MAX889TESA -40 C to +85 C 8 SO 2MHz MAX889SESA -40 C to +85 C 8 SO 1MHz MAX889RESA -40 C to +85 C 8 SO 0.5MHz. Maxim Integrated Products 1

Transcription

1 ; Rev ; 7/ EVALUATION KIT AVAILABLE High-Frequency, Regulated, General Description The inverting charge pump delivers a regulated negative output voltage at loads of up to 2. The device operates with inputs from 2.7V to 5.5V to produce an adjustable, regulated output from -2.5V to -V. The is available with an operating frequency of 2MHz (T version), 1MHz (S version), or.5mhz (R version). The higher switching frequency devices allow the use of smaller capacitors for space-limited applications. The lower frequency devices have lower quiescent current. The also features a.1µa logic-controlled shutdown mode and is available in an 8-pin SO package. An evaluation kit, SEVKIT, is available. Features 2 Output Current Up to 2MHz Switching Frequency Small Capacitors (1µF) +2.7V to +5.5V Input Voltage Range Adjustable Regulated Negative Output (-2.5V to -V).1µA Logic-Controlled Shutdown Low.5Ω Output Resistance (in regulation) Soft-Start and Foldback Current Limited Short-Circuit and Thermal Shutdown Protected 8-Pin SO Package Applications TFT Panels Hard Disk Drives Camcorders Digital Cameras Measurement Instruments Battery-Powered Applications Ordering Information TEMP. P- SWITCHG PART RANGE PACKAGE FREQUENCY TESA -4 C to +85 C 8 SO 2MHz SESA -4 C to +85 C 8 SO 1MHz RESA -4 C to +85 C 8 SO.5MHz Typical Operating Circuit Pin Configuration PUT +2.7V TO +5.5V TOP VIEW OFF ON SHDN CAP+ FB REGULATED NEGATIVE PUT (UP TO -1 V, UP TO 2) CAP+ GND AGND FB SHDN 4 5 AGND GND SO Maxim Integrated Products 1 For free samples and the latest literature, visit or phone For small orders, phone

2 ABSOLUTE MAXIMUM RATGS to GND...-.3V to +6V FB, SHDN, CAP+ to GND...-.3V to (V +.3V) AGND to GND...-.3V to +.3V to GND...-6V to +.3V to GND...(V -.3V) to +.3V Continuous Output Current...25 Output Short-Circuit Duration...Indefinite Continuous Power Dissipation (T A = +7 C) 8-Pin SO (derate 5.88mW/ C above +7 C)...471mW Operating Temperature Range...-4 C to +85 C Junction Temperature C Storage Temperature Range C to +15 C Lead Temperature (soldering, 1s)...+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 SHDN = +5V, capacitors from Table 1, T A = C to +85 C, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS Supply Voltage Range V R LOAD = 1Ω V Output Voltage Range V R LOAD = 1Ω V V Maximum Output Current Quiescent Supply Current (Free-Run Mode) Quiescent Supply Current (Regulated Mode) I (MAX)1 V = 5V, V = -3.3V 2 I (MAX)2 V = 3.3V, V = -2.5V 145 R 6 12 I Q(FREE-RUN) No load, V FB = V S T I Q(REGULATED) No load, V regulated to -3.3V R S T Shutdown Supply Current I SHDN V SHDN =.1 5 µa Open-Loop Output Resistance (Free-Run Mode) R O V FB = V Ω Output Resistance R O(REG1) V regulated to -3.3V.5 Ω SHDN, FB Input Bias Current ±1 µa FB Input Offset Voltage I LOAD = ±3 ±35 mv Load Regulation I = to 2 1 mv Undervoltage Lockout Threshold V rising (3mV hysteresis) V SHDN Logic High V IH.7 x V SHDN Logic Low V IL V = +2.7V to +5.5V R Switching Frequency f OSC S T x V V MHz Thermal Shutdown Threshold Junction temperature rising (15 C hysteresis) 16 C 2

3 ELECTRICAL CHARACTERISTICS (V = V SHDN = +5V, capacitors from Table 1, T A = -4 C to +85 C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS M MAX UNITS Supply Voltage Range V R LOAD = 1Ω V Output Voltage Range V R LOAD = 1Ω V V Maximum Output Current Quiescent Supply Current (Free-Run Mode) I (MAX)1 V = 5V, V = -3.3V 2 I (MAX)2 V = 3.3V, V = -2.5V 145 R 12 I Q(FREE-RUN) No load, V FB = V S 24 T 48 Quiescent Supply Current (Regulated Mode) I Q(REGULATED) No load, V regulated to -3.3V R 7 S 12 T 22 Shutdown Supply Current I SHDN V SHDN = 5 µa Open-Loop Output Resistance (Free-Run Mode) R O V FB = V 4.5 Ω SHDN FB Input Bias Current ±1 µa FB Input Offset Voltage I LOAD = ±35 mv Undervoltage Lockout Threshold V rising (3mV hysteresis) V SHDN Logic High V IH.7 x V SHDN Logic Low V IL V = +2.7V to +5.5V R Switching Frequency f OSC S T x V V MHz Note 1: Specifications to -4 C are guaranteed by design, not production tested. Typical Operating Characteristics (Circuit of Figure 1, V = V SHDN = +5V, capacitors from Table 1, T A = +25 C, unless otherwise noted.) PUT VOLTAGE vs. LOAD CURRENT toc1 4 R PUT RIPPLE vs. LOAD CURRENT vs. C toc2 4 S PUT RIPPLE vs. LOAD CURRENT vs. C C = 4.7µF toc3 PUT VOLTAGE (V) T S PUT RIPPLE (mv) 3 2 C = 1µF C = 22µF PUT RIPPLE (mv) 3 2 C = 1µF C = 22µF R C = 47µF PUT LOAD CURRENT () LOAD CURRENT () LOAD CURRENT () 3

4 PUT RIPPLE (mv) T PUT RIPPLE vs. LOAD CURRENT vs. C C = 2.2µF C = 4.7µF C = 1µF LOAD CURRENT () toc4 EFFICIENCY (%) Typical Operating Characteristics (continued) (Circuit of Figure 1, V = V SHDN = +5V, capacitors from Table 1, T A = +25 C, unless otherwise noted.) R (Ω) FREE-RUN PUT RESISTANCE vs. PUT VOLTAGE toc7 R (Ω) EFFICIENCY vs. LOAD CURRENT (V = 5V, V = -3.3V) R T S LOAD CURRENT () FREE-RUN PUT RESISTANCE vs. TEMPERATURE toc5 toc8 EFFICENCY (%) QUIESCENT CURRENT () EFFICIENCY vs. LOAD CURRENT (V = 3.3V, V = -2.5V) 1 9 R T 5 S LOAD CURRENT () QUIESCENT SUPPLY CURRENT vs. PUT VOLTAGE (REGULATED MODE) T S R toc6 toc PUT VOLTAGE (V) S LOAD-TRANSIENT RESPONSE TEMPERATURE ( C) S LE-TRANSIENT RESPONSE V = -2.5V PUT VOLTAGE (V) S STARTUP AND SHUTDOWN toc1 toc11 toc12 A A A B B B C 4µs/div 4µs/div 2ms/div 2 TO 2 LOAD STEP I = 2 I = 2 CIRCUIT OF FIGURE 4 CIRCUIT OF FIGURE 4 A: V, 1V/div A: I, 1/div A: V, 2V/div B: I, 1/div B: V, 2mV/div, AC-COUPLED B: V, 1mV/div, AC-COUPLED C: V SHDN, 1V/div 4

5 P NAME FUNCTION 1 Power-Supply Positive Voltage Input 2 CAP+ Positive Terminal of Flying Capacitor 3 GND Power Ground 4 Negative Terminal of Flying Capacitor Pin Description 5 Inverting Charge-Pump Output 6 SHDN Shutdown Control Input. Drive SHDN low to shut down the. Connect SHDN to for normal operation. 7 FB Feedback Input. Connect FB to a resistor-divider from (or other positive reference voltage source) to for regulated output voltages. Connect to for free-run mode. 8 AGND Analog Ground Detailed Description The high-current regulated charge-pump DC- DC inverter provides up to 2. It features the highest available output current while using small capacitors (Table 1). The three versions available differ in their switching frequencies (fosc) R/ S/T with fosc = 5kHz/1MHz/2MHz, respectively. Higher frequencies allow the use of smaller components (Table 1). Even smaller capacitor values than those listed in Table 1 are suitable when the devices are loaded at less than their rated output current. Designed specifically for compact applications, a complete regulating circuit requires only three small capacitors and two resistors, Figure 1. In addition, the includes soft-start, shutdown control, short-circuit, and thermal protection. The oscillator, control circuitry, and four power MOSFET switches are included on-chip. The charge pump runs continuously at the operating frequency. During one-half of the oscillator period, switches S1 and S2 close (Figure 2), charging the transfer capacitor (C FLY ) to the input voltage ( = GND, CAP+ = ). During the other half cycle, switches S3 and S4 close (Figure 3), transferring the charge on C FLY to the output capacitor (CAP+ = GND, = ). Voltage Regulation Voltage regulation is achieved by controlling the flyingcapacitor charging rate. The controls the charge on CFLY by modulating the gate drive to S1 (Figure 2) to supply the charge necessary to maintain output regulation. When the output voltage droops, CFLY charges higher due to increased gate drive. Since the device switches continuously, the regulation scheme minimizes output ripple, and the output noise spectrum contains well-defined frequency components. Feedback voltage is sensed with a resistor-divider between an externally supplied positive reference or the supply voltage and the negative inverted output. The feedback loop servos FB to GND. The effective output impedance in regulation is.5ω. The output remains in regulation until dropout is reached. Dropout depends on the output voltage setting and load current (see Output Voltage vs. Load Current in Typical Operating Characteristics). Free-Run Mode (Unregulated Voltage Inverter) The may be used in an unregulated voltage inverter mode that does not require external feedback resistors, minimizing board space. Connecting FB to places the in free-run mode. In this mode, the charge pump operates to invert directly the input supply voltage (V = -(V - I x RO)). Output resistance is typically 2Ω and can be approximated by the following equation: RO [1 / (fosc x CFLY) ] + 2RSW + 4ESRCFLY + ESRC The first term is the effective resistance of an ideal switched-capacitor circuit (Figures 2 and 3), and RSW is the sum of the charge pump s internal switch resistances (typically.8ω at V = 5V). The last two terms take into consideration the equivalent series resistance 5

6 (ESR) of the flying and output capacitors. The typical output impedance is more accurately determined from the Typical Operating Characteristics. Current Limit and Soft-Start The features a foldback current-limit/soft-start scheme that allows it to limit inrush currents during startup, overload, and output short-circuit conditions. Additionally, it permits a safe, timed recovery from fault conditions. This protects the and prevents low-current or higher output impedance input supplies (such as alkaline cells) from being overloaded at startup or short-circuit conditions. The features two current-limit/soft-start levels with corresponding response to rising and falling output voltage thresholds of -.6V and -1.5V. When the falling output voltage crosses -1.5V, such as during an overload condition, the input current is immediately limited to 4 by weakening the charge-pump switches. When the falling output voltage crosses -.6V, such as during a short-circuit condition, the further weakens the charge-pump switches, immediately limiting input current to 2. During startup or short-circuit recovery, the limits input current to 2 with charge-pump switches at their weakest level. Rising output voltage crossing -.6V initiates a 2ms timer, after which the increases switch strength to the next level. The rising output voltage crossing -1.5V initiates a 2ms timer, after which the provides full-strength operation. Shutdown When SHDN (a CMOS-compatible input) is driven low, the enters.1µa shutdown mode. Chargepump switching halts. Connect SHDN to or drive high for normal operation. Thermal Shutdown The features thermal shutdown with hysteresis for added protection against fault conditions. When the die temperature exceeds 16 C, the internal oscillator stops, suspending device operation. The resumes operation when the die temperature falls 15 C. This prevents the device from rapidly oscillating around the temperature trip point. Applications Information Resistor Selection (Setting the Output Voltage) The accuracy of V depends on the accuracy of the voltage biasing R1 in Figure 1. Use a separate reference voltage if greater accuracy than provided by V is desired (Figure 4). Keep the feedback node as small as possible, with resistors mounted close to the FB pin. F OSC S1 S2 C FLY CAP+ S3 S4 C Figure 2. Charging C FLY PUT 5.V OFF C 4.7µF C FLY 1µF ON C 4.7µF R1 1k R1 66.5k PUT -3.3V F OSC S1 S2 C FLY CAP+ 1 SHDN FB CAP+ T GND 8 3 S3 S4 C Figure 1. Typical Application Circuit. Figure 3. Transferring Charge on C FLY to C 6

7 Adjust the output voltage to a negative voltage from -2.5V to -V with external resistors R1 and R2 as shown in Figures 1 and 4. FB servos to GND. Choose R1 to be 1kΩ or less. Calculate R2 for the desired output voltage: V = -V REF (R2 / R1) R2 = R1 (V / -VREF) where V REF can be either V or a positive reference source. Typically, choose a voltage-divider current of at least 3µA to minimize the effect of FB input current and capacitance: R1 V REF / 3µA R2 < -V / 3µA Capacitor Selection The appropriate capacitors used with the depend on the switching frequency. Table 1 provides suggested values for C, C FLY, and C. Surface-mount ceramic capacitors are preferred for C, C, and C FLY due to their small size, low cost, and low ESR. To ensure proper operation over the entire temperature range, choose ceramic capacitors with X7R (or equivalent) low-temperature-coefficient (tempco) dielectrics. See Table 2 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 five-times greater than the flying capacitor. Output voltage ripple is largely dependent on C. Choosing a low-esr capacitor of sufficient value is important in minimizing the peak-to-peak output voltage ripple, which is approximated by the following equation: I V = RIPPLE + 2 x f OSC C 2 x I ESRC where C is the output capacitor value, ESR C is the output capacitor s ESR, and f OSC is the switching frequency. Ceramic capacitors have the lowest ESR and are recommended for C. Where larger capacitance at low cost is desired, a low-esr tantalum capacitor may be used for C. See Table 2 for a list of suggested capacitor suppliers. To ensure stability over the entire operating temperature range, choose a low-esr output capacitor using the following equation: C where C is the output capacitor value, and f M is the minimum oscillator frequency in the Electrical Characteristics table. To ensure stability for regulated output mode, suitable output capacitor ESR should be determined by the following equation: R ESR 15.5 R1 f M R1 + R x 1 I I R2 1 + R1 Power Dissipation The power dissipated in the depends on the input voltage, output voltage, and output current. Device power dissipation is accurately described by: P DISS = I (V - (-V )) + (I Q V ) where IQ is the device quiescent current. PDISS must be less than the package dissipation rating (see Absolute Maximum Ratings). Pay particular attention to power dissipation limits when generating small negative voltages from large positive input voltages. Layout Considerations The s high oscillator frequencies demand good layout techniques that ensure stability and help maintain the output voltage under heavy loads. Take the following steps to ensure optimum layout: 1) Mount all components as close together as possible. 2) Place the feedback resistors R1 and R2 close to the FB pin, and minimize the PC trace length at the FB circuit node. 3) Keep traces short to minimize parasitic inductance and capacitance. 4) Use a ground plane with C and C placed in a star ground configuration (see the SEVKIT layout). 7

8 Table 1. Capacitor Selection Table PART FREQUENCY C FLY C C REGULATED C FREE-RUN R.5MHz 4.7µF 22µF 22µF 4.7µF S 1MHz 2.2µF 1µF 1µF 2.2µF T 2MHz 1µF 4.7µF 4.7µF 1µF Table 2. Low-ESR Capacitor Manufacturers PRODUCTION METHOD MANUFACTURER SERIES PHONE FAX AVX TPS series Surface-Mount Kemet 494 series Tantalum Matsuo 267 series Sprague 593D, 595D series S ur face- M ount P ol ym er Sanyo POSAPA S ur face- M ount C er am i c AVX X7R Kemet X7R Matsuo X7R Murata GRM X7R Chip Information TRANSISTOR COUNT: 184 PROCESS: BiCMOS Package Information SOICN.EPS PUT 5.V OFF C 4.7µF C FLY 1µF ON SHDN FB CAP+ T AGND GND V REF 5V R1 1k R2 66.5k PUT C -3.3V 4.7µF V = -V REF R2 R1 Figure 4. Separate VREF for Voltage Divider 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, 12 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.