19-3329; Rev 1; 10/04 KIT ATION EVALU E L B A IL AVA High-Efficiency LCD Boost with True Shutdown Features ♦ 15V or Adjustable Output Voltage Up to 28V ♦ Safety Features Protect Against Output Faults ♦ 20mA at 20V from a Single Li+ Battery ♦ True Shutdown ♦ 87% Efficiency ♦ Up to 800kHz Switching Frequency ♦ Small 6-Pin SOT23 Package Ordering Information PART TEMP RANGE PINPACKAGE TOP MARK MAX8570EUT-T -40°C to +85°C 6 SOT23-6 ABTJ MAX8571EUT-T -40°C to +85°C 6 SOT23-6 ABTK MAX8572EUT-T -40°C to +85°C 6 SOT23-6 ABTL MAX8573EUT-T -40°C to +85°C 6 SOT23-6 ABTM MAX8574EUT-T -40°C to +85°C 6 SOT23-6 ABTN MAX8575EUT-T -40°C to +85°C 6 SOT23-6 ABTO Selector Guide Applications PART CURRENT LIMIT OUTPUT VOLTAGE MAX8570EUT 110mA Adjustable MAX8571EUT 250mA Adjustable Cellular or Cordless Phones MAX8572EUT 110mA 15V Palmtop Computers MAX8573EUT 250mA 15V Personal Digital Assistants (PDAs) MAX8574EUT 500mA Adjustable Organizers MAX8575EUT 500mA 15V LCD Bias Generators Polymer LEDs (OLED) Handy Terminals Pin Configurations Typical Operating Circuit TOP VIEW VOUT = VCC TO 28V FB 1 GND 2 MAX8570 MAX8571 MAX8574 SHDN 3 SOT23-6 6 VCC OUT 1 5 SW GND 2 4 LX SHDN 3 MAX8572 MAX8573 MAX8575 6 VCC 5 SW 4 LX VCC = 2.7V TO 5.5V SW LX VCC MAX8572 MAX8573 MAX8575 OUT SOT23-6 True Shutdown is a trademark of Maxim Integrated Products, Inc. ON SHDN GND OFF ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX8570–MAX8575 General Description The MAX8570 family of LCD step-up converters uses an internal n-channel switch and an internal p-channel output isolation switch. These converters operate from a 2.7V to 5.5V supply voltage and deliver up to 28V at the output. A unique control scheme provides the highest efficiency over a wide range of load conditions. The internal MOSFET switch reduces external component count and a high switching frequency (up to 800kHz) allows for tiny surface-mount components. Three current-limit options are available. The MAX8570 and MAX8572 use a 110mA current limit to reduce ripple and component size in low-current applications. For high-power requirements, the MAX8574 and MAX8575 use a 500mA current limit and supply up to 20mA at 20V. The MAX8571 and MAX8573 use a 250mA current limit for a compromise between ripple and power. Built-in safety features protect the internal switch and down-stream components from fault conditions. Additional features include a low quiescent current and a True Shutdown mode to save power. The MAX8570/ MAX8571/MAX8574 allow the user to set the output voltage between 3V and 28V, and the MAX8572/ MAX8573/MAX8575 have a preset 15V output. These step-up converters are ideal for small LCD panels with low current requirements, but can also be used in other applications. The MAX8571 evaluation kit is available to help reduce design time. MAX8570–MAX8575 High-Efficiency LCD Boost with True Shutdown ABSOLUTE MAXIMUM RATINGS VCC, SHDN to GND ..................................................-0.3V to +6V SW to GND .................................................-0.3V to (VCC + 0.3V) FB to GND (MAX8570/MAX8571/ MAX8574)...............................................-0.3V to (VCC + 0.3V) OUT to GND (MAX8572/MAX8573/MAX8575) .......-0.3V to +30V LX to GND ..............................................................-0.3V to +30V ILX, ICC ..............................................................................600mA Continuous Power Dissipation (TA = +70°C) SOT23-6 (derate 8.7 mW/°C above +70°C).............695.7 mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°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 (VCC = V SHDN = 3.6V, SW floating, VFB = 1.3V (MAX8570/MAX8571/MAX8574) or VOUT = 16V (MAX8572/MAX8573/MAX8575), TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS 5.50 V 2.5 2.65 V 25 35 µA TA = +25°C 0.05 1 TA = -40°C to +85°C 0.05 VCC Input Voltage Range VCC Undervoltage Lockout 2.70 VCC rising, 50mV typical hysteresis 2.33 VCC Supply Current VCC Shutdown Current SHDN = GND, VCC = 5.5V Line Regulation Circuit of Figure 3, VOUT = 15V, ILOAD = 5mA, VCC = 2.7V to 5.5V Load Regulation FB Regulation Voltage Circuit of Figure 3, VOUT = 15V, ILOAD = 0 to 5mA OUT Input Bias Current 0.1 TA = -40°C to +85°C 1.2137 -50 -4 +50 TA = 0°C to +85°C 14.85 15 15.15 TA = -40°C to +85°C 14.813 VOUT = 15V 1.226 LX On-Resistance LX Leakage Current 1.2383 15.187 2.4 SHDN High Level (VIH) SHDN Leakage Current 2 V 0.241 0.267 0.101 0.108 MAX8574/MAX8575 0.425 0.484 0.540 MAX8571/MAX8573/MAX8574/MAX8575, ILX = 100mA 0.9 1.5 MAX8570/MAX8572, ILX = 50mA 1.5 2.4 TA = +25°C 0.01 2 TA = -40°C to +85°C 0.05 11 14 VFB > 1V or VOUT > 12.2V 0.8 1 1.2 VFB = 0.25V or VOUT = 3.4V 4.0 5 6.0 55 2.7V ≤ VCC ≤ 5.5V 1.5 2.7V ≤ VCC < 4.2V 1.4 -1 _______________________________________________________________________________________ A Ω µA µs µs ns 0.7 4.2V ≤ VCC ≤ 5.5V V µA 0.088 8 nA 28 0.217 VLX = 28V V 4.4 MAX8570/MAX8572 Current-Limit Propagation Delay SHDN Low Level (VIL) 1.236 MAX8571/MAX8573 Maximum LX On-Time Minimum LX Off-Time %/mA 1.216 LX Voltage Range LX Switch Current Limit (Note 2) %/V TA = 0°C to +85°C FB Input Bias Current OUT Regulation Voltage 0.1 µA V V +1 µA High-Efficiency LCD Boost with True Shutdown (VCC = V SHDN = 3.6V, SW floating, VFB = 1.3V (MAX8570/MAX8571/MAX8574) or VOUT = 16V (MAX8572/MAX8573/MAX8575), TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS SW PMOS Current Limit MIN TYP MAX VCC = 3.6V, VSW = 0V, VFB = 0V, ICC (peak) 0.45 0.75 1.10 VCC = 3.6V, VSW = 0V, VFB = 0V, ICC (average) 0.15 0.30 0.60 1.5 2.5 TA = +25°C 0.01 1 TA = -40°C to +85°C 0.02 SW PMOS On-Resistance VCC = 2.7V, VFB = 0V, ISW = 100mA SW PMOS Leakage Current SW = GND, VCC = 5.5V, VFB = 0V SW Soft-Start Time VCC = 2.7V, CSW = 4.7µF 0.2 UNITS A Ω µA 1 ms Note 1: Parameters are production tested at TA = +25°C. Limits over temperature are guaranteed by design. Note 2: Specified currents are measured at DC. Actual LX current limits are slightly higher in circuit due to current-limit comparator delay. Actual currents (with 2µH) are 110mA (MAX8570/MAX8572), 250mA (MAX8571/MAX8573), and 500mA (MAX8574/MAX8575). Typical Operating Characteristics (MAX8571, VCC = 3.6V, VOUT = 18V, Circuit of Figure 2, TA = +25°C, unless otherwise noted.) 18.1 18.0 1mA LOAD 17.9 17.8 17.7 1mA LOAD 15.2 15.1 15.0 14.9 5mA LOAD 14.8 L1 = MURATA LQH32CN220K23 R1 = 3.9MΩ, R2 = 287kΩ 17.5 2.7 3.1 3.5 3.9 4.3 14.6 14.5 4.7 5.1 5.5 18.2 18.0 17.8 3.1 3.5 3.9 4.3 4.7 5.1 MAX8570/71/73/74/75 toc05 18.2 18.1 18.0 17.9 LOAD CURRENT (mA) 20 25 3.7 4.0 4.3 L1 = TOKO A914BYW-470M 95 47µH, 5mA LOAD 47µH, 1mA LOAD 90 80 75 1mA LOAD -15 4.9 85 22µH, 1mA LOAD 22µH, 5mA LOAD -40 4.6 100 17.8 17.6 15 3.4 EFFICIENCY vs. SUPPLY VOLTAGE MAX8571 10 3.1 5.5 17.7 5 L1 = TOKO S1024-100M R1 = 1.1MΩ, R2 = 75kΩ, C4 = 4.7pF SUPPLY VOLTAGE (V) 18.3 R1 = 3.9MΩ, R2 = 287kΩ, C4 = 10pF 0 17.6 17.0 18.4 OUTPUT VOLTAGE (V) 18.4 MAX8570/71/73/74/75 toc04 OUTPUT VOLTAGE (V) MAX8574, R1 = 1.1MΩ, R2 = 75kΩ, C4 = 4.7pF 17.4 20mA LOAD 17.8 OUTPUT VOLTAGE vs. TEMPERATURE L1 = MURATA LQH32CN220K23 MAX8570 18.0 SUPPLY VOLTAGE (V) 18.8 17.6 18.2 17.2 L1 = MURATA LQH32CN220K23 2.7 OUTPUT VOLTAGE vs. LOAD CURRENT 18.6 18.4 17.4 SUPPLY VOLTAGE (V) 19.0 5mA LOAD 18.6 14.7 17.6 MAX8570/71/73/74/75 toc03 15.3 18.8 MAX8570/71/73/74/75 toc06 18.2 15.4 19.0 EFFICIENCY (%) OUTPUT VOLTAGE (V) 18.3 MAX8570/71/73/74/75 toc02 5mA LOAD 15.5 OUTPUT VOLTAGE (V) MAX8570/71/73/74/75 toc01 18.5 18.4 OUTPUT VOLTAGE vs. SUPPLY VOLTAGE (MAX8574) OUTPUT VOLTAGE vs. SUPPLY VOLTAGE (FIGURE 3, MAX8573) OUTPUT VOLTAGE (V) OUTPUT VOLTAGE vs. SUPPLY VOLTAGE (MAX8571) L1 = MURATA LQH32CN220K23 70 10 35 TEMPERATURE (°C) 60 85 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 3 MAX8570–MAX8575 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (MAX8571, VCC = 3.6V, VOUT = 18V, Circuit of Figure 2, TA = +25°C, unless otherwise noted.) 1mA LOAD 70 60 50 MAX8570, MURATA LQH32CN220K23 90 80 MAX8571, MURATA LQH32CN220K23 70 MAX8574, TOKO A914BYW-220M 60 100 MAX8570, L1 = MURATA LQH32CN470K23 90 EFFICIENCY (%) 80 100 50 VCC = 3.6V 80 MAX8571, L1 = TOKO A914BYW-470M 70 60 50 L1 = MURATA LQH32CN220K23 40 0 2 4 6 8 10 12 40 1 0.1 BATTERY VOLTAGE (V) MAX8571 300 MAX8570 100 80 60 40 2.7 3.1 3.5 3.9 4.3 4.7 5.1 L1 = MURATA LQH32CN220K23 0 5.5 5 60 50 40 MAX8573, FIGURE 3 30 L1 = MURATA LQH32CN220K23 NO SWITCHING 0 0 15 10 1 2 3 4 LINE TRANSIENT 3V TO 5.5V (FIGURE 3, MAX8573) LINE TRANSIENT 3V TO 5.5V (MAX8571) MAX8570/71/73/74/75 toc14 MAX8570/71/73/74/75 toc13 200mV/div (AC-COUPLED) 200mV/div (AC-COUPLED) VOUT VCC VCC 2V/div 2V/div 0 0 100µs/div 100µs/div 3.6kΩ LOAD, R1 = 3.9MΩ, R2 = 287kΩ 4 5 SUPPLY VOLTAGE (V) LOAD CURRENT (mA) SUPPLY VOLTAGE (V) VOUT R1 = 3.9MΩ R2 = 287kΩ R1 = 7.87MΩ R2 = 576kΩ 70 10 0 0 80 20 20 100 100 NO-LOAD CURRENT vs. SUPPLY VOLTAGE MAX8570/71/73/74/75 toc11 500 10 LOAD CURRENT (mA) 120 SUPPLY CURRENT (mA) MAX8574 200 1 0.1 SUPPLY CURRENT vs. LOAD CURRENT MAX8570/71/73/74/75 toc10 700 400 100 LOAD CURRENT (mA) PEAK INDUCTOR CURRENT LIMIT vs. SUPPLY VOLTAGE 600 10 MAX8570/71/73/74/75 toc12 40 SUPPLY CURRENT (µA) EFFICIENCY (%) 90 EFFICIENCY vs. LOAD CURRENT WITH 47µH INDUCTOR MAX8570/71/73/74/75 toc08 5mA LOAD EFFICIENCY (%) MAX8570/71/73/74/75 toc07 100 EFFICIENCY vs. LOAD CURRENT WITH 22µH INDUCTOR MAX8570/71/73/74/75 toc09 EFFICIENCY vs. BATTERY VOLTAGE (FIGURE 4) CURRENT LIMIT (mA) MAX8570–MAX8575 High-Efficiency LCD Boost with True Shutdown 3kΩ LOAD _______________________________________________________________________________________ 6 High-Efficiency LCD Boost with True Shutdown STARTUP AND SHUTDOWN WAVEFORMS LOAD TRANSIENT MAX8570/71/73/74/75 toc16 MAX8570/71/73/74/75 toc15 5V/div VSHDN VOUT 100mV/div (AC-COUPLED) BOOST SOFT-START SW TURN-ON 10V/div VOUT 0 5mA/div IOUT 0 ILX 200mA/div 0 400µs/div 100µs/div 1.8Ω LOAD Pin Description PIN NAME FUNCTION FB (MAX8570/ Feedback for setting the output voltage. Connect FB to the center of a resistor voltage-divider from the MAX8571/ output to GND to set positive output voltages. MAX8574) 1 OUT (MAX8572/ Output. The output voltage is preset to 15V. Connect a 1µF ceramic capacitor from OUT to GND. In MAX8573/ shutdown, OUT is pulled to GND by an internal 7.5MΩ resistor. MAX8575) 2 GND Ground 3 SHDN Shutdown Input. A logic low at SHDN places the part in low-power shutdown mode. Pull SHDN high or connect to VCC for normal operation. 4 LX Inductor Switching Connection 5 SW Isolation Switch Output. Internally connected to the drain of a p-channel MOSFET used to isolate the output from the input during shutdown. Connect a 4.7µF ceramic capacitor from SW to GND. If true shutdown is not required, SW can be left open with the input supply connected directly to the inductor. 6 VCC Input Voltage Supply. Connect a 2.7V to 5.5V input supply to VCC. Connect a 1µF ceramic capacitor from VCC to GND. _______________________________________________________________________________________ 5 MAX8570–MAX8575 Typical Operating Characteristics (continued) (MAX8571, VCC = 3.6V, VOUT = 18V, Circuit of Figure 2, TA = +25°C, unless otherwise noted.) MAX8570–MAX8575 High-Efficiency LCD Boost with True Shutdown VCC SW LX SHDN THERMAL SHUTDOWN OUT (MAX8572/MAX8573/ MAX8575 ONLY) ILIM MAX8570– MAX8575 CONTROL LOGIC FB (MAX8570/MAX8571/ MAX8574 ONLY) EA 1.226V GND Figure 1. Functional Diagram L1 22µH L1 22µH D1 C3 4.7µF VCC = 2.7V TO 5.5V C1 1µF ON VCC VOUT = VCC TO 28V LX SW MAX8570 MAX8571 MAX8574 C4 10pF R1 D1 C2 1µF C3 4.7µF VCC = 2.7V TO 5.5V FB R2 ON GND SHDN L1 22µH D1 VCC VOUT = VBATT TO 28V D1 LX SW MAX8570 MAX8571 MAX8574 C4 10pF R1 C2 1µF C3 4.7µF VCC = 2.7V TO 5.5V FB C1 1µF R2 SHDN Figure 4. Using a Separate Input Supply for the Inductor MAX8570 MAX8571 MAX8574 C4 10pF C2 1µF R1 R2 FB C6 0.1µF D3 -VOUT SHDN GND OFF VCC +VOUT LX SW D2 ON ON 6 Figure 3. Typical Application Circuit with 15V Preset Output Voltage L1 22µH VBATT = 0.8V TO 28V C1 1µF GND OFF Figure 2. Typical Application Circuit with Adjustable Output Voltage VCC = 2.7V TO 5.5V C2 1µF MAX8572 MAX8573 MAX8575 OUT SHDN OFF C3 4.7µF VCC C1 1µF VOUT = 15V LX SW GND OFF Figure 5. Negative Output Voltage for LCD Bias _______________________________________________________________________________________ C5 1µF High-Efficiency LCD Boost with True Shutdown The MAX8570 family of compact, step-up DC-DC converters operate from a 2.7V to 5.5V supply. Consuming only 25µA of supply current, these ICs include an internal MOSFET switch with a low on-resistance. A trueshutdown feature disconnects the battery from the load and reduces the supply current to 0.05µA (typ). These DC-DC converters are available with either a fixed 15V output or are adjustable up to 28V. Three current-limit options are available: 110mA, 250mA, and 500mA. See the Selector Guide on page 1. Control Scheme The MAX8570 family features a minimum off-time current-limited control scheme operating in discontinuous mode. An internal p-channel MOSFET switch connects VCC to SW to provide power to the inductor when the converter is operating. When the converter is shut down, this switch disconnects the input supply from the inductor (see Figure 1). To boost the output voltage, an n-channel MOSFET switch turns on and allows current to ramp up in the inductor. Once this current reaches the current limit, the switch turns off and the inductor current flows through D1 to supply the output. The switching frequency varies depending on the load and input voltage and can be up to 800kHz. Setting the Output Voltage The output voltage of the MAX8570, MAX8571, and MAX8574 is adjustable from VCC to 28V by using a resistor voltage-divider (see Figure 2). Select R2 from 10kΩ to 600kΩ and calculate R1 with the following equation: V R1 = R2 OUT − 1 VFB where VFB = 1.226V and VOUT can range from VCC to 28V. For best accuracy, ensure that the bias current through the feedback resistors is at least 2µA. The MAX8572, MAX8573, and MAX8575 have a fixed 15V output. When using these parts, connect OUT directly to the output (see Figure 3). Shutdown (SHDN) Drive SHDN low to enter shutdown. During shutdown the supply current drops to 0.05µA (typ), the output is disconnected from the input, and LX enters a highimpedance state. The capacitance and load at the output determine the rate at which VOUT decays. SHDN can be pulled as high as 6V regardless of the input and output voltages. With a typical step-up converter circuit, the output remains connected to the input through the inductor and output rectifier, holding the output voltage to one diode drop below VCC when the converter is shut down and allowing the output to draw power from the input. The MAX8570 family features true-shutdown mode, disconnecting the output from the input with an internal pchannel MOSFET switch when shut down. This eliminates power draw from the input during shutdown. Soft-Start The MAX8570 family uses two soft-start mechanisms. When the true-shutdown feature is used (SW is connected as in Figure 2 and Figure 3), the gate of the internal high-side p-channel switch turns on slowly to prevent inrush current. This takes approximately 200µs. When SW is fully turned on, the internal n-channel switch begins boosting the input to set the output voltage. When VFB is less than 0.5V (with or without the use of true shutdown), the minimum off-time of the internal n-channel switch increases from 1µs to 5µs to control inrush current. Separate Power for Inductor Separate power supplies can be used for the IC and the inductor. This allows power to be used from a battery or supply with a voltage as low as 0.8V, or higher than the VCC operating range of the converter. When using a separate inductor supply, SW is left unconnected and the supply is connected directly to the inductor (see Figure 4). Note that in this configuration the output is no longer disconnected from the input during shutdown. In shutdown the output voltage goes to a diode drop below the inductor supply voltage. Protection Features The MAX8570 family has protection features designed to make it extremely robust to application errors (see Table 1). If the output capacitor in the application is missing, the MAX8570 family protects the internal switch from being damaged. If the top feedback resistor or the external diode is disconnected, the converter stops switching and the output is resistively loaded to ground. Similarly, if the external diode polarity is reversed, the converter discontinues switching. If the bottom feedback resistor is missing, the output stays at a diode drop less than the inductor supply voltage or 1.226V (whichever is greater). In fact, in response to most fault conditions, the MAX8570 family protects not only itself, but also the downstream circuitry. _______________________________________________________________________________________ 7 MAX8570–MAX8575 Detailed Description MAX8570–MAX8575 High-Efficiency LCD Boost with True Shutdown Table 1. Protection Features RESULT WITH COMPETING STEP-UP CONVERTERS COMMON APPLICATION FAULTS RESULT WITH MAX8570 FAMILY OUT voltage rises until the output capacitor is destroyed and/or downstream components are damaged. Converter stops switching. Output cap missing and FB floating. OUT voltage rises until the output capacitor is destroyed and/or downstream components are damaged. LX may boost one or two times before the FB voltage exceeds the trip point. In the rare case where the capacitive loading and external loading on OUT is small enough that the energy in one cycle can slew it more than 50V, the internal MOSFET will clamp between 35V and 70V (nondestructively). FB shorted to GND. OUT voltage rises until the output capacitor is destroyed and/or downstream components are damaged. Converter stops switching and OUT is resistively loaded to GND. Diode missing or disconnected. Diode reverse polarity. Inductor energy forces LX node high, possibly damaging the internal switch. OUT is resistively loaded to GND and the converter stops switching. FB node floating. Unpredictable, possibly boosting output voltage beyond acceptable design range. FB node driven above its regulation point, the converter stops switching, and OUT is resistively loaded to GND. OUT shorted to ground. Current ramps up through inductor and diode, generally destroying one of the devices. True off-switch detects short, opens when current reaches pMOS current limit, and restarts soft-start. This protects the inductor and diode. OUT to FB resistor missing or disconnected. Design Procedure Inductor Selection Smaller inductance values typically offer smaller physical size for a given series resistance or saturation current. Circuits using larger inductance values may provide more output power. The inductor’s saturation current rating should be greater than the peak switching current. Recommended inductor values range from 10µH to 100µH. value. See the Selector Guide on page 1 for selecting the IC with the correct current limit. Diode Selection The high switching frequency of up to 800kHz requires a high-speed rectifier. Schottky diodes are recommended due to their low forward-voltage drop. To maintain high efficiency, the average current rating of the diode should be greater than the peak switching current. Choose a reverse breakdown voltage greater than the output voltage. Selecting the Current Limit The peak LX current limit (ILX(MAX)) required for the application is calculated from the following equation: ILX(MAX) ≥1.25 × 2 POUT(MAX) POUT(MAX) + 1.25 × + 3µs × VBATT(MIN) VBATT(MIN) L POUT(MAX) where P OUT(MAX) is the maximum output power required by the load and VBATT(MIN) is the minimum supply voltage used to supply the inductor (this is VCC unless a separate supply is used for the inductor). The IC current limit must be greater than this calculated 8 Capacitors Small ceramic surface-mount capacitors with X7R or X5R temperature characteristics are recommended due to their small size, low cost, low equivalent series resistance (ESR), and low equivalent series inductance (ESL). If nonceramic capacitors are used, it is important that they have low ESR to reduce the output ripple voltage and peak-peak load-transient voltage. For most applications, use a 1µF ceramic capacitor for the output and VCC bypass capacitors. For SW or the inductor supply, a 4.7µF or greater ceramic capacitor is recommended. _______________________________________________________________________________________ High-Efficiency LCD Boost with True Shutdown Applications Information PC Board Layout Careful printed circuit layout is important for minimizing ground bounce and noise. Keep the GND pin and ground pads for the input and output capacitors as close together as possible. Keep the connection to LX as short as possible. Locate the feedback resistors as close as possible to the FB pin and keep the feedback traces routed away from noisy areas such as LX. Refer to the MAX8571EVKIT for a layout example. Negative Output Voltage for LCD Bias A negative output voltage can be generated by adding a diode/capacitor charge pump as shown in Figure 5. In this configuration, the negative output is lower in magnitude than the positive output by a forward diode drop. If there is little or no load on the positive output, the negative output drifts from its nominal voltage. To prevent this, it may be necessary to preload the positive output with a few hundred microamps, which can be done by selecting lower than normal values of R1 and R2. Chip Information TRANSISTOR COUNT: 742 PROCESS: BiCMOS _______________________________________________________________________________________ 9 MAX8570–MAX8575 For the MAX8570/MAX8571/MAX8574 a feed-forward capacitor (C4 in Figures 2 and 3) connected from the output to FB improves stability over a wide range of battery voltages. A 10pF capacitor is recommended for the MAX8571 and MAX8574. A 10pF to 47pF capacitor is recommended for the MAX8570. Note that increasing C4 degrades line and load regulation. Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) 6LSOT.EPS MAX8570–MAX8575 High-Efficiency LCD Boost with True Shutdown PACKAGE OUTLINE, SOT-23, 6L 21-0058 F 1 1 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. 10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.