Zeno phenomenon avoidance in power controller handoff

A control circuit eliminates the Zeno phenomenon in a power supply controller while transferring control from a primary side controller to a secondary side controller. The primary side controller generates a feedback voltage (e.g., threshold voltage) that is input to a comparator. An output node voltage of the control circuit is fed back to the linear amplifier to be compared with the threshold voltage. While the output node voltage is less than the threshold voltage, a charge pump is coupled to the output node of the control circuit. After the output node voltage has toggled around the threshold voltage a number of times, the comparator output node is coupled to the output node of the control circuit and the charge pump is decoupled from the output node. When the output node voltage has discharged to be equal to the threshold voltage, control is handed off from the primary side controller to the secondary side controller.

FIELD OF THE DISCLOSURE

This document pertains generally, but not by way of limitation, to the field of integrated circuits and, in particular, to power supply controllers having multiple controllers.

BACKGROUND

The Zeno phenomenon may occur around a boundary situation in which a system is to switch from one state to another state. One simple example of the Zeno phenomenon is the condition statement of “if (x≥0), jump to state 1; else if (x<0), jump to state 2”. While this executes accurately in the digital domain, in the analog domain the state of x may be affected by noise, measurement errors, or parasitics. Thus, if x is close to the boundary of 0V, it may traverse that boundary multiple times or even approaching an infinite number of times within a finite time. This causes the state change to have multiple or approaching an infinite number of switches between state 1 and state 2 in the finite time.

The Zeno phenomenon may occur in a system where control is passed from one powering up controller to another powering up controller. During a startup procedure when handing over control from an open loop control to a closed loop control, the Zeno phenomenon may occur during the second controller power-up when the voltage to the second controller reaches a value close to a feedback voltage. This may result in an offset in the output voltage of the system.

SUMMARY OF THE DISCLOSURE

The present inventors have recognized, among other things, that Zeno phenomenon may occur in a system in which control is passed from one powering up controller to another powering up controller. During a startup procedure when handing over control from an open loop control to a closed loop control, the Zeno phenomenon may occur during the second controller power-up when the voltage to the second controller reaches a value close to a feedback voltage. This may result in an offset in the output voltage of the system.

The present inventors have also recognized, among other things, a need for a control circuit for eliminating the Zeno phenomenon from the handover of control from a primary side controller to a secondary side controller of a power supply controller. This document relates generally to forcing a voltage that powers the secondary side controller to be equal to a feedback voltage controlled by the primary side controller.

A control circuit may be used for controlling an output voltage to reduce an offset voltage in the output voltage of the secondary side controller. A linear amplifier has a threshold voltage input node, a feedback voltage input node, and a linear amplifier output node that is switchably coupled to an output node of the control circuit. The feedback voltage input node is coupled to the output node of the control circuit. A charge pump is switchably coupled to the output node of the control circuit. A controller is configured to control coupling of the charge pump to the output node of the control circuit when the output voltage is less than a threshold voltage on the threshold voltage input node. The controller is further configured to control coupling of the linear amplifier output node to the output node of the control circuit when the output voltage is greater than the threshold voltage.

A power supply controller may be used for controlling an output voltage to reduce an offset voltage in the output voltage. A primary controller is coupled to a secondary controller through a micro-transformer. A control circuit is coupled to the secondary controller and to the primary controller through the micro-transformer. The control circuit includes a linear amplifier that has a threshold voltage input node, a feedback voltage input node, and a linear amplifier output node switchably coupled to an output node of the control circuit. The feedback voltage input node is coupled to the output node of the control circuit. A charge pump is switchably coupled to the output node of the control circuit. A controller is configured to control coupling of the charge pump to the output node of the control circuit when the output voltage is less than a threshold voltage on the threshold voltage input node. The controller is further configured to control coupling of the linear amplifier output node to the output node of the control circuit after the output voltage has toggled around the threshold voltage for a number of times.

A method for control handover in a power supply controller includes applying a threshold voltage from a primary controller to a comparator. An output voltage that powers a secondary controller is compared to the threshold voltage. If the output voltage is less than the threshold voltage, a charge pump is coupled to an output of the power supply controller. If the output voltage is greater than the threshold voltage, the charge pump is decoupled from the output of the power supply controller. An output of the linear amplifier is coupled to the output of the power supply controller after the output voltage has toggled around the threshold voltage a number of times. Control of the power supply controller is transferred from the primary controller to the secondary controller when the output voltage equals the threshold voltage after the output voltage has toggled around the threshold voltage for the number of times and the output of the linear amplifier is coupled to the output of the power supply controller.

DETAILED DESCRIPTION

A power supply controller may be used for monitoring an output voltage and controlling power output of a power supply. The power supply controller includes multiple control circuits to perform this task. For example, the power supply controller includes a primary side controller for the initial power-up of the power supply controller and a secondary side controller for completing the power-up sequence of the power supply controller and eventually taking control of the power supply controller from the primary side control circuit. The primary side controller is isolated from the secondary side controller by a transformer (e.g., micro-transformer) so that the two controllers can communicate with each other through the transformer while still maintaining the isolation between the primary side and the secondary side of the controller.

The power-up sequence for the power supply controller includes the primary side controller being powered up first before the secondary side controller. This enables the primary side controller to monitor the input current to the power supply controller. The secondary side controller is then powered by the same controller output voltage (VOUT) that is being monitored and controlled by the power supply controller. This operation is illustrated inFIG. 1.

FIG. 1is a plot showing voltages for controlling operation of multiple controllers, such as in accordance with various embodiments. The Primary Control Circuit Start voltage100is the control voltage that turns on the primary control circuit. It can be seen inFIG. 1, that when the Primary Control Circuit Start Voltage100goes from 0V to some fixed voltage greater than 0V, the Output Voltage103(i.e., solid line) begins to ramp up from 0V. The Output Voltage103is shaped by setting the ramp of a current limit of the primary power controller to control primary side system current.

A feedback voltage Vfb107also begins to ramp up from 0V when the Primary Output Voltage103begins to ramp up. The feedback voltage Vfb107is the controller output voltage VOUTthat is being controlled by the power supply controller. The feedback voltage Vfb107is generated and controlled by the primary side controller based on the Output Voltage103.

An under-voltage lock-out (UVLO) voltage101is used to indicate a safe turn-on time to the secondary control circuit. The turn-on time may be based on a particular threshold voltage102of the Output voltage103. Thus, the voltage at102is the UVLO point for the secondary control circuit to turn on. When the UVLO voltage goes low, that is an indication to the secondary control circuit to begin its power-up.

The UVLO voltage101is generated by a UVLO circuit that provides a default lock-out signal101(e.g., non-zero voltage) when the power supply controller is powered down or the Output voltage103is below a lock-out threshold voltage102. Upon start-up, as the Output voltage103begins to rise, the UVLO voltage101can change state104when the Output voltage103satisfies the lock-out threshold voltage102. Thus, the UVLO voltage101prevents the secondary controller from powering on until the Output Voltage103reaches a predetermined value.

InFIG. 1, voltage105is a scaled up version of voltage111. Once UVLO voltage101changes state104to a low value (e.g., 0V), the secondary controller begins to power on and an internal tracking signal105(i.e., dashed line) ramps up from 0V. The internal tracking signal SS2105is used on the secondary side of the power supply controller that acts as a reference to control the rise of the output voltage up to the set point voltage in a controlled fashion. The soft start voltage VSS2111also begins to ramp up from 0V at this time. It is desirable that both the feedback voltage Vfb107which is a scaled version of the output voltage103through a resistive divider and the Soft Start Voltage VSS2111each increase linearly to a respective fixed voltage (e.g., 1.2V-1.4V) without any voltage offsets. A voltage offset in either of the Soft Start Voltage VSS2111can cause the same offset to occur in the controller output voltage VOUTthat is controlled by the power supply controller.

The control circuit ofFIG. 2, as described subsequently, forces VSS2111to be equal to Vfb107prior to transferring control from the primary controller to the secondary controller. This operation is shown inFIG. 1at voltage120. This occurs at the voltage110where the Secondary Output Voltage105and the Output Voltage103are substantially equal.

FIG. 2is a schematic diagram of the control circuit201for controlling the output voltage VOUTto reduce the offset voltage, such as in accordance with various embodiments. The control circuit201eliminates or substantially reduces the Zeno Phenomenon that can occur when the secondary control circuit powers up so that an offset voltage is reduced or eliminated in the output voltage VOUT.

The control circuit201includes a controller200, a linear amplifier202, a comparator204, a first charge pump210, and a second charge pump211. In an embodiment, the functions of the linear amplifier202and comparator204may be combined. A plurality of switches220,221,222,223are used to switchably couple the circuit elements. The plurality of switches220-223may be implemented by transistors that can be activated and deactivated to respectively couple and decouple a switchably coupled circuit element to another circuit element. The switches220-223include a control node (e.g., base or control gate) on which a signal can be applied to either activate or deactivate the switch.

In an embodiment, the linear amplifier202can be implemented by an operational amplifier (op amp) configured as a negative feedback amplifier. In this embodiment, the feedback voltage Vfbis used as a threshold voltage (Vth) in the circuit and is coupled to a positive input (e.g., threshold voltage input node) of the linear amplifier202. Thus, subsequent references to the circuit ofFIG. 2and its method of operation inFIG. 7refer to the feedback voltage as reference voltage Vthsince the output node voltage VOUTPUT_NODE(i.e., SS2voltage111ofFIG. 1) is being compared to this input voltage.

The negative input (e.g., feedback voltage input node) of the linear amplifier202is coupled to an output node250of the circuit. Thus, during circuit operation, the output voltage (VOUTPUT_NODE) at output node250is compared to Vth. VOUTPUT_NODEis illustrated inFIG. 1as VSS2111. The output of the linear amplifier202is switchably coupled to the output node250through switch223.

The first charge pump210is coupled to a power source node261and switchably coupled, through switch220, to the output node250. The first charge pump210is a source charge pump to supply a current to the output node250. The second charge pump211is coupled to a common circuit node (e.g., circuit ground) and switchably coupled, through switch221, to the output node250. The second charge pump211is a sink charge pump to remove current from the output node250. Switches220and221operate in a complementary manner. In other words, when switch220is open, switch221is closed and when switch220is closed, switch221is open.

As used herein, a charge pump may be defined as a DC-to-DC converter that uses capacitors as energy-storage elements to create either a higher or lower voltage power source. Charge-pump circuits may be capable of relatively high efficiencies (e.g., 90-95%).

The comparator204has an input coupled to the output of the linear amplifier202. The output of the comparator204is switchably coupled, through switch222, to the control nodes of switches220,221. The comparator204includes hysteresis.

The controller200is coupled to the control nodes (e.g., base, control gate) of switches222,223. Thus, the controller200is configured to control the operation (e.g., activation, deactivation) of these switches222,223. The controller is also coupled to the output of the comparator204in order to track the voltage output from the comparator204.

Operation of the control circuit201ofFIG. 2is described with reference toFIG. 3.FIG. 3is a plot of voltages in accordance with an operation of the control circuit201.

The threshold voltage Vthis shown at301as 0V prior to the controller circuit being powered up. After Vthgoes to its initial voltage level at303, VOUTis shown beginning to ramp up from 0V. Referring toFIG. 2, the controller200initially activates switch222so that it acts as a closed switch and couples the output of the comparator204to control nodes of switches220,221. Switch220is activated (e.g., closed) by the non-zero voltage to couple its respective source charge pump210to the output node250to begin to charge up the output node250as shown by the VOUT_NODEramping voltage305ofFIG. 3. The controller has deactivated switch221its respective remove the sink charge pump211from the output node250. The controller200has deactivated switch223(e.g., open) at this time so that the output of the linear amplifier202is not coupled to the output node250. The ramping output node voltage VOUT_NODEis fed back to the linear amplifier202to be compared to the feedback voltage Vfbthat is now acting as a threshold voltage.

Once the output node voltage VOUT_NODEhas passed the threshold voltage (e.g., Vfb) at310, the controller200senses VOUT_NODEexceeding the threshold and deactivates (e.g. opens) switch220, thus removing the source charge pump210, from being coupled to the output node250. Once the source charge pump210, have been removed from supplying a current to the output node250, the output voltage VOUTshown inFIG. 3drops back down below the threshold voltage Vthby activation of the sink charge pump211and switch221. Once VOUT_NODEdrops below Vth, the controller senses VOUT_NODEdropping below the threshold and activates (e.g., closes) switch220and the respective source charge pump210is again coupled to the output node250. This repeats for a number of times (e.g., greater than one) as shown at313ofFIG. 3.

The area of313shows the output voltage VOUT_NODEtoggle around the threshold voltage Vtha number of times (e.g., greater than 1). Thus, the phrase “toggle around” is defined as exceeding the threshold voltage, going back below the threshold voltage, then exceeding the threshold voltage again.

After the certain number of repeated charging and discharging of the output node250as sensed and counted by the controller200, the controller deactivates (e.g., opens) switch222to remove the comparator204from activating switches220,221. The source charge pump210is now no longer coupled to the output node250and the sink charge pump211is not activated. The controller200also activates (e.g., closes) switch223so that the output of the linear amplifier202is now coupled to the output node250. As can be seen inFIG. 3, the controller200waits until VOUT_NODEexceeds Vfbbefore deactivating switch222for the final time and activating switch223.

The output of the linear amplifier202is initially greater than Vthbut is driven by202to eventually be equal to Vthat voltage320. At voltage320when VOUT_NODEand Vthare now equal (e.g., within ±0.5V), control of the power supply controller is handed over from the primary controller to the secondary controller.

In another embodiment, when the output voltage VOUT_NODEtoggles around Vth, as shown by area313ofFIG. 3, the controller200may adjust (e.g., decrease) the time of activating and deactivating switch222in order to decrease the overshoot and undershoot voltages for each cycle. This may be accomplished by the controller200counting the number of overshoot/undershoot cycles and decreasing both the time the switch222is deactivate and the time that it is activated by a certain time difference. This time difference can then be decreased for each subsequent cycle until the certain number of cycles have been counted. In another embodiment the number of toggles can be extended for another voltage to equalize or reach a steady state or the circuit is ready for operation in a different part of the overall circuit or another circuit is ready for the proper (glitch free) operation after the secondary controller takes over control.

FIG. 4is a block diagram of a power supply controller having multiple controllers401,403controlled by the control circuit201, such as in accordance with various embodiments. The block diagram ofFIG. 4is a simplified diagram of a power supply controller for purposes of illustrated operation of the control circuit201. Other embodiments may include additional elements.

The block diagram includes a primary controller401, a secondary controller403, a transformer405, and the control circuit201as described previously. The primary controller401and the secondary controller403are isolated by and communicate through the micro-transformer405. The isolation of the primary side from the secondary side may be defined as multiple megaohms of resistance between the grounds of the two sides.

The primary controller401is coupled to the control circuit201described previously through the micro-transformer405.

The secondary controller403is coupled to the output of the control circuit201. In other embodiments, control circuit201is part of secondary controller403. The output voltage VOUT, that powers the secondary controller403or is powered from some other source on the secondary side, is output to the secondary controller403from the control circuit201. The UVLO secondary voltage, as shown inFIG. 1, is input to the secondary controller403to cause the secondary controller403to begin its power up sequence.

Using the method described subsequently with reference toFIG. 7, control of the power supply controller is initially handled by the primary controller401. Once VOUTreaches a threshold voltage, control is handed over from the primary controller401to the secondary controller403.

FIG. 5is a plot of VOUTversus time for a conventional power supply controller. The plot shows that as VOUTrises500, a voltage offset501occurs at the point where the primary controller hands over control of monitoring the VOUToutput to the secondary controller.

FIG. 6is a plot of VOUTversus time for a power supply controller using the control circuit for controlling output voltage to reduce the offset voltage, such as in accordance with various embodiments. This plot shows that as the VOUTrises600, the voltage offset present in the conventional power supply controller output has been removed by the present embodiments.

FIG. 7is a flowchart of a method for control handover in a power supply controller, such as in accordance with various embodiments. Block701includes a primary controller applying an input voltage (Vth) (e.g., threshold voltage) to a linear amplifier. Block703includes comparing the feedback output voltage that powers a secondary controller to the threshold voltage. Blocks704,705,707,708, and709then determine the number of times that the output voltage toggles around the threshold voltage.

When the output voltage is less than the threshold voltage, block705determines if the output voltage was previously greater than the threshold voltage. If the output voltage is now less than the threshold voltage and the output voltage was previously less than the threshold voltage, the source charge pump is coupled to the output node and the sink charge pump is decoupled from the output node in block704. When the output voltage is greater than the input voltage, block707determines if the output voltage was previously less than the threshold voltage. If the output voltage is now greater than the threshold voltage and was previously greater than the threshold voltage, block708includes coupling the sink charge pump to the output of the power supply controller and decoupling the source charge pump.

If the output voltage is now less than the threshold voltage but the output voltage was previously greater than the threshold voltage, block709increments a counter. When the output voltage is greater than the input voltage but the output voltage was previously less than the threshold voltage, block709increments the counter. The counter counts the number of times the output voltage toggles around the threshold voltage.

Block711determines if the count has reached a threshold count. If the threshold has not been reached (e.g., the output voltage has not toggled around the threshold voltage the certain number of times), the process repeats from block703. If the count threshold has been reached, block713couples the linear amplifier output to the output of the circuit and decouples the source charge pump for a time period x. The time period x is a predetermined time that determines how long the linear amplifier operates before the rest of the control circuitry takes over.

Block715includes transferring control of the power supply controller from the primary controller to the secondary controller when the output voltage equals the threshold voltage after the output voltage has toggled around the threshold voltage for the number of times and the output of the linear amplifier is coupled to the output of the power supply controller.