Systems for controlling a slew rate of a switch

Systems and methods are described herein for controlling a switch. In some embodiments, circuitry may detect a voltage across the switch. A current reference signal may be generated based on the voltage across the switch. The switch may be controlled based, at least in part, on the current reference signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional of U.S. Provisional Application Ser. No. 62/608,000, entitled “TURN-ON SLEW-RATE CONTROL SWITCH WITH SMART DYNAMIC CURRENT TECHNIQUE”, filed Dec. 20, 2017, which is incorporated herein by reference in its entirety.

BACKGROUND

Electronic systems, such as mobile devices, for example, are powered by a power source which may be a battery, a wired power source, or a wireless power source. A power switch electrically connected between the electronic system and the power source controls the supply of power to the electronic system.

BRIEF SUMMARY

According to some embodiments, an apparatus for controlling a switch is provided. The apparatus comprises circuitry configured to: 1) detect a voltage across the switch; 2) generate a current reference signal based on the voltage across the switch; and 3) control the switch based, at least in part, on the current reference signal.

In some embodiments, the circuitry is further configured to, in response to a reduction in amplitude of the voltage across the switch, increase the amplitude of the current reference signal.

In some embodiments, the circuitry is further configured to receive a feedback current signal representing a current level in the switch. In some embodiments, the circuitry is further configured to control the switch based on the current reference signal and the feedback current signal.

In some embodiments, controlling the switch based, at least in part, on the current reference signal comprises determining, based on the current reference signal, a maximum input to be provided to an input of the switch to limit a current level in the switch.

In some embodiments, the circuitry is further configured to generate a difference signal proportional to the voltage across the switch. In some embodiments, the difference signal is a current signal that is limited by a peak current signal. In further embodiments, the circuitry is further configured to generate the peak current signal.

In some embodiments, the circuitry is further configured to add a minimum current reference signal to the current reference signal.

In some embodiments, the circuitry is further configured to apply a gain to the current reference signal.

According to some embodiments, an method for controlling a switch is provided. The method comprises: 1) detecting a voltage across the switch; 2) generating a current reference signal based on the voltage across the switch; and 3) controlling the switch based, at least in part, on the current reference signal.

In some embodiments, the method further comprises, in response to a reduction in amplitude of the voltage across the switch, increasing the amplitude of the current reference signal. In some embodiments, the method further comprises receiving a feedback current signal representing a current level in the switch.

In some embodiments, the method further comprises controlling the switch based on the current reference signal and the feedback current signal.

In some embodiments, controlling the switch based, at least in part, on the current reference signal comprises determining, based on the current reference signal, a maximum input to be provided to an input of the switch to limit a current level in the switch.

In some embodiments, the method further comprises generating a difference signal proportional to the voltage across the switch. In some embodiments, the difference signal is a current signal that is limited by a peak current signal. In some embodiments, the method further comprises generating the peak current signal.

In some embodiments, the method further comprises adding a minimum current reference signal to the current reference signal and/or applying a gain to the current reference signal.

According to some embodiments, an apparatus for controlling a switch is provided. The apparatus comprises: device circuitry connected to the switch, the device circuitry being configured to receive electrical power through the switch from a power source; and switch control circuitry connected to the switch and configured to: 1) detect a voltage across the switch; 2) generate a current reference signal based on the voltage across the switch; and 3) control the switch based, at least in part, on the current reference signal.

The foregoing summary is provided by way of illustration and is not intended to be limiting.

DETAILED DESCRIPTION

Described herein are systems and methods for controlling an electrical switch, such as a power switch between a power source and an electronic system. In some embodiments, circuitry may be configured to detect a voltage across the switch. Based on the voltage across the switch, the circuitry may generate a current reference signal. In some embodiments, the current reference signal may be used to limit the amount of current through the switch. The circuitry may control the switch based, at least in part, on the current reference signal, for example by controlling an electrical input to the switch. Such systems and methods may limit power dissipation in the switch.

The inventors have recognized and appreciated that, when an electrical switch is closed, a rapid inrush of current may occur due to the voltage difference across the switch. For example, when a power switch is turned on to supply power to an electronic system initially there may be a large voltage across the switch due to the different voltages at the power source and the electronic system. This voltage difference may cause an inrush of current from the power source to the electronic system. Such a large inrush of current may produce large power dissipation and damage the switch. To avoid a large power dissipation in the switch the inventors have appreciated it may be beneficial to control the slew rate of the current through the switch while the voltage across the switch is large.

In some conventional approaches, an amplifier may be used to control the switch using a single, fixed reference signal, indicative of a limit on the maximum current allowed to flow through the switch. For example, an operational amplifier may receive a feedback current, indicative of a measured current flow through the switch, and a fixed reference signal. The output of the op-amp may then be used to control the switch in order to limit the current flow. However, in such embodiments, the inventors have appreciated that it may be difficult to select a single reference current signal, since a large reference current signal may lead to initially high power dissipation in the switch.

In other conventional approaches, more than one fixed reference current signal may be used. One reference current signal may be selected at a time by comparing a feedback signal to a selection voltage level that indicates when to switch between reference current signals, each of which may represent separate and distinct reference signal levels (e.g., a high reference signal and a low reference signal). For example, two reference current signals may be de-multiplexed and provided to an operational amplifier to control the switch. In such embodiments, a jump discontinuity may be created in the power dissipated by the switch when the current reference signal is switched. Such a switch between reference current signals creates a current reference that is a step function, rather than a continuous or smooth function. However, switching between separate reference signals (e.g., using a de-multiplexer) creates a potentially disadvantageous and rapid spike in the power dissipation of the switch.

The inventors have recognized and appreciated that the preceding embodiments may be improved upon by dynamically adjusting a reference current signal. In some embodiments, a reference current signal may be generated based on the voltage difference across the switch. For example, the reference current signal may be inversely proportional to the voltage difference, such that the reference current signal may begin at the low amplitude end of a range when the voltage difference is large and the reference current signal may reach the high amplitude end of the range when the voltage difference is small. A reference current signal that begins at a low amplitude and increases as the voltage difference decreases can improve the switch control by limiting the power dissipation. Also, the reference current signal may be a smooth function that improves power efficiency of the switch and prevents spikes in power dissipation. Furthermore, the power dissipation and current limits may be configurable. For example, the current limit may be configured to increase or decrease at desired rates.

FIG.1shows an illustrative device100in which some embodiments of the technology described herein may operate.FIG.1illustrates the device100, which includes power source101, switch103, switch control circuit105, and device circuitry107. The device100and/or the device circuitry107may be switched between ‘on’ and ‘off’ states by the switch103that connects the device circuitry107to the power source101.

The device100may be any suitable device. For example, the device100may be an electronic device such as a mobile or stationary computing device. The device100may include processing circuitry (e.g., a field programmable gate array (FPGA), application specific integrated circuit (ASIC), and/or processor) for carrying out the techniques and methods described herein. Furthermore, the illustrated components of the device100are shown as a non-limiting example and the device100may include additional or different components without departing from the scope of the present disclosure.

The device100includes the power source101, which may be any suitable source of electrical energy for the device100. For example, the power source101may be a battery, such as a lithium ion battery, a lithium polymer battery, or any suitable battery, a super capacitor, and/or any suitable energy storage device. The power source101may be internal to the device100(e.g. a battery), external, and/or a combination of both internal and external power sources. For example, the power source101may include a battery and/or connections to interface with external power supplies. The power source101may supply alternating or direct current to the device100. The power source101may be configured to supply power at a particular voltage and/or within a range of voltages. The power source101may also have a maximum amount of current that can be supplied.

The device circuitry107may be any suitable circuitry that is configured to receive electrical power from the power source101. The device circuitry107may include multiple circuits. For example, the device circuitry may include a display (e.g., an LED or LCD panel), processing circuitry (e.g., a microprocessor), computer memory, and/or communication devices (e.g., a wireless internet transceiver). In some embodiments, the device circuitry107may be configured to receive electrical power within a tolerable range of voltage and/or current levels.

The switch103connects the power source101to the device circuitry107. The switch103may allow or block the transmission of electrical power from the power source101to the device circuitry107. The switch103may be any suitable switching circuitry. In some embodiments, the switch103is a transistor. For example, the switch103may be a metal-oxide-semiconductor field-effect transistor (MOSFET) or a bipolar junction transistor (BJT). In such embodiments, the switch103is controlled with an electrical signal on an input to the switch103, such as a gate of a transistor. In some embodiments, the switch103includes two conduction terminals, such as a source and drain in a MOSFET or a collector and emitter in a BJT, and a control terminal, such as a MOSFET gate or BJT base. In the example ofFIG.1, the conduction terminals of the switch103are connected to the power source101and the device circuitry107respectively. The control terminal of the switch103is connected to the switch control circuitry105. As used herein, the voltage across the switch103is measured between the conduction terminals.

The switch103may be controlled by the switch control circuitry105, which may be connected to each side of the switch and configured to measure the voltage across the switch. The inventors have recognized and appreciated that a reference current signal may be dynamically generated based on the voltage across the switch103. For example, the reference current signal may be set inversely proportional to the voltage across the switch103, such that the reference current signal may begin at the low amplitude end of a range when the voltage is large and the reference current signal may reach the high amplitude end of the range when the voltage is small. The reference current signal may be a smooth function that improves the power efficiency of turning on the switch and limit the power dissipation. In some embodiments, the power dissipation and current limits may be configurable using the switch control circuitry105. For example, the reference current signal and therefore the current limit may be configured to increase or decrease at desired rates.

The switch103may be controlled by providing an electrical signal to the switch103from the switch control circuitry105. In some embodiments, the control signal may be based on the reference current signal and/or a feedback current signal sensed as current flowing through the switch. For example, the switch control circuitry105may transmit a voltage signal to the switch103. In a further example, the voltage signal may be the output of comparing, using an amplifier, the feedback current signal to the reference current signal.

FIG.2illustrates a block diagram of a switch control circuit205according to an illustrative embodiment. In the illustrative embodiment ofFIG.2, the switch203is connected to the switch control circuitry205that includes difference signal circuitry211, reference signal circuitry213, feedback current circuitry215, and control circuitry217. The switch control circuitry205may be operative to control the switch203.

The difference signal circuitry211receives an input voltage, Vin, and an output voltage, Vout, from opposite sides of the switch203. The input voltage may be connected to a power source, such as power source101. The output voltage may be connected to circuitry (e.g., device circuitry107) that is powered in response to the switch203being closed to allow electrical power to flow from the power source. In some embodiments, the difference between the input voltage and the output voltage will range from the initial input voltage when the switch203is completely open and then is reduced to a conduction voltage drop across the switch when the switch203has completely closed for a suitable period of time.

In some embodiments, the difference signal circuitry211may generate a voltage difference signal based on the voltage across the switch. The voltage difference signal may be any suitable voltage or current signal. In some embodiments, the voltage difference signal is proportional to the voltage across the switch203. In some embodiments, the voltage difference signal is limited by a peak signal that indicates a maximum reference current. In some embodiments, the difference signal circuitry211transmits the voltage difference signal to the reference signal circuitry213. Exemplary implementations of difference signal circuitry are described with reference toFIGS.3(311),4(411), and5(511).

The reference signal circuitry213receives a signal (e.g., the voltage difference signal) indicative of the voltage across the switch203from the difference signal circuitry211. Based on the voltage across the switch, the reference signal circuitry213generates a current reference signal. The current reference signal is used by the switch control circuitry205to control the amount of current that is allowed to flow through the switch203. The current reference signal may represent the difference between a peak current reference signal and the voltage across the switch. Exemplary implementations of reference signal circuitry are described with reference toFIGS.3(313),4(413), and5(513).

In some embodiments, the reference signal circuitry sets the current reference signal to be inversely proportional to the voltage across the switch203. For example, when the switch203is initially closed, the voltage across the switch may be at a maximum value and the current reference signal may, in response, be at a minimum value. As the switch closes, in response to a reduction in the amplitude of the voltage across the switch, the reference signal circuitry increases the amplitude of the current reference signal. In some embodiments, the current reference signal may be generated based on the voltage across the switch, a peak current reference value, a minimum current reference value, and/or a gain. For example, in such embodiments, the current reference signal may range between a minimum current reference value and a value equal to the sum of 1) the minimum current reference and 2) the product of the peak current reference value and the gain.

In some embodiments, the current reference signal may be a suitable current or voltage signal. In some embodiments, the voltage difference signal received by the reference signal circuitry213and the current reference signal may either or both be current signals or voltage signals. In some embodiments, the difference signal and/or the current reference signal may be converted between the voltage and current domain. In some embodiments, the reference signal circuitry213converts a current signal to a voltage signal before transmitting the current reference signal to the control circuit217.

The feedback current circuitry215provides a second input to the control circuitry217in addition to the current reference signal. The feedback current circuitry215is connected to the switch203and configured to receive a sensed current signal representing a current level in the switch203. In some embodiments, the feedback current circuitry215is configured to generate a feedback current signal based on the sensed current signal. For example, a current sensor may generate a current signal representing current sensed in the switch203and provide the current signal to a resistor, and the voltage drop across the resistor may generate a voltage signal that is the feedback current signal. Exemplary implementations of feedback current circuitry are described with reference toFIGS.3(315),4(415), and5(515).

The control circuitry217receives the current reference signal and the feedback current signal. Based on the current reference signal and/or the feedback current signal, the control circuitry217controls the switch203. In some embodiments, the control circuitry217may generate an output signal based on the difference between the current reference signal and the feedback current signal. For example, the control circuitry may include an amplifier (e.g., an operational amplifier) that produces an output that is proportional to the difference. The output signal maybe configured to have suitable electrical characteristics for controlling the switch203. As a first example, in some embodiments, when feedback current signal is greater than the current reference signal, the output signal may be increased when the switch203is a PMOS device. However, in other embodiments, the output signal may be decreased when the switch203is an NMOS device. As another example, when the feedback current signal is less than the current reference signal, the output signal may be decreased when the switch203is a PMOS device. However, in other embodiments, the output signal may be increased when the switch203is an NMOS device.

In some embodiments, the control circuitry transmits the output signal to the switch203. In some embodiments, the output signal is transmitted to the gate of a transistor in the switch203. The output signal may cover a continuous range of values that controls the degree to which the switch is open, from completely closed to completely open with controllable point in between. Exemplary implementations of control circuitry are described with reference toFIGS.3(317),4(417), and5(517).

FIG.3is a circuit diagram of switch control circuitry305, according to a non-limiting embodiment of the present application.FIG.3includes a switch303and switch control circuitry305, which includes difference signal circuitry311, reference signal circuitry313, feedback current circuitry315, and control circuitry317. The difference signal circuitry311includes resistors321aand321b, slope resistor323, PMOS transistors325,327, and333, and NMOS transistors329,331a, and331b, and peak current reference source335. In some embodiments, the peak current reference source335may be implemented as and/or considered to be part of the reference signal circuitry313without departing from the scope of this disclosure. The reference signal circuitry313includes PMOS transistors337,339,343, and345, bias transistor341, minimum overcurrent current source347, and reference resistor349. The feedback current circuitry315includes sensed current source351and feedback resistor353. The control circuitry317includes amplifier355. As was discussed with reference toFIGS.1and2, the switch control circuitry305is operable to control the switch303based, at least in part, on a current reference signal that is generated based on a voltage across the switch.

Difference signal circuitry311generates a difference signal indicating a voltage across the switch303, for example as was discussed with reference to difference signal circuitry211inFIG.2. The input and output voltages on either side of the switch303are connected to the resistors321aand321brespectively. The resistor321ais connected to the slope resistor323, which is connected to the source of the PMOS transistor325. The gate and drain of the PMOS transistor325are connected to the gate of the PMOS transistor327. The drains of PMOS transistors325and327are connected, respectively, to the drains of NMOS transistors331aand331b, which are configured to mirror the current through NMOS transistor329.

The source of PMOS transistor333is connected to the slope resistor323. The gate of PMOS transistor333is connected to the drain of PMOS transistor327. In the exemplary circuitry configuration ofFIG.3, the difference signal circuitry311is configured to create a current signal through the PMOS transistor333. In some embodiments, the magnitude of the current signal is equal to the difference between the input and output voltages (on opposite sides of the switch303) divided by the resistance value of the slope resistor323. The slope resistor323may be configured to be any suitable resistance value. For example, the resistance value of the slope resistor323may be configured based on the allowable range of voltages across the switch303, the allowable range of reference currents, and/or other parameters of the switch control circuitry305such as a desired slew rate for closing the switch303, which turns the switch303‘on’ and allows the flow of current.

In the illustrated embodiment, the peak current reference source335is a suitable current source/sink configured to sink the current passing through the PMOS transistor333. In some embodiments, the peak current source335may be configured to source the maximum current that may flow through the PMOS transistor333. For example, the peak current source335may be configured to sink current equal to the maximum input voltage (e.g., the voltage supplied by a battery) divided by the resistance value of the slope resistor323.

In the illustrated embodiment, the peak current reference source335is connected to the reference signal circuitry313. When the current signal through the PMOS transistor333is less than the maximum current that is sinked by the peak current reference source335, additional current may be sourced from the reference signal circuitry313and sinked by the peak current reference source335. In the illustrated embodiment, the PMOS transistors337and339are configured such that the current through the PMOS transistors337and339is equal to the difference between the peak current reference and the difference signal.

In some embodiments, the bias transistor341may be configured to bias the current from the PMOS transistor339and the peak current reference source335. In some embodiments, bias transistor341and the voltage signal, VBias, input to the bias transistor341are configured to clamp the node voltage of the peak current reference source335. The operation headroom and region of the peak current reference source335may be configured using the bias transistor341.

The PMOS transistors337and339are paired with PMOS transistors343and345. In some embodiments, the PMOS transistors343and345may be larger than PMOS transistors337and339, respectively, by a constant factor, K. K may be any suitable scaling factor (e.g., an integer or real number). In further embodiments, K is larger than or equal to 1. For example, K may be 1, 1.275, 2, 2.5, 5, 10, or any suitable scaling factor. In some embodiments, K may be smaller than 1. For example, K may be any of 0.25, 0.5, 1, 1.25, 1.5, 2, 2.5, or 5. Due to the size mismatch, the current through the PMOS transistors343and345is K times the current that flows through the PMOS transistors337and339. The current through PMOS transistors343and345is combined with the minimum overcurrent signal from minimum overcurrent current source347to create a reference current signal equal to K*(the peak current reference−the difference signal)+(the minimum overcurrent signal). In such embodiments, the difference signal may be less than or equal to the peak current reference.

The combined reference signal creates a voltage drop across the reference resistor349to represent the combined reference signal in the voltage domain. Feedback current circuitry315receives an indication of the current flowing through the switch303. The sensed current source351represents a current signal indicating the current level through the switch303. The sensed current level creates a voltage drop across the feedback resistor353to generate a voltage signal indicating the current level in the switch303. The feedback and reference voltages are input to the amplifier355in the control circuitry317. The output of the amplifier355is connected to the switch303to control the switch303. In the illustrated embodiment, the output of the amplifier355is connected to the gate of the switch303.

FIG.4illustrates a circuit diagram of switch control circuitry405, according to a non-limiting embodiment of the present application.FIG.4includes a switch403and switch control circuitry405, which includes difference signal circuitry411, reference signal circuitry413, feedback current circuitry415, and control circuitry417. The difference signal circuitry411includes resistors421a,421b,461a, and461b, PMOS transistors425,427, and433, and NMOS transistors429,431a, and431b. In some embodiments, the difference signal circuitry411includes amplifier463, NMOS transistor465, and slope resistor423. The reference signal circuitry413, as illustrated, includes amplifier463, NMOS transistor465, slope resistor423, PMOS transistors467,469,471,473,437,439,443, and445, minimum overcurrent current source447, and reference resistor449. The feedback current circuitry415includes sensed current source451and feedback resistor453. The control circuitry417includes amplifier455. As was discussed with reference toFIGS.1,2, and3, the switch control circuitry405is operable to control the switch403based, at least in part, on a current reference signal that is generated based on a voltage across the switch.

In contrast with the difference signal circuitry311discussed with reference toFIG.3, the difference signal circuitry411is configured to generate a voltage difference signal in the voltage domain. In particular, the difference signal circuitry411includes resistors461aand461b. The difference signal is generated as a voltage signal. The amplitude of the voltage signal is equal to the voltage across the switch multiplied by the ratio of the resistance value of resistor461band the resistance value of resistor461a.

The difference signal circuitry411transmits the voltage domain difference signal to the reference signal circuitry413. The voltage domain difference signal is input to the amplifier463, which is connected to NMOS transistor465. The amplifier463is therefore configured to control the current through the slope resistor423based on the voltage domain difference signal. The voltage domain difference signal is thereby converted to a current domain difference signal by the amplifier463, NMOS transistor465, and slope resistor423. The reference signal circuitry413, as illustrated, includes an additional set of transistors, PMOS transistors467and469paired with PMOS transistors471and473. The PMOS transistors471and473may be larger than PMOS transistors467and469by a scaling factor K1, for example as was described with reference to the scaling factor K inFIG.2. Scaling factor K1 may apply a gain to the current domain representation of the difference signal. In some embodiments, the scaling factor K1 may be a unity gain or any suitable gain. The remaining circuitry in the reference signal circuitry may then function as was described with reference to the reference signal circuitry313.

FIG.5illustrates a circuit diagram of switch control circuitry505, according to a non-limiting embodiment of the present application.FIG.5includes a switch503and switch control circuitry505, which includes difference signal circuitry511, reference signal circuitry513, feedback current circuitry515, and control circuitry517. The difference signal circuitry511includes amplifiers581a,581b, and583and resistors585a,585b,587a, and587b. In some embodiments, the difference signal circuitry511includes amplifier563, NMOS transistor565, and slope resistor523. The reference signal circuitry513, as illustrated, includes amplifier563, NMOS transistor565, slope resistor523, PMOS transistors567,569,571,573,537,539,543, and545, minimum overcurrent current source547, and reference resistor549. The feedback current circuitry515includes sensed current source551and feedback resistor553. The control circuitry517includes amplifier555. As was described with reference toFIGS.1,2,3, and4the switch control circuitry505is operable to control the switch503based, at least in part, on a current reference signal that is generated based on a voltage across the switch.

The difference signal circuitry511generates a voltage domain difference signal, e.g. as was described with reference toFIG.4. The amplifiers581aand581bare configured as unity gain buffers for receiving the voltages on either side of the switch503. In some embodiments, the amplifiers581aand581bmay be configured to provide any suitable gain.

The outputs of the amplifiers581aand581bare connected to the amplifier583, which is configured to generate a difference signal in the voltage domain. The difference signal generated by the amplifier583is equal to the voltage difference multiplied by the ratio of the resistance value of resistors585aand585bto the resistance value of resistors587aand587b. In the illustrative embodiment, each pair of resistors585aand585band587aand587bare configured to have a same resistance value for each resistor in the pair. It should be appreciated that any suitable resistance values may be utilized to configure the gain applied to the voltage difference in order to generate the difference signal. The reference signal circuitry513may function as was described with reference toFIG.4.

FIG.6shows an illustrative process flow600for controlling a switch. The process flow may be performed by the switch control circuitry described with reference to any of the earlier figures.

At act601, a voltage across the switch is detected. This may be performed, for example, by suitable difference signal circuitry. In some embodiments, a difference signal may be generated that is proportional to the voltage across the switch. In further embodiments, the difference signal is a current signal that is limited by a peak current signal. The peak current signal may be generated by suitable circuitry.

At act603, a current reference signal based on the voltage across the switch is generated. This may be performed, for example, by suitable reference signal circuitry. In some embodiments, in response to a reduction in amplitude of the voltage across the switch, the amplitude of the current reference signal is increased by suitable circuitry. In some embodiments, the circuitry is further configured to add a minimum current reference signal to the current reference signal. In further embodiments, the circuitry is further configured to apply a gain to the current reference signal.

At act605, the switch is controlled based, at least in part, on the current reference signal generated in act603. This may be performed by suitable feedback current circuitry and/or control circuitry. In some embodiments, controlling the switch based, at least in part, on the current reference signal includes determining, based on the current reference signal, a maximum input to be provided to an input of the switch to limit a current level in the switch. In some embodiments, the circuitry is further configured to receive a feedback current signal representing a current level in the switch. In further embodiments, the circuitry is further configured to control the switch based on the current reference signal and the feedback current signal.