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19-1257; Rev 1; 3/98
Low-Dropout, 120mA Linear Regulators
_______________General Description
The MAX8873T/S/R and MAX8874T/S/R low-dropout linear regulators operate from a +2.5V to +6.5V input range and deliver up to 120mA. A PMOS pass transistor allows the low, 82A supply current to remain independent of load, making these devices ideal for battery-operated portable equipment such as cellular phones and cordless phones. The devices feature Dual ModeTM operation: their output voltage is preset (at 3.15V for the T versions, 2.84V for the S versions, or 2.80V for the R versions) or can be adjusted with an external resistor divider. Total error on the output is 3.5%. Output voltages are set on the low side of popular ranges so that power drain is minimized for longer battery life. Other features include low-power shutdown, short-circuit protection, thermal shutdown protection, and reverse battery protection. The MAX8874 also includes an auto-discharge function, which actively discharges the output voltage to ground when the device is placed in shutdown mode. Both devices come in a miniature 5-pin SOT23 package. For dual versions, refer to the MAX8865/MAX8866 data sheet. For low-noise versions with 30VRMS output noise, refer to the MAX8877/MAX8878.
____________________________Features
o LP2980 Pin-Compatible SOT23 Package o Low, 55mV Dropout Voltage at 50mA IOUT (130mV at 120mA) o Low, 73A No-Load Supply Current Low, 82A Operating Supply Current (even in dropout) o Miniature External Components o Thermal Overload Protection o Output Current Limit o Reverse Battery Protection o Dual Mode Operation: Fixed or Adjustable (1.25V to 6.5V) Output o Low-Power Shutdown
MAX8873T/S/R, MAX8874T/S/R
______________Ordering Information
PART TEMP. RANGE PINPACKAGE 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5 SOT TOP MARK ABZH ABZI ABZL ABZJ ABZK ABZM
________________________Applications
Cordless Telephones PCS Telephones Cellular Telephones PCMCIA Cards Modems Hand-Held Instruments Palmtop Computers Electronic Planners
MAX8873TEUK-T -40C to +85C MAX8873SEUK-T -40C to +85C MAX8873REUK-T -40C to +85C MAX8874TEUK-T -40C to +85C MAX8874SEUK-T -40C to +85C MAX8874REUK-T -40C to +85C
__________Typical Operating Circuit
__________________Pin Configuration
TOP VIEW
IN 1 5 OUT
IN
OUT
OUTPUT VOLTAGE COUT 1F GND 2
BATTERY
CIN 1F
MAX8873 MAX8874
SHDN GND SET
MAX8873 MAX8874
SHDN 3
4 SET
SOT23-5
Dual Mode is a trademark of Maxim Integrated Products.
________________________________________________________________ Maxim Integrated Products 1
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Low-Dropout, 120mA Linear Regulators MAX8873T/S/R, MAX8874T/S/R
ABSOLUTE MAXIMUM RATINGS
VIN to GND ..................................................................-7V to +7V Output Short-Circuit Duration ............................................Infinite SET to GND ..............................................................-0.3V to +7V SHDN to GND..............................................................-7V to +7V SHDN to IN .................................................................-7V to 0.3V OUT to GND ................................................-0.3V to (VIN + 0.3V) Continuous Power Dissipation (TA = +70C) SOT23-5 (derate 7.1mW/C above +70C) .................571mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C JA ..................................................................................140C/W Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+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 = +3.6V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Input Voltage (Note 2) Output Voltage Adjustable Output Voltage Range (Note 3) Maximum Output Current Current Limit (Note 4) Ground Pin Current Dropout Voltage (Note 5) Line Regulation Load Regulation Output Voltage Noise SHUTDOWN SHDN Input Threshold SHDN Input Bias Current Shutdown Supply Current Shutdown Discharge Resistance (MAX8874) VIH VIL ISHDN IQSHDN V SHDN = VIN VOUT = 0V TA = +25C TA = TMAX TA = +25C TA = TMAX 0 0.05 0.0001 0.02 300 1 2.0 0.4 100 V nA A VLNR VLDR ILIM IQ SET = GND IOUT = 1mA IOUT = 50mA VIN = 2.5V to 6.5V, SET tied to OUT, IOUT = 1mA IOUT = 0mA to 50mA 10Hz to 1MHz SET = GND SET tied to OUT COUT = 1F COUT = 100F -0.15 IOUT = 0mA IOUT = 50mA SYMBOL VIN VOUT 0mA IOUT 50mA, SET = GND MAX887_T MAX887_S MAX887_R VOUT CONDITIONS MIN 2.5 3.05 2.75 2.70 VSET 120 280 73 82 1.1 55 0 0.011 0.006 350 220 120 0.15 0.030 150 3.15 2.84 2.80 TYP MAX 6.5 3.25 2.93 2.88 6.5 V mA mA A mV %/V %/mA VRMS V UNITS V
2
_______________________________________________________________________________________
Low-Dropout, 120mA Linear Regulators
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +3.6V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER SET INPUT SET Reference Voltage (Note 3) SET Input Leakage Current (Note 3) THERMAL PROTECTION Thermal Shutdown Temperature Thermal Shutdown Hysteresis TSHDN TSHDN 170 20 C C VSET ISET VIN = 2.5V to 6.5V, IOUT = 1mA VSET = 1.3V TA = +25C TA = TMIN to TMAX TA = +25C TA = TMAX 1.225 1.215 1.25 1.25 0.015 0.5 1.275 1.285 2.5 V nA SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX8873T/S/R, MAX8874T/S/R
Note 1: Limits are 100% production tested at TA = +25C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. Note 2: Guaranteed by line-regulation test. Note 3: Adjustable mode only. Note 4: For design purposes, the current limit should be considered 120mA minimum to 420mA maximum. Note 5: The dropout voltage is defined as (VIN - VOUT) when VOUT is 100mV below the value of VOUT for VIN = VOUT + 2V.
__________________________________________Typical Operating Characteristics
(VIN = +3.6V, CIN = 1F, COUT = 1F, MAX887_T, TA = +25C, unless otherwise noted.)
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX8873/74-01
SUPPLY CURRENT vs. LOAD CURRENT
MAX8873/74-02
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX8873/74-03
3.30 3.25 OUTPUT VOLTAGE (V) 3.20 3.15 3.10 3.05 3.00 0 20 40 60 80 100
100 95 90 SUPPLY CURRENT (A) 85 80 75 70 65 60 55 50
3.5 3.0 OUTPUT VOLTAGE (V) 2.5 2.0 NO LOAD 1.5 1.0 0.5 0
120
0
20
40
60
80
100
120
0
1
2
3
4
5
6
7
LOAD CURRENT (mA)
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
_______________________________________________________________________________________
3
Low-Dropout, 120mA Linear Regulators MAX8873T/S/R, MAX8874T/S/R
____________________________Typical Operating Characteristics (continued)
(VIN = +3.6V, CIN = 1F, COUT = 1F, MAX887_T, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. INPUT VOLTAGE
MAX8873/74-04
OUTPUT VOLTAGE vs. TEMPERATURE
MAX8873/74-05
SUPPLY CURRENT vs. TEMPERATURE
90 80 SUPPLY CURRENT (A) 70 60 50 40 30 20 10 ILOAD = 50mA
MAX8863/4-06
100 90 80 SUPPLY CURRENT (A) 70 60 50 40 30 20 10 0 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) ILOAD = 0mA ILOAD = 50mA
3.30 ILOAD = 50mA 3.25 OUTPUT VOLTAGE (V) 3.20 3.15 3.10 3.05 3.00 -40 -20 0 20 40 60 80
100
0 100 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) TEMPERATURE (C)
DROPOUT VOLTAGE vs. LOAD CURRENT
MAX8873/74-07
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX8873/74-08
OUTPUT SPECTRAL NOISE DENSITY vs. FREQUENCY
OUTPUT SPECTRAL NOISE DENSITY (V/Hz) RL = 50 COUT = 1F 1
MAX8873/74-8A
160 140 DROPOUT VOLTAGE (mV) 120 TA = +85C
70 60 50 PSRR (dB) 40 30 20 10 0
VOUT = 3.15V RL = 100
10
100 80 60 40 20 0 0 20 40
TA = +25C
COUT = 10F
COUT = 100F 0.10
TA = -40C
COUT = 1F
0.01 0.01 0.1 1 10 FREQUENCY (kHz) 100 1000 0.1 1 10 FREQUENCY (kHz) 100 1000
60
80
100
120
LOAD CURRENT (mA)
REGION OF STABLE COUT ESR vs. LOAD CURRENT
COUT = 1F 100 COUT ESR () INTERNAL FEEDBACK
MAX8873/74-8B
OUTPUT NOISE DC TO 1MHz
1000
10
VOUT
EXTERNAL FEEDBACK STABLE REGION
1
0.1
0.01 0 20 40 60 80 100 120 LOAD CURRENT (mA)
1ms/div ILOAD = 50mA, VOUT IS AC COUPLED
4
_______________________________________________________________________________________
Low-Dropout, 120mA Linear Regulators
____________________________Typical Operating Characteristics (continued)
(VIN = +3.6V, CIN = 1F, COUT = 1F, MAX887_T, TA = +25C, unless otherwise noted.) LINE-TRANSIENT RESPONSE
3.16V VOUT 3.15V 3.14V 3.16V VOUT 3.15V 3.14V
MAX8873T/S/R, MAX8874T/S/R
LOAD-TRANSIENT RESPONSE
VIN
4.6V 3.6V 50s/div ILOAD = 50mA, VOUT IS AC COUPLED
50mA ILOAD 0mA 10s/div ILOAD = 0mA to 50mA, CIN = 10F, VOUT IS AC COUPLED
LOAD-TRANSIENT RESPONSE
3.16V VOUT 3.15V 3.14V 3.16V VOUT 3.15V 3.14V
LOAD-TRANSIENT RESPONSE
50mA ILOAD 0mA 10s/div VIN = VOUT + 0.2V, ILOAD = 0mA to 50mA, CIN = 10F, VOUT IS AC COUPLED
50mA ILOAD 0mA 10s/div VIN = VOUT + 0.1V, ILOAD = 0mA to 50mA, CIN = 10F, VOUT IS AC COUPLED
MAX8874 SHUTDOWN (NO LOAD)
4V VOUT 2V 0V VOUT
MAX8874 SHUTDOWN
4V 2V 0V
VSHDN
2V VSHDN 0V
2V 0V
500s/div NO LOAD ILOAD = 50mA
200s/div
_______________________________________________________________________________________
5
Low-Dropout, 120mA Linear Regulators MAX8873T/S/R, MAX8874T/S/R
______________________________________________________________Pin Description
PIN 1 2 3 NAME IN GND SHDN FUNCTION Regulator Input. Supply voltage can range from 2.5V to 6.5V. Bypass with 1F to GND (see Capacitor Selection and Regulator Stability). Ground. This pin also functions as a heatsink. Solder to large pads or the circuit board ground plane to maximize thermal dissipation. Active-Low Shutdown Input. A logic low reduces the supply current to 0.1nA. On the MAX8874, a logic low also causes the output voltage to discharge to GND. Connect to IN for normal operation. Feedback Input for Setting the Output Voltage. Connect to GND to set the output voltage to the preset 2.80V (MAX887_R), 2.84V (MAX887_S), or 3.15V (MAX887_T). Connect to an external resistor divider for adjustable-output operation. DO NOT LEAVE THIS PIN UNCONNECTED. Regulator Output. Fixed or adjustable from 1.25V to 6.5V. Sources up to 120mA. Bypass with a 1F, <0.2 typical ESR capacitor to GND.
4
SET
5
OUT
_______________Detailed Description
The MAX8873/MAX8874 are low-dropout, low-quiescentcurrent linear regulators designed primarily for batterypowered applications. They supply an adjustable 1.25V to 6.5V output or a preselected 2.80V (MAX887_R), 2.84V (MAX887_S), or 3.15V (MAX887_T) output for load currents up to 120mA. These devices consist of a 1.25V reference, error amplifier, MOSFET driver, P-channel pass transistor, dual-mode comparator, and internal feedback voltage divider (Figure 1). The 1.25V bandgap reference is connected to the error amplifier's inverting input. The error amplifier compares this reference with the selected feedback voltage and amplifies the difference. The MOSFET driver reads the error signal
and applies the appropriate drive to the P-channel pass transistor. If the feedback voltage is lower than the reference, the pass-transistor gate is pulled lower, allowing more current to pass and increasing the output voltage. If the feedback voltage is too high, the pass-transistor gate is pulled up, allowing less current to pass to the output. The output voltage is fed back through either an internal resistor voltage divider connected to the OUT pin, or an external resistor network connected to the SET pin. The dual-mode comparator examines the SET voltage and selects the feedback path. If SET is below 60mV, internal feedback is used and the output voltage is regulated to the preset output voltage. Additional blocks include a current limiter, reverse battery protection, thermal sensor, and shutdown logic.
IN SHDN
REVERSE BATTERY PROTECTION
ERROR AMP
MOS DRIVER WITH ILIMIT
P OUT N
MAX8873 MAX8874
SHUTDOWN LOGIC
*
THERMAL SENSOR 1.25V REF DUAL-MODE COMPARATOR 60mV
SET
GND * AUTO-DISCHARGE, MAX8874 ONLY
Figure 1. Functional Diagram
6 _______________________________________________________________________________________
Low-Dropout, 120mA Linear Regulators
Choose R2 = 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 VSET tolerance is typically less than 25mV, the output can be set using fixed resistors instead of trim pots. Connect a 10pF to 25pF capacitor across R1 to compensate for layout-induced parasitic capacitances. In preset voltage mode, impedances between SET and ground should be less than 100k. Otherwise, spurious conditions could cause the voltage at SET to exceed the 60mV dual-mode threshold.
MAX8873T/S/R, MAX8874T/S/R
1
IN
OUT
5
OUTPUT VOLTAGE
3 CIN BATTERY 1F
MAX8873 MAX8874
SHDN GND 2 SET
R1 20pF 4 COUT 1F RL
R2
Shutdown
Figure 2. Adjustable Output Using External Feedback Resistors
Internal P-Channel Pass Transistor
The MAX8873/MAX8874 feature a 1.1 typical P-channel MOSFET pass transistor. This provides several advantages over similar designs using PNP pass transistors, including longer battery life. The P-channel MOSFET requires no base drive current, which reduces quiescent current considerably. PNPbased regulators waste considerable amounts of current in dropout when the pass transistor saturates. They also use high base-drive currents under large loads. The MAX8873/MAX8874 do not suffer from these problems, and consume only 82A of quiescent current, whether in dropout, light load, or heavy load applications (see Typical Operating Characteristics).
A low input on the SHDN pin shuts down the MAX8873/MAX8874. In shutdown mode, the pass transistor, control circuit, reference, and all biases are turned off, reducing the supply current to typically 0.1nA. Connect SHDN to IN for normal operation. The MAX8874 output voltage is actively discharged to ground when the part is placed in shutdown (see Typical Operating Characteristics).
Current Limit
The MAX8873/MAX8874 include a current limiter that monitors and controls the pass transistor's gate voltage, estimating the output current and limiting it to about 280mA. For design purposes, the current limit should be considered 120mA to 420mA. The output can be shorted to ground for an indefinite time period without damaging the part.
Thermal Overload Protection
Thermal overload protection limits total power dissipation in the MAX8873/MAX8874. When the junction temperature exceeds T J = +170C, the thermal sensor sends a signal to the shutdown logic, turning off the pass transistor and allowing the IC to cool. The thermal sensor turns the pass transistor on again after the IC's junction temperature typically cools by 20C, resulting in a pulsed output during continuous thermal overload conditions. Thermal overload protection is designed to protect the MAX8873/MAX8874 in the event of fault conditions. Stressing the device with high load currents and high input-output differential voltages (which result in die temperatures above +125C) may cause a momentary overshoot (2% to 8% for 200ms) when the load is completely removed. This can be remedied by raising the minimum load current from 0A (+125C) to 100A (+150C). For continuous operation, do not exceed the absolute maximum junction temperature rating of TJ = +150C.
Output Voltage Selection
The MAX8873/MAX8874 feature Dual Mode operation: they operate in either a preset voltage mode or an adjustable mode. In preset voltage mode, internal, trimmed feedback resistors set the MAX887_R output to 2.80V, the MAX887_S output to 2.84V, and the MAX887_T output to 3.15V. Select this mode by connecting SET to ground. In adjustable mode, select an output between 1.25V and 6.5V using two external resistors connected as a voltage divider to SET (Figure 2). The output voltage is set by the following equation: VOUT = VSET (1 + R1 / R2) where VSET = 1.25V. To simplify resistor selection: V R1 = R2 OUT VSET - 1
_______________________________________________________________________________________
7
Low-Dropout, 120mA Linear Regulators MAX8873T/S/R, MAX8874T/S/R
Operating Region and Power Dissipation
Maximum power dissipation of the MAX8873/MAX8874 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 dissipation across the device is P = IOUT (VIN VOUT). The resulting maximum power dissipation is: PMAX = (TJ - TA) / JA where (TJ - TA) is the temperature difference between the MAX8873/MAX8874 die junction and the surrounding air, and JA is the thermal resistance of the chosen package to the surrounding air. The GND pin of the MAX8873/MAX8874 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.
Noise
The MAX8873/MAX8874 exhibit 350VRMS noise during normal operation. When using the MAX8873/MAX8874 in applications that include analog-to-digital converters (ADCs) of greater than 12 bits, consider the ADC's power-supply rejection specifications (see the Output Noise DC to 1MHz photo in the Typical Operating Characteristics). For devices with lower output noise, refer to the MAX8877/MAX8878.
Power-Supply Rejection and Operation from Sources Other than Batteries
The MAX8873/MAX8874 are designed to deliver low dropout voltages and low quiescent currents in batterypowered systems. Power-supply rejection is 62dB at low frequencies and rolls off above 300Hz. As the frequency increases above 20kHz, the output capacitor is the major contributor to the rejection of power-supply noise (see the Power-Supply Rejection Ratio vs. Frequency graph in the Typical Operating Characteristics). When operating from sources other than batteries, improve supply-noise rejection and transient response by increasing the values of the input and output capacitors, and by using passive filtering techniques (see the supply and load-transient responses in the Typical Operating Characteristics).
Reverse Battery Protection
The MAX8873/MAX8874 have a unique protection scheme that limits the reverse supply current to less than 1mA when either VIN or V SHDN falls below ground. The circuitry monitors the polarity of these two pins, disconnecting the internal circuitry and parasitic diodes when the battery is reversed. This feature prevents the device from overheating and damaging the battery.
VIN > 5.5V Minimum Load Current When operating the MAX8873/MAX8874 with an input voltage above 5.5V, a minimum load current of 20A is required to maintain regulation in preset voltage mode. When setting the output with external resistors, the minimum current through the external feedback resistors and load must be 30A.
Load-Transient Considerations
The MAX8873/MAX8874 load-transient response graphs (see Typical Operating Characteristics) show two components of the output response: a DC shift of the output voltage due to the different load currents and the transient response. Typical overshoot for step changes in the load current from 0mA to 50mA is 14mV. Increasing the output capacitor's value and decreasing its ESR attenuates transient spikes.
__________Applications Information
Capacitor Selection and Regulator Stability
Normally, use a 1F capacitor on the input and a 1F capacitor on the output of the MAX8873/MAX8874. Larger input capacitor values and lower ESR provide better supply-noise rejection and transient response. A higher-value input capacitor (10F) may be necessary if large, fast transients are anticipated and the device is located several inches from the power source. Improve load-transient response, stability, and power-supply rejection by using large output capacitors. For stable operation over the full temperature range, with load currents up to 120mA, a minimum of 1F is recommended.
Input-Output (Dropout) Voltage
A regulator's minimum input-output voltage differential (or dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this will determine the useful end-of-life battery voltage. Because the MAX8873/MAX8874 use a P-channel MOSFET pass transistor, their dropout voltage is a function of RDS(ON) multiplied by the load current (see Electrical Characteristics).
___________________Chip Information
TRANSISTOR COUNT: 148
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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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