SECTION 4 SWITCHED CAPACITOR VOLTAGE CONVERTERS Walt .
SWITCHED CAPACITOR VOLTAGE CONVERTERSSECTION 4SWITCHED CAPACITOR VOLTAGECONVERTERSWalt Kester, Brian Erisman, Gurjit ThandiINTRODUCTIONIn the previous section, we saw how inductors can be used to transfer energy andperform voltage conversions. This section examines switched capacitor voltageconverters which accomplish energy transfer and voltage conversion usingcapacitors.The two most common switched capacitor voltage converters are the voltage inverterand the voltage doubler circuit shown in Figure 4.1. In the voltage inverter, thecharge pump capacitor, C1, is charged to the input voltage during the first half ofthe switching cycle. During the second half of the switching cycle, its voltage isinverted and applied to capacitor C2 and the load. The output voltage is thenegative of the input voltage, and the average input current is approximately equalto the output current. The switching frequency impacts the size of the externalcapacitors required, and higher switching frequencies allow the use of smallercapacitors. The duty cycle - defined as the ratio of charging time for C1 to the entireswitching cycle time - is usually 50%, because that generally yields the optimalcharge transfer efficiency.After initial start-up transient conditions and when a steady-state condition isreached, the charge pump capacitor only has to supply a small amount of charge tothe output capacitor on each switching cycle. The amount of charge transferreddepends upon the load current and the switching frequency. During the time thepump capacitor is charged by the input voltage, the output capacitor C2 must supplythe load current. The load current flowing out of C2 causes a droop in the outputvoltage which corresponds to a component of output voltage ripple. Higherswitching frequencies allow smaller capacitors for the same amount of droop. Thereare, however, practical limitations on the switching speeds and switching losses, andswitching frequencies are generally limited to a few hundred kHz.The voltage doubler works similarly to the inverter; however, the pump capacitor isplaced in series with the input voltage during its discharge cycle, therebyaccomplishing the voltage doubling function. In the voltage doubler, the averageinput current is approximately twice the average output current.The basic inverter and doubler circuits provide no output voltage regulation,however, techniques exist to add regulated capability and have been implemented inthe ADP3603/3604/3605/3607.4.1
SWITCHED CAPACITOR VOLTAGE CONVERTERSBASIC SWITCHED CAPACITOR VOLTAGEINVERTER AND VOLTAGE DOUBLERINVERTERVIN C1C2LOADVOUT –VINIOUTDOUBLERVOUT 2VINIOUTVIN C1C2LOADFigure 4.1There are certain advantages and disadvantages of using switched capacitortechniques rather than inductor-based switching regulators. An obvious keyadvantage is the elimination of the inductor and the related magnetic design issues.In addition, these converters typically have relatively low noise and minimalradiated EMI. Application circuits are simple, and usually only two or three externalcapacitors are required. Because there is no need for an inductor, the final PCBcomponent height can generally be made smaller than a comparable switchingregulator. This is important in many applications such as display panels.Switched capacitor inverters are low cost and compact and are capable of achievingefficiencies greater than 90%. Obviously, the current output is limited by the size ofthe capacitors and the current carrying capacity of the switches. Typical IC switchedcapacitor inverters have maximum output currents of about 150mA maximum.Switched capacitor voltage converters do not maintain high efficiency for a widerange of ratios of input to output voltages, unlike their switching regulatorcounterparts. Because the input to output current ratio is scaled according to thebasic voltage conversion (i.e., doubled for a doubler, inverted for an inverter)regardless of whether or not regulation is used to reduce the doubled or invertedvoltage, any output voltage magnitude less than 2VIN for a doubler or less than VIN for an inverter will result in additional power dissipation within theconverter, and efficiency will be degraded proportionally.4.2
SWITCHED CAPACITOR VOLTAGE CONVERTERSSWITCHED CAPACITOR VOLTAGE CONVERTERSn No Inductors!n Minimal Radiated EMIn Simple Implementation: Only 2 External Capacitors(Plus an Input Capacitor if Required)n Efficiency 90% Achievablen Optimized for Doubling or Inverting Supply Voltage Efficiency Degrades for Other Output Voltagesn Low Cost, Compact, Low Profile (Height)n Parts with Voltage Regulation are Available:ADP3603/ADP3604/ADP3605/ADP3607Figure 4.2The voltage inverter is useful where a relatively low current negative voltage isrequired in addition to the primary positive voltage. This may occur in a singlesupply system where only a few high performance parts require the negativevoltage. Similarly, voltage doublers are useful in low current applications where avoltage greater than the primary supply voltage is required.CHARGE TRANSFER USING CAPACITORSA fundamental understanding of capacitors (theoretical and real) is required inorder to master the subtleties of switched capacitor voltage converters. Figure 4.3shows the theoretical capacitor and its real-world counterpart. If the capacitor ischarged to a voltage V, then the total charge stored in the capacitor, q, is given by q CV. Real capacitors have equivalent series resistance (ESR) and inductance (ESL)as shown in the diagram, but these parasitics do not affect the ability of thecapacitor to store charge. They can, however, have a large effect on the overallefficiency of the switched capacitor voltage converter.4.3
SWITCHED CAPACITOR VOLTAGE CONVERTERSSTORED CHARGE IN A CAPACITORSTORED CHARGEESRq CV CVCV-ESLIDEALACTUALFigure 4.3If an ideal capacitor is charged with an ideal voltage source as shown in Figure4.4(A), the capacitor charge buildup occurs instantaneously, corresponding to a unitimpulse of current. A practical circuit (Figure 4.4 (B)) will have resistance in theswitch (RSW) as well as the equivalent series resistance (ESR) of the capacitor. Inaddition, the capacitor has an equivalent series inductance (ESL). The chargingcurrent path also has an effective series inductance which can be minimized withproper component layout techniques. These parasitics serve to limit the peakcurrent, and also increase the charge transfer time as shown in the diagram. Typicalswitch resistances can range from 1Ω to 50Ω, and ESRs between 50mΩ and 200mΩ.Typical capacitor values may range from about 0.1µF to 10µF, and typical ESLvalues 1 to 5nH. Although the equivalent RLC circuit of the capacitor can beunderdamped or overdamped, the relatively large switch resistance generally makesthe final output voltage response overdamped.4.4
SWITCHED CAPACITOR VOLTAGE CONVERTERSCHARGING A CAPACITOR FROM A VOLTAGE SOURCEIDEAL (A)ACTUAL (B)vOUTVIN iVIN CvOUTRSWCiESRESLVINVINvOUTvOUT00IPEAK Õ iitÕÕ000Figure 4.4The law of conservation of charge states that if two capacitors are connectedtogether, the total charge on the parallel combination is equal to the sum of theoriginal charges on the capacitors. Figure 4.5 shows two capacitors, C1 and C2, eachcharged to voltages V1 and V2, respectively. When the switch is closed, an impulseof current flows, and the charge is redistributed. The total charge on the parallelcombination of the two capacitors is qT C1·V1 C2·V2. This charge is distributedbetween the two capacitors, so the new voltage, VT, across the parallel combinationis equal to qT/(C1 C2), orVT qTC1 V1 C2 V2 C1 C2 V2 . V1 C1 C2 C1 C2 C1 C2C1 C2This principle may be used in the simple charge pump circuit shown in Figure 4.6.Note that this circuit is neither a doubler nor inverter, but only a voltage replicator.The pump capacitor is C1, and the initial charge on C2 is zero. The pump capacitoris initially charged to VIN. When it is connected to C2, the charge is redistributed,and the output voltage is VIN/2 (assuming C1 C2). On the second transfer cycle,the output voltage is pumped to VIN/2 VIN/4. On the third transfer cycle, theoutput voltage is pumped to VIN/2 VIN/4 VIN/8. The waveform shows how theoutput voltage exponentially approaches VIN.4.5
SWITCHED CAPACITOR VOLTAGE CONVERTERSCHARGE REDISTRIBUTIONBETWEEN CAPACITORSq1 C1·V1 V1-q2 C2·V2C1 V2-C2CONSERVATION OFCHARGE:qT C1 V1 C2 V 2 VTC1-VT qTC1 C2VT C2C1 V1 V2C1 C2C1 C2C2Figure 4.5CONTINUOUS SWITCHINGVINvOUT C2C1vOUTASSUME: ZERO INITIAL CHARGE ON C2, AND C1 C2VINVIN2t0Figure 4.64.6
SWITCHED CAPACITOR VOLTAGE CONVERTERSFigure 4.7 shows a pump capacitor, C1, switched continuously between the source,V1, and C2 in parallel with the load. The conditions shown are after a steady statecondition has been reached. The charge transferred each cycle is q C1(V1 – V2).This charge is transferred at the switching frequency, f. This corresponds to anaverage current (current charge transferred per unit time) ofI f q f·C1(V1 – V2), orI V1 V2.1f C1CONTINUOUS SWITCHING, STEADY STATEV1I V2fC2LOADC1CHARGE TRANSFERRED / CYCLE C1(V1- V2)I CHARGE TRANSFERREDV1 V 2V1 V 2 f C 1( V 1 V 2 ) 1TIME"R"f C1V1 IV21" R" f C1C2LOADFigure 4.7Notice that the quantity, 1/f·C1, can be considered an equivalent resistance, "R",connected between the source and the load. The power dissipation associated withthis virtual resistance, "R", is essentially forced to be dissipated in the switch onresistance and the capacitor ESR, regardless of how low those values are reduced. (Itshould be noted that capacitor ESR and the switch on-resistance cause additionalpower losses as will be discussed shortly.)In a typical switched capacitor voltage inverter, a capacitance of 10µF switched at100kHz corresponds to "R" 1Ω. Obviously, minimizing "R" by increasing thefrequency minimizes power loss in the circuit. However, increasing switchingfrequency tends to increase switching losses. The optimum switched capacitoroperating frequency is therefore highly process and device dependent. Therefore,specific recommendations are given in the data sheet for each device.4.7
SWITCHED CAPACITOR VOLTAGE CONVERTERSUNREGULATED SWITCHED CAPACITOR INVERTER ANDDOUBLER IMPLEMENTATIONSAn unregulated switched capacitor inverter implementation is shown in Figure 4.8.Notice that the SPDT switches (shown in previous diagrams) actually comprise twoSPST switches. The control circuit consists of an oscillator and the switch drivesignal generators. Most IC switched capacitor inverters and doublers contain all thecontrol circuits as well as the switches and the oscillator. The pump capacitor, C1,and the load capacitor, C2, are external. Not shown in the diagram is a capacitor onthe input which is generally required to ensure low source impedance at thefrequencies contained in the switching transients.The switches used in IC switched capacitor voltage converters may be CMOS orbipolar as shown in Figure 4.9. Standard CMOS processes allow low on-resistanceMOSFET switches to be fabricated along with the oscillator and other necessarycontrol circuits. Bipolar processes can also be used, but add cost and increase powerdissipation.SWITCHED CAPACITOR VOLTAGE INVERTERIMPLEMENTATIONS1S3VIN C1S2OSCILLATOR ANDSWITCH DRIVE CIRCUITSFigure 4.84.8-VINS4C2LOAD
SWITCHED CAPACITOR VOLTAGE CONVERTERSSWITCHES USED IN VOLTAGE NPNFigure 4.9VOLTAGE INVERTER AND DOUBLER DYNAMICOPERATIONThe steady-state current and voltage waveforms for a switched capacitor voltageinverter are shown in Figure 4.10. The average value of the input current waveform(A) must be equal to IOUT. When the pump capacitor is connected to the input, acharging current flows. The initial value of this charging current depends on theinitial voltage across C1, the ESR of C1, and the resistance of the switches. Theswitching frequency, switch resistance, and the capacitor ESRs generally limit thepeak amplitude of the charging current to less than 2.5IOUT. The charging currentthen decays exponentially as C1 is charged. The waveforms in Figure 4.10 assumethat the time constant due to capacitor C1, the switch resistance, and the ESR of C1is several times greater than the switching period (1/f). Smaller time constants willcause the peak currents to increase as well as increase the slopes of thecharge/discharge waveforms. Long time constants cause longer start-up times andrequire larger and more costly capacitors. For the conditions shown in Figure 4.10(A), the peak value of the input current is only slightly greater than 2IOUT.The output current waveform of C1 is shown in Figure 4.10 (B). When C1 isconnected to the output capacitor, the step change in the output capacitor current isapproximately 2IOUT. This current step therefore creates an output voltage stepequal to 2IOUT ESRC2 as shown in Figure 4.10(C). After the step change, C2charges linearly by an amount equal to IOUT/2f C2. When C1 is connected back tothe input, the ripple waveform reverses direction as shown in the diagram. The totalpeak-to-peak output ripple voltage is therefore:IVRIPPLE 2IOUT ESRC2 OUT .2f C24.9
SWITCHED CAPACITOR VOLTAGE CONVERTERSVOLTAGE INVERTER WAVEFORMSiINVIN C1ESRC1LOADC2ESRC2iOUTVOUT –VINIOUT2IOUT(A)iINVRIPPLE 2IOUT ESRC 20I OUT2f C 20(B)iOUT- 2IOUT(C)VRIPPLEFigure 4.10VOLTAGE DOUBLER WAVEFORMSiINiOUTVINVOUT 2VINIOUT C1ESRC1C2ESRC2LOAD(A) 2IOUTiINVRIPPLE 2IOUT ESRC 22IOUT(B)iOUTI OUT2f C 20(C)VRIPPLEFigure 4.114.10
SWITCHED CAPACITOR VOLTAGE CONVERTERSThe current and voltage waveforms for a simple voltage doubler are shown in Figure4.11 and are similar to those of the inverter. Typical voltage ripple for practicalswitched capacitor voltage inverter/doublers range from 25mV to 100mV, but can bereduced by filtering techniques as described in Section 8 of this book.Note that the input current waveform has an average value of 2IOUT because VINis connected to C1 during C1's charge cycle and to the load during C1's dischargecycle. The expression for the ripple voltage is identical to that of the voltageinverter.SWITCHED CAPACITOR VOLTAGE CONVERTER POWERLOSSESThe various sources of power loss in a switched capacitor voltage inverter are shownin Figure 4.12. In addition to the inherent switched capacitor resistance, "R" 1/f·C1, there are resistances associated with each switch, as well as the ESRs of thecapacitors. The quiescent power dissipation, Iq·VIN, must also be included, where Iqis the quiescent current drawn by the IC itself.VOLTAGE INVERTER POWER LOSSESRSWVIN C2C1IqLOADESRC1ESRC2RSWIOUTVOUTPLOSS IOUT ( VIN VOUT ) IqVIN IOUT2 ROUT IqVINROUT 8R SW 4ESRC1 1 ESRC2f C1Figure 4.124.11
SWITCHED CAPACITOR VOLTAGE CONVERTERSThe power dissipated in the switching arm is first calculated. When C1 is connectedto VIN, a current of 2IOUT flows through the switch resistances (2RSW) and theESR of C1, ESRC1. When C1 is connected to the output, a current of 2IOUTcontinues to flow through C1, 2RSW, and ESRC1. Therefore, there is always an rmscurrent of 2IOUT flowing through these resistances, resulting in a power dissipationin the switching arm of:PSW (2IOUT)2 (2RSW ESRC1) IOUT2 (8RSW 4ESRC1).In addition to these purely resistive losses, an rms current of IOUT flows throughthe "resistance" of the switched capacitor, C1, yielding an additional loss of:" PC1 " IOUT 2 " RC1 " IOUT 2 1.f C1The rms current flowing through ESRC2 is IOUT, yielding a power dissipation of:PESR IOUT2 ESRC2.C2Adding all the resistive power dissipations to the quiescent power dissipation yields:1 PLOSS IOUT 2 8R SW 4 ESRC1 ESRC2 IqVIN . f C1 All of the resistive losses can be grouped into an equivalent ROUT as shown in thediagram.ROUT 8RSW 4ESRC1 1/f C1 ESRC2.Typical values for switch resistances are between 1 - 20Ω, and ESRs between 50 and200mΩ. The values of C1 and f are generally chosen such that the term, 1/f·C1, isless than 1Ω. For instance, 10µF @ 100kHz yields "R" 1Ω. The dominant sources ofpower loss in most inverters are therefore the switch resistances and the ESRs ofthe pump capacitor and output capacitor.The ADP3603/3604/3605/3607 series regulators have a shutdown control pin whichcan be asserted when load current is not required. When activated, the shutdownfeature reduces quiescent current to a few tens of microamperes.Power losses in a voltage doubler circuit are shown in Figure 4.13, and the analysisis similar to that of the inverter.4.12
SWITCHED CAPACITOR VOLTAGE CONVERTERSVOLTAGE DOUBLER POWER LOSSESVOUTRSWIOUTVIN C1IqC2ESRC1LOADESRC2RSWPLOSS IOUT ( 2VIN VOUT ) IqVIN IOUT2 ROUT IqVINROUT 8R SW 4ESRC1 1 ESRC2f C1Figure 4.13UNREGULATED INVERTER/DOUBLER DESIGN EXAMPLEThe ADM660 is a popular switched capacitor voltage inverter/doubler IC (see Figure4.14). Switching frequency is selectable (25kHz/120kHz) using the FC input. Whenthe FC input is open, the switching frequency is 25kHz. When it is connected to V ,the frequency increases to 120kHz. Only two external electrolytic capacitors (ESRshould be less than 200mΩ) are required for operation (see Figure 4.14). The choiceof the value of these capacitors is somewhat flexible. For a 25kHz switchingfrequency 10µF is recommended, and for 120kHz operation 2.2µF providescomparable performance.If frequencies less than the selected output frequency are desired, an externalcapacitor can be placed between the OSC input and ground. The internal oscillatorcan also be overridden by driving the OSC input with an external logic signal, inwhich case the internal charge pump frequency is one-half the external clockfrequency.The ADM8660 is similar to the ADM660, however it is optimized for inverteroperation and includes a "shutdown" feature which reduces the quiescent current to5µA. Shutdown recovery time is 500µs. Key specifications for theADM660/ADM8660 series are given in Figure 4.15.Efficiency for the ADM660/ADM8660 is greater than 90% for output currents up to50mA and greater than 80% for output currents to 100mA (see Figure 4.16).4.13
SWITCHED CAPACITOR VOLTAGE CONVERTERSADM660 SWITCHED CAPACITORVOLTAGE CONVERTERINVERTERDOUBLERVOUT 2VINVIN 1.5 TO 7VFCV CAP C1 10µFOSCGNDOSCCAP C1 ADM660 LVCAP-V FCVOUT -VINOUTADM660 LV10µFCAP-GNDOUTC2 10µFVIN 2.5 TO 7VFigure 4.14ADM660 / ADM8660 KEY SPECIFICATIONSn ADM660: Inverts or Doubles Input Supply Voltagen ADM8660: Inverts Input Supply Voltagen Input Range Inverting: 1.5V to 7Vn Input Range Doubling: 2.5 to 7V (ADM660)n 100mA Output Currentn Selectable Switching Frequency: 120kHz or 25kHzn 2.2µF or 10µF External Capacitors (120kHz / 25kHz)n 600µA Quiescent Currentn Shutdown Function (ADM8660), 5µA Shutdown Currentn 500µs Shutdown Recovery Timen 8-Pin SOICFigure 4.154.14C2 10µF
SWITCHED CAPACITOR VOLTAGE CONVERTERSADM660 / ADM8660 TYPICAL EFFICIENCYC1 C2 (2.2µF / 120kHz, 10µF / 25kHz)100VIN �4.2VoltsVOUT20–4.60020406080–5100LOAD CURRENT - mAFigure 4.16REGULATED OUTPUT SWITCHED CAPACITOR VOLTAGECONVERTERSAdding regulation to the simple switched capacitor voltage converter greatlyenhances its usefulness in many applications. There are three general techniques foradding regulation to a switched capacitor converter. The most straightforward is tofollow the switched capacitor inverter/doubler with a low dropout (LDO) linearregulator. The LDO provides the regulated output and also reduces the ripple of theswitched capacitor converter. This approach, however, adds complexity and reducesthe available output voltage by the dropout voltage of the LDO.Another approach to regulation is to vary the duty cycle of the switch control signalwith the output of an error amplifier which compares the output voltage with areferen
SWITCHED CAPACITOR VOLTAGE CONVERTERS 4.3 SWITCHED CAPACITOR VOLTAGE CONVERTERS n No Inductors! n Minimal Radiated EMI n Simple Implementation: Only 2 External Capacitors (Plus an Input Capacitor if Required) n Efficiency 90% Achievable n Optimized for Doubling or Inverting Supply Voltage - Efficiency Degrades for Other Output Voltages n Low Cost, Compact, Low Profile (Height)
Switched Capacitor Regulated Voltage Inverter The LTC 1261L is a switched-capacitor voltage inverter designed to provide a regulated negative voltage from a single positive supply. The LTC1261L operates from a single 2.7V to 5.25V supply and provides an adjustable output voltage from -1.23V to -5V. The LTC1261L-4/
4 ABB Capacitor Banks Series 100, 300, 500, 700, 300R and 500R Low Voltage Capacitor Banks The ABB capacitor bank: – is a powerful and compact automatic bank. – is very easy to install and to operate. – provide a high level of reliability and security. ABB Capacitor Banks Series 100, 300, 500, 700, 300R and 500R
Coupling Capacitor Voltage Transformer. IM-001 rev 0 - August 2018 Page 1 of 15 . READ THIS INSTRUCTION MANUAL BEFORE INSTALLATION AND OPERATION OF THE UNIT . Acronyms: CCVT - Coupling Capacitor Voltage Transformers . CVD - Capacitor Voltage Divider . PGS - Potential Grounding Switch . CGS - Carrier Grounding Switch . EMU .
Coupling Capacitor-Lower Unit Tap Capacitor The potential device voltage supply is a section of the stack capacitor tapped at 5 kv. The voltage across this section is brought through two porcelain bushings into the base housing. Older style potential devices developed this supply voltage across an auxiliary capacitor located in the base hous
Notee:Rated capacitor current (1000 x kvar) / ( 3 x voltage) (amps) Where: Voltage line-to-line voltage kvar Three-phase kvar rating of capacitor (nameplate rating) Example: 500 kvar capacitor, 480 V system: Rated capacitor current (500 x 1000) / ( 3 x 480) 601 A The breaker shall be rated to carry the 601 A x 135% or 811 A
Applications - Wide frequency range DC blocking - Optical devices - mmWave devices AC pass band ( 20GHz, 40GHz, 60GHz) ※ HIGH Q CAPACITOR VS BROADBAND CAPACITOR. NOTE : Reducing self resonance of capacitor. Broadband capacitor. High Q capacitor
Applying high temperature gas or heat ray to capacitor can cause the same phenomenon. (17) Do not tilt lay down or twist the capacitor body after the capacitor are soldered to the P.C. board. (18) Do not carry the P.C. board by grasping the soldered capacitor. (19) Please do not allow anything to touch the capacitor after soldering.
Accounting theory also includes the reporting of account-ing and financial information. There has been and will continue to be exten - sive discussion and argumentation as to what these basic assumptions, definitions, principles, and concepts should be; thus, accounting theory is never a final and finished product. Dialogue always continues, particularly as new issues and problems arise. As .
