General Description
The MAX8940 low-noise, low-dropout (LDO) linear reg-
ulator 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 25µVRMS 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 (40µA).
The regulator is designed and optimized to work with low-
value, low-cost ceramic capacitors. The MAX8940
requires only 1µF (typ) of output capacitance for stability
with any load. When disabled, current consumption drops
to below 1µA.
Package is a 5-pin SC70.
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
Features
♦Space-Saving SC70
♦25µVRMS Output Noise at 100Hz to 100kHz
Bandwidth
♦65dB PSRR at 10kHz
♦120mV Dropout at 120mA Load
♦Stable with 1µF Ceramic Capacitor for Any Load
♦Guaranteed 120mA Output
♦Output Voltages: 2.8V or 3V
♦Low 40µA Ground Current
♦Excellent Load/Line Transient
♦Overcurrent and Thermal Protection
MAX8940
Low-Noise, High PSRR,
Low-Dropout, 120mA Linear Regulator
________________________________________________________________
Maxim Integrated Products
1
GND
BP
SHDN
1
2
3
5
4
OUT
IN
MAX8940
SC70
TOP VIEW
Pin Configuration
Ordering Information
MAX8940
PRESET OUTPUT
2.8V OR 3.0V
IN
INPUT
2V TO 6V
OFF SHDN CBP = 10nF
COUT = 1µF
CIN = 1µF
OUT
ON BP
GND
Typical Operating Circuit
19-4662; Rev 0; 6/09
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.
PART* TEMP RANGE PIN-PACKAGE
MAX8940EXKxy-T -40°C to +85°C 5 SC70
MAX8940EXKxy+T -40°C to +85°C 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 VOUT (V) TOP MARK
MAX8940EXK28-T 2.8 AUE
MAX8940EXK30-T 3 AUD
MAX8940
Low-Noise, High PSRR,
Low-Dropout, 120mA Linear Regulator
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = VOUT + 0.5V, TA = -40°C to +85°C, unless otherwise noted. CIN = 1µF, COUT = 1µF, CBP = 10nF. Typical values are at +25°C;
the MAX8940 is tested with 2.45V output, unless otherwise noted.) (Note 1)
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.
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= +70°C)
5-Pin SC70 (derate 3.1mW/°C above +70°C)..............0.247W
θJA
5-Pin SC70 ................................................................324°C/W
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
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Voltage Range VIN 2.8 6 V
IOUT = 1mA, TA = +25°C -1 +1
IOUT = 100µA to 80mA, TA = +25°C -2 +2Output Voltage Accuracy
IOUT = 100µA to 80mA -3 +3
%
Maximum Output Current IOUT 120 mA
Current Limit ILIM OUT = 90% of nominal value 130 200 300 mA
VOUT = 3V, IOUT = 80mA 80 170
VOUT = 3V, IOUT = 120mA 120
VOUT = 2.8V, IOUT = 80mA 90 200
Dropout Voltage (Note 2)
VOUT = 2.8V, IOUT = 120mA 135
mV
IOUT = 0.05mA 40 90
Ground Current IQVIN = VOUT (nom) - 0.1V, IOUT = 0mA 220 500 µA
Line Regulation VLNR VIN = (VOUT + 0.5V) to 6V, IOUT = 0.1mA 0.001 %/V
Load Regulation VLDR IOUT = 1mA to 80mA 0.003 %/mA
TA = +25°C 0.003 1
Shutdown Supply Current ISHDN SHDN = 0V TA = +85°C 0.05 µA
f = 10kHz, IOUT = 10mA 65
Ripple Rejection PSRR f = 100kHz, IOUT = 10mA 45 dB
MAX8940
Low-Noise, High PSRR,
Low-Dropout, 120mA Linear Regulator
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VOUT + 0.5V, TA = -40°C to +85°C, unless otherwise noted. CIN = 1µF, COUT = 1µF, CBP = 10nF. Typical values are at +25°C;
the MAX8940 is tested with 2.45V output, unless otherwise noted.) (Note 1)
Note 1: Limits are 100% tested at +25°C. 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.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
f = 100Hz to 100kHz, ILOAD = 10mA 25
Output Noise Voltage
(RMS) f = 100Hz to 100kHz, ILOAD = 80mA 13 µV
Shutdown Exit Delay RLOAD = 50Ω (Note 3) 300 µs
SHDN Logic Low Level VIN = 2.8V to 6V 0.4 V
SHDN Logic High Level VIN = 2.8V to 6V 1.5 V
TA = +25°C
SHDN Input Bias Current VIN = 6V, SHDN = 0V or
6V TA = +85°C 0.01 µA
Thermal Shutdown 160 °C
Thermal-Shutdown
Hysteresis 10 °C
Typical Operating Characteristics
(VIN = VOUT + 0.5V, CIN = 1µF, COUT = 1µF, CBP = 10nF, TA= +25°C, unless otherwise noted.)
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX8940 toc01
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
54321
0.5
1.0
1.5
2.0
2.5
3.0
0.0
06
IOUT = 120mA
IOUT = 0mA
OUTPUT VOLTAGE ACCURACY
vs. LOAD CURRENT
MAX8940 toc02
LOAD CURRENT (mA)
% DEVIATION (%)
10080604020
-0.4
-0.2
0
0.2
0.4
0.6
-0.6
0 120
OUTPUT VOLTAGE ACCURACY
vs. TEMPERATURE
MAX8940 toc03
TEMPERATURE (°C)
% DEVIATION (%)
603510-15
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1.0
-1.0
-40 85
IOUT = 1mA
MAX8940
Low-Noise, High PSRR,
Low-Dropout, 120mA Linear Regulator
4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VIN = VOUT + 0.5V, CIN = 1µF, COUT = 1µF, CBP = 10nF, TA= +25°C, unless otherwise noted.)
DROPOUT VOLTAGE vs. LOAD CURRENT
MAX8940 toc04
LOAD CURRENT (mA)
DROPOUT VOLTAGE (mV)
10080604020
30
60
90
120
150
0
0 120
TA = +85°C
TA = +25°C
TA = -40°C
GROUND PIN CURRENT vs. INPUT VOLTAGE
MAX8940 toc05
INPUT VOLTAGE (V)
GROUND PIN CURRENT (µA)
4321
150
200
50
100
250
300
350
0
05
IOUT = 120mA
IOUT = 0mA
GROUND PIN CURRENT vs. LOAD CURRENT
MAX8940 toc 06
LOAD CURRENT (mA)
GROUND PIN CURRENT (µA)
10080604020
40
80
120
160
200
240
0
0120
VIN = 3.8V
VIN = 5.5V
GROUND PIN CURRENT vs. TEMPERATURE
MAX8940 toc07
TEMPERATURE (°C)
GROUND PIN CURRENT (µA)
603510-15
35
40
45
50
30
-40 85
PSRR vs. FREQUENCY
MAX8940 toc08
FREQUENCY (kHz)
PSRR (dB)
1101000.1
40
50
60
10
20
30
70
80
90
0
0.01 1000
ILOAD = 10mA
CBP = 10nF
20µV/div
OUTPUT NOISE
MAX8940 toc09
400µs/div
VIN = 3.8V
ILOAD = 10mA
VNOISE = 25µVRMS
OUTPUT NOISE SPECTRAL DENSITY
vs. FREQUENCY
MAX8940 toc10
FREQUENCY (kHz)
OUTPUT NOISE DENSITY (nV/√Hz)
0.1 1 10 100
1.E+03
1.E+02
1.E+04
1.E+01
0.01 1000
MAX8940
Low-Noise, High PSRR,
Low-Dropout, 120mA Linear Regulator
_______________________________________________________________________________________
5
Typical Operating Characteristics (continued)
(VIN = VOUT + 0.5V, CIN = 1µF, COUT = 1µF, CBP = 10nF, TA= +25°C, unless otherwise noted.)
OUTPUT NOISE vs. BP CAPACITANCE
MAX8940 toc11
BP CAPACITANCE (nF)
OUTPUT NOISE (µV)
10
5
10
15
20
25
0
1100
1ms/div
LOAD TRANSIENT RESPONSE
MAX8940 toc12
VIN = 3.5V
ILOAD = 0 TO 50mA
VOUT
10mV/div
LOAD TRANSIENT
RESPONSE NEAR DROPOUT
MAX8940 toc13
1ms/div
VIN = 3.1V
ILOAD = 0 TO 50mA
VOUT = 3V
VOUT
10mV/div
LINE TRANSIENT RESPONSE
MAX8940 toc14
200µs/div
VIN = 3.5V TO 4V
VOUT
2mV/div
EXITING SHUTDOWN WAVEFORM
MAX8940 toc15
20µs/div
VOUT = 2.8V
RLOAD = 47Ω
OUTPUT VOLTAGE
2V/div
SHUTDOWN VOLTAGE
ENTERING SHUTDOWN DELAY
MAX8940 toc16
40µs/div
CBP = 0.01µF
VOUT = 2.8V
OUTPUT VOLTAGE
2V/div
SHUTDOWN
VOLTAGE
SHUTDOWN EXIT DELAY
MAX8940 toc17
20µs/div
VOUT
1V/div
SHUTDOWN
VOLTAGE
VOUT = 3V
CBP = 100nF
REGION OF STABLE COUT ESR
vs. LOAD CURRENT
MAX8940 toc18
LOAD CURRENT (mA)
COUT ESR (Ω)
80604020
0.1
1
10
100
0.01
0 120100
STABLE REGION
MAX8940
Low-Noise, High PSRR,
Low-Dropout, 120mA Linear Regulator
6 _______________________________________________________________________________________
Detailed Description
The MAX8940 is a low-noise, low-dropout, low-quies-
cent current linear regulator designed for space-
restricted 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 volt-
age-divider.
The 1.225V bandgap reference is connected to the
error amplifier’s inverting input. The error amplifier com-
pares 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 feed-
back 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 resis-
tor 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.
Internal P-Channel Pass Transistor
The MAX8940 features a 1Ω(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 cur-
rent. 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
consume only 40µA of quiescent current in light load
and 220µA in dropout (see the
Typical Operating
Characteristics
).
Shutdown
The MAX8940 features a low-power shutdown mode that
reduces quiescent current less than 1µA. Driving SHDN
low disables the voltage reference, error amplifier, gate-
drive circuitry, and pass transistor (see the
Functional
Diagram
), and the device output enters a high-imped-
ance 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, con-
sider 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= +160°C, 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 transis-
tor on again after the IC’s junction temperature drops by
10°C, 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 junc-
tion temperature rating of TJ = +150°C.
Operating Region and Power Dissipation
The MAX8940 maximum power dissipation depends on
the thermal resistance of the case and circuit board,
Pin Description
MAX8940
the temperature difference between the die junction
and ambient, and the rate of airflow. The power dissi-
pation across the device is:
P = IOUT (VIN - VOUT)
The maximum power dissipation is:
PMAX = (TJ- TA)/(θJC + θCA)
where TJ- TAis the temperature difference between
the MAX8940 die junction and the surrounding air, θJC
is the thermal resistance of the package, and θCA 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 func-
tion of providing an electrical connection to ground and
channeling heat away. Connect the GND pin to ground
using a large pad or ground plane.
Noise Reduction
For the MAX8940, an external 0.01µF bypass capacitor
between BP and OUT with innovative noise bypass
scheme reduces output noises dramatically, exhibiting
25µVRMS of output voltage noise with CBP = 0.01µF
and COUT = 1µF. Startup time is minimized by a power-
on circuit that precharges the bypass capacitor.
Applications Information
Capacitor Selection
and Regulator Stability
Use a 1µF capacitor on the MAX8940 input and a 1µF
capacitor on the output. Larger input capacitor values
and lower ESRs provide better noise rejection and line-
transient 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
ESR variation with temperature. With dielectrics such as
Z5U and Y5V, it may be necessary to use a 2.2µF or
larger output capacitor to ensure stability at tempera-
tures below -10°C. With X7R or X5R dielectrics, 1µF 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 0.01µF bypass capacitor at BP for low-output volt-
age noise. The leakage current going into the BP pin
should be less than 10nA. Increasing the capacitance
slightly decreases the output noise. Values above 0.1µF
and below 0.001µF are not recommended.
Noise, PSRR, and Transient Response
The MAX8940 is designed to deliver low noise and high
PSRR, as well as low dropout and low quiescent cur-
rents 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 fil-
tering techniques. The
Typical Operating Characteristics
show the MAX8940 line- and load-transient responses.
Dropout Voltage
A regulator’s minimum dropout voltage determines the
lowest usable supply voltage. In battery-powered sys-
tems, this determines the useful end-of-life battery volt-
age. Because the MAX8940 uses a p-channel MOSFET
pass transistor, the dropout voltage is a function of drain-
to-source on-resistance (RDS(ON)) multiplied by the
load current (see the
Typical Operating Characteristics
).
Low-Noise, High PSRR,
Low-Dropout, 120mA Linear Regulator
_______________________________________________________________________________________ 7
Chip Information
TRANSISTOR COUNT: 284
PROCESS: BiCMOS
MAX8940
Low-Noise, High PSRR,
Low-Dropout, 120mA Linear Regulator
8 _______________________________________________________________________________________
P
OUT
BP
MAX8940
ERROR
AMP
IN
SHDN
GND
SHUTDOWN AND
POWER-ON CONTROL
THERMAL
SENSOR
MOS DRIVER
WITH ILIMIT
1.225V REFERENCE
AND NOISE BYPASS
Functional Diagram
MAX8940
Low-Noise, High PSRR,
Low-Dropout, 120mA Linear Regulator
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
© 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
SC70, 5L.EPS
PACKAGE OUTLINE, 5L SC70
21-0076
1
1
E
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
5 SC70 X5-1 21-0076
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
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