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19-2662; Rev 0; 10/02
High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers
General Description
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 0.5 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. 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. The MAX1534 is available in a small 16-pin thin QFN (4mm 4mm) package, occupying 33% less board space than discrete solutions.
Features
o One Switching and Two Linear Regulators o 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 0.5 PMOS Switch 100% Maximum Duty Cycle for Low-Dropout Operation o 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 o 1.5% Accurate Output Voltage o 4% Accurate Shutdown for Low Battery Detection o Thermal Shutdown Protection o POK Output o 1mW Typical Standby Power
MAX1534
Applications
Notebook and SubNotebook Computers Wake-On LAN 2 to 4 Li+ Cells BatteryPowered Devices Hand-Held Devices Keep-Alive Supplies Standby Supplies
PART MAX1534ETE
Ordering Information
TEMP RANGE PIN-PACKAGE -40C to +85C 16 Thin QFN (4mm x 4mm)
Pin Configuration appears at end of data sheet.
Typical Operating Circuit
VIN = +7V TO +24V POK BP SHDN IN FB3
PRESET ILIM FB1 FB2 VOUT1 = +3.3V ALWAYS VOUT2 = +1.8V ALWAYS OUT1 OUT2 GND LDOIN LX VOUT3 = +5V ALWAYS
MAX1534
________________________________________________________________ Maxim Integrated Products
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
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 = +70C) 16-Pin Thin QFN (derate 16.9mW/C above +70C)............................................................1349mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Input Voltage Range Input Supply Current Input Supply Current in Dropout Shutdown Supply Current Input UVLO Threshold BUCK REGULATOR FB3 Voltage Accuracy (Preset Mode) (Note 1) FB3 Set Voltage (Adjustable Mode) (Note 1) FB3 Bias Current LX Switch Minimum Off-Time LX Switch Minimum On-Time LX Switch Maximum On-Time LX Switch On-Resistance LX Current Limit LX Zero-Crossing Threshold LX Zero-Crossing Timeout LX Switch Leakage Current Dropout Voltage Line Regulation Load Regulation LINEAR REGULATORS LDOIN Input Voltage LDOIN Undervoltage Lockout VLDOIN VUVLO(LDO) VLDOIN rising, hysteresis = 40mV typ 2.5 2.15 5.5 2.4 V V LX does not rise above threshold VIN = 24V, not switching VOUT3(DROPOUT) ILX(DC) = 500mA VIN = 8V to 24V, ILX(DC) = 200mA ILX(DC) = 80mA to 400mA TA = +25C TA = 0C to +85C 250 0.1 0.9 VFB3 IFB3 tOFF(MIN) tON(MIN) tON(MAX) RLX ILX(PEAK) VIN = 6V VIN = 4.5V ILIM = IN ILIM = GND 800 425 -75 30 1 10 9 PRESET = GND PRESET = IN VFB3 = 5.5V 0.22 TA = +25C to +85C TA = 0C to +85C TA = +25C to +85C TA = 0C to +85C 4.92 4.90 0.985 0.98 5.00 5.00 1.00 1.00 3.5 0.42 0.50 10 0.5 0.6 1000 500 11 1.0 1.2 1200 575 +75 5.08 5.10 1.015 1.02 6.25 0.62 V V A s s s mA mV s A mV %/V % VUVLO SYMBOL VIN IIN IIN(DROP) No load, FB3 = 5.2V, LDOIN = GND No load, FB3 = VIN = 4.5V, LDOIN = GND SHDN = GND VIN rising VIN falling 3.6 3.5 CONDITIONS MIN 4.5 15 60 3.5 4.0 3.9 TYP MAX 24 30 110 7 4.4 4.3 UNITS V A A A V
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VIN = 12V, ILIM = GND, PRESET = GND, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER OUT1 Voltage Accuracy (Preset Mode) OUT2 Voltage Accuracy (Preset Mode) FB1, FB2 Set Voltage (Adjustable Mode) FB1, FB2 Bias Current OUT1, OUT2 Adjustable Output Voltage Range Maximum OUT1 Output Current OUT1 Current Limit Maximum OUT2 Output Current OUT2 Current Limit LDOIN Current LDO_ Dropout Voltage LDO_ Line Regulation FAULT DETECTION POK Threshold POK Propagation Delay POK Output Low Voltage POK Leakage Current Thermal Shutdown Threshold INPUTS AND OUTPUTS SHDN Input Trip Level Input Leakage Current PRESET, ILIM Logic Levels Rising trip level, 100mV hysteresis V SHDN, V PRESET, VILIM = 0 or 24V Low High 2.2 0.96 -1 1.0 1.04 +1 0.5 V A V V OUT1, OUT2, and FB3 rising edge, 1% hysteresis (Note 3) Falling edge, 50mV overdrive ISINK = 1mA High state, forced to 5.5V Typical hysteresis = 15C +160 -13 -11 10 0.4 1 -9 % s V A C IOUT1 = IOUT2 = 0, VLDOIN = 5.5V IOUT_ = 80mA (Note 2) VLDOIN = (VOUT_ + 0.4V) or +2.5V to +5.5V, IOUT_ = 1mA -0.2 IOUT2(MAX) Continuous VOUT1, VOUT2 IOUT1(MAX) SYMBOL VOUT1 VOUT2 VFB1, VFB2 CONDITIONS PRESET = GND PRESET = GND PRESET = IN IOUT1 = 100A to 160mA IOUT2 = 100A to 160mA IOUT_ = 100A to 160mA MIN 3.20 1.74 0.97 -25 1.0 160 160 160 160 165 120 0 550 265 240 +0.2 550 TYP 3.30 1.80 1.00 MAX 3.37 1.84 1.02 +25 VLDOIN UNITS V V V nA V mA mA mA mA A mV %/V
MAX1534
PRESET = IN, VFB1 = VFB2 = 1.1V PRESET = IN Continuous
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, VIN = 12V, ILIM = GND, PRESET = GND, TA = -40C to +85C, unless otherwise noted.) (Note 4)
PARAMETER Input Voltage Range Input Undervoltage Lockout Threshold BUCK REGULATOR FB3 Voltage Accuracy (Preset Mode) FB3 Set Voltage (Adjustable Mode) LX Switch Minimum Off-Time LX Switch Maximum On-Time LX Switch On-Resistance LX Current Limit LINEAR REGULATORS LDOIN Input Voltage LDOIN UVLO OUT1 Voltage Accuracy (Preset Mode) OUT2 Voltage Accuracy (Preset Mode) FB1, FB2 Set Voltage (Adjustable Mode) OUT1, OUT2 Adjustable Output Voltage Range Maximum OUT1 Output Current OUT1 Current Limit Maximum OUT2 Output Current OUT2 Current Limit LDO_ Dropout Voltage LDO_ Line Regulation FAULT DETECTION POK Threshold OUT1, OUT2, and FB3 rising edge, 1% hysteresis (Note 3) -13 -8 % IOUT_ = 80mA (Note 2) VLDOIN = (VOUT_ + 0.4V) or +2.5V to +5.5V, IOUT_ = 1mA -0.2 IOUT2(MAX) Continuous VLDOIN VUVLO(LDO) VLDOIN rising, hysteresis = 40mV (typ) VOUT1 VOUT2 VFB1, VFB2 VOUT1, VOUT2 IOUT1(MAX) PRESET = GND PRESET = GND PRESET = IN PRESET = IN Continuous IOUT1 = 100A to 160mA IOUT2 = 100A to 160mA IOUT_ = 100A to 160mA 2.5 2.15 3.20 1.74 0.97 1.0 160 160 160 160 550 250 +0.2 550 5.5 2.40 3.40 1.86 1.03 VLDOIN V V V V V V mA mA mA mA mV %/V VFB3 tOFF(MIN) tON(MAX) RLX ILX(PEAK) VIN = 6V VIN = 4.5V ILIM = IN ILIM = GND 800 425 PRESET = GND PRESET = IN 4.85 0.97 0.22 8 5.15 1.03 0.62 12 1.0 1.2 1200 575 V V s s mA SYMBOL VIN VUVLO VIN VIN rising VIN falling CONDITIONS MIN 4.5 3.6 3.5 TYP MAX 24 4.4 4.3 UNITS V V
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VIN = 12V, ILIM = GND, PRESET = GND, TA = -40C to +85C, unless otherwise noted.) (Note 4)
PARAMETER INPUTS AND OUTPUTS SHDN Input Trip Level PRESET, ILIM Logic Levels Rising trip level, 100mV hysteresis Low High 2.2 0.96 1.04 0.5 V V V SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX1534
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 -40C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Circuit of Figure 1, VIN = +12V, PRESET = GND, TA = +25C, unless otherwise noted.)
BUCK OUTPUT VOLTAGE vs. LOAD CURRENT, CIRCUIT 1
MAX1534 toc01
BUCK EFFICIENCY vs. LOAD CURRENT, CIRCUIT 1
MAX1534 toc02
BUCK EFFICIENCY vs. LOAD CURRENT, CIRCUIT 2
95 90 EFFICIENCY (%) 85 80 75 70 65 60 VIN = 20V VIN = 12V VIN = 7V
MAX1534 toc03
5.20 5.15 5.10 VOUT3 (V) 5.05 5.00 4.95 4.90 4.85 ILIM = IN 4.80 0 VIN = 6V (tON LIMITED) VIN = 20V VIN = 12V
100 95 90 EFFICIENCY (%) 85 80 75 70 65 60 55 50 0.1
100
VIN = 6V
VIN = 12V VIN = 20V
ILIM = IN 1 10 IOUT3 (mA) 100 1000
55 50 0.1 1 10 IOUT3 (mA)
ILIM = GND 100 1000
50 100 150 200 250 300 350 400 450 500 IOUT3 (mA)
BUCK EFFICIENCY vs. LOAD CURRENT CIRCUIT 1, VIN = 12V
89 87 EFFICIENCY (%) 85 83 81 L = 10H 79 77 ILIM = IN 75 0.1 1 10 IOUT3 (mA) 100 1000 L = 15H
MAX1534 toc04
SWITCHING FREQUENCY vs. VIN, CIRCUIT 1, ILIM = IN
180 160 FREQUENCY (kHz) 140 120 100 80 60 40 20 0 6 10 14 VIN (V) 18 22 26 IOUT3 = 100mA IOUT3 = 50mA IOUT3 = 10mA IOUT3 = 250mA IOUT3 = 500mA
MAX1534 toc05
200
L = 22H
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = +12V, PRESET = GND, TA = +25C, unless otherwise noted.)
SWITCHING FREQUENCY vs. LOAD CURRENT, CIRCUIT 1, ILIM = IN
180 160 FREQUENCY (kHz) 140 120 100 80 60 40 20 0 0 50 100 150 200 250 300 350 400 450 500 IOUT3 (mA) VIN = 7V VIN = 12V VIN = 20V
MAX1534 toc06
NO-LOAD SUPPLY CURRENT vs. VIN, CIRCUIT 1, ILIM = GND
120 SUPPLY CURRENT (A) 100 80 60 40 20 0 6 10 14 VIN (V) 18 22 26 SHDN = IN VOUT3 NOT CONNECTED TO VLDOIN SHDN = GND SHDN = IN
MAX1534 toc07
200
140
PEAK SWITCH CURRENT vs. VIN, CIRCUIT 1, ILIM = IN
MAX1534 toc08
BUCK LOAD TRANSIENT
MAX1534 toc09
1.4 1.3 PEAK SWITCH CURRENT (A) 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 6 10 14 VIN (V) 18 22 IOUT3 = 300mA L = 15H L = 22H L = 10H
VOUT3 200mV/div AC-COUPLED 1A 0 10V 0 500mA 0 IOUT3 500mA/div ILX 1A/div VLX 10V/div
26
40s/div VIN = 12V, IOUT3 = 100mA TO 450mA
LINE TRANSIENT
MAX1534 toc10
LINE TRANSIENT NEAR DROPOUT
MAX1534 toc11
15V 10V
VIN 5V/div VOUT3 200mV/div AC-COUPLED
10V 5V
VIN 5V/div VOUT3 200mV/div AC-COUPLED
1A ILX 500mA/div 0
1A ILX 500mA/div 0
100s/div VIN = 10V TO 15V, IOUT3 = 300mA
100s/div VIN = 5.2V TO 10V, IOUT3 = 300mA
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = +12V, PRESET = GND, TA = +25C, unless otherwise noted.)
LDO DROPOUT VOLTAGE vs. LOAD CURRENT
MAX1534 toc12
LDO DROPOUT VOLTAGE vs. VOUT1
MAX1534 toc13
100 90 80 DROPOUT VOLTAGE (mV) 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70
120 100 DROPOUT VOLTAGE (mV) 80 60 40 20 0
IOUT1 = 80mA 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3
80
IOUT1 (mA)
VOUT1 (V)
LDO PSRR vs. FREQUENCY
100 LOAD 60 50 PSRR (dB) 40 150mA 30 20 10 0 0.01 0.1 1 FREQUENCY (kHz) 10 100 0
MAX1534 toc14
LDO LOAD TRANSIENT
MAX1534 toc15
70
VOUT1 20mV/div AC-COUPLED
IOUT1 50mA/div
20s/div VLDOIN = 5V, IOUT1 = 10mA TO 150mA
STARTUP WAVEFORMS
MAX1534 toc16
SHUTDOWN WAVEFORMS
MAX1534 toc17
0
0 0 0 0 1A 0
SHDN 5V/div VOUT3 2V/div VOUT1 2V/div VOUT2 2V/div POK 5V/div ILX 1A/div
0 4V VOUT1 VOUT2 0 0 1A 0 VOUT3
SHDN 5V/div
VOUT_ 2V/div
POK 5V/div ILX 1A/div 100s/div VIN = 12V, ROUT1 = 33, ROUT2 = 18, ROUT3 = 50
100s/div VIN = 12V, ROUT1 = 33, ROUT2 = 18, ROUT3 = 50
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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 3.5A. Connect SHDN to IN for automatic startup. SHDN can be connected to IN through a resistive voltage-divider to implement a programmable undervoltage lockout. Open-Drain Power-OK (POK) Output. POK asserts low while any output voltage is below the reset threshold. Connect a 100k pullup resistor to OUT_. POK is driven low in shut down. If not used, leave this pin unconnected. Ground. Connect backside pad to GND. Peak LX Current Control Input. Connect to IN for 1000mA peak LX current. Connect to GND for 500mA peak LX current. 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. Buck Regulator Input Supply Voltage. Input voltage range is 4.5V to 24V. Both IN pins must be connected together on the PC board. Regulated LDO2 Output Voltage. Sources up to 160mA guaranteed. Bypass with 2.2F (<0.2 typical ESR) ceramic capacitor to GND. Input Supply for both LDOs. Supply voltage can range from 2.5V to 5.5V. Bypass with 2.2F capacitor to GND (see Capacitor Selection and LDO Stability). Regulated LDO1 Output Voltage. Sources up to 160mA guaranteed. Bypass with 2.2F (<0.2 typical ESR) ceramic capacitor to GND. LDO Reference Noise Bypass. Bypass with a low-leakage 0.01F ceramic capacitor for reduced noise at both outputs. 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. 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. 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. 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.
1
SHDN
2 3 4 5, 8 6, 7 9 10 11 12 13 14
POK GND ILIM LX IN OUT2 LDOIN OUT1 BP FB1 FB2
15
PRESET
16
FB3
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
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only 1mW, and in shutdown mode, it draws only 3.5A. 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.
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
VIN = +7V TO +24V 10F SHDN POK BP 0.01F PRESET 100k ILIM FB1 FB2 VOUT1 = +3.3V ALWAYS VOUT2 = +1.8V ALWAYS OUT2 2.2F 2.2F 2.2F GND OUT1 LDOIN VOUT3 = +5V ALWAYS FB3 LX COUT3 D1 IN L1 VOUT3 = +5V ALWAYS
MAX1534
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 10s 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 0.42s 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 1.5 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
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
Table 1. Recommended Components
CIRCUIT 1 Input voltage Max frequency On-time Buck output ILIM connection L1 D1 COUT3 7V 73kHz 8.8s 5V, 500mA IN 15H, 57m, 1.60A Sumida CDRH6D38R-150 1A, 30V Schottky Nihon EP10QY03 47F, 6.3V, ceramic TDK C3225X5R0J476M 24V 175kHz 1s 7V 71kHz 9s 5V, 250mA GND 33H, 124m, 1.10A Sumida CDRH6D38R-330 0.5A, 30V Schottky Nihon EP05Q03L 33F, 6.3V, ceramic TDK C3225X5R0J336M CIRCUIT 2 24V 160kHz 1s
Table 2. Component Suppliers
SUPPLIER DIODES Central Semiconductor Fairchild Semiconductor General Semiconductor International Rectifier Nihon ON Semiconductor Vishay-Siliconix Zetex CAPACITORS AVX Kemet Nichicon Sanyo TDK Taiyo Yuden INDUCTORS Coilcraft Coiltronics Pulse Engineering Sumida USA Toko www.coilcraft.com www.cooperet.com www.pulseeng.com www.sumida.com www.tokoam.com www.avxcorp.com www.kemet.com www.nichicon-us.com www.sanyo.com www.components.tdk.com www.t-yuden.com www.centralsemi.com www.fairchildsemi.com www.gensemi.com www.irf.com www.niec.co.jp www.onsemi.com www.vishay.com www.zetex.com WEBSITE
Table 3. Current-Limit Configuration
ILIM IN GND PEAK LX CURRENT LIMIT (mA) 1000 500 MAXIMUM BUCK OUTPUT CURRENT (mA) 500 250
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 0.01F 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-
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
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
IN
1V BP 0.01F GND 1V
MAX1534
VL REG REF TSDN STARTUP IPEAK VL ENABLE PMOS DRIVER ZX VL 1V FB3 VL LX
SHDN
POK
OUT3_OK OUT2_OK
LDOIN PRESET
OUT1_OK
PRESET 0.9V LDOIN
PMOS DRIVER OUT1
1V OUT2_OK
1V
PMOS DRIVER OUT2
LDOIN
0.9V
FB1 0.9V PRESET PRESET
OUT1_OK PRESET PRESET
FB2
Figure 2. MAX1534 Functional Block Diagram
down, the supply current drops to 3.5A, 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.
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 = +160C, 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 15C, 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 continu11
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-
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
ous operation, do not exceed the absolute maximum junction temperature rating of TJ = +150C.
Table 4. PRESET Setting
PRESET IN GND MODE Adjustable Preset OUT_ AND FB_ FB_ regulates to 1.0V OUT1 = 3.3V, FB1 = GND, OUT2 = 1.8V, FB2 = GND, OUT3 = FB3 = 5.0V
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) / (JB + BA) where TJ - TA is the temperature difference between the MAX1534 die junction and the surrounding air, JB (or JC) is the thermal resistance of the package, and BA 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.
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 10H and 50H 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) =
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_ = 100k 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 10A. Since the VFB_ tolerance is typically less than
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(VIN(MAX) - VOUT3 ) x tON(MIN)
ILX(PEAK)
where tON(MIN) = 0.5s. 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
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
VOUT1 OUT1 PRESET VIN = +7V TO +24V IN
VOUT3 50mV/div AC-COUPLED 10V 0 1A ILX 500mA/div 0 VLX 10V/div
VOUT2
RTOP1 FB1
MAX1534
RBOT1
VOUT3 LX RTOP3
OUT2 RTOP2 FB2
FB3 RBOT3
4s/div VIN = 12V, IOUT3 = 300mA
RBOT2
GND
Figure 3. Normal Buck Operation
Figure 4. Adjustable Output Voltages
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) 10s / 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
VRIPPLE(C) =
L x (IPEAK - IOUT3 )2 VIN V -V 2COUT3 x VOUT3 IN OUT3
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 xV VIN 4 IRMS = OUT3 OUT3 x -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
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
input capacitor that exhibits less than +10C 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. 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.
Linear Regulators
Capacitor Selection and LDO Stability Use a 2.2F capacitor on the MAX1534 LDOIN pin and a 2.2F 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 10F). For stable operation over the full temperature range and with load currents up to 80mA, use 2.2F. 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 4.7F or more to ensure stability at temperatures below -10C. With X7R or X5R dielectrics, 2.2F is sufficient at all operating temperatures. These regulators are optimized for ceramic capacitors, and tantalum capacitors are not recommended. Use a 0.01F bypass capacitor at BP for low output voltage noise. Increasing the capacitance slightly decreases the output noise, but increases the startup time.
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.
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. 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:
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers
Pin Configuration
FB3 16 SHDN POK GND ILIM 1 2 PRESET 15 FB2 14 FB1 13 12 11 BP OUT1 LDOIN OUT2
MAX1534
Chip Information
TRANSISTOR COUNT: 1512 PROCESS: BiCMOS
MAX1534
3 4 5 LX 6 IN 7 IN 8 LX 10 9
16 THIN QFN
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High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers MAX1534
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
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 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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