Regulated, 125mA-Output, Charge-Pump DC-DC Inverter MAX1673ESA. Features. General Description. Ordering Information. Applications

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1 9-33; Rev ; /9 Regulated, ma-output, General Description The charge-pump inverter provides a lowcost, compact means of generating a regulated negative output from a positive input at up to ma. It requires only three small capacitors, and only two resistors to set its output voltage. The input range is V to.v. The regulated output can be set from V to -V in Skip regulation mode or -.V to -V in Linear (L) regulation mode. In Skip mode, the regulates by varying its switching frequency as a function of load current. This On-Demand switching gives the two advantages: very small capacitors and very low quiescent supply current. At heavy loads, it transfers energy from the input to the output by switching at up to 3kHz. It switches more slowly at light loads, using only 3µA quiescent supply current. In Linear mode, the switches at a constant 3kHz at all loads and regulates by controlling the current-path resistance. This provides constantfrequency ripple, which is easily filtered for low-noise applications. This device also features a µa logic-controlled shutdown mode and is available in a standard -pin SO package. For a device that delivers about ma and fits in a smaller package, refer to the MAX. Applications Hard Disk Drives Camcorders Analog Signal-Processing Applications Measurement Instruments Modems Digital Cameras Features Regulated Negative Output Voltage (up to - x V ) ma Output Current 3µA Quiescent Supply Current (Skip-mode regulation) 3kHz Fixed-Frequency, Low-Noise Output (Linear-mode regulation) V to.v Input Range µa Logic-Controlled Shutdown Ordering Information PART ESA TEMP. RANGE - C to + C P-PACKAGE SO Typical Operating Circuit Pin Configuration PUT V TO.V TOP VIEW 3 7 GND ON OFF L/SKIP L/SKIP GND REGULATED NEGATIVE PUT (UP TO - x V, UP TO ma) SO On-Demand is a trademark of Maxim Integrated Products. Maxim Integrated Products For free samples & the latest literature: or phone For small orders, phone ext. 3.

2 ABSOLUTE MAXIMUM RATGS...-.3V to +V,, L/SKIP...-.3V to (V +.3V)...-.3V to +V,...-V to +.3V Continuous Output Current...3mA Output Short-Circuit Duration to GND (Note )...sec Note : Shorting to may damage the device and should be avoided. Continuous Power Dissipation (T A = +7 C) (derate.mw/ C above +7 C)...mW Operating Temperature Range...- C to + C Junction Temperature...+ C Storage Temperature Range...- 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 = V = +V, C = µf, C = µf, C FLY =.µf, T A = - C to + C, unless otherwise noted. Typical values are at T A = + C.) (Note ) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS L/SKIP = GND (Skip mode).. Input Voltage Range V L/SKIP = (L mode).7. Minimum Output Voltage L/SKIP = GND V L/SKIP = -. Maximum Output Current I (MAX) ma V V Output Voltage V R =kω, ±%, R =.kω, ±%, I = ma to ma, Figure L/SKIP = (L mode) L/SKIP = GND (Skip mode) V Quiescent Current (I Current) Shutdown Current (I Current) I = GND. µa L/SKIP = V. =.V to.v, (L mode) Line Regulation V LNR Figure, V REF V L/SKIP = GND (Skip mode) L/SKIP = I. = ma to (L mode) Load Regulation V LDR ma, Figure L/SKIP = GND. (Skip mode) Open-Loop Output Resistance (Dropout) Output Resistance to Ground in Shutdown Mode I Q V = -mv, V = -3V, L/SKIP = (L mode) V = -mv, V = -3V, L/SKIP = GND (Skip mode) = GND.3. R O L/SKIP = GND (Skip mode) 3. Ω ma %/V %/ma Ω

3 ELECTRICAL CHARACTERISTICS (continued) (V = V = +V, C = µf, C = µf, C FLY =.µf, T A = - C to + C, unless otherwise noted. Typical values are at T A = + C.) (Note ) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS Switching Frequency (L Mode) Threshold V T L/SKIP = GND (Skip mode) - mv L/SKIP = (L mode) Input Bias Current I V = -mv L/SKIP = GND V = -mv (Skip mode) Input Bias Current (, L/SKIP) Logic High Input (, L/SKIP) Logic Low Input (, L/SKIP) T A = + C 3 ƒ OSC T A = - C to + C V IH V V.V.7 x V V V IL V V.V.3 x V V khz na µa Note : Specifications to - C are guaranteed by design, not production tested. 3

4 Typical Operating Characteristics (Circuit of Figure, V = +V, C FLY =.µf, C = µf, T A = + C, unless otherwise noted.) PEAK-TO-PEAK RIPPLE (mv) PUT RIPPLE vs. LOAD CURRENT (L MODE) C FLY = C C = µf C = µf C = 7µF 7 RTOC PEAK-TO-PEAK RIPPLE (mv) PUT RIPPLE vs. LOAD CURRENT (SKIP MODE) C = µf C = µf C = 7µF C FLY = C 7 TOC V (V) PUT VOLTAGE vs. LOAD CURRENT SKIP MODE L MODE 7 TOC3 EFFICIENCY (%) EFFICIENCY vs. LOAD CURRENT (SKIP MODE) V REF V V = 3.V V = V V = V TOC EFFICIENCY (%) EFFICIENCY vs. LOAD CURRENT (L MODE) V = V V =.V V = V V REF V TOC EFFICIENCY (%) EFFICIENCY vs. PUT VOLTAGE V REF V ma LOAD V = -3V V (V) SKIP MODE L MODE TOC RDROP (Ω) DROP PUT RESISTANCE vs. PUT VOLTAGE T A = + C T A = + C T A = - C 3 V (V) TOC7 QUIESCENT CURRENT (ma) QUIESCENT CURRENT vs. PUT VOLTAGE (L MODE) DOES NOT CLUDE BIAS CURRENT FOR RESISTOR DIVIDER V REF V 3 V (V) TOC QUIESCENT CURRENT (µa) 3 3 QUIESCENT CURRENT vs. PUT VOLTAGE (SKIP MODE) DOES NOT CLUDE BIAS CURRENT FOR RESISTOR DIVIDER 3 V (V) TOC9

5 Typical Operating Characteristics (continued) (Circuit of Figure, V = +V, C FLY =.µf, C = µf, T A = + C, unless otherwise noted.) I ma/div LOAD-TRANSIENT RESPONSE (L MODE) TOC ma ma I ma/div LOAD-TRANSIENT RESPONSE (SKIP MODE) TOC ma ma V mv/div V mv/div µs/div µs/div V V/div LE-TRANSIENT RESPONSE (L MODE) TOC.V.V V V/div LE-TRANSIENT RESPONSE (SKIP MODE) TOC3 I = ma.v.v V mv/div I = ma µs/div V mv/div µs/div

6 Pin Description P 3 NAME L/SKIP Positive Terminal of Flying Capacitor Negative Terminal of Flying Capacitor FUNCTION Regulation-Mode Select Input. Driving L/SKIP high or connecting it to selects L mode, with regulation accomplished by modulating switch resistance. Driving L/SKIP low or connecting it to GND selects Skip mode, where the device regulates by skipping charge-pump pulses. 7 GND Shutdown Control Input. Drive low to shut down the. Connect to for normal operation. connects to GND through a Ω (typical) resistor in shutdown mode. Inverting Charge-Pump Output Feedback Input. Connect to a resistor-divider from (or other reference source) to for regulated output voltages (Figures and ). Ground Power-Supply Positive Voltage Input Detailed Description The new-generation, high-output-current, regulated charge-pump DC-DC inverter provides up to ma. Designed specifically for compact applications, a complete regulating circuit requires only three small capacitors and two resistors. The employs On-Demand regulation circuitry, providing output regulation modes optimized for either lowest output noise or lowest supply current. In addition, the includes shutdown control. In Linear (L) mode or when heavily loaded in Skip mode, the charge pump runs continuously at 3kHz. During one-half of the oscillator period, switches S and S close (Figure ), charging the transfer capacitor (C FLY ) to the input voltage ( = GND, and = ). During the other half cycle, switches S3 and S close (Figure 3), transferring the charge on C FLY to the output capacitor ( = GND, = ). S S3 S C FLY S C 3kHz PUT.V ON C µf OFF R k Figure. Charging C FLY L C FLY.µF SKIP 3 L/SKIP GND 7 C µf R.k PUT -3V 3kHz S S C FLY S3 S C Figure. Standard Application Circuit Figure 3. Transferring Charge on C FLY to C

7 Linear Mode (Constant-Frequency Mode) In L mode (L/SKIP = ), the charge pump runs continuously at 3kHz. The controls the charge on C FLY by varying the gate drive on S (Figure ). When the output voltage falls, C FLY charges faster due to increased gate drive. Since the device switches continuously, the regulation scheme minimizes output ripple, the output noise contains well-defined frequency components, and the circuit requires much smaller external capacitors than in Skip mode for a given output ripple.* However, L mode is less efficient than Skip mode due to higher operating current (ma typical). PUT.V ON L C µf C FLY.µF OFF SKIP 3 L/SKIP GND 7 R k R.k V REF V C µf V = -V REF x R R PUT -3V Skip Mode In Skip mode (L/SKIP = GND), the device switches only as needed to maintain regulation on. Switching cycles are skipped until the voltage on rises above GND. Skip mode has higher output noise than L mode, but minimizes operating current. Figure. Separate V REF for Voltage Divider Shutdown Mode When (a CMOS-compatible input) is driven low, the enters low-power shutdown mode. Charge-pump switching action halts and an internal Ω switch pulls V to ground. Connect to or drive high for normal operation. *See Output Ripple vs. Load Current in Typical Operating Characteristics. Applications Information Resistor Selection (Output Voltage Selection) The accuracy of V depends on the accuracy of the voltage biasing the voltage-divider network (R, R). Use a separate reference voltage if V is an unregulated voltage or if greater accuracy is desired (Figure ). Adjust the output voltage from -.V to -V in L mode or V to -V in Skip mode with external resistors R and R as shown in Figures and. In either regulating mode (L or Skip), servos to V. Use the following equations to select R and R for the desired output voltage: R V = - VREF R where V REF can be either V or some other positive reference source. Typically, choose a voltage-divider current of µa to minimize the effect of input current: R = V REF / µa R = -V / µa Capacitor Selection A C FLY value of µf or more is sufficient to supply the specified load current. However, for minimum ripple in Skip mode, this value may need to be increased. Maxim recommends.µf. Surface-mount ceramic capacitors are preferred for C FLY, due to their small size, low cost, and low equivalent series resistance (ESR). To ensure proper operation over the entire temperature range, choose ceramic capacitors with X7R (or equivalent) low-temperaturecoefficient (tempco) dielectrics. See Table for a list of suggested capacitor suppliers. The output capacitor stores the charge transferred from the flying capacitor and services the load between oscillator cycles. A good general rule is to make the output capacitance at least ten times greater than that of the flying capacitor. When in Skip mode, output ripple depends mostly on two parameters: charge transfer between the capacitance values of C FLY and C, and the ESR of C. The ESR ripple contribution occurs as C charges. The charging current creates a negative voltage pulse across the capacitor s ESR that recedes as C charges. At equilibrium, when the voltage on C FLY approaches that on C, no charging current flows. Secondly, the ripple contribution due to charge transfer between capacitors creates a pulse as charge flows to C. Adding the two terms does not determine peakto-peak ripple because their peaks do not occur at the same time. It is best to use only the dominant term. The expression for the ripple component predominantly due to C ESR is: 7

8 V RIPPLE(ESR) = V V ESR C f OSC R C FLY The expression for the ripple component predominantly due to charge transfer is: V RIPPLE(ESR) = V V f R (C C ) OSC + FLY where C FLY and C are their respective capacitance values, ESR C is the equivalent series resistance of C, R is the open-loop output impedance (typically 3.Ω, and f OSC is the switching frequency (typically 3kHz). If ESR C is very small, as is likely when ceramic capacitors are used, V RIPPLE (TRANSFER) dominates. If ESR is relatively large, as with low-cost tantalum capacitors, then V RIP- PLE (ESR) dominates. When operating in L mode, use the following equation to approximate peak-to-peak output voltage ripple: V = RIPPLE I f C OSC + I ESR C where C is the output capacitor value, and f M is the minimum oscillator frequency (khz). See Table for a list of suggested capacitor suppliers. Layout Considerations The s high oscillator frequency requires good layout technique, which ensures stability and helps maintain the output voltage under heavy loads. Take the following steps to ensure good layout: Mount all components as close together as possible. Place the feedback resistors R and R close to the pin, and minimize the PC trace length at the circuit node. Keep traces short to minimize parasitic inductance and capacitance. Use a ground plane. Chip Information TRANSISTOR COUNT: 3 SUBSTRATE CONNECTED TO: where C is the output capacitor value, ESR C is the output capacitor s ESR, and f OSC is the oscillator frequency (typically 3kHz). To ensure L mode stability over the entire temperature range, choose a low-esr (no more than mω) output capacitance using the following equation: C = 7 x - R R + R I Table. Partial Listing of Capacitor Vendors PRODUCTION METHOD MANUFACTURER SERIES PHONE FAX AVX TPS (3) 9-9 (3) -7 Surface-Mount Tantalum Matsuo 7 (7) 99-9 (7) 9-9 Sprague 93D, 9D (3) -9 (3) -3 Surface-Mount Ceramic AVX X7R (3) 9-9 (3) -33 Matsuo X7R (7) 99-9 (7) 9-9 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, CA Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.