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2 9-; Rev ; /9 Switched-apacitor Voltage onverters General Description The MX and are monolithic, MOS switched-capacitor voltage converters that invert, double, divide, or multiply a positive input voltage. They are pin compatible with the industry-standard and LT. Operation is guaranteed from.v to V with no external diode over the full temperature range. They deliver m with a.v output drop. The MX has a OOST pin that raises the oscillator frequency above the audio band and reduces external capacitor size requirements. The MX/ combine low quiescent current and high efficiency. Oscillator control circuitry and four power MOSFET switches are included on-chip. pplications include generating a -V supply from a +V logic supply to power analog circuitry. For applications requiring more power, the MX delivers up to m with a voltage drop of less than.v. pplications -V Supply from +V Logic Supply Personal ommunications Equipment Portable Telephones Op-mp Power Supplies EI/TI-E and EI/TI- Power Supplies Data-cquisition Systems Hand-Held Instruments Panel Meters Typical Operating ircuit Features Miniature µmx Package.V to.v Operating Supply Voltage Range 9% Typical Power-onversion Efficiency Invert, Double, Divide, or Multiply Input Voltages OOST Pin Increases Switching Frequencies (MX) No-Load Supply urrent: µ Max at V No External Diode Required for Higher-Voltage Operation Ordering Information PRT TEMP. RNGE PIN-PKGE MXP to + Plastic DIP MXS to + SO MX/D to + Dice* MXEP - to + Plastic DIP Ordering Information continued at end of data sheet. * ontact factory for dice specifications. Pin onfigurations TOP VIEW (N..) OOST P+ GND MX OS MX/ P+ MX INPUT SUPPLY VOLTGE N.. DIP/SO/µMX ND SE OS P- GND NEGTIVE OUTPUT VOLTGE P+ GND NEGTIVE VOLTGE ONVERTER ( ) RE FOR P- P- TO-99 Maxim Integrated Products all toll free for free samples or literature.

3 MX/ SOLUTE MXIMUM RTINGS Supply Voltage ( to GND, or GND to )...V Input Voltage on Pins,, and...-.v V IN ( +.V) Input urrent...µ Output Short-ircuit Duration (.V)...ontinuous ontinuous Power Dissipation (T = + ) Plastic DIP (derate 9.9mW/ above + )...mw SO (derate.mw/ above + )...mw µmx (derate.mw/ above + )...mw ERDIP (derate.mw/ above + )...mw TO-99 (derate.mw/ above + )...mw Operating Temperature Ranges MX /... to + MXE /E...- to + MXM /M...- to + Storage Temperature Range...- to + Lead Temperature (soldering, sec)...+ Stresses beyond those listed under bsolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELETRIL HRTERISTIS (ircuit of Figure, =.V, pin = V, OOST pin = open, I LOD = m, T = T MIN to T MX, unless otherwise noted.) PRMETER ONDITIONS MX MIN TYP MX MIN TYP MX UNITS R L =, T = + pins and T = to + Supply urrent no connection, open T = - to + T = - to + µ R L =, pins and = = V Supply Voltage R L = kω, open.. Range (Note ) R L = kω, to GND... V T = + Output Resistance I L = m, T = to + f OS = khz, T = - to + open T = - to + f OS =.khz (), T = + Ω f OS = khz (MX), = V, IL = m, to GND T = to + T = - to + T = - to + Oscillator Frequency OS = pf, = V to GND (Note ) = V khz Power Efficiency R L = kω, T = +, f OS khz, open % Voltage onversion Efficiency R L =, T = +, open % Oscillator Sink or Pin = V V OS = V or, open Source urrent Pin = µ Oscillator Impedance T = + = V.. MΩ = V kω Note : The Maxim and MX can operate without an external output diode over the full temperature and voltage ranges. The Maxim can also be used with an external output diode in series with pin (cathode at ) when replacing the Intersil. Tests are performed without diode in circuit. Note : f OS is tested with OS = pf to minimize the effects of test fixture capacitance loading. The pf frequency is correlated to this pf test point, and is intended to simulate pin s capacitance when the device is plugged into a test socket with no external capacitor. For this test, the pin is connected to GND for comparison to the original manufacturer s device, which automatically connects this pin to GND for ( > V).

4 Typical Operating haracteristics ( = V; YPSS =.µf; = = µf; = open; OS = open; T = + ; unless otherwise noted.) OUTPUT VOLTGE (V) OUTPUT VOLTGE and OUTPUT RIPPLE vs. LOD URRENT -. OUTPUT VOLTGE -. : MX with OOST = : -. : MX with OOST = OPEN -. = V = GND OUTPUT RIPPLE 9 LOD URRENT (m) MX-Fig OUTPUT RIPPLE (mvp-p) OUTPUT VOLTGE (V) OUTPUT VOLTGE and OUTPUT RIPPLE vs. LOD URRENT OUTPUT VOLTGE : MX with OOST = -. : : MX with -. OOST = OPEN = V = OPEN OUTPUT RIPPLE LOD URRENT (m) MX-Fig OUTPUT RIPPLE (mvp-p) OUTPUT VOLTGE (V) OUTPUT VOLTGE and OUTPUT RIPPLE vs. LOD URRENT - -9 OUTPUT - VOLTGE - : MX with OOST = 9 - : - : MX with OOST = OPEN - OUTPUT - = V RIPPLE = OPEN - - LOD URRENT (m) MX-Fig OUTPUT RIPPLE (mvp-p) MX/ EFFIIENY (%) 9 EFFIIENY and SUPPLY URRENT vs. LOD URRENT EFFIIENY SUPPLY URRENT = V = GND 9 LOD URRENT (m) MX-Fig 9 SUPPLY URRENT (m) EFFIIENY (%) 9 EFFIIENY and SUPPLY URRENT vs. LOD URRENT EFFIIENY : MX with OOST = : : MX with OOST = OPEN LOD URRENT (m) SUPPLY URRENT = V = OPEN MX-Fig SUPPLY URRENT (m) EFFIIENY (%) EFFIIENY and SUPPLY URRENT vs. LOD URRENT 9, EFFIIENY : MX with OOST = : : MX with OOST = OPEN SUPPLY URRENT = V = OPEN LOD URRENT (m) MX-Fig SUPPLY URRENT (m) EFFIIENY (%) 9 EFFIIENY vs. OSILLTOR FREQUENY, = µf, = µf, = µf EXTERNL HMOS OSILLTOR x OSILLTOR FREQUENY (Hz) MX-Fig OSILLTOR FREQUENY (Hz),,. OSILLTOR FREQUENY vs. EXTERNL PITNE and MX with OOST = OPEN MX with OOST -,, OS (pf) MX-Fig OSILLTOR FREQUENY (Hz),, OSILLTOR FREQUENY vs. SUPPLY VOLTGE FROM TOP TO OTTOM T V MX, OOST =, = GND MX, OOST =, = OPEN, = GND, = OPEN MX, OOST = OPEN, = GND MX, OOST = OPEN, = OPEN 9 SUPPLY VOLTGE (V) MX-Fig 9

5 MX/ Typical Operating haracteristics (continued) ( = V; YPSS =.µf; = = µf; = open; OS = open; T = + ; unless otherwise noted.) OSILLTOR FREQUENY (khz) - OSILLTOR FREQUENY vs. TEMPERTURE : MX with OOST = : IL : MX with OOST = OPEN - TEMPERTURE ( ) MX-Fig QUIESENT URRENT (µ), QUIESENT URRENT vs. OSILLTOR FREQUENY USING EXTERNL PITOR USING EXTERNL HMOS OSILLTOR x OSILLTOR FREQUENY (Hz) MX-Fig QUIESENT URRENT (µ) QUIESENT URRENT vs. SUPPLY VOLTGE D : MX, OOST =, = GND : MX, OOST =, = OPEN : and MX with OOST = OPEN, = GND; OVE V, MX ONLY D: and MX with OOST = OPEN, = OPEN. 9 SUPPLY VOLTGE (V) MX-Fig QUIESENT URRENT (µ) QUIESENT URRENT vs. TEMPERTURE MX with OOST =, MX with OOST = OPEN - - TEMPERTURE ( ) MX-Fig RESISTNE (Ω) 9, = µf OUTPUT RESISTNE vs. OSILLTOR FREQUENY, = µf, = µf EXTERNL HMOS OSILLTOR MX-Fig OUTPUT RESISTNE (Ω) OUTPUT RESISTNE vs. SUPPLY VOLTGE MX-Fig OUTPUT RESISTNE (Ω) OUTPUT RESISTNE vs. TEMPERTURE, MX with OOST = OPEN MX with OOST = MX-Fig FREQUENY (Hz) 9 SUPPLY VOLTGE (V) TEMPERTURE ( )

6 Pin Description PIN NME OOST (MX) N.. () FUNTION Frequency oost. onnecting OOST to increases the oscillator frequency by a factor of six. When the oscillator is driven externally, OOST has no effect and should be left open. No onnection P+ onnection to positive terminal of harge-pump apacitor GND Ground. For most applications, the positive terminal of the reservoir capacitor is connected to this pin. P- onnection to negative terminal of harge-pump apacitor Negative Voltage Output. For most applications, the negative terminal of the reservoir capacitor is connected to this pin. MX/ OS Low-Voltage Operation. onnect to ground for supply voltages below.v. : Leave open for supply voltages above V. Oscillator ontrol Input. onnecting an external capacitor reduces the oscillator frequency. Minimize stray capacitance at this pin. Power-Supply Positive Voltage Input. (.V to V). is also the substrate connection. µf OOST P+ GND P- MX OS YPSS =.µf µf EXTERNL OSILLTOR Figure. Maxim MX/ Test ircuit OS Detailed Description The MX/ are charge-pump voltage converters. They work by first accumulating charge in a bucket capacitor and then transfer it into a reservoir capacitor. The ideal voltage inverter circuit in Figure illustrates this operation. R L During the first half of each cycle, switches S & S close and switches S & S open, which connects the bucket capacitor across and charges. During the second half of each cycle, switches S & S close and switches S & S open, which connects the positive terminal of to ground and shifts the negative terminal to. This connects in parallel with the reservoir capacitor. If the voltage across is smaller than the voltage across, then charge flows from to until the voltages across them are equal. During successive cycles, will continue pouring charge into until the voltage across reaches - (). In an actual voltage inverter, the output is less than - () since the switches S S have resistance and the load drains charge from. dditional qualities of the MX/ can be understood by using a switched-capacitor circuit model. Switching the bucket capacitor,, between the input and output of the circuit synthesizes a resistance (Figures a and b.) When the switch in Figure a is in the left position, capacitor charges to. When the switch moves to the right position, is discharged to. The charge transferred per cycle is: Q = ( - ). If the switch is cycled at frequency f, then the resulting

7 MX/ S S S S Figure. Ideal Voltage Inverter f = -() current is: I = f x Q = f x ( - ). Rewriting this equation in Ohm s law form defines an equivalent resistance synthesized by the switched-capacitor circuit where: ( - V ) I = OUT / (f x ) and REQUIV = f x where f is one-half the oscillator frequency. This resistance is a major component of the output impedance of switched-capacitor circuits like the MX/. s shown in Figure, the MX/ contain MOSFET switches, the necessary transistor drive circuitry, and a timing oscillator. Design Information The MX/ are designed to provide a simple, compact, low-cost solution where negative or doubled supply voltages are needed for a few lowpower components. Figure shows the basic negative voltage converter circuit. For many applications, only two external capacitors are needed. The type of capacitor used is not critical. R LOD Proper Use of the Low-Voltage () Pin Figure shows an internal voltage regulator inside the MX/. Use the pin to bypass this regulator, in order to improve low-voltage performance Figure a. Switched apacitor Model pin S P+ pin S R EQUIV M R EQUIV = f R LOD VOUT OOST pin OS pin OSILLTOR pin Q Q INTERNL REGULTOR S GND pin S P- pin pin Figure b. Equivalent ircuit Figure. MX and Functional Diagram

8 µf MX Figure. asic Negative Voltage onverter = -() *REQUIRED FOR <.V µf and allow operation down to.v. For low-voltage operation and compatibility with the industry-standard LT and, the pin should be connected to ground for supply voltages below.v and left open for supply voltages above.v. The MX s pin can be grounded for all operating conditions. The advantage is improved low-voltage performance and increased oscillator frequency. The disadvantage is increased quiescent current and reduced efficiency at higher supply voltages. For Maxim s, the pin must be left open for supply voltages above V. When operating at low supply voltages with open, connections to the, OOST, and OS pins should be short or shielded to prevent EMI from causing oscillator jitter. Oscillator Frequency onsiderations For normal operation, leave the OOST and OS pins of the MX/ open and use the nominal oscillator frequency. Increasing the frequency reduces audio interference, output resistance, voltage ripple, and required capacitor sizes. Decreasing frequency reduces quiescent current and improves efficiency. Oscillator Frequency Specifications The MX/ do not have a precise oscillator frequency. Only minimum values of khz and khz for the MX and a typical value of khz for the are specified. If a specific oscillator frequency is required, use an external oscillator to drive the OS pin. Increasing Oscillator Frequency Using the OOST Pin For the MX, connecting the OOST pin to the pin raises the oscillator frequency by a factor of about. * YPSS MX µf OS = -() µf Figure shows this connection. Higher frequency operation lowers output impedance, reduces output ripple, allows the use of smaller capacitors, and shifts switching noise out of the audio band. When the oscillator is driven externally, OOST has no effect and should be left open. The OOST pin should also be left open for normal operation. Reducing the Oscillator Frequency Using OS n external capacitor can be connected to the OS pin to lower the oscillator frequency (Figure ). Lower frequency operation improves efficiency at low load currents by reducing the I s quiescent supply current. It also increases output ripple and output impedance. This can be offset by using larger values for and. onnections to the OS pin should be short to prevent stray capacitance from reducing the oscillator frequency. Overdriving the OS Pin with an External Oscillator Driving OS with an external oscillator is useful when the frequency must be synchronized, or when higher frequencies are required to reduce audio interference. The MX/ can be driven up to khz. The pump and output ripple frequencies are one-half the external clock frequency. Driving the MX/ at a higher frequency increases the ripple frequency and allows the use of smaller capacitors. It also increases the quiescent current. The OS input threshold is -.V when V, and is / for < V. If the external clock does not swing all the way to, use a kω pull-up resistor (Figure ). Output Voltage onsiderations The MX/ output voltage is not regulated. The output voltages will vary under load according to the output resistance. The output resistance is primarily ONNETION FROM TO OOST Figure. Negative Voltage onverter with OS and OOST MX/

9 MX/ µf MX Figure. External locking a function of oscillator frequency and the capacitor value. Oscillator frequency, in turn, is influenced by temperature and supply voltage. For example, with a V input voltage and µf charge-pump capacitors, the output resistance is typically Ω. Thus, the output voltage is about -V under light loads, and decreases to about -.V with a m load current. Minor supply voltage variations that are inconsequential to digital circuits can affect some analog circuits. Therefore, when using the MX/ for powering sensitive analog circuits, the power-supply rejection ratio of those circuits must be considered. The output ripple and output drop increase under heavy loads. If necessary, the MX/ output impedance can be reduced by paralleling devices, increasing the capacitance of and, or connecting the MX s OOST pin to to increase the oscillator frequency. Inrush urrent and EMI onsiderations During start-up, pump capacitors and must be charged. onsequently, the MX/ develop inrush currents during start-up. While operating, short bursts of current are drawn from the supply to, and then from to to replenish the charge drawn by the load during each charge-pump cycle. If the voltage converters are being powered by a highimpedance source, the supply voltage may drop too low during the current bursts for them to function properly. Furthermore, if the supply or ground impedance is too high, or if the traces between the converter I and charge-pump capacitors are long or have large loops, kω REQUIRED FOR TTL = -() µf MOS or TTL GTE switching noise and EMI may be generated. To reduce these effects: ) Power the MX/IL from a low-impedance source. ) dd a power-supply bypass capacitor with low effective series resistance (ESR) close to the I between the and ground pins. ) Shorten traces between the I and the charge-pump capacitors. ) rrange the components to keep the ground pins of the capacitors and the I as close as possible. ) Leave extra copper on the board around the voltage converter as power and ground planes. This is easily done on a double-sided P board. Efficiency, Output Ripple, and Output Impedance The power efficiency of a switched-capacitor voltage converter is affected by the internal losses in the converter I, resistive losses of the pump capacitors, and conversion losses during charge transfer between the capacitors. The total power loss is: P = P +P +P +P LOSS The internal losses are associated with the I s internal functions such as driving the switches, oscillator, etc. These losses are affected by operating conditions such as input voltage, temperature, frequency, and connections to the, OOST, and OS pins. The next two losses are associated with the output resistance of the voltage converter circuit. Switch losses occur because of the on-resistances of the MOSFET switches in the I. harge-pump capacitor losses occur because of their ESR. The relationship between these losses and the output resistance is as follows: where: INTERNL LOSSES P + P = I OUT x ROUT PUMP PITOR LOSSES SWITH LOSSES SWITH LOSSES ROUT + (f OS / ) x ( RSWITHES + ESR)+ ESR and f OS is the oscillator frequency. PUMP PITOR LOSSES ONVERSION LOSSES

10 The first term is the effective resistance from the switched-capacitor circuit. onversion losses occur during the transfer of charge between capacitors and when there is a voltage difference between them. The power loss is: PONV.LOSS = (V + ) + V RIPPLE VOUTV RIPPLE x f OS / Increasing Efficiency Efficiency can be improved by lowering output voltage ripple and output impedance. oth output voltage ripple and output impedance can be reduced by using large capacitors with low ESR. The output voltage ripple can be calculated by noting that the output current is supplied solely from capacitor during one-half of the charge-pump cycle. VRIPPLE + x ESR IOUT x f OS x Slowing the oscillator frequency reduces quiescent current. The oscillator frequency can be reduced by connecting a capacitor to the OS pin. Reducing the oscillator frequency increases the ripple voltage in the MX/. ompensate by increasing the values of the bucket and reservoir capacitors. For example, in a negative voltage converter, the pump frequency is around khz or khz. With the recommended µf bucket and reservoir capacitors, the circuit consumes about µ of quiescent current while providing m of output current. Setting the oscillator to Hz by connecting a pf capacitor to OS reduces the quiescent current to about µ. Maintaining m output current capability requires increasing the bucket and reservoir capacitors to µf. Note that lower capacitor values can be used for lower output currents. For example, setting the oscillator to Hz by connecting a pf capacitor to OS provides the highest efficiency possible. Leaving the bucket and reservoir capacitors at µf gives a maximum I OUT of m, a no-load quiescent current of µ, and a power conversion efficiency of 9%. General Precautions ) onnecting any input terminal to voltages greater than or less than ground may cause latchup. Do not apply any input sources operating from external supplies before device power-up. ) Never exceed maximum supply voltage ratings. ) Do not connect and with the wrong polarity. ) Do not short to ground for extended periods with supply voltages above.v present on other pins. ) Ensure that (pin ) does not go more positive than GND (pin ). dding a diode in parallel with, with the anode connected to and cathode to, will prevent this condition. pplication ircuits Negative Voltage onverter Figure shows a negative voltage converter, the most popular application of the MX/. Only two external capacitors are needed. third power-supply bypass capacitor is recommended (.µf to µf) MX/ µf OOST MX YPSS.µF = -() µf MX = () - V D Figure. Negative Voltage onverter with OOST and onnections Figure 9. Voltage Doubler 9

11 MX/ µf = Figure. Voltage Divider µf MX Positive Voltage Doubler Figure 9 illustrates the recommended voltage doubler circuit for the MX/. To reduce the voltage drops contributed by the diodes (V D ), use Schottky diodes. For true voltage doubling or higher output currents, use the MX. Voltage Divider The voltage divider shown in Figure splits the power supply in half. third capacitor can be added between and. ombined Positive Multiplication and Negative Voltage onversion Figure illustrates this dual-function circuit. apacitors and perform the bucket and reservoir functions for generating the negative voltage. apacitors and are the bucket and reservoir MX = () - V D Figure. ombined Positive and Negative onverter capacitors for the doubled positive voltage. This circuit has higher output impedances resulting from the use of a common charge-pump driver. ascading Devices Larger negative multiples of the supply voltage can be obtained by cascading MX/ devices (Figure ). The output voltage is nominally = -n() where n is the number of devices cascaded. The output voltage is reduced slightly by the output resistance of the first device, multiplied by the quiescent current of the second, etc. Three or more devices can be cascaded in this way, but output impedance rises dramatically. For example, the output resistance of two cascaded MXs is approximately five times the output resistance of a single voltage converter. better solution may be an inductive switching regulator, such as the MX, MX9, MX, or MX. = -() µf MX µf MX µf MX = -n() µf µf µf Figure. ascading MX/ for Increased Output Voltage

12 MX MX n = -() Paralleling Devices Paralleling multiple MX/s reduces output resistance and increases current capability. s illustrated in Figure, each device requires its own pump capacitor, but the reservoir capacitor serves all devices. The equation for calculating output resistance is: R OUT = R OUT(of MX or ) n (number of devices) Shutdown Schemes Figures a c illustrate three ways of adding shutdown capability to the MX/. When using these circuits, be aware that the additional capacitive loading on the OS pin will reduce the oscillator frequency. The first circuit has the least loading on the OS pin and has the added advantage of controlling shutdown with a high or low logic level, depending on the orientation of the switching diode. MX/ Figure. Paralleling MX/ to Reduce Output Resistance µf a) b) MX MX kω REQUIRED FOR TTL N MOS or TTL GTE = -() µf H OPEN-DRIN OR LS OPEN-OLLETOR NND GTES _Ordering Information (continued) PRT MXES MXMJ P S U /D EP ES MJ MTV TEMP. RNGE - to + - to + to + to + to + to + - to + - to + - to + - to + PIN-PKGE SO ERDIP** Plastic DIP SO µmx Dice* Plastic DIP SO ERDIP** TO-99** * ontact factory for dice specifications. ** ontact factory for availability. The Maxim meets or exceeds all and S specifications. MX OUTPUT ENLE H OR LS TRI-STTE UFFER c) Figure a-c. Shutdown Schemes for MX/

13 MX/ hip Topographies P- P- MX GND P+ OOST OS." (.9mm) P+ GND." (.mm) OS." (.9mm) TRNSISTOR OUNT: SUSTRTE ONNETED TO." (.mm) TRNSISTOR OUNT: SUSTRTE ONNETED TO Package Information D E H DIM D E e H L α MIN INHES. MX MILLIMETERS MIN MX e.mm. in L α -PIN µmx PKGE Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, San Gabriel Drive, Sunnyvale, 9 () - 99 Maxim Integrated Products Printed US is a registered trademark of Maxim Integrated Products.