NUM>, while the first switch <NUM> is still ON and phase I starts again.

Referring to Figure <NUM>, a motor vehicle <NUM> is shown.

The motor vehicle <NUM> includes the pre-driver IC <NUM>, the high-side switch <NUM> and load <NUM> interposed between the batter <NUM> and ground GND. The pre-driver IC <NUM> is controlled by a controller <NUM>.

Claim 1:
A monolithic integrated circuit (<NUM>) for controlling a high-side switching element (<NUM>) for a load (<NUM>) using a bootstrap capacitor (<NUM>), the integrated circuit comprising:
a first supply voltage input (<NUM>) for receiving a first input supply voltage (V<NUM>);
a second supply voltage input (<NUM>) for receiving a second, current-limited input supply voltage (VCP);
a voltage-sensing input (<NUM>) for receiving the source voltage of the switching element;
a first output (<NUM>) for providing a drive signal (VG) to the switching element (<NUM>);
a second output (<NUM>) for providing a charging signal (VBS) to the bootstrap capacitor (<NUM>);
a pre-driver (<NUM>) for generating the drive signal, the pre-driver having:
a voltage input (<NUM>); and
an output (<NUM>) which is coupled to the first output; and
a power supply control section (<NUM>) comprising:
first and second switches (<NUM>, <NUM>);
wherein the first and second switches (<NUM>, <NUM>) are arranged in series between the first input (<NUM>) and the second output (<NUM>), the second input (<NUM>) is coupled to a node (<NUM>) between the first and second switches (<NUM>), and the node (<NUM>) is coupled to the voltage input (<NUM>) of the pre-driver, and wherein the bootstrap capacitor (<NUM>) is coupled between the second output (<NUM>) and the voltage-sensing input (<NUM>);
wherein the first and second switches are selectively operable following switching of the switching element from an ON state to an OFF state: in response to a determination that the source voltage is below a predetermined level, to decouple the second output (<NUM>); and, thereafter, in response to determination that the source voltage is above the predetermined level, to couple the second output (<NUM>) to the first input (<NUM>).