Control unit for a converter circuit with multiple switching converter blocks

The present document describes a control unit for a converter circuit comprising a plurality of converter blocks, wherein each converter block comprises one or more switches which are turned on or off during switching events, and wherein at least some of the converter blocks share a common supply rail. The control unit is configured to determine that a first converter block from the plurality of converter blocks requests a switching event at a first time instant. Furthermore, the control unit is configured to determine whether a second converter block from the plurality of converter blocks, with which the first converter block shares a common supply rail, has a reserved switching time slot for a switching event at the first time instant. In addition, the control unit is configured to delay the switching event of the first converter block to a time instant subsequent to the reserved switching time slot, if it is determined that the second converter block has a reserved switching time slot at the first time instant.

TECHNICAL FIELD

The present document relates to switching converters. In particular, the present document relates to controlling operation of a circuit, notably an integrated circuit, comprising multiple switching converters or converter phases.

BACKGROUND

Switching converters such as buck, boost, buck-boost and other types of switching converters typically generate significant noise at switching events. This noise is typically associated with under- or over-voltage events which are created on the power or supply rails due to the presence of parasitic elements (mainly parasitic inductances and/or parasitic resistances) and/or due to the relatively high level of currents through the switches and/or due to the relatively fast and frequent switching events of the converters to maintain regulation.

At each switching event energy is transferred between parasitic elements thereby causing a relatively fast voltage variation on the power or supply rails. This voltage variation introduces noise and causes stress to the power switches, which may gradually and/or permanently change the characteristics of the power switches. Furthermore, the generated noise may cause interference with other circuits and may disrupt operation of the other circuits (e.g. other switching converters). Hence, the noise and stress caused by switching events may lead to a degradation of the performance of switching converters.

SUMMARY

The present document addresses the technical problem of reducing the stress caused by switching events of switching converters, notably in order to reduce crosstalk, to increase the lifetime of the switching converters and/or to achieve an increased integration level.

According to an aspect, a control unit for a converter circuit comprising a plurality of converter blocks is described. Each converter block comprises one or more switches which are turned on or off during switching events, wherein at least some of the converter blocks share a common supply rail (also referred to as power rail), from or to which the one or more switches may draw or sink current.

The control unit may be configured to determine that a first converter block from the plurality of converter blocks requests a switching event at a first time instant. Furthermore, the control unit may be configured to determine whether a second converter block from the plurality of converter blocks, with which the first converter block shares a common supply rail, has a reserved switching time slot for a switching event at the first time instant. In addition, the control unit may be configured to delay the switching event of the first converter block to a time instant subsequent to the reserved switching time slot, if it is determined that the second converter block has a reserved switching time slot at the first time instant.

According to a further aspect, a converter circuit comprising the control circuit described in the present document is described.

According to a further aspect, a method for controlling a converter circuit comprising a plurality of converter blocks is described, wherein each converter block comprises one or more switches which are turned on or off during switching events. At least some of the converter blocks share a common supply or power rail.

The method comprises determining that a first converter block from the plurality of converter blocks requests a switching event at a first time instant. In addition, the method comprises determining whether a second converter block from the plurality of converter blocks, with which the first converter block shares a common supply rail, has a reserved switching time slot for a switching event at the first time instant. In addition, the method comprises delaying the switching event of the first converter block to a time instant subsequent to the reserved switching time slot, if it is determined that the second converter block has a reserved switching time slot at the first time instant.

According to a further aspect, a software or hard coded program is described. The program may be adapted for execution on a processor or executed by customized logic hardware and for performing the method steps outlined in the present document when carried out.

According to another aspect, a storage medium is described. The storage medium may comprise a software program adapted for execution on a processor or customized logic and for performing the method steps outlined in the present document when carried out.

According to a further aspect, a computer program product is described. The computer program may comprise executable instructions for performing the method steps outlined in the present document when executed on a computer.

It should be noted that the methods and systems including its preferred embodiments as outlined in the present document may be used stand-alone or in combination with the other methods and systems disclosed in this document. In addition, the features outlined in the context of a system are also applicable to a corresponding method. Furthermore, all aspects of the methods and systems outlined in the present document may be arbitrarily combined. In particular, the features of the claims may be combined with one another in an arbitrary manner.

In the present document, the term “couple” or “coupled” refers to elements being in electrical communication with each other, whether directly connected e.g., via wires, or in some other manner.

DETAILED DESCRIPTION

As outlined above, the present document is directed at decreasing the stress caused by the switching events of switching converters.FIG. 1shows an example switching converter100with a high side power switch103and a low side power switch104, which are arranged between a rail at a supply voltage101and a rail at a reference voltage121(e.g. ground). The switching converter100is configured to provide an output voltage102based on the supply voltage101via an inductor105, wherein the output voltage102may be provided at an output capacitor106. The switches103,104are driven using driver circuits108and a control unit107based on one or more control signals109. In particular, the switches103,104may be operated in order to regulate the output voltage102to a given target voltage and/or to regulate the output current to a given target current. The time instants for switching events of the switches103,104may be set in dependence of the regulation or control scheme.

FIG. 1also shows various parasitic elements, such as a parasitic inductance110and a parasitic resistance111of the rail for the supply voltage101, and a parasitic inductance115and a parasitic resistance111of the rail for the reference voltage121. Furthermore,FIG. 1illustrates further parasitic elements112,113,114,116,117.

At each switching edge (also referred to as switching event) of a converter block (also referred to as a phase), the energy accumulated in the parasitic elements110,115is transferred. This energy transfer causes supply variation.FIG. 2Aillustrates a simplified example200of this principle using the switching sequence of the output stage of a buck converter100. At turn off of the high side switch103, the differential supply (voltage221compared to voltage222) increases momentarily (see diagram251) and the opposite occurs at turn on of the high side switch103(see diagram252). Furthermore, it is shown that the current211through the high side switch103decreases at a turn off of the high side switch103and increases at a turn on of the low side switch104. In addition, it is shown that the current212through the low side switch103increases at a turn off of the high side switch103and decreases at a turn on of the low side switch104.

The energy associated with a switching event is proportional to the square of the current211,212through the inductor105. This means that if another converter block is connected to the same rail at the supply voltage221and/or to the same rail at the reference voltage222with the same current level, and switches at the same time, the energy associated with the simultaneous switching events may be increased by a factor four. This increased energy may be sufficient to cause permanent damage to a converter block, depending on the supply conditions and characteristic of the power switches103,104.

In terms of voltage variation on a rail ofFIG. 2A, simultaneous switching events with the same energy as depicted inFIG. 2Bwould cause the supply variation to double. In case of a turn off of the high side switch103(reference sign251), the increase of the supply voltage221would cause a substantial overvoltage stress which could lead to damage of some devices in a power converter100. In case of a turn on of the high side switch103(reference sign252), the decrease of the supply voltage221could lead to an unexpected turn off of a block or circuit powered from the same rail.

FIG. 3shows an example converter circuit300with a plurality of converter blocks301,302,303,304,305,306, wherein each converter block may comprise a switching converter100. The different converter blocks may share common rails. As can be seen fromFIG. 3,blocks301and302share the rail to the reference voltage121;blocks302and303share the rail to the supply voltage101; andblocks304and305share the rail to the reference voltage101.

Based on these dependencies, the dependency map shown in Table 1 may be provided for the circuit300ofFIG. 3(wherein “Y” indicates a dependency and wherein “N” indicates that there is no dependency).

A control unit310of the circuit300may be configured provide a switching arbitration control scheme between the power switches103,104of the different converter blocks301,302,303,304,305,306by adding a time margin between switching events of dependent converter blocks, i.e. of converter blocks that share the same parasitics110,115on a common rail. By adding a time margin, cross disturbance and stress may be reduced and/or avoided.

At each switching edge (i.e. switching event) requested by a power switch103,104, the switching permission may be withheld for a certain time, also referred to as a switching time slot, until a previous switching event of a dependent converter block is finalized. If the switching events of the dependent converter blocks are sufficiently apart in time such that no crosstalk occurs (i.e. a previous switching time slot expires before another related switching edge occurs), the permission for switching may be granted immediately.

The arbitration of the switching time slots is preferably selective and (only) applies to related or dependent power switches103,104(i.e. power switches103,104which share a common rail) in order to minimize time or delay overhead. The time or delay overhead, which may be caused by arbitration may cause relatively small jitter and/or noise, which typically does not affect operation of the converter blocks301-306. The arbitration allows reducing the stress which is generated by switching events. Furthermore, the arbitration reduces the risk of permanent damage and/or degradation caused by overvoltage stress. In addition, the arbitration allows for reduced voltage variations on the rails, thereby reducing crosstalk between the related converter blocks301-306or power switches103,104.

A switching event usually has a duration241of approximately 1-4 ns. Hence, the overhead which may be introduced by arbitration is relatively small. In particular, the maximum possible delay may be: max_delay=(number of related blocks−1)*event_duration). On-chip power connections are usually shared by only two adjacent blocks301-306at most. Hence, the maximum overhead introduced may be as small as 1-4 ns+tlogic, where tlogic is the overhead delay introduced by the arbitration circuit (i.e. by the control unit310).

The arbitration typically only occurs for blocks301-306that share the same supply parasitics110,115. This means that in the example ofFIG. 3, blocks303and301are independent from each other, but both depend on block302, while block302depends on block301and on block303. The dependency is always reciprocal, i.e. if a block x depends on a block y, block y also depends on block x.

FIG. 4shows an example of an arbitrator block diagram implemented e.g. within a control unit310. A switch controller401of a block301-306requests a switching edge or event to the switching event register402of the respective block301-306(messages404,405, indicating also the edge type). Based on the edge type, the switch event register402will determine the required slot duration and request the slot to the arbitrator403(message402′) which assigns the slot to the requesting block (messages406,407) and which blocks any other related switch controllers401for the required slot duration. The other switching event registers402monitor other switching requests from other blocks301-306and hold them back until the arbitrator403grants permission.

Hence, a control circuit310is described in the present document, which implements an arbitration scheme for switching events of switching converter blocks301-306such that blocks301-306sharing the same parasitics110,115on one or more supply rails do not perform simultaneous switching events. Switching events can be arbitrated according to the type of switching events, in order to reduce the blocking time which is caused by arbitration. The control circuit310may be configured to assign a switching time slot to a switching event (i.e. to a switching edge). Furthermore, the control circuit310may be configured to delay a switching event if a relevant switching time slot is already taken, until the next available switching time slot.

As a result of arbitration, the stress caused by simultaneous switching events when sharing the same supply parasitics110,115can be reduced. Furthermore, noise and ringing amplitude on the supply rails can be reduced. In addition, power conversion density and system integrity can be increased. Furthermore, by reducing the stress, crosstalk can be reduced and integration capability can be increased.

Hence, a control unit310for a converter circuit300comprising a plurality of converter blocks301,302,303,304,305,306is described. The control unit310may comprise a processor. Each converter block301,302,303,304,305,306may comprise one or more switches103,104which are turned on or off during switching events. A switching event may be related to turning on a switch103and/or to turning off a switch103.

In particular, a converter block301,302,303,304,305,306(e.g. each one of the plurality of converter blocks) may comprise a first switch103which is coupled to a first supply rail (notably for supplying a supply voltage101) and a second switch104which is coupled to a second supply rail (notably for coupling the second switch104to a reference voltage121). The first switch103and the second switch104(e.g. forming a half bridge) may be turned on and/or turned off in an alternating and mutually exclusive manner.

At least some of the converter blocks301,302,303,304,305,306may share a common supply rail. By way of example, a first converter block301and a second converter block302may be coupled to the same supply rail (e.g. for providing the supply voltage101or the reference voltage121). The dependencies between the different converter blocks may be indicated by a dependency map, wherein the dependency map may indicate pairs of converter blocks from the plurality of converter blocks301,302,303,304,305,306that share a common supply rail (e.g. as shown in Table 1).

A supply rail may exhibit an inductance110,115, notably a parasitic inductance. By way of example, a supply rail may be coupled to the supply voltage101or to the reference voltage121(e.g. ground).

The control unit310may be configured to determine that a first converter block301from the plurality of converter blocks301,302,303,304,305,306requests a switching event at a first time instant. By way of example, the control unit310may be configured to control operation of the one or more switches103,104of first converter block301(and of the one or more other converter blocks). In this context, the control unit310may be configured to determine the first time instant for a switching event of the first converter block301based on a target voltage and/or a target current at an output of the first converter block301. Alternatively, or in addition, the control unit310may be configured to determine the first time instant for a switching event of the first converter block301based on an indication of an actual voltage and/or an actual current at the output of the first converter block301. In particular, the control unit310may be configured to determine the first time instant for a switching event of the first converter block301based on a control scheme for controlling or setting or regulating the actual voltage and/or the actual current at the output of the first converter block301to the target voltage and/or the target current at the output of the first converter block301. Hence, the first time instant may be the result of a control scheme which is performed by the first converter block301(e.g. to regulate the output voltage and/or output current to a target voltage and/or target current).

Furthermore, the control unit310may be configured to determine whether the second converter block302from the plurality of converter blocks301,302,303,304,305,306, with which the first converter block301shares a common supply rail, has a reserved switching time slot for a switching event at the first time instant. In other words, it may be determined, whether or not a switching time slot (which includes the first time instant) has already been reserved for the second converter block301. For this purpose, the control unit310may comprise a storage element for storing a time slot table, that indicates the switching time slots which have already been assigned to each one of the plurality of converter blocks (notably to each one of the converter blocks that share a common supply rail with another one of the converter blocks).

Furthermore, the control unit310may be configured to delay the switching event of the first converter block301to a time instant subsequent to the reserved switching time slot, if it is determined that the second converter block302has a reserved switching time slot at the first time instant. In addition, the control unit310may be configured to reserve a switching time slot at the first time instant for the first converter block301and/or to assign a switching time slot at the first time instant to the first converter block301, if it is determined that the second converter block302does not have a reserved switching time slot at the first time instant.

Overall, the control unit310may be configured to assign switching time slots for switching events to the plurality of converter blocks301,302,303,304,305,306such that converter blocks301,302,303,304,305,306sharing a common rail do not exhibit simultaneous switching events (at least switching events of the same event type). In particular, the control unit310may be configured to assign switching time slots for switching events to the plurality of converter blocks301,302,303,304,305,306such that converter blocks301,302,303,304,305,306sharing a common rail do not draw or sink current from or to the common rail simultaneous. Furthermore, it may be achieved that the switching events (with the same event type) of converter blocks sharing a common supply rail exhibit a minimum time distance from one another. The minimum distance may depend on the duration241of a switching event. By way of example, the minimum distance may be one time or two times the duration241or more.

By avoiding simultaneous switching events (of the same event type), the stress incurred by the converter blocks301,302,303,304,305,306may be decreased, thereby increasing the reliability of the converter circuit300.

The control unit310may be configured to determine whether any converter block302from the plurality of converter blocks301,302,303,304,305,306that the first converter block301shares a common supply rail with has a reserved switching time slot for a switching event at the first time instant. Furthermore, the control unit310may be configured to assign a switching time slot at the first time instant to the first converter block301, (notably only) if it is determined that none of the converter blocks302that the first converter block301shares a common supply rail with has a reserved switching time slot for a switching event at the first time instant. Alternatively, or in addition, the control unit310may be configured to assign a switching time slot to the first converter block301, which is subsequent to the reserved switching time slots of the one or more converter blocks302that the first converter block301shares a common supply rail with and that already have a reserved switching time slot for a switching event at or subsequent to the first time instant. By doing this, it can be ensured in an efficient and reliable manner that converter blocks that share a common supply rail do not perform switching events (of the same event type) simultaneously.

Hence, the control unit310may be configured to assign exclusive switching time slots for switching events (notably for switching events of the same type) to converter blocks301,302,303,304,305,306sharing a common rail. The switching time slots may be assigned according to the order of requested time instants for the switching events. In particular, switching time slots may be assigned sequentially according to the requested time instants for the switching events. By doing this, the overall delay of switching events may be reduced, thereby reducing the impact of delaying switching events on the operations of the one or more converter blocks, notably the impact with regards to regulation.

The control unit310may be configured to determine the type of switching event (i.e. the event type) from a plurality of different types of switching events, which is requested by the first converter block301. Furthermore, the control unit310may be configured to determine the type of switching event from the plurality of different types of switching events that the second converter block302has a reserved switching time slot for.

The plurality of different types of switching events may comprise a first type which leads to an increase of current on the common supply rail that is shared with the second converter block302. In other words, a first type of switching event may be a switching event which leads to an increase of the current that is drawn from or sunk to the common supply rail. Furthermore, the plurality of different types of switching events may comprise a second type which leads to a decrease of current on the common supply rail that is shared with the second converter block302. In other words, a second type of switching event may be a switching event which leads to a decrease of the current that is drawn from or sunk to the common supply rail.

The control unit may be configured to delay the switching event of the first converter block301if, notably only if, the event types for the switching events of the first converter block301and of the second converter block302are the same. In other words, a delay of the switching event of the first converter block301may only occur, if the switching event of the second converter block302also leads to an increase or alternatively to a decrease of the current which is drawn from or sunk to the common supply rail. In yet other words, a delay of the switching event of the first converter block301may only occur if the switching events of the first converter block301and of the second converter block302cause the same type of stress to the common supply rail. Otherwise, the control unit may refrain from delaying the switching event of the first converter block301. By doing this, the number of instances that switching events are delayed may be reduced, thereby reducing the impact of the switching event arbitration scheme onto the operations of the converter blocks.

The control unit310may be configured to determine that the first converter block301requests a switching event of the first event type at the first time instant. Furthermore, the control unit310may be configured to determine that the second converter block302requests a switching event of the second event type at the second time instant, wherein the first and second types of switching events are different from one another. In particular, the control unit310may be configured to determine that two converter blocks301,302sharing a common supply rail request switching events which are complementary to one another and/or which cause complementary stress to the common supply rail.

The control unit310may be further configured to assign the same switching time slot or at least partially overlapping switching time slots for the switching events of the first converter block301and the second converter block302. In particular, the control unit310may be configured to move the switching events of the first and second converter blocks301,302closer to one another, notably such that the complementary effects of the switching events onto the common supply rail compensate each other at least partially. By doing this, the stress which is caused by the switching events of converter blocks301,302may be decreased further.

The control unit310may be configured to determine that the first time instant and the second time instant are apart from one another by a pre-determined gap time or less. The pre-determined gap time may e.g. two times or only one time the duration241of a switching time slot. Furthermore, the control unit310may be configured to assign the same switching time slot or at least partially overlapping switching time slots for the switching events of the first converter block301and the second converter block302only if it is determined that the first time instant and the second time instant are apart from one another by the pre-determined gap time or less. In other words, the complementary time switching events may only be moved closer to one another, if the initially requested time instants for the switching events are sufficiently close to one another, thereby limiting the average delay of switching time instants and the average impact on the operations of the converter blocks.

The control unit310may be configured to determine the one or more converter blocks from the plurality of converter blocks301,302,303,304,305,306that the first converter block301shares a common supply rail with, using a dependency map, which indicates pairs of converter blocks from the plurality of converter blocks301,302,303,304,305,306that share a common supply rail. The dependency map may be stored in a storage element of the control unit310. By making use of a dependency map, interdependencies between converter blocks may be defined and determined in a reliable and flexible manner.

The control unit310may be configured to determine the duration241of a switching event. Furthermore, the control unit310may be configured to reserve a switching time slot for the switching event in accordance with the determined duration241of the switching event. By taking into account the (average) duration241of switching events when defining the duration of reserved switching time slots, the stress incurred by switching events may be reduced in a reliable manner.

FIG. 5shows a flow chart of an example method500for controlling a converter circuit300comprising a plurality of converter blocks301,302,303,304,305,306. Each converter block301,302,303,304,305,306may comprise one or more switches103,104which are turned on or off during switching events. At least some of the converter blocks301,302,303,304,305,306may share a common supply rail.

The method500comprises determining501that a first converter block301from the plurality of converter blocks301,302,303,304,305,306requests a switching event at a first time instant. Furthermore, the method500comprises determining502whether a second converter block302from the plurality of converter blocks301,302,303,304,305,306, with which the first converter block301shares a common supply rail, has a reserved switching time slot at the first time instant for a switching event. In addition, the method500comprises delaying503the switching event of the first converter block301to a time instant subsequent to the reserved switching time slot, if it is determined that the second converter block302has a reserved switching time slot at the first time instant.