Patent Description:
The invention defines a pyro-fuse control circuit according to claim <NUM> and a method for controlling a pyro-fuse according to claim <NUM>.

In this description, the term "couple" or "couples" means either an indirect or direct wired or wireless connection. Thus, if a first device couples to a second device, that connection may be through a direct connection or through an indirect connection via other devices and connections. Also, in this description, the recitation "based on" means "based at least in part on. " Therefore, if X is based on Y, then X may be a function of Y and any number of other factors.

A pyro-fuse is also known as pyrotechnic fuse, a pyroswitch, a pyrotechnic switch, etc. A pyro-fuse is a device that is disposed along a conductor, and includes an electrically activated pyrotechnic charge. Activation of the pyrotechnic charge drives a piston, which includes a nonconductive severing member, such as a plastic or ceramic blade, though the conductor, thereby separating the conductor and creating an open circuit in the conductor. While the pyro-fuse should be activated quickly in the event of possible overcurrent event, or an event that could produce a short circuit, when used in a vehicle, activation of the pyro-fuse responsive to an erroneous indication of an overcurrent event effectively disables the vehicle, which is undesirable if the vehicle is in use.

The pyro-fuse circuits described herein include all analog implementations that trigger activation of a pyro-fuse without the delays introduced by use of software-based systems to detect a pyro-fuse triggering condition and activate the pyro-fuse. Implementations of the pyro-fuse control systems also include diagnostic circuitry to verify that overcurrent detection is not caused by an open circuit in current sensing circuitry. The diagnostic circuitry allows a pyro-fuse control circuit to trigger a pyro-fuse only if an overcurrent condition is detected, and the diagnostic circuitry indicates that no open circuits are present in connection of the current measurement circuitry to a shunt resistor. Thus, the pyro-fuse circuits described herein reduce or avoid activation of the pyro-fuse based on false overcurrent detections.

<FIG> shows a schematic diagram of a first example of a pyro-fuse circuit <NUM> in accordance with example embodiments. The pyro-fuse circuit <NUM> includes a pyro-fuse control circuit <NUM>, a conductor <NUM>, a shunt resistor <NUM>, and a pyro-fuse <NUM>. The conductor <NUM> transmits electrical energy from an energy source, such as one or more batteries of a vehicle, to a load circuit, such as the electrical systems of a vehicle. The shunt resistor <NUM> is a current sensing resistor that is connected in series with conductor <NUM>, and used, by the pyro-fuse control circuit <NUM>, to measure the current flowing in the conductor <NUM> by measuring the voltage dropped across the shunt resistor <NUM>. The pyro-fuse <NUM> is coupled to the conductor <NUM>, and includes a piston driven cutting element <NUM> for severing the conductor <NUM> and an ignition control circuit <NUM> that activates a pyrotechnic charge to engage the piston driven cutting element <NUM> responsive to receipt of a triggering signal <NUM> provided by the pyro-fuse control circuit <NUM>.

The pyro-fuse control circuit <NUM> triggers activation of the pyro-fuse <NUM> responsive to excessive current flow in the conductor <NUM>. For example, if the current flow in the conductor <NUM> is indicative of a short circuit of the conductor <NUM> to ground, then the pyro-fuse control circuit <NUM> triggers activation of the pyro-fuse <NUM> to sever the conductor <NUM> and isolate the power source from the load circuit. The pyro-fuse control circuit <NUM> includes a current sensing circuit <NUM> and a diagnostic circuit <NUM> that is coupled to the current sensing circuit <NUM>. The current sensing circuit <NUM> measures the current flowing in the conductor <NUM> via the shunt resistor <NUM>, and determines whether the current flowing in the conductor <NUM> exceeds a threshold. The diagnostic circuit <NUM> assesses the validity of the measurement performed by the current sensing circuit <NUM> by testing the paths of current flow to the current sensing circuit <NUM>. Accordingly, the diagnostic circuit <NUM> determines whether an indication of current exceeding the threshold current generated by the current sensing circuit <NUM> is caused by current flowing in the conductor (<NUM>), or by a fault in the current sensing circuit <NUM>.

The current sensing circuit <NUM> includes an isolation amplifier <NUM> and a comparator <NUM>. The circuitry of the pyro-fuse control circuit <NUM> operates across two power domains (i.e., the power domain <NUM> and the power domain <NUM>), which may be referenced to different ground potentials. The isolation amplifier <NUM> measures voltage across the shunt resistor <NUM>, and communicates the voltage across the shunt resistor <NUM> from the power domain <NUM> to the power domain <NUM>. The isolation amplifier <NUM> includes an input section <NUM> (i.e., input circuits) that is disposed in the power domain <NUM> and an output section <NUM> (i.e., output circuits) that is disposed in the power domain <NUM>. For example, the isolation amplifier <NUM> is an AMC1301 reinforced isolated amplifier produced by Texas Instruments Incorporated, or other suitable isolation amplifier. The isolation amplifier <NUM> includes an input terminal <NUM> that is coupled to the shunt resistor <NUM> and an input terminal <NUM> that is coupled to the shunt resistor <NUM>. An output signal <NUM> generated by the isolation amplifier <NUM> is provided to the comparator <NUM>.

The comparator <NUM> is coupled to the isolation amplifier <NUM> in the power domain <NUM>, and compares the output signal <NUM> received from the isolation amplifier <NUM> to a threshold voltage <NUM>. The threshold voltage <NUM> is representative of a threshold current that corresponds to excessive current flowing in the conductor <NUM>. If the voltage of the output signal <NUM> exceeds the threshold voltage <NUM>, then the comparator <NUM> generates an output signal <NUM> that indicates excessive current is flowing in the conductor <NUM>.

The pyro-fuse <NUM> may be triggered by on an indication of excessive current flowing in the conductor <NUM>. However, if such an indication is erroneous, then triggering the pyro-fuse <NUM>, which will disable a vehicle, is undesirable. The measurement of current flowing in the conductor <NUM> will be in error if an electrical connection between the isolation amplifier <NUM> and the conductor <NUM> is faulty. The diagnostic circuit <NUM> verifies the electrical connections between the conductor <NUM> and the isolation amplifier <NUM> to enable triggering of the pyro-fuse <NUM> when the current sensing circuit <NUM> generates an indication of excessive current flow in the conductor <NUM>.

The diagnostic circuit <NUM> includes an isolator <NUM>, a switch <NUM>, an isolation amplifier <NUM>, and a comparator <NUM>. The isolator <NUM> is coupled to the comparator <NUM>, and includes input circuitry <NUM> that is disposed in the power domain <NUM> and output circuitry <NUM> that is disposed in the power domain <NUM>. The isolator <NUM> communicates the output signal <NUM> generated by the comparator <NUM> from the power domain <NUM> to the power domain <NUM>. In some implementations of the pyro-fuse control circuit <NUM>, the isolator <NUM> is implemented using an ISO7710 by Texas Instruments Incorporated, or other suitable isolator circuit.

The isolator <NUM> is coupled to the switch <NUM> (i.e., to a control input of the switch <NUM>). The switch <NUM> is implemented using an N-channel metal oxide semiconductor field effect transistor (MOSFET) in some implementations of the pyro-fuse control circuit <NUM>. The output signal <NUM> is propagated through the isolator <NUM> and closes the switch <NUM> to allow current to flow through the switch <NUM> to the input terminal <NUM> of the isolation amplifier <NUM>, through the shunt resistor <NUM> to the input terminal <NUM> of the isolation amplifier <NUM>, and through the resistor <NUM> to the ground in the power domain <NUM>. The current flowing through the switch <NUM> is set by the resistor <NUM>. The isolation amplifier <NUM> is coupled to the input terminal <NUM> of the isolation amplifier <NUM>. The isolation amplifier <NUM> measures the voltage dropped across the resistor <NUM> as a measure of the current flowing in the input terminal <NUM>, the shunt resistor <NUM>, and the input terminal <NUM> by way of the switch <NUM>. The isolation amplifier <NUM> communicates the voltage across the resistor <NUM> from the power domain <NUM> to the power domain <NUM>. The isolation amplifier <NUM> includes an input section <NUM> (i.e., input circuits) that is disposed in the power domain <NUM> and an output section <NUM> (i.e., output circuits) that is disposed in the power domain <NUM>. For example, the isolation amplifier <NUM> is an AMC1311 reinforced isolated amplifier produced by Texas Instruments Incorporated, or other suitable isolation amplifier. An output signal <NUM> generated by the isolation amplifier <NUM> is provided to the comparator <NUM>.

The comparator <NUM> is coupled to the isolation amplifier <NUM> in the power domain <NUM>, and the compares the output signal <NUM> received from the isolation amplifier <NUM> to a threshold voltage <NUM>. The threshold voltage <NUM> is representative of current flow in the input terminal <NUM> of the isolation amplifier <NUM> that indicates intact electrical connections between the isolation amplifier <NUM> and the conductor <NUM>. If the voltage of the output signal <NUM> exceeds the threshold voltage <NUM>, then the comparator <NUM> generates an output signal <NUM> that indicates electrical connection of the isolation amplifier <NUM> to the conductor <NUM>.

The pyro-fuse control circuit <NUM> includes control circuity <NUM> that triggers the pyro-fuse <NUM> based on the output signal <NUM> generated by the comparator <NUM> and the output signal <NUM> generated by the comparator <NUM>. In the pyro-fuse control circuit <NUM>, the control circuity <NUM> includes a logic gate (i.e., an AND gate) <NUM> that generates a triggering signal <NUM> to trigger activation of the pyro-fuse <NUM> if the output signal <NUM> indicates that excessive current is flowing in the conductor <NUM> and the output signal <NUM> indicates that the isolation amplifier <NUM> is electrically connected to the conductor <NUM>. The logic gate <NUM> is coupled to the pyro-fuse <NUM>.

Some implementations of pyro-fuse control circuit <NUM> provide the output signal <NUM> and the output signal <NUM> to circuits external to the pyro-fuse control circuit <NUM> for use in evaluating the status of the pyro-fuse circuit <NUM>. Some implementations of the pyro-fuse control circuit <NUM> include a logic gate (i.e., an OR gate) <NUM> that asserts an output signal <NUM> if either of the output signal <NUM> or the output signal <NUM> is a logic one. Thus, the output signal <NUM> is a fault indicator signifying that excessive current has been detected or a fault in the pyro-fuse circuit <NUM> has been detected. For example, if the output signal <NUM> is active and the output signal <NUM> and the output signal <NUM> are active, then excessive current flow in the conductor <NUM> has been detected. If the output signal <NUM> is active, the output signal <NUM> is active, and the output signal <NUM> is inactive, then there is a fault in the electrical connection of the isolation amplifier <NUM> to the conductor <NUM> that should be corrected.

The pyro-fuse control circuit <NUM> also includes a power supply <NUM> that generates power supply voltages for use by the control circuity <NUM> of the isolator <NUM>, the input section <NUM> of the isolation amplifier <NUM>, and the input section <NUM> of the isolation amplifier <NUM>. Power signals are transmitted from the power domain <NUM> to the power domain <NUM> via a transformer <NUM>.

The pyro-circuit <NUM> provides a dedicated hardware pyro-fuse control circuit implementation that avoids software related issues, such as execution latency that delays triggering of the pyro-fuse <NUM>, and software execution errors.

<FIG> shows a schematic diagram of a second example of a pyro-fuse circuit <NUM> in accordance with example embodiments. The pyro-fuse circuit <NUM> includes a pyro-fuse control circuit <NUM>, a conductor <NUM>, a shunt resistor <NUM>, a pyro-fuse <NUM>, and processor <NUM>. The conductor <NUM> transmits electrical energy from an energy source, such as one or more batteries of a vehicle, to a load circuit, such as the electrical systems of a vehicle. The shunt resistor <NUM> is a resistor used, by the pyro-fuse control circuit <NUM>, to measure the current flowing in the conductor <NUM> by measuring the voltage dropped across the shunt resistor <NUM>. The pyro-fuse <NUM> includes a piston driven cutting element <NUM> for severing the conductor <NUM> and an ignition control circuit <NUM> that activates a pyrotechnic charge to engage the <NUM> responsive to receipt of a triggering signal <NUM> provided by the pyro-fuse control circuit <NUM>.

The pyro-fuse control circuit <NUM> triggers activation of the pyro-fuse <NUM> responsive to excessive current flow in the conductor <NUM>. For example, if the current flow in the conductor <NUM> is indicative of a short circuit of the conductor <NUM> to ground, then the pyro-fuse control circuit <NUM> triggers activation of the pyro-fuse <NUM> to isolate the power source from the load circuit. The pyro-fuse control circuit <NUM> includes a current sensing circuit <NUM> and a diagnostic circuit <NUM>. The current sensing circuit <NUM> measures the current flowing in the conductor <NUM> via the shunt resistor <NUM>. The diagnostic circuit <NUM> assesses the validity of the measurement performed by the current sensing circuit <NUM> by testing the paths of current flow to the current sensing circuit <NUM>.

The current sensing circuit <NUM> includes an isolation amplifier <NUM> and a comparator <NUM>. The circuitry of the pyro-fuse control circuit <NUM> operates across two power domains (i.e., the power domain <NUM> and the power domain <NUM>) that are, for example, referenced to different ground potentials. The isolation amplifier <NUM> communicates the voltage across the shunt resistor <NUM> from the power domain <NUM> to the power domain <NUM>. The isolation amplifier <NUM> includes an input section <NUM> that is disposed in the power domain <NUM> and an output section <NUM> that is disposed in the power domain <NUM>. For example, the isolation amplifier <NUM> is an AMC1301 reinforced isolated amplifier produced by Texas Instruments Incorporated, or other suitable isolation amplifier. The isolation amplifier <NUM> includes an input terminal <NUM> that is coupled to the shunt resistor <NUM> and an input terminal <NUM> that is coupled to the shunt resistor <NUM>. An output signal <NUM> generated by the isolation amplifier <NUM> is provided to the comparator <NUM>.

The comparator <NUM> is coupled to the isolation amplifier <NUM>, and compares the output signal <NUM> received from the isolation amplifier <NUM> to a threshold voltage <NUM>. The threshold voltage <NUM> is representative of a threshold current that corresponds to excessive current flowing in the conductor <NUM>. If the voltage of the output signal <NUM> exceeds the threshold voltage <NUM>, then the comparator <NUM> generates an output signal <NUM> that indicates excessive current is flowing in the conductor <NUM>.

The output signal <NUM> is provided to the processor <NUM>. The processor <NUM> may be a microcontroller, a general-purpose microprocessor, or other device that executes instructions retrieved from a computer-readable medium to provide logical, arithmetic, and/or data transfer functionality. In various implementations of the pyro-fuse circuit <NUM>, the processor <NUM> may be included in the pyro-fuse control circuit <NUM>, or provided external to the pyro-fuse control circuit <NUM>.

The processor <NUM> is coupled to the pyro-fuse <NUM>, and may trigger the pyro-fuse <NUM> based on an indication of excessive current flowing in the conductor <NUM>. However, if such an indication is erroneous, then triggering the pyro-fuse <NUM>, which will disable a vehicle, is undesirable. The measurement of current flowing in the conductor <NUM> will be in error if an electrical connection between the isolation amplifier <NUM> and the conductor <NUM> is faulty. The diagnostic circuit <NUM> verifies the electrical connections between the conductor <NUM> and the isolation amplifier <NUM> to enable triggering of the pyro-fuse <NUM> when the current sensing circuit <NUM> generates an indication of excessive current flow in the conductor <NUM>.

The diagnostic circuit <NUM> includes an isolator <NUM>, a switch <NUM>, an isolation amplifier <NUM>, and a comparator <NUM>. The isolator <NUM> is coupled to the processor <NUM>, and includes input circuitry <NUM> that is disposed in the power domain <NUM> and output circuitry <NUM> that is disposed in the power domain <NUM>. When the processor <NUM> receives the output signal <NUM>, the processor <NUM> activates the signal <NUM> to initiate diagnostic testing of the electrical connections between the isolation amplifier <NUM> and the conductor <NUM>. The isolator <NUM> communicates the signal <NUM> generated by the processor <NUM> from the power domain <NUM> to the power domain <NUM>. In some implementations of the pyro-fuse control circuit <NUM>, the isolator <NUM> is implemented using an ISO7710 by Texas Instruments Incorporated, or other suitable isolator circuit.

The isolator <NUM> is coupled to the switch <NUM> in the power domain <NUM>. The switch <NUM> is implemented using an N-channel MOSFET in some implementations of the pyro-fuse control circuit <NUM>. The signal <NUM> propagates through the isolator <NUM> and closes the switch <NUM> to allow current to flow through the switch <NUM> to the input terminal <NUM> of the isolation amplifier <NUM>, through the shunt resistor <NUM> to the input terminal <NUM> of the isolation amplifier <NUM>, and through the resistor <NUM> to the ground in the power domain <NUM>. The current flowing through the switch <NUM> is set by the resistor <NUM>. The isolation amplifier <NUM> is coupled to the input terminal <NUM> of the isolation amplifier <NUM>. The isolation amplifier <NUM> measures the voltage dropped across the resistor <NUM> as a measure of the current flowing in the input terminal <NUM>, the shunt resistor <NUM>, and the input terminal <NUM> by way of the switch <NUM>. The isolation amplifier <NUM> communicates the voltage across the resistor <NUM> from the power domain <NUM> to the power domain <NUM>. The isolation amplifier <NUM> includes an input section <NUM> that is disposed in the power domain <NUM> and an output section <NUM> that is disposed in the power domain <NUM>. For example, the isolation amplifier <NUM> is an AMC1311 reinforced isolated amplifier produced by Texas Instruments Incorporated, or other suitable isolation amplifier. An output signal <NUM> generated by the isolation amplifier <NUM> is provided to the comparator <NUM>.

The comparator <NUM> is coupled to the isolation amplifier <NUM>, and compares the output signal <NUM> received from the isolation amplifier <NUM> to a threshold voltage <NUM>. The threshold voltage <NUM> is representative of a current flow in the input terminal <NUM> of the isolation amplifier <NUM> that indicates intact electrical connections between the isolation amplifier <NUM> and the conductor <NUM>. If the voltage of the output signal <NUM> exceeds the threshold voltage <NUM>, then the comparator <NUM> generates an output signal <NUM> that indicates electrical connection of the isolation amplifier <NUM> to the conductor <NUM>. The comparator <NUM> is coupled to the processor <NUM>, and the output signal <NUM> is provided to the processor <NUM>.

In the pyro-fuse control circuit <NUM>, the functionality of the control circuity <NUM> of the pyro-fuse control circuit <NUM> is provided by the processor <NUM>. The processor <NUM> triggers the pyro-fuse <NUM> based on the output signal <NUM> generated by the comparator <NUM> and the output signal <NUM> generated by the comparator <NUM>. The processor <NUM> is coupled to the pyro-fuse <NUM>, and generates a signal <NUM> to trigger activation of the pyro-fuse <NUM> if the output signal <NUM> indicates that excessive current is flowing in the conductor <NUM> and the output signal <NUM> indicates that the isolation amplifier <NUM> is electrically connected to the conductor <NUM>.

The processor <NUM> monitors the output signal <NUM> and the output signal <NUM> to evaluate the status of the pyro-fuse circuit <NUM>. For example, if the output signal <NUM> and the output signal <NUM> are active, then excessive current flow in the conductor <NUM> has been detected. If the output signal <NUM> is active, and the output signal <NUM> is inactive, then there is a fault in the electrical connection of the isolation amplifier <NUM> to the conductor <NUM> that should be corrected.

The pyro-fuse control circuit <NUM> also includes a power supply <NUM> that generates power supply voltages for use by the output circuity <NUM> of the isolator <NUM>, the input section <NUM> of the isolation amplifier <NUM>, and the input section <NUM> of the isolation amplifier <NUM>. Power signals are transmitted from the power domain <NUM> to the power domain <NUM> via a transformer <NUM>.

<FIG> shows a flow diagram for a method <NUM> for controlling a pyro-fuse <NUM> in accordance with example embodiments. Though depicted sequentially as a matter of convenience, at least some of the actions shown can be performed in a different order and/or performed in parallel. Also, some implementations may perform only some of the actions shown.

In block <NUM>, current is flowing in the conductor <NUM> and the current sensing circuit <NUM> is measuring the current flow in the conductor <NUM> via the voltage drop across the shunt resistor <NUM>.

The comparator <NUM> is comparing the output signal <NUM> of the isolation amplifier <NUM> to a threshold voltage <NUM> that is representative of threshold current indicative of excessive current flow in the conductor <NUM>. If, in block <NUM>, the current flowing in the conductor <NUM> exceeds the threshold current, as shown by the output signal <NUM> exceeding the threshold voltage <NUM>, then, the diagnostic circuit <NUM> is activated to test the electrical connection of the isolation amplifier <NUM> to the conductor <NUM>.

To test the electrical connection of the isolation amplifier <NUM> to the conductor <NUM>, in block <NUM>, the switch <NUM> is closed to switch a current onto the input terminal <NUM> of the isolation amplifier <NUM>. Closing of the switch <NUM> is controlled by the processor <NUM> or the comparator <NUM>, via the isolator <NUM>, in various implementations. If the input terminal <NUM> and the input terminal <NUM> of the isolation amplifier <NUM> are electrically connected to the conductor <NUM>, then the current enabled by closing the switch <NUM> flows through the shunt resistor <NUM> to the input terminal <NUM>, and through the resistor <NUM>.

In block <NUM>, the diagnostic circuit <NUM> measures the current flowing in the input terminal <NUM> via the voltage drop across the resistor <NUM>.

The comparator <NUM> is comparing the output signal <NUM> of the isolation amplifier <NUM> to a threshold voltage <NUM> that is representative of threshold current indicative of an electrical connection of the input terminal <NUM> and the input terminal <NUM> to the conductor <NUM>. If, in block <NUM>, the current flowing in the input terminal <NUM> exceeds the threshold current, as shown by the output signal <NUM> exceeding the threshold voltage <NUM>, then, in block <NUM>, activation of the pyro-fuse <NUM> is triggered. Triggering of the pyro-fuse <NUM> is controlled by the processor <NUM> or the logic gate <NUM> in various implementations.

If, in block <NUM>, the current flowing in the input terminal <NUM> of the isolation amplifier <NUM> does not exceed the threshold current, then the detection of excess current flowing in the conductor <NUM> of block <NUM> may be due an open circuit fault (i.e., an open circuit in the electrical connection between the isolation amplifier <NUM> and the conductor <NUM>) and the triggering of the pyro-fuse <NUM> is inhibited by the logic gate <NUM> or the processor <NUM>. A fault indication may be generated responsive to the comparison of block <NUM> and/or the comparison block <NUM> indicating that a threshold has been exceeded.

Claim 1:
A pyro-fuse control circuit (<NUM>), comprising:
a current sensing circuit (<NUM>) configured to determine whether the current flowing in a conductor (<NUM>) exceeds a threshold current; and
a diagnostic circuit (<NUM>) coupled to the current sensing circuit (<NUM>), and configured to determine whether an indication of current exceeding the threshold current generated by the current sensing circuit (<NUM>) is caused by current flowing in the conductor (<NUM>) and is not caused by a fault in the current sensing circuit (<NUM>),
characterized in that
the current sensing circuit (<NUM>) comprises a first isolation amplifier configured to measure a voltage across a shunt resistor disposed in the conductor (<NUM>);
wherein the current sensing circuit (<NUM>) comprises a first comparator coupled to an output of the first isolation amplifier, the first comparator configured to compare an output voltage of the first isolation amplifier to a threshold voltage representative of the threshold current;
wherein the diagnostic circuit (<NUM>) comprises:
a switch coupled to a first input terminal of the first isolation amplifier; and
a second isolation amplifier coupled to a second input terminal of the first isolation amplifier, the second isolation amplifier configured to detect current flow from the switch through the second input terminal of the first isolation amplifier;
a second comparator coupled to an output of the second isolation amplifier, the comparator configured to compare an output voltage of the second isolation amplifier to a threshold voltage representative of a predetermined current flowing in the second input terminal of the first isolation amplifier;
further comprising control circuitry configured to trigger a pyro-fuse based on the output of the first comparator indicating that current exceeds the threshold current and the output of the second comparator indicating that current flowing in the second terminal of the first isolation amplifier exceeds the predetermined current.