Abstract:
The invention relates to a DC/DC converter design. The converter requires only one single inductor to draw energy from one input source and distribute it to more than one outputs, employing Flexible-Order Power-Distributive Control (FOPDC). It include a single inductor, a number of power switches, comparators, only one error amplifier, a detecting circuit and a control block to regulate outputs. This converter can correctly regulate multiple outputs with fast transient response, low cross regulation, and effective switching frequency for each output. It can work in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM). Moreover, with FOPDC, future output extension is simple, making a shorter time-to-market process for next versions of the converter. The design can be applied to different types of DC-DC converter.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to DC-DC switching converters, and more specifically, to single-inductor multiple-output DC-DC converters. 
       BACKGROUND OF THE INVENTION 
       [0002]    DC/DC switching converter is an indispensable part of many power management systems. As all designs are put into an effort of size reduction, converter cannot stay out of that trend. Designers, therefore, are exploring the way to shrink the size in both on-chip and off-chip implementation. Of all the approaches, Single-Inductor Multiple-Output (SIMO) converters come to prevail. With only one single inductor to regulate more than one output, the implementation can avoid problems that happen in conventional types of converters, such as too many bulky power devices as inductors, capacitors, and control ICs. Hence, the cost of mass-production is obviously much reduced. Single Inductor Multiple Output (SIMO) shows up as a most suitable and cost-effective solution in future development of DC-DC converter. However, it is still a big challenge to DC-DC converter designers because before the disclose of this invention, there is no proper control method that can be practical. That is the reason why there has been no SIMO switching DC-DC converter commercially sold on the market. Some approaches to Multiple Outputs converters are discussed in the following part of the invention. 
         [0003]    In  FIG. 1 , a conventional existing commercial SIMO DC-DC converter is shown, but it is not a fully switching SIMO type. It consists of one inductor L, Boost converter  501 , and Low-Drop-Output converters (LDOs)  502 ˜ n . Inductor L with Boost converter  501  generates output Vo 1  with the highest voltage, and all other outputs Vo 2 ˜Von are generated by LDOs  502 ˜ n , respectively. This structure has been widely used by many power-chip-making companies and proved fine functioning in real applications. It gives designers a simple way of implementation and a short time-to-market for a product with low ripple in LDO outputs. However, once the voltage difference between Vo 1  and LDO outputs increases, efficiency decreases remarkably. This is because of the voltage drop over the series power transistor of LDOs. The loss over the power transistor becomes more serious when LDO output currents are increased in heavy loads. An effort to improve the performance of LDOs using a power transistor with larger size for high output current faces with chip area consumption which is not favorable in IC designs. 
         [0004]      FIG. 2  and  FIG. 3  show another conventional approach on SIMO switching DC-DC converters. The control scheme of the converter is Time-multiplexing. All outputs share the inductor and the main switch Sx, and each occupies a certain none-overlapped cycle and works as a separate boost converter. As shown in  FIG. 3 , in Φ 1 , inductor L, switch Sx and S 1  work as a normal separated boost converter to transfer energy to Vo 1 . In Φ 2 , inductor L, switch Sx and S 2  work as a normal separated boost converter to transfer energy to Vo 2 . In Φn, inductor L, switch Sx and Sn work as a normal separated boost converter to transfer energy to Von. The phases reserved for outputs are none-overlapped and controlled by the controller  600 . In an effort to handle large output currents and suppress cross regulations, the converter is designed to work in pseudo-continuous or discontinuous conduction mode (PCCM/DCM). With PCCM, freewheel switch Sf is switched in both continuous conduction mode (CCM) and DCM to reduce loading effects from one to other outputs. That means, the freewheel switch Sf is turned on in any switching cycle at a determined level Idc, even the inductor current Idc is not zero, causing energy dissipation in the resistance of the inductor and the freewheel switch due to the none-zero inductor current during the freewheel time, The overall efficiency, therefore, is badly influenced, especially when the number of outputs increases. Moreover, the converter using PCCM has n separate proportional-integral (PI) control loops for n outputs, where each PI loop requires one error amplifier and one compensation network. It is clear that implementation of n compensation networks will be really bulky. That is not to mention a complex current sensing circuit for each output to make proper Idc level. 
         [0005]    The drawbacks of the conventional techniques, therefore, urge the development of a new control method for multiple-output converter, which can reduce area consumption while maintaining good regulations for outputs. The converter using this method should also work properly in DCM and CCM. In additions, it is desirable to have a new method of simplicity and flexibility in implementation that can be applied to different converter types of multiple-output topologies for different application requirements. 
       SUMMARY OF THE INVENTION 
       [0006]    A multiple-output DC-DC converter is provided by the present invention which comprises an inductor for storing energy, a charging switch electrically connected in series with the inductor, a plurality of N output switches, wherein first ends of the output switches are connected to a node between the inductor and the charging switch and second end of each output switch is connected to a corresponding output terminal, wherein N is an integer of two or more, a detecting circuit for detecting current of the inductor and voltages of the output terminals, and a control circuit for sequentially controlling ON and OFF of the charging switch so as to store energy into the inductor, controlling ON and OFF of the first to N−1th output switches so as to distribute the energy to the corresponding output terminals, and controlling ON and OFF of the Nth output switch so as to distribute the energy to the corresponding output terminal. 
         [0007]    According to an embodiment of the present invention, the control circuit of the multiple-output DC-DC converter may turns on the first to N−1th output switches simultaneously so as to distribute the energy to the corresponding output terminals. 
         [0008]    According to an embodiment of the present invention, the control circuit of the multiple-output DC-DC converter may turns off the output switch when the voltage of the corresponding output terminal has reached a predetermined value. 
         [0009]    According to an embodiment of the present invention, the control circuit of the multiple-output DC-DC converter may urns on the Nth output switch so as to distribute the energy to the corresponding output terminal when the each voltage of the first to N−1th output terminal has once reached a predetermined value. 
         [0010]    According to an embodiment of the present invention, the multiple-output DC-DC converter may further comprise a freewheel switch electrically connected in parallel with the inductor, wherein the control circuit turns on the freewheel switch when the energy stored in the inductor is fully discharged. 
         [0011]    According to an embodiment of the present invention the multiple-output DC-DC converter may further comprise a plurality of charging capacitors each electrically connected with the corresponding output terminals. 
         [0012]    Also, a method of converting DC to DC is provided by the present invention which comprises the steps of (a) storing energy into a passive element, (b) distributing the stored energy to first to N−1th output terminals, and (c) distributing the stored energy to Nth output terminal after the step of (b), wherein N is an integer of two or more. 
         [0013]    According to an embodiment of the present invention, the distribution of the stored energy to the first to N−1th output terminals may be simultaneously started. 
         [0014]    According to an embodiment of the present invention, the distribution of the stored energy to the specific output terminal may be finished in case an amount of energy distributed to the output terminal has reached a predetermined value. 
         [0015]    According to an embodiment of the present invention, the method of converting DC to DC may further comprise the step of (d) freewheeling the passive element when the energy stored in the passive element is fully discharged. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  diagrammatically illustrates a conventional method of SIMO converter with LDOs. 
           [0017]      FIG. 2  diagrammatically illustrates a conventional method of SIMO converter with PCCM control. 
           [0018]      FIG. 3  graphically illustrates the waveforms of real inductor current and timing diagram of the power switches of the converter shown in  FIG. 2 . 
           [0019]      FIG. 4  diagrammatically illustrates the invented method of SIMO converter with Flexible Ordered Power-Distributive Control. 
           [0020]      FIG. 5  graphically illustrates one possible timing diagram of the power switches of the converter shown in  FIG. 4 , where the output power switches are turned on one-by-one in a none-overlap pattern. 
           [0021]      FIG. 6  graphically illustrates one possible timing diagram of the power switches of the converter shown in  FIG. 4 , where the power switches of the preceding outputs are turned on at the same time at the beginning of a discharge cycle and off separately by a signal from its correspondent comparator, and the power switch of the last output is turned on after all preceding output power switches are off. 
           [0022]      FIG. 7  graphically illustrates one possible timing diagram of the power switches of the converter shown in  FIG. 4 , where the power switches of the preceding outputs are turned on in an overlap pattern and off separately by a signal from its correspondent comparator, and the power switch of the last output is turned on after all preceding output power switches are off. 
       
    
    
       [0023]    Each of  FIG. 8-10  graphically illustrates one possible timing diagram of the power switches of the converter shown in  FIG. 4 . 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0024]    From now, the description disclosed in this invention will only be about a 4-output converter. The number 4 of outputs is chosen to imply the characteristic of multiple outputs. However, it is clear that the scope of this invention is not limited to 4-output converters. The number of output can be any integer of two or more, but a converter is still in the range of this invention if it uses the same control method of comparator(s) and one error amplifier. 
         [0025]    A DC/DC switching power supply, which can power four positive outputs, includes one inductor  105 , three comparators  161 ,  162 ,  163 , and one error amplifier (EA)  164  in feedback loops, one control circuit, one inductor and six power switches (four output switches  141 ,  142 ,  143 ,  144 ; one main shared switch  140  and one freewheel switch  145 ). The three comparators  161 ,  162 , and  163  are put in the feedback loops of the first three outputs to sense their voltage levels. The error amplifier  164 , which is, usually but not limited, to one Operational Transconductance Amplifier (OTA), is put in the feedback loop of the last output to control the errors of all outputs, then, dependent on which, it decides the duty cycle of the main switch  140 , or in fact, it decides the charge in the inductor  105 . The power switches  141 ,  142 ,  143 , and  144  are turned on and off in a certain order by Control Block  200  following the Flexible Ordered Power-Distributive Control to regulate outputs. The power switch  145  is to short the two terminals of the inductor L to the source, which is normally, but not limited to, a battery, to suppress possible ringing at node  110  when all the other power switches are off and the inductor  105 &#39;s current is close to zero. 
         [0026]    The Flexible Ordered Power-Distributive Control (FOPDC) sets one rule of order and control over all output that, in the discharge time of a cycle when the energy stored in the inductor is distributed to outputs, the output Vo 4  has the last priority to receive energy and is controlled by PI control with an error amplifier (EA) in its feedback loop, while the other outputs have higher priority to receive first portions of energy and are controlled by comparators in their feedback loops, and are, thus, called bang-bang outputs. The preceding outputs Vo 1 , Vo 2 , and Vo 3  can get energy one-by-one in none-overlap time sharing, or together in overlap time sharing as long as the output voltages are regulated by comparators. As it can be seen in this FOPDC, all of the errors of the preceding bang-bang outputs are transferred and accumulated to the last output Vo 4 , which is the only one requiring a compensation network in the feedback loop. Depending on the errors, the PI loop determines the duty cycle of the switch  140  to control the charge in the inductor  105 . 
         [0027]    The invention of FOPDC for SIMO converters helps regulate more than one DC outputs. The invention can be applied to different multiple output architectures, and different number of outputs. Of course, it can also work correctly in both CCM and DCM operations with the presence of the switch  145 . 
         [0028]    In this invention, various embodiments of the present invention will be described in detail with reference to the drawings, where like reference numerals and names represent like parts and appear throughout several views. Although the claimed invention is described with step-up converter, the scope of this invention is not limited to only step-up converters. A converter with FOPDC using one EA and n−1 comparators in feedback loops for n outputs is claimed to be within the scope of this invention. 
         [0029]    A schematic diagram of the preferred embodiment of the multiple output boost converter is illustrated in  FIG. 4 . A positive terminal of an input power source  100  is connected to a first terminal of an inductor  105 . A second terminal of the inductor  105  is connected to a charging switch  140 . Four output switches  141 ,  142 ,  143  and  144  are provided in the converter. The first ends of all output switches  141 ,  142 ,  143  and  144  are connected to the node between the inductor  105  and the charging switch  140  and the second end of each output switches  141 ,  142 ,  143  and  144  is connected to the corresponding output terminals Vo 1 , Vo 2 , Vo 3  and Vo 4 . A freewheel switch  145  is connected in parallel with the inductor  105 . The freewheel switch  145  is active only in DCM mode. Charging capacitors Co 1 , Co 2 , Co 3  and Co 4  are coupled between the ground and the output terminals Vo 1 , Vo 2 , Vo 3  and Vo 4 , respectively. Load  181 ,  182 ,  183  and  184  are coupled across capacitors Co 1 , Co 2 , Co 3  and Co 4 , respectively. 
         [0030]    A Control circuit  200  has output control lines  130 ,  131 ,  132 ,  133 ,  134 , and  135  to turn on or off the switches  140 ,  141 ,  142 ,  143 ,  144  and  145 , respectively. Also, a detecting circuit for detecting the current of the inductor and voltages of the output terminals Vo 1 , Vo 2 , Vo 3  and Vo 4  is provided in the converter. The Control circuit  200  has input inductor current signal  175  from the detecting circuit, input error signal  174  from EA  164 , and input digital signal  171 ,  172 ,  173  from outputs of comparators  161 ,  162 ,  163 , respectively. First inputs of the comparators  161 ,  162 ,  163  and EA  164  are connected, but not limited to, a reference voltage Vref. Voltage scalers Scaler  1 , Sealer  2 , Scaler  3 , Scaler  4  are coupled between second inputs of the comparators  161 ,  162 ,  163 , EA  164  and output lines  151 ,  152 ,  153   154  of Vo 1 , Vo 2 , Vo 3 , Vo 4 , respectively. Reference voltages for outputs can be from only one Vref, or different between outputs. The voltage scalers, together with the reference voltage (or the reference voltages), decide regulated output voltage levels. 
         [0031]    In this invention of FOPDC, the output voltages Vo 1 , Vo 2 , and Vo 3  are regulated with comparators while the last output Vo 4  is regulated with EA  164 . Outputs  171  (or  172 , or  173 ) of the comparator  161  (or  162 , or  163 ) changes its status, to HIGH in this drawing, to turn off switch  141  (or  142 , or  143 ), when the output voltage Vo 1  (or Vo 2 , or Vo 3 ) reaches to the required voltage determined by the reference voltage Vref and voltage Scaler  1  (or Scaler  2 , or Scaler  3 ). Since controlled by comparators, the output Vo 1 , Vo 2  and Vo 3  have very fast and robust responses. Moreover, they do not need compensation network in their feedback loops. 
         [0032]    In the invention of FOPDC, the output voltage Vo 4  is put as the last one and regulated by the error amplifier EA  164 . In one switching cycle, or more correctly, in one energy distribution cycle, the output Vo 4  is the last to receive charge from the inductor  105 , when the other output Vo 1 , Vo 2  and Vo 3  are already at the required voltage. In other words to interpret the important points of the invention of FOPDC, the output which is regulated by error amplifier should be orderedly put as the last one to receive a portion of charge, when the other outputs already have enough charge. With the position as the last output to receive energy, Vo 4  reflects the total energy needs of all the outputs. EA  164  integrates the voltage level of Vo 4  every switching cycle to control the duty cycle (turn-on time) of the switch  140  to charge more or less energy to the inductor  105  in pulse with modulation (PWM) control. Therefore, the voltage loop of the last output Vo 4  also takes the responsibility for total current charge in the inductor  105  every switching cycle. 
         [0033]    The invention of FOPDC with comparators and one error amplifier in the last output loop can be applied to different switching patterns. Some different exemplary switching patterns used to describe FOPDC are illustrated in  FIGS. 5 ,  6 ,  7  and  8 . 
         [0034]      FIG. 5  will be described in relation with  FIG. 4 . In  FIG. 5 , during a charge cycle DT, the switch  140  is on and the inductor is charged. The time DT of PWM control is determined by the feedback loop of Vo 4  with EA  164  and the Control circuit  200 . The four output switches  141 ,  142 ,  143 ,  144  and the freewheel switch  145  (only active in DCM) share D′T to turn on. As mentioned in FOPDC, the outputs are arranged in the Control circuit  200  as Vo 1 , Vo 2 , Vo 3 , and Vo 4  in descending order of priority to get energy. The capacitor Co 1  of the output Vo 1  gets the first portion of charge in D 1 T when the switch  141  is turned on after the switch  140  is off. As soon as the portion of charge transferred to the capacitor Co 1  makes Vo 1  rise over its required voltage determined by its reference voltage and Voltage Scaler  1 , making the comparator  161  change its output state, the line voltage  171  change to HIGH, the switch  141  is turned off by the output signal  131  from the Control circuit  200 . Right after the switch  141  is off, the switch  142  of the output Vo 2  is turned on in D 2 T if Vo 2  is detected by the comparator  162  to be smaller than its pre-determined voltage, and then, turned off at the end of D 2 T when Vo 2  goes over that pre-determined voltage. The switch  143  of Vo 3 , then, has the same operation with that of Vo 2  and after Vo 2 . Then, the capacitor Co 4  of Vo 4  gets the last portion of charge. Dependent on the amount of the last portion, the EA  164  of Vo 4  controls its voltage loop and the total current charge from the turn-on time (duty) of the switch  140  to make sure that the portion is enough to keep Vo 4  at a pre-determined voltage while good regulation is already made in the preceding outputs. Before the start of a new switching cycle, if the charge stored in the inductor  105  is fully discharged to outputs, all the switches are turned off except for the switch  145  on during D f T to suppress possible ringing at line  110 . With the switch  145  in active mode, the converter is said to work in DCM operation. In CCM, since full discharge in the inductor  105  does not happen, the switch  145  is always off and D f T does not exist in switching cycles. 
         [0035]      FIG. 6  will be described in relation with  FIG. 4 . In  FIG. 6 , during a charge cycle DT, the switch  140  is on and the inductor  105  is charged. The time DT of PWM control is determined by the feedback loop of Vo 4  with EA  164  and the Control circuit  200 . The four output switches  141 ,  142 ,  143 ,  144  and the freewheel switch  145  (active in DCM) share D′T to turn on. As mentioned in FOPDC, the outputs are arranged in the Control circuit  200  that Vo 1 , Vo 2  and Vo 3  have a priority over Vo 4  to get energy. In this switching pattern, the Control circuit  200  arranges that the switches  141 ,  142  and  143  on together in the discharge cycle of a cycle. The capacitors Co 1 , Co 2  and Co 3  together share the first portion of energy from the inductor  105 . Outputs  171 ,  172  and  173  of comparators  161 ,  162  and  163  change states to HIGH to turn off the switches  141 ,  142  and  143 , respectively, when the outputs Vo 1 , Vo 2 , and Vo 3  reach the required voltages pre-determined by the reference voltage and scalers. As soon as all the switches  141 ,  142  and  143  are off in a discharge cycle D′T, the switch  144  is turned on for the capacitor Co 4  of Vo 4  to get the last portion of charge. Also as mentioned in FOPDC, dependent on the amount of that portion, the EA  164  of Vo 4  controls its voltage loop and the total current charge from the turn-on time (duty) of the switch  140  to make sure that the portion is enough to keep Vo 4  at a pre-determined voltage while good regulation is already made in the preceding outputs. Before the start of a new switching cycle, if the charge stored in the inductor  105  is fully discharged to outputs, all the switches are turned off except for the switch  145  which is on during D f T to suppress possible ringing at line  110 . With the switch  145  in active mode, the converter is said to work in DCM operation. In CCM, since full discharge does not happen, the switch  145  is always off, and D f T does not exist in switching cycles. 
         [0036]    Compared with the switching pattern in  FIG. 5 , the switching pattern in  FIG. 6  has some more advantages in operation. With the switching pattern in  FIG. 6 , difficulties in deadtime control between the on-states of the output switches  141 ,  142 ,  143 , which are obvious in the pattern of  FIG. 5 , are eliminated. As designers all know, if deadtime controls are not exact, the voltage of line  110  does not change properly, causing efficiency reduction for the converter performance. In the switching pattern shown in  FIG. 6 , deadtime control for output switch  141 ,  142 , and  143  are not necessary, thus, simplifying the design. Moreover, by turning on these three switches together, the charge, which is in form of current in the inductor  105 , is shared simultaneously between the preceding outputs Vo 1 , Vo 2 , Vo 3 , reducing the peak current charged to each of them, so that the voltage ripples at output lines  151 ,  152 , and  153  are reduced. 
         [0037]    The switching pattern in  FIG. 7  is the general view of that in  FIGS. 5 and 6 . The pattern shows that the switch  142  does not need to wait for off-state of the switch  141 , and that the switch  143  does not need to wait for off-state of the switches  141  and  142 , and that these output switches do not need to change from off to on-state together like in the pattern shown  FIG. 6 . Dependent on the arrangement of the Control circuit  200 , two or three switches can be together on-state some period of time in the discharge cycle as long as each of them is still controlled with a signal from the feedback comparator ( 161 ,  162 , or  163 ). While the order of charge transfer for the preceding output Vo 1 , Vo 2  and Vo 3  can be changed flexibly, the output Vo 4  with EA  164  in its feedback loop always stays as the last to get charge. 
         [0038]    The switching pattern in  FIG. 7  also shares the advantages that were mentioned with the switching pattern in  FIG. 6 . In addition, the switching pattern in  FIG. 7  gives designers the flexibility in designing on-state timings of the preceding output switches  141 ,  142  and  143 . While the over-lap between on-states of the switches  141 ,  142  and  143  are available, the on-state timings can be designed, calculated, and controlled by the Control circuit  200  so that the maximum total efficiency for the converter is archieved. Therefore, the switching pattern in  FIG. 7  is the general view of that in  FIG. 5  and  FIG. 6 , but with more advantages to designers of SIMO converters and to the performance of SIMO converters themselves. 
         [0039]    The switching patterns in  FIG. 8 ,  FIG. 9 , and  FIG. 10  are the general cases of those in  FIG. 5 ,  FIG. 6 , and  FIG. 7 , respectively. To make it simple to understand, the above discriptions of this invention assume that the switching cycle T is identical with the energy distribution cycle T ED . However, one energy distribution cycle T ED  is defined to include one or more than one switching cycle T that have one on-state of the switch  144 . Therefore, in one energy distribution cycle, all output capacitors receive charge. Whereas, in one switching cycle, which is defined with one on-state of the switch  140 , the number of output capacitors to get charge can be from one to four depending on the output voltage levels. In other words, in one switching cycle, the number of output switches to be on can be from one switch to all the four switches ( 141 ,  142 ,  143 ,  144 ). As mentioned above, the switch  145  is only active in DCM or at the boundary of DCM and CCM in  FIG. 8 ,  9 ,  10 . When it is always off-state, the converter is said to work in CCM operation.