19-2662; Rev 0; 10/02 High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers Features The MAX1534 is a high-efficiency, triple-output power supply for keep-alive (always on) voltage rails. The 500mA buck regulator with an internal current-limited 0.5Ω PMOS steps down the battery or wall adapter supply rail to a fixed 5V or an adjustable output voltage. Two integrated low-voltage linear regulators follow this output and provide two independent preset output voltages of 3.3V and 1.8V, or adjustable output voltages. The buck regulator utilizes a peak current-limit, pulsefrequency modulation (PFM) architecture for highest light-load efficiency to conserve battery life. High switching frequencies (up to 200kHz) allow the use of tiny surface-mount inductors and output capacitors. Operation to 100% duty cycle minimizes dropout voltage (250mV at 500mA). The low-dropout linear regulators use an internal P-channel metal-oxide (PMOS) pass transistor to minimize supply current and deliver up to 160mA each of continuous current. ♦ One Switching and Two Linear Regulators ♦ Switching Regulator +4.5V to +24V Input Voltage Range Over 95% Efficiency Up to 500mA Output Current Up to 200kHz Switching Frequency Fixed 5V or Adjustable Output Voltage Internal 0.5Ω PMOS Switch 100% Maximum Duty Cycle for Low-Dropout Operation ♦ Two Low-Dropout Linear Regulators Up to 160mA Output Current (Each) 3.3V/Adj Output Voltage for OUT1 1.8V/Adj Output Voltage for OUT2 ♦ ±1.5% Accurate Output Voltage ♦ ±4% Accurate Shutdown for Low Battery Detection The MAX1534 includes a power-OK (POK) signal that indicates all outputs are in regulation. The 4% accurate threshold of the SHDN input permits its use as a lowbattery detector. ♦ Thermal Shutdown Protection ♦ POK Output ♦ 1mW Typical Standby Power The MAX1534 is available in a small 16-pin thin QFN (4mm ✕ 4mm) package, occupying 33% less board space than discrete solutions. Applications Notebook and SubNotebook Computers Wake-On LAN 2 to 4 Li+ Cells BatteryPowered Devices Ordering Information Hand-Held Devices Keep-Alive Supplies Standby Supplies PART MAX1534ETE TEMP RANGE PIN-PACKAGE -40°C to +85°C 16 Thin QFN (4mm × 4mm) Pin Configuration appears at end of data sheet. Typical Operating Circuit VIN = +7V TO +24V POK BP IN SHDN FB3 PRESET ILIM FB1 FB2 VOUT1 = +3.3V ALWAYS OUT1 VOUT2 = +1.8V ALWAYS OUT2 LX VOUT3 = +5V ALWAYS MAX1534 LDOIN GND ________________________________________________________________ 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 MAX1534 General Description MAX1534 High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers ABSOLUTE MAXIMUM RATINGS IN, ILIM, PRESET, SHDN to GND...........................-0.3V to +25V FB1, FB2, FB3, LDOIN, BP to GND..........................-0.3V to +6V OUT1, OUT2, POK to GND ...................-0.3V to (VLDOIN + 0.3V) LX to GND.......................................................-2V to (VIN + 0.3V) OUT1, OUT2 Short Circuit to GND.............................Continuous Peak IN Current........................................................................2A Maximum IN DC Current...................................................500mA Continuous Power Dissipation (TA = +70°C) 16-Pin Thin QFN (derate 16.9mW/°C above +70°C)............................................................1349mW 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 (Circuit of Figure 1, VIN = 12V, ILIM = GND, PRESET = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Input Voltage Range VIN Input Supply Current IIN Input Supply Current in Dropout IIN(DROP) Shutdown Supply Current Input UVLO Threshold VUVLO CONDITIONS MIN TYP 4.5 MAX UNITS 24 V No load, FB3 = 5.2V, LDOIN = GND 15 30 µA No load, FB3 = VIN = 4.5V, LDOIN = GND 60 110 µA SHDN = GND 3.5 7 µA VIN rising 3.6 4.0 4.4 VIN falling 3.5 3.9 4.3 TA = +25°C to +85°C 4.92 5.00 5.08 TA = 0°C to +85°C 4.90 5.00 5.10 TA = +25°C to +85°C 0.985 1.00 1.015 TA = 0°C to +85°C 0.98 1.00 1.02 3.5 6.25 µA 0.22 0.42 0.62 µs 10 11 µs VIN = 6V 0.5 1.0 VIN = 4.5V 0.6 1.2 V BUCK REGULATOR FB3 Voltage Accuracy (Preset Mode) (Note 1) FB3 Set Voltage (Adjustable Mode) (Note 1) FB3 Bias Current LX Switch Minimum Off-Time PRESET = GND VFB3 PRESET = IN IFB3 VFB3 = 5.5V tOFF(MIN) LX Switch Minimum On-Time tON(MIN) LX Switch Maximum On-Time tON(MAX) LX Switch On-Resistance LX Current Limit RLX ILX(PEAK) 0.50 9 800 1000 1200 ILIM = GND 425 500 575 -75 LX Zero-Crossing Timeout LX does not rise above threshold LX Switch Leakage Current VIN = 24V, not switching Dropout Voltage +75 30 Ω mA mV µs TA = +25°C 1 TA = 0°C to +85°C 10 VOUT3(DROPOUT) ILX(DC) = 500mA V µs ILIM = IN LX Zero-Crossing Threshold V µA 250 mV Line Regulation VIN = 8V to 24V, ILX(DC) = 200mA 0.1 %/V Load Regulation ILX(DC) = 80mA to 400mA 0.9 % LINEAR REGULATORS LDOIN Input Voltage LDOIN Undervoltage Lockout 2 VLDOIN VUVLO(LDO) VLDOIN rising, hysteresis = 40mV typ 2.5 5.5 V 2.15 2.4 V _______________________________________________________________________________________ High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers (Circuit of Figure 1, VIN = 12V, ILIM = GND, PRESET = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS OUT1 Voltage Accuracy (Preset Mode) VOUT1 PRESET = GND IOUT1 = 100µA to 160mA 3.20 3.30 3.37 V OUT2 Voltage Accuracy (Preset Mode) VOUT2 PRESET = GND IOUT2 = 100µA to 160mA 1.74 1.80 1.84 V PRESET = IN IOUT_ = 100µA to 160mA 0.97 1.00 1.02 V FB1, FB2 Set Voltage (Adjustable Mode) VFB1, VFB2 FB1, FB2 Bias Current OUT1, OUT2 Adjustable Output Voltage Range VOUT1, VOUT2 Maximum OUT1 Output Current IOUT1(MAX) PRESET = IN, VFB1 = VFB2 = 1.1V -25 +25 nA PRESET = IN 1.0 VLDOIN V Continuous 160 OUT1 Current Limit mA 160 Maximum OUT2 Output Current IOUT2(MAX) Continuous OUT2 Current Limit 550 160 mA mA 160 550 mA LDOIN Current IOUT1 = IOUT2 = 0, VLDOIN = 5.5V 165 265 µA LDO_ Dropout Voltage IOUT_ = 80mA (Note 2) 120 240 mV LDO_ Line Regulation VLDOIN = (VOUT_ + 0.4V) or +2.5V to +5.5V, IOUT_ = 1mA -0.2 0 +0.2 %/V POK Threshold OUT1, OUT2, and FB3 rising edge, 1% hysteresis (Note 3) -13 -11 -9 % POK Propagation Delay Falling edge, 50mV overdrive POK Output Low Voltage ISINK = 1mA POK Leakage Current High state, forced to 5.5V Thermal Shutdown Threshold Typical hysteresis = 15°C FAULT DETECTION 10 µs 0.4 V 1 µA +160 °C INPUTS AND OUTPUTS SHDN Input Trip Level Rising trip level, 100mV hysteresis 0.96 Input Leakage Current V SHDN, V PRESET, VILIM = 0 or 24V -1 PRESET, ILIM Logic Levels Low High 2.2 1.0 1.04 V +1 µA 0.5 V V _______________________________________________________________________________________ 3 MAX1534 ELECTRICAL CHARACTERISTICS (continued) MAX1534 High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers ELECTRICAL CHARACTERISTICS (Circuit of Figure 1, VIN = 12V, ILIM = GND, PRESET = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 4) PARAMETER Input Voltage Range Input Undervoltage Lockout Threshold SYMBOL VIN VUVLO CONDITIONS MIN TYP MAX UNITS V VIN 4.5 24 VIN rising 3.6 4.4 VIN falling 3.5 4.3 PRESET = GND 4.85 5.15 V PRESET = IN 0.97 1.03 V 0.22 0.62 µs 12 µs V BUCK REGULATOR FB3 Voltage Accuracy (Preset Mode) FB3 Set Voltage (Adjustable Mode) VFB3 LX Switch Minimum Off-Time tOFF(MIN) LX Switch Maximum On-Time tON(MAX) LX Switch On-Resistance LX Current Limit RLX ILX(PEAK) 8 VIN = 6V 1.0 VIN = 4.5V 1.2 ILIM = IN 800 1200 ILIM = GND 425 575 Ω mA LINEAR REGULATORS LDOIN Input Voltage LDOIN UVLO VLDOIN VUVLO(LDO) VLDOIN rising, hysteresis = 40mV (typ) 2.5 5.5 V 2.15 2.40 V OUT1 Voltage Accuracy (Preset Mode) VOUT1 PRESET = GND IOUT1 = 100µA to 160mA 3.20 3.40 V OUT2 Voltage Accuracy (Preset Mode) VOUT2 PRESET = GND IOUT2 = 100µA to 160mA 1.74 1.86 V VFB1, VFB2 PRESET = IN IOUT_ = 100µA to 160mA 0.97 1.03 V OUT1, OUT2 Adjustable Output Voltage Range VOUT1, VOUT2 PRESET = IN 1.0 VLDOIN V Maximum OUT1 Output Current IOUT1(MAX) Continuous 160 FB1, FB2 Set Voltage (Adjustable Mode) OUT1 Current Limit Maximum OUT2 Output Current 160 IOUT2(MAX) Continuous OUT2 Current Limit 160 160 LDO_ Dropout Voltage IOUT_ = 80mA (Note 2) LDO_ Line Regulation VLDOIN = (VOUT_ + 0.4V) or +2.5V to +5.5V, IOUT_ = 1mA OUT1, OUT2, and FB3 rising edge, 1% hysteresis (Note 3) mA 550 mA mA 550 mA 250 mV -0.2 +0.2 %/V -13 -8 % FAULT DETECTION POK Threshold 4 _______________________________________________________________________________________ High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534 ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VIN = 12V, ILIM = GND, PRESET = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 4) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS INPUTS AND OUTPUTS SHDN Input Trip Level Rising trip level, 100mV hysteresis 0.96 1.04 V 0.5 V Low PRESET, ILIM Logic Levels High 2.2 V Note 1: The output voltage at light loads has a DC regulation level higher than the error comparator threshold by half the ripple voltage. Note 2: The dropout voltage is defined as VLDOIN - VOUT_ when VLDOIN = VOUT_(NOM). Specification only applies when VOUT_ ≥ 2.5V. Note 3: OUT1, OUT2 DC set point, FB3 set point at the DC trip threshold of buck regulator. Note 4: Specifications to -40°C are guaranteed by design, not production tested. Typical Operating Characteristics (Circuit of Figure 1, VIN = +12V, PRESET = GND, TA = +25°C, unless otherwise noted.) 90 EFFICIENCY (%) VIN = 12V 5.05 5.00 VIN = 20V 4.90 VIN = 6V (tON LIMITED) 4.85 ILIM = IN 100 90 85 80 VIN = 12V 75 VIN = 20V 70 70 60 VIN = 20V 55 ILIM = IN ILIM = GND 50 0.1 1 10 100 1000 0.1 1 IOUT3 (mA) IOUT3 (mA) 200 L = 15µH 85 180 83 81 L = 10µH IOUT3 = 500mA 160 FREQUENCY (kHz) 87 100 1000 SWITCHING FREQUENCY vs. VIN, CIRCUIT 1, ILIM = IN MAX1534 toc04 L = 22µH 10 IOUT3 (mA) BUCK EFFICIENCY vs. LOAD CURRENT CIRCUIT 1, VIN = 12V 89 75 60 50 100 150 200 250 300 350 400 450 500 EFFICIENCY (%) 0 VIN = 12V 80 65 50 4.80 85 65 55 VIN = 7V 95 140 IOUT3 = 250mA 120 100 80 IOUT3 = 100mA 60 79 77 ILIM = IN MAX1534 toc05 4.95 VIN = 6V 95 EFFICIENCY (%) 5.10 BUCK EFFICIENCY vs. LOAD CURRENT, CIRCUIT 2 MAX1534 toc02 5.15 VOUT3 (V) 100 MAX1534 toc01 5.20 BUCK EFFICIENCY vs. LOAD CURRENT, CIRCUIT 1 MAX1534 toc03 BUCK OUTPUT VOLTAGE vs. LOAD CURRENT, CIRCUIT 1 40 IOUT3 = 50mA 20 IOUT3 = 10mA 0 75 0.1 1 10 IOUT3 (mA) 100 1000 6 10 14 18 22 26 VIN (V) _______________________________________________________________________________________ 5 Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = +12V, PRESET = GND, TA = +25°C, unless otherwise noted.) NO-LOAD SUPPLY CURRENT vs. VIN, CIRCUIT 1, ILIM = GND SWITCHING FREQUENCY vs. LOAD CURRENT, CIRCUIT 1, ILIM = IN 140 120 100 80 VIN = 12V 60 40 100 SHDN = IN 80 60 SHDN = IN VOUT3 NOT CONNECTED TO VLDOIN SHDN = GND 40 20 VIN = 7V 20 120 SUPPLY CURRENT (µA) FREQUENCY (kHz) VIN = 20V MAX1534 toc07 180 160 140 MAX1534 toc06 200 0 0 0 6 50 100 150 200 250 300 350 400 450 500 10 14 18 22 IOUT3 (mA) VIN (V) PEAK SWITCH CURRENT vs. VIN, CIRCUIT 1, ILIM = IN BUCK LOAD TRANSIENT 26 MAX1534 toc09 1.3 MAX1534 toc08 1.4 PEAK SWITCH CURRENT (A) MAX1534 High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers L = 10µH 1.2 VOUT3 200mV/div AC-COUPLED 1A 1.1 ILX 1A/div 0 1.0 L = 22µH L = 15µH 0.9 VLX 10V/div 10V 0.8 0 0.7 500mA 0.6 0.5 IOUT3 500mA/div 0 IOUT3 = 300mA 0.4 6 10 14 18 22 26 40µs/div VIN = 12V, IOUT3 = 100mA TO 450mA VIN (V) LINE TRANSIENT NEAR DROPOUT LINE TRANSIENT MAX1534 toc11 MAX1534 toc10 VIN 5V/div 15V VIN 5V/div 10V 5V 10V VOUT3 200mV/div AC-COUPLED VOUT3 200mV/div AC-COUPLED 1A 1A ILX 500mA/div ILX 500mA/div 0 0 100µs/div VIN = 10V TO 15V, IOUT3 = 300mA 6 100µs/div VIN = 5.2V TO 10V, IOUT3 = 300mA _______________________________________________________________________________________ High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers LDO DROPOUT VOLTAGE vs. LOAD CURRENT LDO DROPOUT VOLTAGE vs. VOUT1 100 DROPOUT VOLTAGE (mV) 80 70 60 50 40 30 20 MAX1534 toc13 90 DROPOUT VOLTAGE (mV) 120 MAX1534 toc12 100 80 60 40 20 IOUT1 = 80mA 10 0 0 0 10 20 30 40 50 60 70 80 2.5 2.6 2.7 2.8 2.9 3.0 3.1 IOUT1 (mA) VOUT1 (V) LDO PSRR vs. FREQUENCY LDO LOAD TRANSIENT 3.2 3.3 MAX1534 toc15 MAX1534 toc14 70 100Ω LOAD 60 VOUT1 20mV/div AC-COUPLED PSRR (dB) 50 40 150mA 30 20 10 IOUT1 50mA/div 0 0 0.01 0.1 1 10 100 20µs/div VLDOIN = 5V, IOUT1 = 10mA TO 150mA FREQUENCY (kHz) STARTUP WAVEFORMS SHUTDOWN WAVEFORMS MAX1534 toc16 0 0 MAX1534 toc17 SHDN 5V/div VOUT3 2V/div VOUT1 2V/div VOUT1 VOUT2 VOUT2 2V/div 0 0 0 1A POK 5V/div 0 ILX 1A/div 1A 100µs/div VIN = 12V, ROUT1 = 33Ω, ROUT2 = 18Ω, ROUT3 = 50Ω VOUT3 4V 0 0 SHDN 5V/div 0 0 VOUT_ 2V/div POK 5V/div ILX 1A/div 100µs/div VIN = 12V, ROUT1 = 33Ω, ROUT2 = 18Ω, ROUT3 = 50Ω _______________________________________________________________________________________ 7 MAX1534 Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = +12V, PRESET = GND, TA = +25°C, unless otherwise noted.) High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534 Pin Description PIN NAME FUNCTION Shutdown Control Input. Drive SHDN above 1V to start up, and below 0.9V to shut down. LX is high impedance in shut down, and supply current reduces to 3.5µA. Connect SHDN to IN for automatic startup. SHDN can be connected to IN through a resistive voltage-divider to implement a programmable undervoltage lockout. 1 SHDN 2 POK Open-Drain Power-OK (POK) Output. POK asserts low while any output voltage is below the reset threshold. Connect a 100kΩ pullup resistor to OUT_. POK is driven low in shut down. If not used, leave this pin unconnected. 3 GND Ground. Connect backside pad to GND. 4 ILIM Peak LX Current Control Input. Connect to IN for 1000mA peak LX current. Connect to GND for 500mA peak LX current. 5, 8 LX Inductor Connection. Connect LX to external inductor and diode as shown in Figure 1. Both LX pins must be connected together on the PC board. 6, 7 IN Buck Regulator Input Supply Voltage. Input voltage range is 4.5V to 24V. Both IN pins must be connected together on the PC board. 9 OUT2 Regulated LDO2 Output Voltage. Sources up to 160mA guaranteed. Bypass with 2.2µF (<0.2Ω typical ESR) ceramic capacitor to GND. 10 LDOIN Input Supply for both LDOs. Supply voltage can range from 2.5V to 5.5V. Bypass with 2.2µF capacitor to GND (see Capacitor Selection and LDO Stability). 11 OUT1 Regulated LDO1 Output Voltage. Sources up to 160mA guaranteed. Bypass with 2.2µF (<0.2Ω typical ESR) ceramic capacitor to GND. 12 BP LDO Reference Noise Bypass. Bypass with a low-leakage 0.01µF ceramic capacitor for reduced noise at both outputs. 13 FB1 Feedback Input for LDO1. For a fixed 3.3V output, connect PRESET and FB1 to GND. For an adjustable output, connect PRESET = IN and connect a resistive divider between OUT1 and GND. 14 FB2 Feedback Input for LDO2. For a fixed 1.8V output, connect PRESET and FB2 to GND. For an adjustable output, connect PRESET = IN and connect a resistive divider between OUT2 and GND. 15 PRESET Preset Feedback Select Input. Connect to GND for the preset 5V buck output voltage, preset 3.3V OUT1 output voltage, and preset 1.8V OUT2 output voltage. Connect PRESET to IN to select adjustable feedback mode for all three regulators. 16 FB3 Buck Output Feedback Input. For a fixed 5.0V output, connect PRESET to GND and FB3 to OUT3. For an adjustable output, connect PRESET to IN and connect a resistive divider between OUT3 and GND. Detailed Description The MAX1534 regulator provides efficient light-load power conversion for notebook computers or hand-held devices that require keep-alive power or standby power. The main step-down buck regulator uses a unique peak current-limited control scheme, providing high efficiency at light loads over a wide load range. Operation up to 100% duty cycle allows the lowest possible dropout voltage, increasing the usable supply voltage range. Under no load, the MAX1534 consumes 8 only 1mW, and in shutdown mode, it draws only 3.5µA. The internal 24V switching MOSFET, internal current sensing, and a high-switching frequency minimize PC board space and component costs. The MAX1534 includes two low-noise, low-dropout, low-quiescent-current linear regulators. The linear regulators are available with preset output voltages of 3.3V and 1.8V. Each linear regulator can supply loads up to 160mA. _______________________________________________________________________________________ High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534 VIN = +7V TO +24V 10µF IN SHDN POK L1 BP COUT3 D1 0.01µF PRESET 100kΩ VOUT3 = +5V ALWAYS LX MAX1534 ILIM FB3 FB1 FB2 VOUT1 = +3.3V ALWAYS OUT1 VOUT3 = +5V ALWAYS LDOIN VOUT2 = +1.8V ALWAYS OUT2 2.2µF 2.2µF 2.2µF GND NOTE: SEE TABLE 1 FOR RECOMMENDED COMPONENT VALUES. SEE TABLE 2 FOR COMPONENT SUPPLIERS. Figure 1. MAX1534 Typical Application Circuit The MAX1534 PFM step-down topology consumes less power than the traditional linear regulator solution when converting from a high-input voltage source. Buck Converter Current-Limited Control Architecture The MAX1534’s buck converter uses a proprietary current-limited control scheme with operation to 100% duty cycle. This DC-to-DC converter pulses as needed to maintain regulation, resulting in a variable switching frequency that increases with the load. This eliminates the high supply currents associated with conventional constant-frequency pulse-width-modulation (PWM) controllers that switch the MOSFET unnecessarily. When the output voltage is too low, the error comparator sets a flip-flop, which turns on the internal P-channel MOSFET and begins a switching cycle (Figure 2). As shown in Figure 3, the inductor current ramps up linearly, storing energy in a magnetic field while charging the output capacitor and servicing the load. The MOSFET turns off when the peak current limit is reached, or when the maximum on-time of 10µs is exceeded and the output voltage is in regulation. If the output is out of regulation and the peak current is never reached, the MOSFET remains on, allowing a duty cycle up to 100%. This feature ensures the lowest possible dropout voltage. Once the MOSFET turns off, the flip-flop resets, the inductor current is pulled through D1, and the current through the inductor ramps back down, transferring the stored energy to the output capacitor and load. The MOSFET remains off until the 0.42µs minimum off-time expires, and the output voltage drops out of regulation. Current Limit (ILIM) The MAX1534’s buck converter has an adjustable peak current limit. Configure this peak current limit by connecting ILIM as shown in Table 3. Choose a current limit that realistically reflects the maximum load current. The maximum output current is half the peak current limit. Although choosing a lower current limit allows using an inductor with a lower current rating, it requires a higher inductance (see Inductor Selection) and does little to reduce inductor package size. ILIM can be dynamically switched to achieve the highest efficiency over the load range. (See Buck Efficiency vs. Load Current (Circuit 1) in the Typical Operating Characteristics. Linear Regulators Internal P-Channel Pass Transistor The MAX1534 features two 1.5Ω P-channel MOSFET pass transistors. A P-channel MOSFET provides several advantages over similar designs using PNP pass transistors, including longer battery life. It requires no _______________________________________________________________________________________ 9 MAX1534 High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers Table 1. Recommended Components CIRCUIT 1 Input voltage CIRCUIT 2 7V 24V 7V 24V Max frequency 73kHz 175kHz 71kHz 160kHz On-time 8.8µs 1µs 9µs 1µs Buck output 5V, 500mA 5V, 250mA IN GND L1 15µH, 57mΩ, 1.60A Sumida CDRH6D38R-150 33µH, 124mΩ, 1.10A Sumida CDRH6D38R-330 D1 1A, 30V Schottky Nihon EP10QY03 0.5A, 30V Schottky Nihon EP05Q03L 47µF, 6.3V, ceramic TDK C3225X5R0J476M 33µF, 6.3V, ceramic TDK C3225X5R0J336M ILIM connection COUT3 Table 2. Component Suppliers SUPPLIER WEBSITE Table 3. Current-Limit Configuration ILIM PEAK LX CURRENT LIMIT (mA) MAXIMUM BUCK OUTPUT CURRENT (mA) DIODES Central Semiconductor www.centralsemi.com IN 1000 500 Fairchild Semiconductor www.fairchildsemi.com GND 500 250 General Semiconductor www.gensemi.com International Rectifier www.irf.com Nihon www.niec.co.jp ON Semiconductor www.onsemi.com Vishay-Siliconix www.vishay.com Zetex www.zetex.com CAPACITORS AVX www.avxcorp.com Kemet www.kemet.com Nichicon www.nichicon-us.com Sanyo www.sanyo.com TDK www.components.tdk.com Taiyo Yuden www.t-yuden.com INDUCTORS Coilcraft www.coilcraft.com Coiltronics www.cooperet.com Pulse Engineering www.pulseeng.com Sumida USA www.sumida.com Toko www.tokoam.com base drive, which reduces quiescent current significantly. PNP-based regulators waste considerable current in dropout when the pass transistor saturates, and they also use high base-drive currents under large 10 loads. The MAX1534 does not suffer from these problems. While a PNP-based regulator has dropout voltage that is independent of the load, a P-channel MOSFET’s dropout voltage is proportional to load current, providing for low dropout voltage at heavy loads and extremely low dropout voltage at lighter loads. Current Limit The MAX1534 contain two independent current limiters, one for each linear regulator, which monitor and control the pass transistor’s gate voltage, limiting the guaranteed maximum output current to 160mA minimum. The output can be shorted to ground for an indefinite time without damaging the part. Low-Noise Operation An external 0.01µF bypass capacitor at BP, in conjunction with an internal resistor, creates a lowpass filter, reducing the LDO output voltage noise. Shutdown (SHDN) The MAX1534’s accurate SHDN input can be used as a low-battery voltage detector. Drive SHDN above the 1V input rising-edge trip level to start up the MAX1534. The 100mV SHDN input hysteresis prevents the MAX1534 from oscillating between startup and shutdown. Drive SHDN low to shut down the MAX1534’s buck converter and linear regulators. When in shut- ______________________________________________________________________________________ High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534 IN 1V MAX1534 VL REG BP REF 0.01µF LX TSDN STARTUP VL IPEAK GND 1V PMOS DRIVER VL ZX VL ENABLE 1V SHDN FB3 POK OUT3_OK LDOIN OUT2_OK PRESET PRESET OUT1_OK 0.9V LDOIN PMOS DRIVER 1V 1V OUT2_OK PMOS DRIVER OUT1 OUT2 LDOIN 0.9V OUT1_OK FB1 FB2 0.9V PRESET PRESET PRESET PRESET Figure 2. MAX1534 Functional Block Diagram down, the supply current drops to 3.5µA, maximizing battery life. The internal P-channel MOSFET in the buck converter and linear regulators turn off to isolate each input from its output. The output capacitance and load current determine the rate at which the output voltage decays. For automatic shutdown and startup, connect SHDN to IN. Connect SHDN to IN through a resistive voltage-divider to implement a programmable undervoltage lockout. Do not leave SHDN floating. Power-OK (POK) The open-drain POK output is useful as a simple error flag, as well as a delayed reset output. POK sinks current when any of the three regulated output voltages is 11% below its regulation point. Connect POK to OUT_ through a high-value resistor for a simple error flag indi- cator. Connect a capacitor from POK to GND to produce a delayed POK signal (delay set by the RC time constant). POK is low in shutdown and is high impedance when all three outputs are in regulation. Thermal-Overload Protection Thermal-overload protection limits total power dissipation in the MAX1534. When the junction temperature exceeds TJ = +160°C, a thermal sensor turns off the pass transistor, allowing the IC to cool. The thermal sensor turns the IC on again after the IC’s junction temperature cools by 15°C, resulting in a pulsed output during continuous thermal-overload conditions. Thermal-overload protection is designed to protect the MAX1534 in the event of fault conditions. For continu- ______________________________________________________________________________________ 11 MAX1534 High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers ous operation, do not exceed the absolute maximum junction temperature rating of TJ = +150°C. Operating Region and Power Dissipation The MAX1534’s maximum power dissipation depends on the thermal resistance of the case and circuit board, the temperature difference between the die junction and ambient air, and the rate of air flow. The power dissipated in the device is the sum of the buck MOSFET switching and conduction losses and the linear regulators’ conduction losses. The maximum power dissipation is: PMAX = (TJ - TA) / (θJB + θBA) where TJ - TA is the temperature difference between the MAX1534 die junction and the surrounding air, θJB (or θJC) is the thermal resistance of the package, and θBA is the thermal resistance through the printed circuit board, copper traces, and other materials to the surrounding air. The exposed backside pad of the MAX1534 provides a low thermal impedance to channel heat out of the package. Connect the exposed backside pad to ground using a large pad or ground plane. Preset and Adjustable Output Voltages (PRESET) The MAX1534 features dual mode operation; it operates in either a preset voltage mode (see Table 4) or an adjustable mode. In preset voltage mode, internal trimmed feedback resistors set the MAX1534 outputs to 3.3V for VOUT1, 1.8V for VOUT2, and 5.0V for FB3 (buck regulator). Select this mode by connecting PRESET to ground. Connect PRESET to IN to operate the MAX1534 in the adjustable mode. Select an output voltage using two external resistors connected as a voltage-divider to FB_ (Figure 4). The output voltage is set by the following equation: RTOP _ VOUT _ = VFB _ 1+ RBOT _ where VFB_ = 1.0V, VOUT1 and VOUT2 can range from 1.0V to VLDOIN, and VOUT3 can range from 1.0V to VIN. To simplify resistor selection: VOUT _ RTOP _ = RBOT _ − 1 VFB _ Choose RBOT_ = 100kΩ to optimize power consumption, accuracy, and high-frequency power-supply rejection. The total current through the external resistive feedback and load resistors should not be less than 10µA. Since the VFB_ tolerance is typically less than 12 Table 4. PRESET Setting PRESET MODE OUT_ AND FB_ IN Adjustable FB_ regulates to 1.0V GND Preset OUT1 = 3.3V, FB1 = GND, OUT2 = 1.8V, FB2 = GND, OUT3 = FB3 = 5.0V ±15mV, the output can be set using fixed resistors instead of trim pots. Design Procedure Buck Converter Inductor Selection When selecting the inductor, consider these four parameters: inductance value, saturation rating, series resistance, and size. The MAX1534 operates with a wide range of inductance values. For most applications, values between 10µH and 50µH work best with the controller’s high switching frequency. Larger inductor values reduce the switching frequency and thereby improve efficiency and EMI. The trade-off for improved efficiency is a higher output ripple and slower transient response. On the other hand, low-value inductors respond faster to transients, improve output ripple, offer smaller physical size, and minimize cost. If the inductor value is too small, the peak inductor current exceeds the current limit due to current-sense comparator propagation delay, potentially exceeding the inductor’s current rating. Calculate the minimum inductance value as follows: L(MIN) = (VIN(MAX) - VOUT3 ) × tON(MIN) ILX(PEAK) where tON(MIN) = 0.5µs. The inductor’s saturation current rating must be greater than the peak switch current limit, plus the overshoot due to the 150ns current-sense comparator propagation delay. Saturation occurs when the inductor’s magnetic flux density reaches the maximum level the core can support and the inductance starts to fall. Choose an inductor with a saturation rating greater than IPEAK in the following equation: IPEAK = ILX(PEAK) + (VIN - VOUT3) ✕ 150ns / L Inductor series resistance affects both efficiency and dropout voltage (see the Buck Dropout Performance section). High series resistance limits the maximum current available at lower input voltages, and increases the dropout ______________________________________________________________________________________ High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers PRESET OUT1 VOUT3 50mV/div AC-COUPLED MAX1534 VOUT1 VIN = +7V TO +24V IN RTOP1 FB1 10V MAX1534 VLX 10V/div 0 RBOT1 VOUT3 LX RTOP3 VOUT2 1A OUT2 ILX 500mA/div FB3 RTOP2 RBOT3 0 FB2 4µs/div RBOT2 GND VIN = 12V, IOUT3 = 300mA Figure 3. Normal Buck Operation voltage. For optimum performance, select an inductor with the lowest possible DC resistance that fits in the allotted dimensions. Some recommended component manufacturers are listed in Table 2. Maximum Buck Output Current The MAX1534’s buck converter’s maximum output current is limited by the peak inductor current. For the typical application, the maximum output current is approximately: IOUT3(MAX) = 1/2 ILX (PEAK)(MIN) For low-input voltages, the maximum on-time can be reached and the load current is limited by: IOUT3 = 1/2 (VIN - VOUT3) ✕ 10µs / L Note that any current provided by the linear regulators comes from the buck regulator and subtracts from the maximum current that the buck provides for other loads. Buck Output Capacitor Selection Choose the output capacitor to service the maximum load current with acceptable voltage ripple. The output ripple has two components: variations in the charge stored in the output capacitor with each LX pulse, and the voltage drop across the capacitor’s equivalent series resistance (ESR) caused by the current into and out of the capacitor: VRIPPLE ≅ VRIPPLE(ESR) + VRIPPLE(C) The output voltage ripple as a consequence of the ESR and output capacitance is: VRIPPLE(ESR) = ESR ✕ IPEAK Figure 4. Adjustable Output Voltages VRIPPLE(C) = L × (IPEAK − IOUT3 )2 VIN 2COUT3 × VOUT3 VIN − VOUT3 where IPEAK is the peak inductor current (see Inductor Selection). The worst-case ripple occurs at no load. These equations are suitable for initial capacitor selection, but final values should be set by testing a prototype or evaluation circuit. As a general rule, a smaller amount of charge delivered in each pulse results in less output ripple. Since the amount of charge delivered in each oscillator pulse is determined by the inductor value and input voltage, the voltage ripple increases with larger inductance, and as the input voltage decreases. See Table 1 for recommended capacitor values and Table 2 for recommended component manufacturers. Buck Input Capacitor Selection The input filter capacitor reduces peak currents drawn from the power source and reduces noise and voltage ripple on the input caused by the circuit’s switching. The input capacitor must meet the ripple-current requirement (IRMS) imposed by the switching current defined by the following equation: I ×V VIN 4 IRMS = OUT3 OUT3 × −1 3 VOUT3 VIN For most applications, nontantalum chemistries (ceramic, aluminum, polymer, or OSCON) are preferred due to their robustness to high inrush currents typical of systems with low-impedance battery inputs. Choose an ______________________________________________________________________________________ 13 MAX1534 High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers input capacitor that exhibits less than +10°C temperature rise at the RMS input current for optimal circuit longevity. Diode Selection The current in the external diode (D1 in Figure 1) changes abruptly from zero to its peak value each time the LX switch turns off. To avoid excessive losses, the diode must have a fast turn-on time and a low forward voltage. Make sure that the diode’s peak current rating exceeds the peak current set by the current limit, and that its breakdown voltage exceeds VIN. Use Schottky diodes when possible. Linear Regulators Capacitor Selection and LDO Stability Use a 2.2µF capacitor on the MAX1534 LDOIN pin and a 2.2µF capacitor on the outputs. Larger input capacitor values and lower ESRs provide better supply-noise rejection and line-transient response. To reduce noise, improve load transients, and for loads up to 160mA, use larger output capacitors (up to 10µF). For stable operation over the full temperature range and with load currents up to 80mA, use 2.2µF. Note that some ceramic dielectrics exhibit large capacitance and ESR variation with temperature. With dielectrics such as Z5U and Y5V, it may be necessary to use 4.7µF or more to ensure stability at temperatures below -10°C. With X7R or X5R dielectrics, 2.2µF is sufficient at all operating temperatures. These regulators are optimized for ceramic capacitors, and tantalum capacitors are not recommended. Use a 0.01µF bypass capacitor at BP for low output voltage noise. Increasing the capacitance slightly decreases the output noise, but increases the startup time. Applications Information Buck Dropout Performance A step-down converter’s minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this limits the useful end-of-life battery voltage. To maximize battery life, the MAX1534 operates with duty cycles up to 100%, which minimizes the dropout voltage and eliminates switching losses while in dropout. When the supply voltage approaches the output voltage, the P-channel MOSFET remains on continuously to supply the load. VDROPOUT(BUCK) = IOUT3 ✕ (RLX + RINDUCTOR) LDO PSRR The MAX1534’s linear regulators are designed to deliver low dropout voltages and low quiescent currents in battery-powered systems. Power-supply rejection is 55dB at low frequencies and rolls off above 20kHz. (See the LDO PSRR vs. Frequency graph in the Typical Operating Characteristics.) To improve supply-noise rejection and transient response, increase the values of the input and output bypass capacitors or use passive filtering techniques. LDO Dropout Voltage A linear regulator’s minimum input-output voltage differential (or dropout voltage) determines the lowest usable supply voltage. Because the MAX1534 uses a P-channel MOSFET pass transistor, its dropout voltage is a function of drain-to-source on-resistance (R DS(ON)) multiplied by the load current (see LDO Dropout Voltage vs. Load Current in the Typical Operating Characteristics). PC Board Layout Guidelines High switching frequencies and large peak currents make PC board layout an important part of the design. Poor layout introduces switching noise into the feedback path, resulting in jitter, instability, or degraded performance. High current traces, highlighted in the Typical Application Circuit (Figure 1), should be as short and wide as possible. Additionally, the current loops formed by the power components (CIN, COUT3, L1, and D1) should be as short as possible to avoid radiated noise. Connect the ground pins of these power components at a common node in a star-ground configuration. Separate the noisy traces, such as the LX node, from the feedback network with grounded copper. Furthermore, keep the extra copper on the board and integrate it into a pseudoground plane. When using external feedback, place the resistors as close to the feedback pin as possible to minimize noise coupling. For a step-down converter with 100% duty cycle, dropout depends on the MOSFET drain-to-source onresistance and inductor series resistance; therefore, it is proportional to the load current: 14 ______________________________________________________________________________________ High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers FB3 PRESET FB2 FB1 16 15 14 13 Chip Information TRANSISTOR COUNT: 1512 PROCESS: BiCMOS SHDN 1 12 BP POK 2 11 OUT1 GND 3 10 LDOIN ILIM 4 9 OUT2 MAX1534 5 6 7 8 LX IN IN LX 16 THIN QFN ______________________________________________________________________________________ 15 MAX1534 Pin Configuration 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.) 24L QFN THIN.EPS MAX1534 High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm 21-0139 A PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm 21-0139 A 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. 16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.