Compact, Dual-Output Charge Pump

9-7; Rev ; 7/97 Compact, Dual-Output Charge Pump General Description The is a CMOS charge-pump DC-DC converter in an ultra-small µmax package. It produces positive and negative outputs from a single positive input, and requires only four capacitors. The charge pump first doubles the input voltage, then inverts the doubled voltage. The input voltage ranges from +.5V to +.V. The internal oscillator is guaranteed to be between khz and 38kHz, keeping noise above the audio range while consuming minimal supply current. A 75Ω output impedance permits useful output currents up to ma. The comes in a.mm-high, 8-pin µmax package that occupies half the board area of a standard 8-pin SOIC. For a device with selectable frequencies and logic-controlled shutdown, refer to the MAX8 data sheet. Applications Low-Voltage GaAsFET Bias in Wireless Handsets VCO and GaAsFET Supplies Split Supply from 3 Ni Cells or Li+ Cell Low-Cost Split Supply for Low-Voltage Data-Acquisition Systems Split Supply for Analog Circuitry LCD Panels Features.mm-High µmax Package Compact: Circuit Fits in.8in Requires Only Four Capacitors Dual Outputs (positive and negative) +.5V to +.V Input Voltage khz (min) Frequency (above the audio range) Ordering Information PART TEMP. RANGE P-PACKAGE C/D C to +7 C Dice EUA - C to +85 C 8 µmax Typical Operating Circuit Pin Configuration V (+.5V to +.V) TOP VIEW C+ +*V C- C- C+ 3 8 7 5 C+ C+ -*V µmax +V to ±V CONVERTER Maxim Integrated Products For free samples & the latest literature: http://www.maxim-ic.com, or phone -8-998-88. For small orders, phone 8-737-7 ext. 38.

ABSOLUTE MAXIMUM RATGS to...+v, -.3V to...+.v, -.3V to...-v, +.3V Output Current...mA Short-Circuit to...indefinite Continuous Power Dissipation (T A = +7 C) µmax (derate.mw/ C above +7 C)...33mW Operating Temperature Range EUA...- C to +85 C Storage Temperature Range...-5 C to + C Lead Temperature (soldering, sec)...+3 C Stresses beyond those listed under Absolute 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. ELECTRICAL CHARACTERISTICS (V = 5V, C = C = C3 = C =, T A = T M to T MAX, unless otherwise noted. Typical values are at T A = +5 C.) PARAMETER CONDITIONS M TYP MAX UNITS Minimum Supply Voltage R LOAD = kω..5 V Maximum Supply Voltage R LOAD = kω. V Supply Current T A = +5 C T A = - C to +85 C (Note )..5.5 ma Oscillator Frequency T A = +5 C T A = - C to +85 C (Note ) 9.5 3.5 8 3 khz Output Resistance I = ma, I = ma = V (forced), I = ma T A = +5 C T A = T M to T MAX T A = +5 C T A = T M to T MAX 5 8 75 Ω Power Efficiency I L = 5mA 85 % Voltage Conversion Efficiency, R L =, R L = 95 99 9 98 % Note : These specifications are guaranteed by design and are not production tested. Typical Operating Characteristics (Circuit of Figure, V = 5V, T A = +5 C, unless otherwise noted.) EFFICIENCY (%) 9 8 7 5 3 EFFICIENCY vs. OUTPUT CURRENT (V = 5V) - EFFICIENCY (%) 9 8 7 5 3 EFFICIENCY vs. OUTPUT CURRENT (V = 3.3V) - EFFICIENCY (%) 9 8 7 5 3 EFFICIENCY vs. OUTPUT CURRENT (V = V) -3 8 8 OUTPUT CURRENT (ma) 3 5 7 8 OUTPUT CURRENT (ma).5..5..5 OUTPUT CURRENT (ma)

OUTPUT VOLTAGE,, (V) Typical Operating Characteristics (continued) (Circuit of Figure, V = 5V, T A = +5 C, unless otherwise noted.) 8 - - - -8 - OUTPUT VOLTAGE vs. OUTPUT CURRENT BOTH AND LOADED EQUALLY C = C = C3 = C = V =.75V 8 OUTPUT CURRENT (ma) - OUTPUT VOLTAGE RIPPLE (mvp-p) 35 3 5 5 5 OUTPUT VOLTAGE RIPPLE vs. PUMP CAPACITANCE C = C = C3 = C F A D E A:, =.75V, + = V B:, = 3.5V, + = V C:, =.9V, + = V D:, =.75V, + = V E:, = 3.5V, + = V F:, =.9V, + = V B C 5 5 5 3 35 5 5 PUMP CAPACITANCE (µf) -5 OUTPUT CURRENT, TO (ma) 7 5 3 OUTPUT CURRENT vs. PUMP CAPACITANCE V =.75V, + = V V = 3.5V, + = V V =.9V, + = V C = C = C3 = C 5 5 5 3 35 5 5 PUMP CAPACITANCE (µf) - SUPPLY CURRENT (µa) 9 8 7 5 3 SUPPLY CURRENT vs. SUPPLY VOLTAGE C = C = C3 = C = -7 OUTPUT RESISTANCE (Ω) 3 5 5 5 OUTPUT RESISTANCE vs. TEMPERATURE C = C = C3 = C =, V = 3.3V, V = 5.V, V = 5.V, V = 3.3V -8..5 3. 3.5..5 5. 5.5. SUPPLY VOLTAGE (V) -55-35 -5 5 5 5 5 85 5 5 TEMPERATURE ( C) PUMP FREQUENCY (khz) 7 5 3 9 7 PUMP FREQUENCY vs. TEMPERATURE V = 5.V V = 3.3V V =.V C = C = C3 = C = -9 OUTPUT RESISTANCE (Ω) 5 5 5 OUTPUT RESISTANCE vs. SUPPLY VOLTAGE C = C = C3 = C = - 5 - - 8 TEMPERATURE ( C)..5 3. 3.5..5 5. 5.5. SUPPLY VOLTAGE (V) 3

Typical Operating Characteristics (continued) (Circuit of Figure, V = 5V, T A = +5 C, unless otherwise noted.) OUTPUT RIPPLE (C = C = C3 = C = µf) OUTPUT RIPPLE (C = C = C3 = C = ) OUTPUT mv/div OUTPUT mv/div OUTPUT 5mV/div OUTPUT mv/div V =.75V, ma LOAD µs/div V =.75V, ma LOAD µs/div Pin Description P NAME FUNCTION V C- Negative Terminal of the Flying Boost Capacitor C+ Positive Terminal of the Flying Inverting Capacitor C- C+ I V + OUT+ 3 Negative Terminal of the Flying Inverting Capacitor Output of the Inverting Charge Pump C+ R L + 5 Ground Positive Power-Supply Input 7 Output of the Boost Charge Pump I V - R L - 8 C+ Positive Terminal of the Flying Boost Capacitor OUT- Figure. Test Circuit

Detailed Description The contains all the circuitry needed to implement a voltage doubler/inverter. Only four external capacitors are needed. These may be polarized electrolytic or ceramic capacitors with values ranging from µf to µf. Figure a shows the ideal operation of the positive voltage doubler. The on-chip oscillator generates a 5% duty-cycle clock signal. During the first half cycle, switches S and S open, switches S and S3 close, and capacitor C charges to the input voltage (V). During the second half cycle, switches S and S3 open, switches S and S close, and capacitor C is level shifted upward by V. Assuming ideal switches and no load on C3, charge transfers into C3 from C such that the voltage on C3 will be V, generating the positive supply output (). Figure b illustrates the ideal operation of the negative converter. The switches of the negative converter are out of phase with the positive converter. During the second half cycle, switches S and S8 open and switches S5 and S7 close, charging C from (pumped up to V by the positive charge pump) to. In the first half of the clock cycle, switches S5 and S7 open, switches S and S8 close, and the charge on capacitor C transfers to C, generating the negative supply. The eight switches are CMOS power MOSFETs. Switches S, S, S, and S5 are P-channel devices, while switches S3, S, S7, and S8 are N-channel devices. Charge-Pump Output The is not a voltage regulator: the output source resistance of either charge pump is approximately 5Ω at room temperature with V = +5V, and and will approach +V and -V, respectively, when lightly loaded. Both and will droop toward as the current draw from either or increases, since is derived from. Treating each converter separately, the droop of the negative supply (VDROOP-) is the product of the current draw from (I) and the source resistance of the negative converter (RS-): V = I x RS - DROOP- The droop of the positive supply (VDROOP+) is the product of the current draw from the positive supply (ILOAD+) and the source resistance of the positive a) b) S C+ S S5 C+ S S3 C S C3 I N I V + R L + S7 C C- S8 C I V - R L - Figure. Idealized Voltage Quadrupler: a) Positive Charge Pump; b) Negative Charge Pump 5

converter (RS+), where ILOAD+ is the combination of IVand the external load on (I): Determine and as follows: ( ) V = I x RS+ = I + I x RS+ DROOP+ LOAD+ = V - VDROOP+ V - = ( - V DROOP) = -(V - VDROOP+ - V DROOP-) The output resistance for the positive and negative charge pumps are tested and specified separately. The positive charge pump is tested with unloaded. The negative charge pump is tested with supplied from an external source, isolating the negative charge pump. Current draw from either or is supplied by the reservoir capacitor alone during one half cycle of the clock. Calculate the resulting ripple voltage on either output as follows: V RIPPLE = I LOAD ( / f PUMP) ( / C RESERVOIR) where ILOAD is the load on either or. For the typical fpump of 3kHz with reservoir capacitors, the ripple is 5mV when ILOAD is 5mA. Remember that, in most applications, the total load on is the load current (I) and the current taken by the negative charge pump (I). Efficiency Considerations Theoretically, a charge-pump voltage multiplier can approach % power efficiency under the following conditions: The charge-pump switches have virtually no offset and extremely low on-resistance. The drive circuitry consumes minimal power. The impedances of the reservoir and pump capacitors are negligible. For the, the energy loss per clock cycle is the sum of the energy loss in the positive and negative converters, as follows: LOSS CYCLE = LOSS POS + LOSSNEG = C ( V + ) V + V ( ) ( ) + C ( V + ) ( V ) The average power loss is simply: P = LOSS x f LOSS CYCLE PUMP Resulting in an efficiency of: ( ) η = Total Output Power / Total Output Power P LOSS V C- C+ 8 C- C+ 8 OUT+ 3 7 3 C+ 7 5 5 OUT- Figure 3. Paralleling s

A substantial voltage difference exists between ( - V) and V for the positive pump, and between and if the impedances of the pump capacitors (C and C) are large with respect to their output loads. Larger values of reservoir capacitors (C3 and C) reduce output ripple. Larger values of both pump and reservoir capacitors improve power efficiency. Charge-Pump Capacitor Selection To maintain the lowest output resistance, use capacitors with low effective series resistance (ESR). The chargepump output resistance is a function of C, C, C3, and C s ESR. Therefore, minimizing the charge-pump capacitors ESR minimizes the total output resistance. Applications Information Positive and Negative Converter The is most commonly used as a dual chargepump voltage converter that provides positive and negative outputs of two times a positive input voltage. The Typical Operating Circuit shows that only four external components are needed: capacitors C and C3 for the positive pump, C and C for the negative pump. In most applications, all four capacitors are low-cost, polarized electrolytics. For applications where PC board space is at a premium and very low currents are being drawn from the, µf capacitors may be used for the pump capacitors C and C, with µf reservoir capacitors C3 and C. Capacitors C and C must be rated at V or greater. Paralleling Devices Paralleling multiple s (Figure 3) reduces the output resistance of both the positive and negative converters. The effective output resistance is the output resistance of one device divided by the number of devices. Separate C and C charge-pump capacitors are required for each, but the reservoir capacitors C3 and C can be shared. Heavy Output Current Loads When under heavy loads, where is sourcing current into (i.e., load current flows from to, rather than from supply to ground), do not allow the supply to pull above ground. In applications where large currents flow from to, use a Schottky diode (N587) between and, with the anode connected to (Figure ). Layout and Grounding Good layout is important, primarily for good noise performance. To ensure good layout: Mount all components as close together as possible Keep traces short to minimize parasitic inductance and capacitance Use a ground plane. Figure. A Schottky diode protects the when large currents flow from to. 7

Chip Topography TRANSISTOR COUNT: 8 SUBSTRATE CONNECTED TO C- C+ C+.8" (.3mm).58" (.7mm) Package Information e B A A.mm. in C L α DIM A A B C D E e H L α M.3...5...88. CHES.5 MAX..8..7...98. MILLIMETERS M MAX.9....5.3.3.8.95 3.5.95 3.5.5.78. 5.3. -3D E H D 8-P µmax MICROMAX SMALL-OUTLE PACKAGE 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. 8 Maxim Integrated Products, San Gabriel Drive, Sunnyvale, CA 98 8-737-7 997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.