Patent Description:
Electronic systems can include devices that require a regulated power source. Power converter circuits can be used to provide a regulated voltage to a load. A large step change in current at the load of a power converter circuit may cause the regulated output voltage to exceed the desired regulation range. This may negatively affect the operation of the load device.

<CIT>relates to a current mode DC/DC converter provided with a current mode control circuit, serving as a feedback circuit for stabilizing an output voltage supplied to a load resister, which detects a coil current flowing through a choke coil and control switching operation of a switching element according to a result of comparison between a detection signal of the coil current and an error signal from an error amplifier serving as a reference signal. The current mode control circuit is provided with a feed forward circuit which detects a variation in a load current Io flowing through a load resister and adds the variation to the detection signal of a coil current. Accordingly, a switching pulse, by which the coil current changes quickly in response to an abrupt change in the load current, can be fed to the switching element.

<CIT> relates to a linear regulator which includes a drive circuit having an input and an output, with the output configured to drive a control terminal of a power transistor for the delivery of a load current. An error amplifier functions to amplify a difference between a reference signal and a feedback signal to generate an error signal at the input of the drive circuit. A compensation circuit includes a series circuit formed by a compensation capacitor and a variable resistance circuit, where the series circuit is coupled to the input of the drive circuit. A current sensing circuit operates to sense the load current. The resistance of the variable resistance circuit is varied in response to the sensed load current.

Aspects of the invention are described in accordance with the appended set of claims.

Power converter circuits may be used to provide a regulated voltage output for an electronic system. Some power converter circuits are switching power converter circuits that convert the input voltage to the regulated output voltage. The regulated voltage conversion can provide a regulated output voltage that is higher than the input voltage of the regulator, lower than the input voltage, or inverted from the input voltage. The regulation is typically achieved by recurrently charging an inductor from an energy source and then discharging the energy of the inductor to drive a load. The charging and discharging can be accomplished using electronic switches that include transistors.

A challenge in control of power converters is to provide a regulated output voltage regardless of the change in the load current. When the load current has a step change with high slew rate and large amplitude, the output voltage might be out of the desired regulation range, which could negatively affect the operation of the load device. One possible solution is to increase the output capacitance. However, it is desired for most of applications to have minimized capacitance at the output for higher efficiency, and lower volume and cost. Another approach is to increase the bandwidth of the controller of the power converter circuit so that the output voltage is regulated in the desired range with minimized output capacitance.

Power converters can include an inductor. Energy is switched onto the inductor and energy of the inductor is used to provide the regulated voltage. Current-mode controlled power converters control the inductor current directly. This type of power converter can provide robustness against overcurrent failure of the switch transistor and relatively simple compensation can provide large phase and gain margins of the output voltage control loop. The devices and methods described herein include a control scheme that increases the bandwidth of the output voltage control loop by taking advantage of the control structure of the current-mode controlled power converters.

<FIG> are circuit diagrams of a switching power converter circuit <NUM> in an aspect. In <FIG> the circuit includes an inductor <NUM>, a diode <NUM>, and a switch circuit <NUM>. The inductor <NUM> receives input energy from the input circuit node <NUM> when the switch circuit <NUM> is activated. The circuit topology of the switching power converter circuit <NUM> is a buck converter with the switch circuit <NUM> arranged between the input circuit node <NUM> and the inductor <NUM>, the inductor coupled to the regulated circuit node <NUM>, and the diode coupled from the switch circuit to the circuit ground node. The buck converter regulates the voltage of the regulated circuit node to a voltage less than the value of the input voltage Vin.

<FIG> shows a control circuit <NUM> for the switching power converter circuit <NUM>. The control circuit <NUM> modulates activation of the switch circuit (e.g., using pulse width modulation or PWM) to regulate the voltage of the regulated circuit node <NUM>. In the example of <FIG>, the control circuit <NUM> implements a feedback control loop to regulate the voltage of the regulated circuit node. The control circuit <NUM> includes an error amplifier <NUM> that produces a current proportional to a difference between a reference voltage (Vref) and the voltage at the regulated circuit node (Vout). Depending on the value of Vref, the regulated voltage Vout may be scaled (e.g., scaled to a smaller voltage value) for the comparison to Vref. The output of the error amplifier <NUM> is provided to one input of a comparator <NUM> of the control circuit <NUM>.

The switching power converter circuit <NUM> includes an inductor current sensing circuit element <NUM> coupled in series with the inductor <NUM>. The inductor current sensing element may also be positioned in series with the switch circuit <NUM>, or in series with the diode <NUM>. In the example of <FIG>, the inductor current sensing circuit element <NUM> can be a resistive circuit element (e.g., resistor RSENSE) and the voltage across the resistive circuit element is provided to inputs of voltage amplifier <NUM> having amplifier gain AL. The output of the voltage amplifier <NUM> is provided to the other input of comparator <NUM>. The output of the comparator <NUM> is provided to a flip-flop circuit <NUM>. The flip-flop circuit <NUM> is coupled to the switch circuit <NUM> so that the output of comparator is used to modulate activation of the switch circuit <NUM>. Thus, the switching power converter circuit is controlled using the inductor current IL and the difference in Vout from Vref.

To increase the bandwidth of the controller circuit <NUM> to improve the transient response of the switching power converter circuit, the load current (ILOAD) is fed forward to the controller circuit. In this way, the input energy to the inductor can be adjusted immediately at the same rate that the load current is changing. Thus, the output voltage is regulated without significant deviation even when the slew rate of the load current is high.

The control circuit <NUM> includes a feedforward circuit <NUM> and the switching power converter circuit includes a load current sensing circuit element <NUM>. The feedforward circuit <NUM> adjusts the modulation of the switch circuit <NUM> according to sensed load current. The control circuit <NUM> includes a compensation circuit <NUM> coupled to a compensation circuit node Vc. The compensation circuit <NUM> provides filtering to the output of the error amplifier <NUM>. In the example of <FIG>, the compensation circuit <NUM> includes an RC circuit that is connected to the output of the feedforward circuit <NUM>. The feedforward circuit <NUM> adjusts the voltage at the compensation circuit, and therefore the input of the comparator <NUM>, to adjust the modulation of the switch circuit <NUM>. Thus, the changing of the inductor current in response to changes at the load is improved.

For example, the output voltage of the switching power converter circuit is kept constant when the average inductor current IL is equal to the average load current. If there is a step change in current at the load, it takes only <NUM> or <NUM> PWM cycles for the inductor current to follow the load current when the load current ILOAD is fed forward to the control circuit <NUM> as in <FIG>. The actual number of PWM cycles needed to respond depends on the input voltage Vin and the inductance L.

<FIG> are circuit diagrams of a switching power converter circuit <NUM>. As in the example of <FIG>, the switching power converter circuit is a buck converter. In the example of <FIG>, the load current sensing circuit element <NUM> is a resistive circuit element (e.g., resistor RIS). The voltage drop across the resistor is fed forward to the feedforward circuit <NUM>. The feedforward circuit <NUM> includes a voltage amplifier <NUM> with gain A<NUM> and a buffer circuit <NUM>. Ideally, the amount of current fed forward to the compensation circuit <NUM> is equal to the sensed load current ILOAD. In the example implementation of <FIG>, the feedforward circuit <NUM> applies a feedforward current IFF equal to <MAT>.

is a circuit diagram of a feedforward circuit <NUM>. The circuit is the same as the example of <FIG>, except that it includes a tuning circuit <NUM> to provide additional adjustment to the amount of feedforward applied. In the example of <FIG>, the tuning circuit <NUM> includes resistors RFF1 and RFF2 as a voltage divider. The feedforward current IFF is <MAT>.

The impedance of the feedforward circuit <NUM>, RFF1 and RFF2 contribute to the stability of the control circuit. In the example of <FIG>, only the impedance of the feedforward circuit <NUM> is present. If the impedance of the feedforward circuit <NUM> is sufficiently less than the impedance of the compensation circuit <NUM>, the stability of the control circuit is not degraded in the example of <FIG>.

<FIG> is a circuit diagram of portions of a switching power converter circuit <NUM> in an aspect. The switching power converter is a boost converter circuit. The load in the example of <FIG> is an amplifier <NUM> (e.g., a power amplifier) and the boost converter provides a regulated voltage to the amplifier. The supply connections to the amplifier <NUM> are the regulated circuit node and circuit ground. The boost converter regulates the voltage of the regulated circuit node to a voltage greater than the value of the input voltage Vin. The switch circuit <NUM> is arranged between the inductor <NUM> and the ground node, and the diode <NUM> is arranged between the inductor <NUM> and the regulated circuit node <NUM>. The switching power converter circuit <NUM> includes an inductor current sensing circuit element <NUM> and a load current sensing circuit element <NUM>. The control circuit (not shown) can include the feedforward circuit of either <FIG> or <FIG>.

Ideally, the amount of current fed forward to the compensation circuit is equal to <MAT> where α is the ratio (Vout/Vin). In the implementation of the feedforward circuit <NUM> of <FIG>, the feedforward current IFF for the boost converter is as shown in equation (<NUM>). For the feedforward circuit <NUM> of <FIG>, the feedforward current IFF is shown in equation (<NUM>).

<FIG> is a circuit diagram of portions of another switching power converter circuit <NUM> in another aspect. The switching power converter is a buck-boost converter circuit. The buck-boost converter regulates the voltage of the regulated circuit node to a voltage greater than or less than the value of the input voltage Vin and the output voltage may have negative polarity. The example in <FIG> is a single ended primary inductance converter (SEPIC). A first inductor <NUM> is arranged between the input circuit node and the switch circuit <NUM>. A second inductor <NUM> is arranged between and the diode <NUM> and the circuit ground node. The switch circuit is arranged between the first inductor <NUM> and the circuit ground node. The diode <NUM> is arranged between the second inductor <NUM> and the regulated circuit node <NUM>. The switching power converter circuit <NUM> includes inductor current sensing circuit element <NUM> and a load current sensing circuit element <NUM>. The control circuit (not shown) can include the feedforward circuit of either <FIG> or <FIG>.

<FIG> is a circuit diagram of a feedforward circuit <NUM> in another aspect. Instead of a voltage amplifier as in <FIG> and <FIG>, the feedforward circuit <NUM> of <FIG> includes a transconductance amplifier <NUM> having amplifier inputs coupled to the load current sensing circuit element (e.g., any of <NUM>, <NUM>, <NUM> of <FIG>, <FIG>), and an amplifier output operatively coupled to the compensation circuit <NUM> to adjust a voltage at the compensation circuit node Vc. The feedforward circuit <NUM> includes a feedforward resistor RFF. Because the amplifier of the feedforward circuit of <FIG> is a current-type amplifier, the feedforward circuit <NUM> does not affect the impedance of the compensation circuit <NUM>.

The feedforward current IFF applied to the compensation circuit <NUM> by the feedforward circuit <NUM> is <MAT> where gI is the transconductance of the transconductance amplifier <NUM>.

It can be seen from equation (<NUM>) that the resistor RFF is used to tune the amount of feedforward current provided to the compensation circuit <NUM>. The feedforward circuit <NUM> gives more flexibility over the example of <FIG> because the feedforward amount can be either increased or decreased by adjusting RFF while the feedforward circuit <NUM> of <FIG> can only decrease the feedforward amount.

However, for a buck-boost converter, the input voltage may typically vary widely, and it may not be practical to tune the IFF by changing RFF. In cases where the input Vin to a buck-boost converter varies widely, it may be more practical to fix the amount of feedforward current provided to the compensation circuit. It should be noted that the load current feedforward can be applied to other current-mode controlled converters, such as an inverting buck-boost converter, a Cúk converter, a four-switch buck-boost converter circuit, or a flyback converter if the amount of feedforward current is set appropriately.

Returning to <FIG>, in some aspects the load current sensing circuit element <NUM> is a magnetic current sensor. Some examples of a magnetic current sensor are a current transducer (or Hall Effect sensor) and an anisotropic magnetoResistive (AMR) sensor. Whether a voltage type feedforward circuit or a current type feedforward circuit is used for a magnetic current sensor depends on whether the output of the sensor is a voltage or a current.

<FIG> is a circuit diagram of portions of a switching power converter circuit <NUM> in another aspect. The circuit topology is a buck converter circuit as in <FIG>, but the load current sensing circuit element is a current transducer <NUM>. Because the output of the current transducer in the example is a current source, the feedforward circuit <NUM> is a current type feedforward circuit that includes a feedforward resistor RFF coupled to the compensation circuit <NUM>. The feedforward current IFF applied to the compensation circuit <NUM> by the feedforward circuit <NUM> is <MAT> where n is the turns ratio (e.g., a <NUM>:n turns ratio where n is the number of turns on the feedforward circuit side of the sensor and <NUM> is for the power converter circuit side).

Similar to the current transducer, for an AMR sensor either a voltage-type feedforward circuit or a current-type feedforward circuit can be selected depending on the output type of the AMR sensor. A discrete magnetic sensor product may include additional circuits (e.g., amplifiers, etc.) integrated with the magnetic sensor to convert the measured current to either a current source or a voltage source. The feedforward schemes described herein may be easily implemented even when the feedforward circuit is not integrated with the power converter circuit.

For completeness, <FIG> is a flow diagram of an example of a method <NUM> operating a switching power converter circuit, such as any of the switching power converter circuits described herein. At <NUM>, an inductor is charged using energy provided at an input circuit node of the power converter circuit.

At <NUM>, the charging of the inductor is modulated to regulate a voltage of a regulated circuit node of the power converter circuit using a control circuit loop coupled to the regulated circuit node. In some aspects, PWM is used to modulate the charging of the inductor. The pulse width of an activation signal applied to the switch is modulated according to the inductor current and according to a voltage proportional to the difference between the voltage of the regulated circuit node and a target voltage.

At <NUM>, the control loop is filtered using a compensation circuit coupled to a compensation node of the power converter circuit. An example of the compensation circuit is a series connected resistor-capacitor (RC) circuit coupled to the output of an error amplifier used to monitor the voltage difference between the regulated circuit node and the target voltage.

At <NUM>, the load current of the switching power converter is sensed. The load current is provided to an out circuit node of the switching power supply circuit that may be operatively coupled to a load circuit. At <NUM>, the modulating of the charging of the inductor is adjusted by adjusting a voltage of the compensation circuit node according to sensed load current. Because the compensation circuit node is located at the output of the error amplifier, adjusting the voltage of the compensation node adjusts the charging of the inductor. Tuning of the voltage or current applied to the compensation node can be used to further adjust the voltage at the compensation node.

In some aspects, the switching power converted is a buck converter and the charging of the inductor is modulated to generate a regulated voltage at the regulated circuit node that is less than an input voltage at the input circuit node. The voltage of the compensation can be adjusted by applying a current proportional to the load current, as in any of equations (<NUM>) through (<NUM>) for example, to the compensation circuit node.

In some aspects, the switching power converter circuit is a boost converter and the charging of the inductor is modulated to generate a regulated voltage at the regulated circuit node that is greater than an input voltage at the input circuit node. The voltage of the compensation circuit node can be adjusted by applying a current proportional to the load current to the compensation circuit node.

In some aspects, the switching power converter circuit is a buck-boost converter and the charging of the inductor is modulated to generate a regulated voltage at the regulated circuit node that is greater than or less than an input voltage at the input circuit node. The voltage of the compensation circuit node can be adjusted by applying a current proportional to the load current to the compensation circuit node.

The several examples of systems, devices, and method described can be used to provide a regulated voltage as an electrical circuit supply for an electronic system. The regulated circuit supply is provided with improved transient response to large changes in load current.

Claim 1:
A switching power converter circuit (<NUM>) comprising:
an inductor (<NUM>) arranged to receive input energy from an input circuit node (<NUM>);
a switch circuit (<NUM>) coupled to the inductor (<NUM>);
an inductor current sensing circuit element (<NUM>) for sensing the inductor current (IL) of the inductor (<NUM>);
a load current sensing circuit element (<NUM>) for sensing a load current (ILOAD), the load current sensing circuit element (<NUM>) being coupled to a regulated circuit node (<NUM>) and an output circuit node (<NUM>);
a feedforward circuit (<NUM>) configured to apply a feedforward current (IFF) to a compensation circuit (<NUM>), wherein the feedforward circuit (<NUM>) comprises a transconductance amplifier (<NUM>) having amplifier inputs coupled to the load current sensing circuit element, and an amplifier output operatively coupled to the compensation circuit (<NUM>) and a first terminal of a feedforward resistor (RFF);
the compensation circuit (<NUM>) coupled to a compensation circuit node (Vc) and configured to filter a control loop voltage at the compensation circuit node (Vc), wherein the control loop voltage corresponds to a voltage difference between a reference voltage (VREF) and a voltage at the regulated circuit node (<NUM>);
a circuit (<NUM>, <NUM>, <NUM>) coupled to the inductor current sensing circuit element (<NUM>), the compensation circuit node (VC), and the switch (<NUM>), wherein the circuit (<NUM>, <NUM>, <NUM>) is configured to modulate activation of the switch circuit (<NUM>) using the sensed inductor current (IL) and the control loop voltage (Vc), thereby regulating the voltage at the regulated circuit node (<NUM>);
wherein the feedforward circuit (<NUM>) is configured to apply the feedforward current (IFF) to the compensation circuit (<NUM>) to adjust the control loop voltage at the compensation circuit node (VC) thereby adjusting modulation of the switch circuit (<NUM>) according to the sensed load current of the load current sensing circuit element (<NUM>),
wherein the feedforward resistor (RFF) is configured to tune the amount of the feedforward current provided to the compensation circuit (<NUM>).