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19-4662; Rev 0; 6/09
Low-Noise, High PSRR, Low-Dropout, 120mA Linear Regulator
General Description
The MAX8940 low-noise, low-dropout (LDO) linear regulator is designed to deliver up to 120mA continuous output current. This regulator achieves a low 120mV dropout for 120mA load current. The MAX8940 uses an advanced architecture to achieve low output voltage noise of 25VRMS and PSRR of 45dB at 100kHz. The MAX8940 is preset to either 2.8V or 3.0V. Designed with a p-channel MOSFET series pass transistor, the MAX8940 maintain very low ground current (40A). The regulator is designed and optimized to work with lowvalue, low-cost ceramic capacitors. The MAX8940 requires only 1F (typ) of output capacitance for stability with any load. When disabled, current consumption drops to below 1A. Package is a 5-pin SC70.
Features
Space-Saving SC70 25VRMS Output Noise at 100Hz to 100kHz Bandwidth 65dB PSRR at 10kHz 120mV Dropout at 120mA Load Stable with 1F Ceramic Capacitor for Any Load Guaranteed 120mA Output Output Voltages: 2.8V or 3V
MAX8940
Low 40A Ground Current Excellent Load/Line Transient Overcurrent and Thermal Protection
Applications
Cellular and Cordless Phones PDA and Palmtop Computers Base Stations Bluetooth Portable Radios and Accessories Wireless LANs Digital Cameras Personal Stereos Portable and Battery-Powered Equipment
PART* MAX8940EXKxy-T MAX8940EXKxy+T
Ordering Information
TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 5 SC70 5 SC70
*xy is the output voltage code (see Output Voltage Selector Guide). +Denotes a lead(Pb)-free/RoHS-compliant package.
Output Voltage Selector Guide
PART MAX8940EXK28-T MAX8940EXK30-T VOUT (V) 2.8 3 TOP MARK AUE AUD
Pin Configuration
TOP VIEW
IN 1 5 OUT
Typical Operating Circuit
INPUT 2V TO 6V CIN = 1F ON OFF
IN
OUT
PRESET OUTPUT 2.8V OR 3.0V
GND 2
MAX8940
4 BP
MAX8940
SHDN GND BP
CBP = 10nF COUT = 1F
SHDN 3
SC70
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Low-Noise, High PSRR, Low-Dropout, 120mA Linear Regulator MAX8940
ABSOLUTE MAXIMUM RATINGS
IN to GND .................................................................-0.3V to +7V Output Short-Circuit Duration ............................................Infinite OUT, SHDN to GND ......................................-0.3V to (IN + 0.3V) FB, BP, N.C. to GND..................................-0.3V to (OUT + 0.3V) Continuous Power Dissipation (TA = +70C) 5-Pin SC70 (derate 3.1mW/C above +70C) ..............0.247W JA 5-Pin SC70 ................................................................324C/W 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
(VIN = VOUT + 0.5V, TA = -40C to +85C, unless otherwise noted. CIN = 1F, COUT = 1F, CBP = 10nF. Typical values are at +25C; the MAX8940 is tested with 2.45V output, unless otherwise noted.) (Note 1)
PARAMETER Input Voltage Range Output Voltage Accuracy Maximum Output Current Current Limit IOUT ILIM OUT = 90% of nominal value VOUT = 3V, IOUT = 80mA Dropout Voltage (Note 2) VOUT = 3V, IOUT = 120mA VOUT = 2.8V, IOUT = 80mA VOUT = 2.8V, IOUT = 120mA Ground Current Line Regulation Load Regulation Shutdown Supply Current Ripple Rejection IQ VLNR VLDR ISHDN PSRR IOUT = 0.05mA VIN = VOUT (nom) - 0.1V, IOUT = 0mA VIN = (VOUT + 0.5V) to 6V, IOUT = 0.1mA IOUT = 1mA to 80mA SHDN = 0V f = 10kHz, IOUT = 10mA f = 100kHz, IOUT = 10mA TA = +25C TA = +85C SYMBOL VIN IOUT = 1mA, TA = +25C IOUT = 100A to 80mA, TA = +25C IOUT = 100A to 80mA CONDITIONS MIN 2.8 -1 -2 -3 120 130 200 80 120 90 135 40 220 0.001 0.003 0.003 0.05 65 45 1 90 500 A %/V %/mA A dB 200 300 170 mV TYP MAX 6 +1 +2 +3 mA mA % UNITS V
2
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Low-Noise, High PSRR, Low-Dropout, 120mA Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VOUT + 0.5V, TA = -40C to +85C, unless otherwise noted. CIN = 1F, COUT = 1F, CBP = 10nF. Typical values are at +25C; the MAX8940 is tested with 2.45V output, unless otherwise noted.) (Note 1)
PARAMETER Output Noise Voltage (RMS) Shutdown Exit Delay SHDN Logic Low Level SHDN Logic High Level SHDN Input Bias Current Thermal Shutdown Thermal-Shutdown Hysteresis SYMBOL CONDITIONS f = 100Hz to 100kHz, ILOAD = 10mA f = 100Hz to 100kHz, ILOAD = 80mA RLOAD = 50 (Note 3) VIN = 2.8V to 6V VIN = 2.8V to 6V VIN = 6V, SHDN = 0V or 6V TA = +25C TA = +85C 0.01 160 10 1.5 MIN TYP 25 13 300 0.4 MAX UNITS V s V V A C C
MAX8940
Note 1: Limits are 100% tested at +25C. Limits over operating temperature range are guaranteed by design. Note 2: Dropout is defined as VIN - VOUT when VOUT is 100mV below the value of VOUT for VIN = VOUT + 0.5V. Note 3: Time needed for VOUT to reach 90% of final value.
Typical Operating Characteristics
(VIN = VOUT + 0.5V, CIN = 1F, COUT = 1F, CBP = 10nF, TA = +25C, unless otherwise noted.)
OUTPUT VOLTAGE ACCURACY vs. LOAD CURRENT
MAX8940 toc01 MAX8940 toc02
OUTPUT VOLTAGE vs. INPUT VOLTAGE
3.0 2.5 OUTPUT VOLTAGE (V) IOUT = 0mA % DEVIATION (%) 2.0 1.5 1.0 0.5 0.0 0 1 2 3 4 5 6 INPUT VOLTAGE (V) IOUT = 120mA 0.2 0 -0.2 -0.4 -0.6 0 0.6 0.4
OUTPUT VOLTAGE ACCURACY vs. TEMPERATURE
0.8 0.6 % DEVIATION (%) 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 IOUT = 1mA
MAX8940 toc03
1.0
20
40
60
80
100
120
-40
-15
10
35
60
85
LOAD CURRENT (mA)
TEMPERATURE (C)
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Low-Noise, High PSRR, Low-Dropout, 120mA Linear Regulator MAX8940
Typical Operating Characteristics (continued)
(VIN = VOUT + 0.5V, CIN = 1F, COUT = 1F, CBP = 10nF, TA = +25C, unless otherwise noted.)
DROPOUT VOLTAGE vs. LOAD CURRENT
MAX8940 toc04
GROUND PIN CURRENT vs. INPUT VOLTAGE
MAX8940 toc05
GROUND PIN CURRENT vs. LOAD CURRENT
VIN = 5.5V
MAX8940 toc 06
150 TA = +85C DROPOUT VOLTAGE (mV) 120 TA = +25C 90
350 IOUT = 120mA 300 GROUND PIN CURRENT (A) 250 200 150 100 50 IOUT = 0mA
240 200 160 VIN = 3.8V 120 80 40 0
60 TA = -40C 30
0 0 20 40 60 80 100 120 LOAD CURRENT (mA)
0 0 1 2 3 4 5 INPUT VOLTAGE (V)
GROUND PIN CURRENT (A)
0
20
40
60
80
100
120
LOAD CURRENT (mA)
GROUND PIN CURRENT vs. TEMPERATURE
MAX8940 toc07
PSRR vs. FREQUENCY
80 70 60 PSRR (dB) 50 40 30
MAX8940 toc08
50
90
GROUND PIN CURRENT (A)
45
40
35
20 10 ILOAD = 10mA CBP = 10nF 0.01 0.1 1 10 100 1000
30 -40 -15 10 35 60 85 TEMPERATURE (C)
0 FREQUENCY (kHz)
OUTPUT NOISE
MAX8940 toc09
OUTPUT NOISE SPECTRAL DENSITY vs. FREQUENCY
1.E+04 OUTPUT NOISE DENSITY (nV/Hz)
MAX8940 toc10
VIN = 3.8V ILOAD = 10mA VNOISE = 25VRMS
1.E+03
1.E+02
20V/div 400s/div 1.E+01 0.01 0.1 1 10 100 1000
FREQUENCY (kHz)
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Low-Noise, High PSRR, Low-Dropout, 120mA Linear Regulator
Typical Operating Characteristics (continued)
(VIN = VOUT + 0.5V, CIN = 1F, COUT = 1F, CBP = 10nF, TA = +25C, unless otherwise noted.)
OUTPUT NOISE vs. BP CAPACITANCE
MAX8940 toc11
MAX8940
LOAD TRANSIENT RESPONSE
MAX8940 toc12
LOAD TRANSIENT RESPONSE NEAR DROPOUT
MAX8940 toc13
25
20 OUTPUT NOISE (V)
VIN = 3.5V ILOAD = 0 TO 50mA
VIN = 3.1V ILOAD = 0 TO 50mA VOUT = 3V
15
10 VOUT 10mV/div 5 VOUT 10mV/div
0 1 10 BP CAPACITANCE (nF) 100 1ms/div 1ms/div
LINE TRANSIENT RESPONSE
MAX8940 toc14
EXITING SHUTDOWN WAVEFORM
SHUTDOWN VOLTAGE
ENTERING SHUTDOWN DELAY
MAX8940 toc16
MAX8940 toc15
VIN = 3.5V TO 4V
VOUT = 2.8V RLOAD = 47 SHUTDOWN VOLTAGE
CBP = 0.01F VOUT = 2.8V
OUTPUT VOLTAGE 2V/div VOUT 2mV/div 200s/div 20s/div OUTPUT VOLTAGE 2V/div
40s/div
SHUTDOWN EXIT DELAY
VOUT = 3V CBP = 100nF
REGION OF STABLE COUT ESR vs. LOAD CURRENT
MAX8940 toc18
MAX8940 toc17
100
VOUT 1V/div COUT ESR ()
10
1
SHUTDOWN VOLTAGE
0.1 STABLE REGION 0.01 20s/div 0 20 40 60 80 100 120 LOAD CURRENT (mA)
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Low-Noise, High PSRR, Low-Dropout, 120mA Linear Regulator MAX8940
Pin Description
PIN 1 2 3 4 5 NAME IN GND SHDN BP OUT Unregulated Input Supply Ground Shutdown. Pull low to disable the regulator. Noise Bypass for Low-Noise Operation. Connect a 10nF capacitor from BP to OUT. It is short to OUT in shutdown mode. Regulated Output Voltage. Bypass with a capacitor to GND. See the Capacitor Selection and Regulator Stability section for more details. FUNCTION
Detailed Description
The MAX8940 is a low-noise, low-dropout, low-quiescent current linear regulator designed for spacerestricted applications. The part is available with preset output voltages 2.8V or 3.0V. This device can supply loads up to 120mA. As shown in the Functional Diagram, the MAX8940 consist of an innovative bandgap core and noise bypass circuit, error amplifier, p-channel pass transistor, and internal feedback voltage-divider. The 1.225V bandgap reference is connected to the error amplifier's inverting input. The error amplifier compares this reference with the feedback voltage and amplifies the difference. If the feedback voltage is lower than the reference voltage, the pass-transistor gate is pulled low. This allows more current to pass to the output and increases the output voltage. If the feedback voltage is too high, the pass transistor gate is pulled high, allowing less current to pass to the output. The output voltage is fed back through an internal resistor voltage-divider connected to the OUT pin. An external bypass capacitor connected to BP reduces noise at the output. Additional blocks include a current limiter, thermal sensor, and shutdown logic.
consume only 40A of quiescent current in light load and 220A in dropout (see the Typical Operating Characteristics).
Shutdown
The MAX8940 features a low-power shutdown mode that reduces quiescent current less than 1A. Driving SHDN low disables the voltage reference, error amplifier, gatedrive circuitry, and pass transistor (see the Functional Diagram), and the device output enters a high-impedance state. Connect SHDN to IN for normal operation.
Current Limit
The MAX8940 includes a current limiter, which monitors and controls the pass transistor's gate voltage, limiting the output current to 200mA. For design purposes, consider the current limit to be 130mA (min) to 300mA (max). The output can be shorted to ground for an indefinite amount of time without damaging the part.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation in the MAX8940. When the junction temperature exceeds TJ = +160C, the thermal sensor signals the shutdown logic, turning off the pass transistor and allowing the IC to cool down. The thermal sensor turns the pass transistor on again after the IC's junction temperature drops by 10C, resulting in a pulsed output during continuous thermal-overload conditions. Thermal-overload protection is designed to protect the MAX8940 in the event of a fault condition. For continual operation, do not exceed the absolute maximum junction temperature rating of TJ = +150C.
Internal P-Channel Pass Transistor
The MAX8940 features a 1 (typ) p-channel MOSFET pass transistor. This provides seve-ral advantages over similar designs using a PNP pass transistor, including longer battery life. The p-channel MOSFET requires no base drive, which considerably reduces quiescent current. PNP-based regulators waste considerable current in dropout when the pass transistor saturates. They also use high base-drive current under heavy loads. The MAX8940 does not suffer from these problems and
Operating Region and Power Dissipation
The MAX8940 maximum power dissipation depends on the thermal resistance of the case and circuit board,
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Low-Noise, High PSRR, Low-Dropout, 120mA Linear Regulator
the temperature difference between the die junction and ambient, and the rate of airflow. The power dissipation across the device is: P = IOUT (VIN - VOUT) The maximum power dissipation is: PMAX = (TJ - TA)/(JC + CA) where TJ - TA is the temperature difference between the MAX8940 die junction and the surrounding air, JC is the thermal resistance of the package, and CA is the thermal resistance through the PC board, copper traces, and other materials to the surrounding air. The GND pin of the MAX8940 performs the dual function of providing an electrical connection to ground and channeling heat away. Connect the GND pin to ground using a large pad or ground plane. ESR variation with temperature. With dielectrics such as Z5U and Y5V, it may be necessary to use a 2.2F or larger output capacitor to ensure stability at temperatures below -10C. With X7R or X5R dielectrics, 1F is sufficient at all operating temperatures. A graph of the region of stable COUT ESR vs. load current is shown in the Typical Operating Characteristics. Use a 0.01F bypass capacitor at BP for low-output voltage noise. The leakage current going into the BP pin should be less than 10nA. Increasing the capacitance slightly decreases the output noise. Values above 0.1F and below 0.001F are not recommended.
MAX8940
Noise, PSRR, and Transient Response
The MAX8940 is designed to deliver low noise and high PSRR, as well as low dropout and low quiescent currents in battery-powered systems. The MAX8940 power-supply rejection is 65dB at 1kHz. When operating from sources other than batteries, improved supply-noise rejection and transient response can be achieved by increasing the values of the input and output bypass capacitors, and through passive filtering techniques. The Typical Operating Characteristics show the MAX8940 line- and load-transient responses.
Noise Reduction
For the MAX8940, an external 0.01F bypass capacitor between BP and OUT with innovative noise bypass scheme reduces output noises dramatically, exhibiting 25VRMS of output voltage noise with CBP = 0.01F and COUT = 1F. Startup time is minimized by a poweron circuit that precharges the bypass capacitor.
Applications Information
Capacitor Selection and Regulator Stability
Use a 1F capacitor on the MAX8940 input and a 1F capacitor on the output. Larger input capacitor values and lower ESRs provide better noise rejection and linetransient response. Reduce output noise and improve load-transient response, stability, and power-supply rejection by using large output capacitors. Note that some ceramic dielectrics exhibit large capacitance and
Dropout Voltage
A regulator's minimum dropout voltage determines the lowest usable supply voltage. In battery-powered systems, this determines the useful end-of-life battery voltage. Because the MAX8940 uses a p-channel MOSFET pass transistor, the dropout voltage is a function of drainto-source on-resistance (RDS(ON)) multiplied by the load current (see the Typical Operating Characteristics).
Chip Information
TRANSISTOR COUNT: 284 PROCESS: BiCMOS
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Low-Noise, High PSRR, Low-Dropout, 120mA Linear Regulator MAX8940
Functional Diagram
IN
SHDN
SHUTDOWN AND POWER-ON CONTROL ERROR AMP MOS DRIVER WITH ILIMIT
MAX8940
P OUT
THERMAL SENSOR
1.225V REFERENCE AND NOISE BYPASS
GND
BP
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Low-Noise, High PSRR, Low-Dropout, 120mA Linear Regulator
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 5 SC70 PACKAGE CODE X5-1 DOCUMENT NO. 21-0076
MAX8940
PACKAGE OUTLINE, 5L SC70
21-0076
E
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9
(c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
SC70, 5L.EPS

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