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19-1783; Rev 0; 7/00
200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23
General Description
The MAX1735 negative-output, low-dropout linear regulator operates from a -2.5V to -6.5V input and delivers a guaranteed 200mA with a low 80mV dropout. The highaccuracy (1%) output voltage is preset or can be adjusted from -1.25V to -5.5V with an external resistive voltage-divider. An internal N-channel MOSFET allows for a low 85A quiescent current virtually independent of the load, making this device ideal for battery-powered portable equipment, such as PDAs, mobile phones, cordless phones, and wireless data modems. The device is available in several preset output voltage versions: -5.0V, -3.0V, and -2.5V. All versions offer a 1nA low-power shutdown mode, short-circuit protection, and thermal overload protection. The device is offered in a tiny 5-pin SOT23 package. o Guaranteed 200mA Output Current o Low 80mV Dropout Voltage at 200mA o Low 85A Quiescent Supply Current o Low 1nA Current Shutdown Mode o Stable with 1F COUT o PSRR >60dB at 100Hz o Thermal Overload Protection o Short-Circuit Protection o -5.0V, -3.0V, or -2.5V Output Voltage or Adjustable (-1.25V to -5.5V) o Tiny SOT23-5 Package
Features
MAX1735
Applications
Disk Drives Modems Instrumentation Amplifiers Notebook Computers Mobile and Cordless Telephones PCMCIA Cards GaAsFET Bias Mobile Wireless Data Modems PDAs and Palmtop Computers
PART MAX1735EUK50-T MAX1735EUK30-T MAX1735EUK25-T PART MAX1735EUK50-T MAX1735EUK30-T MAX1735EUK25-T
Ordering Information
TEMP. RANGE -40C to +85C -40C to +85C -40C to +85C PINPACKAGE 5 SOT23-5 5 SOT23-5 5 SOT23-5
Output-Voltage Selector Guide
PRESET OUTPUT VOLTAGE -5.0V or adj -3.0V or adj -2.5V or adj SOT TOP MARK ADOZ ADOY ADOX
Typical Operating Circuit
-6.5V TO -2.5V INPUT IN CIN MAX1735 ON GND OFF ON SHDN GND SET SHDN 3 OUT COUT -5V, -3V, OR -2.5V OUTPUT UP TO 200mA
Pin Configuration
TOP VIEW
GND 1 5 OUT
IN 2
MAX1735
4
SET
SOT23-5
________________________________________________________________ Maxim Integrated Products
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200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23 MAX1735
ABSOLUTE MAXIMUM RATINGS
IN, SET to GND .................................................... -7.0V to +0.3V SHDN to GND ............................................ (VIN - 0.3)V to +7.0V OUT to GND ...............................................(VIN - 0.3)V to +0.3V Output Short-Circuit Duration ........................................Indefinite Continuous Power Dissipation (TA = +70C) 5-Pin SOT23 (derate 7.1mW/C above +70C)........... 571mW 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 2, VIN = VOUT - 1V, V SHDN = VIN, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Input Voltage Output Voltage Accuracy SYMBOL VIN TA = +25C, IOUT = -100A IOUT = -100A, TA = 0C to +85C ILOAD = -100A to -200mA Circuit of Figure 3, IOUT = -100A, TA = 0C to +85C Circuit of Figure 3, ILOAD = -100A to -200mA Maximum Output Current Current Limit Ground-Pin Current Dropout Voltage (Note 2) Line Regulation Load Regulation Output Voltage Noise Power-Supply Rejection Ratio Shutdown Supply Current SHDN Input High Threshold (Note 3) SHDN Input Low Threshold (Note 3) Set Input Bias Current SHDN Input Bias Current Thermal Shutdown Junction Temperature ISET PSRR IOUT ILIM IQ VOUT = 0 IOUT = -100A IOUT = -200mA IOUT = -100mA IOUT = -200mA Circuit of Figure 3, VIN from -6.5V to -2.5V, VOUT = -1.25V IOUT from 0mA to -200mA 10Hz to 1MHz, COUT = 1F f = 100Hz V SHDN = 0 TA = +25C TA = +85C -1.6 +0.4 -0.4 -100 -0.5 160 -15 3.5 +0.5 -1 -0.15 CONDITIONS MIN -6.5 -1 -2 -3 -1.25 TYP MAX -2.5 +1 +2 +2 -1.2375 -1.225 -1.2125 mA -515 -85 -125 40 80 0 0.004 160 60 -0.001 -1 +1.6 240 +0.15 -250 mA A mV %/V %/mA VRMS dB A V V nA A C V % UNITS V
Circuit of Figure 3, TA = +25C, IOUT = -100A -1.2625 SET Regulation Set Point -1.275 -1.275 -200 -1020 -180
Positive voltage at SHDN Negative voltage at SHDN Positive voltage at SHDN Negative voltage at SHDN VSET = -1.25V, TA = +25C TA = +25C Hysteresis = 15C (typ) V SHDN = +6.5V V SHDN = 0, -6.5V
Note 1: Limits are 100% production tested at TA = +25C. Limits over operating temperature range are guaranteed by design. Note 2: The dropout voltage is defined as VOUT - VIN, when VOUT is 100mV above the nominal value of VOUT. Note 3: The SHDN logic input can be driven by either a positive voltage or a negative voltage. | V SHDN | < 0.4V puts the device in shutdown, while | V SHDN | > 1.6V enables the device.
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200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23
Typical Operating Characteristics
(Circuit of Figure 2, VIN = -4.0V, VOUT = -3.0V, TA = +25C, unless otherwise specified.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1735 toc01
MAX1735
SUPPLY CURRENT vs. LOAD CURRENT
MAX1735 toc02
180 160 SUPPLY CURRENT (A) 140 120 100 80 60 40 20 0 0 -1 -2 -3 -4 -5 -6 -7 SUPPLY VOLTAGE (V) ILOAD = 200mA
140 130 SUPPLY CURRENT (A) 120 110 100 90 80 70 0
20 40 60 80 100 120 140 160 180 200 LOAD CURRENT (mA)
SUPPLY CURRENT vs. TEMPERATURE
MAX1735 toc03
DROPOUT VOLTAGE vs. LOAD CURRENT
VOUT = -2.9V DROPOUT VOLTAGE (mV) 80 TA = +25C 60 TA = +85C TA = -40C 20
MAX1735 toc04
180 160 SUPPLY CURRENT (A) 140 120 100 80 60 40 20 0 -40 -15 10 35 60 NO LOAD ILOAD = 200mA
100
40
0 85 0 25 50 75 100 125 150 175 200 TEMPERATURE (C) LOAD CURRENT (mA)
OUTPUT VOLTAGE CHANGE vs. LOAD CURRENT
MAX1735 toc05
OUTPUT VOLTAGE CHANGE vs. TEMPERATURE
0.75 OUTPUT VOLTAGE CHANGE (%) 0.50 0.25 0 -0.25 NO LOAD -0.50 -0.75 -1.00 ILOAD = 200mA
MAX1735 toc06
0 VOUT = -3V OUTPUT VOLTAGE CHANGE (%) -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 0 25 50 75 TA = -40C TA = +85C TA = +25C
1.00
100 125 150 175 200
-40
-15
10
35
60
85
LOAD CURRENT (mA)
TEMPERATURE (C)
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200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23 MAX1735
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = -4.0V, VOUT = -3.0V, TA = +25C, unless otherwise specified.)
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX1735 toc07
OUTPUT NOISE DENSITY vs. FREQUENCY
MAX1735 toc08
OUTPUT NOISE (10Hz TO 1MHz)
500V/div COUT = 1F ILOAD = 50mA
MAX1735 toc09
70 60 50 PSRR (dB) COUT = 10F 40 30 20 10 0 1 10 100 1k 10k 100k COUT = 1.0F
10
OUTPUT NOISE (VRMS/Hz)
1
0.1
0.01 1M 10 1k FREQUENCY (Hz) 100k FREQUENCY (Hz)
TIME (1ms/div)
REGION OF STABLE ESR vs. LOAD CURRENT
COUT = 1F REGION OF STABLE ESR COUT () 10
MAX1735 toc10
LINE-TRANSIENT RESPONSE
MAX1735 toc11
100
1
VOUT 50mV/div
0.1 REGION OF STABILITY 0.01 VIN 1V/div
0.001 0 20 40 60 80 100 120 140 160 180 200 LOAD CURRENT (mA) TIME (100s/div)
LOAD-TRANSIENT RESPONSE (NORMAL OPERATION)
MAX1735 toc12
LOAD-TRANSIENT RESPONSE (NEAR DROPOUT)
MAX1735 toc13
ILOAD STEP 0 to 50mA
ILOAD STEP 0 to 50mA
VOUT 10mV/div
VOUT 10mV/div
TIME (100s/div)
TIME (100s/div)
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200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = -4.0V, VOUT = -3.0V, TA = +25C, unless otherwise specified.)
SHUTDOWN RESPONSE (DRIVEN FROM A POSITIVE VOLTAGE)
MAX1735 toc14a
MAX1735
SHUTDOWN RESPONSE (DRIVEN BY A NEGATIVE VOLTAGE)
MAX1735 toc14b
SHUTDOWN-PIN BIAS CURRENT vs. SHUTDOWN-PIN VOLTAGE
SHUTDOWN-PIN BIAS CURRENT (A)
MAX1735 toc15
2.0
INVALID LOGIC VOLTAGE
1.0
0 VOUT 2V/div
0 VOUT 2V/div
0.5
0
-0.5 TIME (200s/div) TIME (200s/div) -6.5 -5.0 -3.5 -2.0 -0.5 1.0 2.5 4.0 5.5 SHUTDOWN-PIN VOLTAGE (V)
Pin Description
PIN 1 2 NAME GND IN Ground Regulator Input. Supply voltage can range from -2.5V to -6.5V. Bypass with a 1F capacitor to GND (see Capacitor Selection and Regulator Stability). This pin also functions as a heatsink. Solder to a large PC board pad or directly to the PC board power plane to maximize thermal dissipation. Shutdown Input. Drive SHDN to GND to turn the regulator off, reducing the input current to less than 1nA. Drive SHDN above +1.6V or below -1.6V to enable the regulator. Connect SHDN to IN for always-on operation. Dual ModeTM Regulator Feedback Input. Connect SET to GND for the preset output voltage. Use a resistive voltage-divider from OUT to SET to set the output voltage between -1.25V and -5.5V. Regulation setpoint is -1.25V. Regulator Output. OUT supplies up to 200mA in regulation. Bypass to GND with a 1F ceramic capacitor. FUNCTION
3
SHDN
4
SET
5
OUT
Dual Mode is a trademark of Maxim Integrated Products.
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INVALID LOGIC VOLTAGE
VSHDN 2V/div 0
0 VSHDN 2V/div
1.5
5
200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23 MAX1735
IN CIN SHUTDOWN LOGIC ON GND OFF ON SHDN ERROR AMPLIFIER THERMAL SENSOR NMOS PASS TRANSISTOR OUT
MAX1735
COUT
R1
VREF -1.25V Dual Mode COMPARATOR
SET
R2
-270mV GND
Figure 1. Functional Diagram
Detailed Description
The MAX1735 is a low-dropout negative linear voltage regulator. It features Dual Mode operation, allowing a fixed -5.0V, -3.0V, or -2.5V output voltage or an adjustable output from -1.25V to -5.5V. The regulator is guaranteed to supply 200mA of output current. It features 60dB power-supply rejection for noise-sensitive applications and a low 85A operating current that optimizes it for battery-operated devices. As Figure 1 illustrates, the device consists of an internal -1.25V reference, an error amplifier, an N-channel MOSFET, an internal precision-trimmed feedback voltage-divider, and a Dual Mode comparator. The -1.25V reference is connected to the inverting input of the error amplifier. The error amplifier compares the reference voltage with the selected feedback voltage and amplifies the difference. The error amplifier drives the MOSFET to control the output voltage. The feedback voltage for regulation is generated by either an internal or external resistive voltage-divider connected from OUT to SET. The internal Dual Mode
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comparator selects the feedback path based on VSET. Connect SET to GND to use the internal feedback path, setting the output voltage to the preset value. If an external voltage-divider is used, see Output Voltage Selection.
Internal N-Channel MOSFET
The MAX1735 features an N-channel MOSFET pass transistor. Unlike similar designs using NPN bipolar pass transistors, N-channel MOSFETs require extremely low drive currents, reducing overall quiescent current. Also, NPN-based regulators consume still more base current in dropout conditions when the pass transistor saturates. The MAX1735 does not suffer from these problems, consuming only 125A total current at full load and in dropout.
Output Voltage Selection
The MAX1735 features Dual Mode operation, allowing for a preset or adjustable output voltage. In preset voltage mode, the output of the MAX1735 is set to -5.0V, -3.0V, or -2.5V (see Ordering Information). Select this mode by connecting SET to GND (Figure 2).
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200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23 MAX1735
-6.5V TO -2.5V INPUT IN CIN 1F CERAMIC MAX1735 ON ON GND OFF ON SHDN GND SET GND OFF ON SHDN GND R2 SET OUT COUT 1F CERAMIC -5.0V,-3.0V, OR -2.5V FIXED OUTPUT -6.5V TO -2.5V INPUT IN CIN 1F CERAMIC MAX1735 OUT R1 COUT 1F CERAMIC -5.5V TO -1.25V ADJUSTABLE OUTPUT
VOUT = VSET
Figure 2. Typical Application Circuit with Preset Output Voltage
(1 + R1) R2
In adjustable mode, an output voltage between -5.5V and -1.25V is selected using two external resistors connected as a voltage-divider from OUT to SET (Figure 3). The output voltage is determined by the following equation: R1 VOUT = VSET 1+ R2 where VSET = VREFERENCE = -1.25V when in regulation. Since the input bias current at SET is <100nA, use large resistance values for R1 and R2 to minimize power consumption in the feedback network. A typical value of 100k for R2 is acceptable for most applications. Higher values consume less current at the expense of output voltage accuracy. The above equation solved for R1 is: V R1 = R2 OUT - 1 VSET For preset output voltage mode, connect SET directly to GND.
Figure 3. Typical Application Circuit with Adjustable Output Voltage
Current Limiting
The MAX1735 features a current limit that protects the regulator. Short-circuit output current is typically 515mA. The output will withstand a short to ground indefinitely; however, if the increased power dissipation heats the die to +160C, the thermal overload protection will shut off the regulator, preventing damage to the IC.
Thermal Overload Protection
The thermal overload protection circuit protects the regulator against overheating due to prolonged overload conditions. When the die temperature exceeds +160C, an on-chip thermal sensor disables the pass transistor, allowing the IC to cool. The thermal sensor reenables the pass MOSFET once the die temperature drops 15C. A continuous short-circuit fault condition results in a cyclical enabling and disabling of the output. Thermal overload protection is designed to safeguard the MAX1735 in the event of overload fault conditions. For normal operation, do not exceed the absolute maximum junction temperature rating of +150C. Junction temperature is greater than ambient by an amount depending on package heat dissipation and the thermal resistance from the junction to ambient (JA): TJUNCTION = TAMBIENT + (JA)(PDISSIPATION) where JA for the 5-pin SOT23 is about 0.140C/mW.
Shutdown
In shutdown, the N-channel MOSFET, control circuitry, reference, and all internal circuits are turned off, reducing supply current to typically 1nA. SHDN can be driven by either a positive or negative voltage. Drive SHDN above +1.6V or below -1.6V to turn the regulator on. To turn the regulator off, drive SHDN to GND. For always-on operation, connect SHDN to IN. By including a positive threshold at SHDN, it can be driven by a standard 5V TTL level without needing level-shifting circuitry.
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200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23 MAX1735
MAXIMUM OUTPUT CURRENT vs. INPUT-OUTPUT VOLTAGE DIFFERENTIAL
MAX SUPPLY VOLTAGE - MIN OUTPUT VOLTAGE 250 MAXIMUM OUTPUT CURRENT (mA) MAXIMUM CONTINUOUS CURRENT DEVICE IN DROPOUT
200
150 100
TA
AT MAXIMUM JUNCTION TEMP (TJ = +150C)
TA =+ 5 = + 0C 70 =+ C 85 C
TA
selected ambient temperatures. The working principle is that the SOT23-5 package is small enough that in a typical application circuit at room temperature, the package cannot dissipate enough power to allow -6.5V to be regulated to -1.25V at -200mA output (more than 1200mW). As ambient temperature falls, the available power dissipation increases to allow for a greater operating region. The equation for the family of curves follows: T - 70 PMAX - A JA | IOUT | = |VOUT - VIN | where |IOUT| is in mA, |VOUT - VIN| in V, PMAX (571mW) is the absolute maximum rated power dissipation at +70C for the SOT23-5, and JA (0.140C/mW) is the approximate junction-to-ambient thermal resistance of the SOT23-5 in a typical application. A key to reducing CA, thereby increasing thermal conductivity to the PC board, is to provide large PC board pads and traces for IN.
50
0 0 1 2 3 4 5 6 INPUT-OUTPUT VOLTAGE DIFFERENTIAL (V)
Figure 4. Output Current and In-Out Voltage Differential Operating Region Bounded by Available Power Dissipation at Selected Ambient Temperatures
Operating Region and Power Dissipation
Maximum power dissipation of the MAX1735 depends on the thermal resistance of the case and the circuit board, the temperature difference between the die junction and ambient air, and the rate of air flow (see also Thermal Overload Protection). The maximum power that can be dissipated by the device is: T - TA TJMAX - TA PMAX = JMAX = JC + CA JA where the numerator expresses the temperature difference between the maximum allowed die junction (+150C) and the surrounding air, JC (junction to case) is the thermal resistance of the package, and CA (case to ambient) is the thermal resistance from the package through the PC board, traces, and other material to the surrounding air. The former is a characteristic solely of the device in its package, and the latter is completely defined by PC board layout and airflow. It is important to note that the ability to dissipate power is as much a function of the PC board layout and air flow as the packaged part itself. Hence, a manufacturer can reliably provide a value for JC, but not accurately provide a value for the total thermal resistance JA. JA is the sum of JC and CA, and the manufacturer can seldom reliably predict the thermal characteristics of the application circuit. Figure 4 shows the estimated allowable power dissipation for a MAX1735 mounted on a typical PC board at ambient temperatures of +50C, +70C, and +85C. Figure 4 shows the maximum continuous output current for a particular input-to-output voltage differential, for
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__________Applications Information
Capacitor Selection and Regulator Stability
Capacitors are required at the input and output of the MAX1735. Connect a 1F or greater capacitor between IN and GND. This input capacitor serves only to lower the source impedance of the input supply in transient conditions; a smaller value can be used when the regulator is powered from a low-impedance source, such as another regulated supply or low-impedance batteries. For output voltages between -2.5V and -5.5V, connect a 1F or greater capacitor between OUT and GND. For voltages between -1.25V and -2.5V, use a 2.2F or greater output capacitor. The maximum value of the output capacitor to guarantee stability is 10F. The output capacitor's value and equivalent series resistance (ESR) affect stability and output noise. To ensure stability and optimum transient response, output capacitor ESR should be 0.1 or less for output voltages from -1.25V to -2.45V and 0.2 or less for output voltages between -2.5V and -5.5V. Inexpensive surface-mount ceramic capacitors typically have very-low ESR and are commonly available in values up to 10F. Other low-ESR capacitors, such as surface-mount tantalum, may also be used. Do not use low-cost aluminum electrolytic capacitors due to their large size and relatively high ESR. Lastly, make sure the input and output capacitors are as close to the IC as possible to minimize the impact of PC board trace impedance.
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200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23
Noise, PSRR, and Transient Response
MAX1735 output noise is typically 160VRMS. This is suitably low for most applications. See the Output Noise vs. Frequency plot in the Typical Operating Characteristics. The MAX1735 is optimized for battery-powered equipment, with low dropout voltage and low quiescent current. It maintains good transient response, AC rejection, and noise characteristics even near dropout. See Power-Supply Rejection Ratio vs. Frequency in the Typical Operating Characteristics. When operating from very noisy sources, supply noise rejection and transient response can be improved by increasing the input and output capacitance, and by employing passive postfiltering.
Dropout Voltage
A regulator's minimum input-to-output voltage differential dropout voltage determines the lowest usable supply voltage for an application. In battery-powered systems, this determines the useful end-of-life battery voltage. Since the MAX1735's pass element is an N-channel MOSFET, dropout voltage is the product of R DS(ON) and the load current; see Electrical Characteristics and Dropout Voltage vs. Load Current in the Typical Operating Characteristics for details. The MAX1735 operating (ground pin) current typically remains below 125A at full load in dropout.
MAX1735
___________________Chip Information
TRANSISTOR COUNT: 293
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200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23 MAX1735
Package Information
SOT5L.EPS
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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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