KIT ATION EVALU LE B A IL A AV 19-2560; Rev 1; 10/08 Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply The MAX1982/MAX1983 are low-voltage, low-dropout linear regulators with an external bias supply input. The 5V bias supply drives the gate of the internal N-channel pass transistor, making these devices ideal for applications that require low-voltage outputs from low-voltage inputs. The MAX1982 delivers 1.2V (±3%) at 300mA from an input voltage of 1.25V to 5.5V. The MAX1983 delivers an adjustable output voltage from 0.8V to 2V. The MAX1982/MAX1983 include a current-limit and thermal shutdown that protects the regulator in the event of a fault condition. Both devices are offered in a 6-pin SOT23 package and are specified over the extended (-40°C to +85°C) temperature range. Applications Features o Low-Cost 1.2V, 300mA VID Supply o ±3% Output Voltage Accuracy o No Minimum Load Current Required o 1.25V to 5.5V Input Supply Voltage o 5V Input Bias Supply Voltage o Power-Good (PGOOD) Open-Drain Output with 1ms Rising Edge Propagation Delay (MAX1982) o Adjustable Output Voltage (MAX1983) o Low Supply Current (IBIAS + IIN = 165µA typ) o 5µA (max) Shutdown Supply Current o Tiny 6-Pin SOT23 Package Ordering Information Notebook Computers VID Power Supplies PART TEMP RANGE PINPACKAGE TOP MARK Cell Phones MAX1982EUT-T -40°C to +85°C 6 SOT23-6 ABEA Low-Dropout Regulators with External Bias Supply MAX1983EUT-T -40°C to +85°C 6 SOT23-6 ABEB MAX1982EUT+T -40°C to +85°C 6 SOT23-6 ABEA+ MAX1983EUT+T -40°C to +85°C 6 SOT23-6 ABEB+ PDAs +Denotes lead(Pb)-free package/RoHS-compliant package. Typical Operating Circuit Pin Configurations TOP VIEW 4.5V TO 5.5V IN BIAS MAX1982 1.25V TO 5.5V BIAS 1 0.1μF GND 2 GND IN OUT ON MAX1982 5 OUT 4 PGOOD 1.2V 10μF PGOOD SHDN 6 10μF PGOOD SHDN 3 SOT23 Fixed Output Voltage OFF 100kΩ BIAS 1 GND 2 SHDN 3 MAX1983 6 IN 5 OUT 4 ADJ SOT23 Adjustable Output ________________________________________________________________ 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. MAX1982/MAX1983 General Description MAX1982/MAX1983 Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply ABSOLUTE MAXIMUM RATINGS ADJ, IN, BIAS, PGOOD, SHDN, OUT to GND..........-0.3V to +6V Output Short-Circuit Duration ............................................Infinite Continuous Power Dissipation (TA = +70°C) 6-Pin SOT23 (derate 8.7mW/oC above +70°C)............696mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65oC to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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 3, VIN = 1.8V, ILOAD = 1mA, CLOAD = 10µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL Input Voltage VIN BIAS Voltage VBIAS VOUT Voltage Range VOUT CONDITIONS MAX1983 BIAS Input Undervoltage Lockout MAX UNITS 1.25 MIN 5.5 V 4.5 5.5 V 0.8 2.0 V 4.35 V µA 3.8 TYP 4.1 Shutdown Supply Current IIN 1.25V < VIN < 5.5V 1 5 Quiescent BIAS Current IQ 4.5V < VBIAS < 5.5V 140 250 µA Shutdown BIAS Current I SHDN 4.5V < VBIAS < 5.5V 1 5 µA VOUT Input Bias Current MAX1983 ADJ Input Current MAX1982: VIN = open, VOUT = 1.20V 30 MAX1983: VIN = open, 0.8V < VOUT < 2.0V 0V < VADJ < 2.0V 2 µA 1 µA -0.15 +0.15 %/V TA = +25°C, IOUT = 100mA -1 +1 TA = 0°C to +85°C, IOUT = 1mA to 300mA, VOUT + 0.5V < VIN < 5.5V -3 +3 TA = +25°C, IOUT = 100mA -1 +1 TA = 0°C to +85°C, IOUT = 1mA to 300mA, VOUT + 0.5V < VIN < 5.5V -3 +3 REGULATOR CHARACTERISTICS Line Regulation ΔVOUT/ ΔVIN MAX1982 1.20V Output Voltage Accuracy VOUT MAX1983 0.80V Output Voltage Accuracy VOUT Dropout Voltage VDO Current Limit ILIM Thermal-Shutdown Temperature ILOAD = 10mA, 1.5V < VIN < 5.5V ILOAD = 300mA 350 ILOAD = 150mA 175 VIN - VOUT = 1.3V 330 T SHDN 1400 160 Thermal-Shutdown Hysteresis RMS Output Noise 600 10Hz to 100kHz % % mV mA °C 20 °C 65 µVRMS PGOOD COMPARATOR Comparator Threshold Comparator Hysteresis 2 % of regulated output voltage VHYST -12.5 -9 10 _______________________________________________________________________________________ -6 % mV Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply (Circuit of Figure 3, VIN = 1.8V, ILOAD = 1mA, CLOAD = 10µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 0.8 V LOGIC AND I/O SHDN Input High Voltage VIH SHDN Input Low Voltage VIL 2.4 SHDN Input Current V -1 PGOOD Output Low Voltage PGOOD sinking 1mA PGOOD Output High Leakage Current 0 < VPGOOD < VIN -1 +1 µA 0.1 V +1 µA DYNAMICS Positive Load Step tRISE ILOAD = 1mA to full load, CLOAD = 10µF 10 µs Negative Load Step tFALL ILOAD = full load to 1mA, CLOAD = 10µF 50 µs 10Hz < f < 10kHz, ILOAD = 300mA, CLOAD = 10µF -60 dB ILOAD = 300mA, CLOAD = 10µF, 0% to 90% of nominal output voltage 100 µs ILOAD = 300mA, CLOAD = 10µF 0.5 % Falling edge, 3mV under trip threshold 10 µs Ripple Rejection at VIN Startup Response Time tON Startup Overshoot PGOOD Propagation Delay tPD Rising edge within 5% of regulation level 1 4 ms ELECTRICAL CHARACTERISTICS (Circuit of Figure 3, VIN = 1.8V, ILOAD = 1mA, CLOAD = 10µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL Input Voltage VIN BIAS Voltage VBIAS VOUT Voltage Range VOUT CONDITIONS MAX1983 BIAS Input Undervoltage Lockout MIN MAX UNITS 1.25 5.5 V 4.5 5.5 V 0.8 2.0 V 3.8 4.2 V µA Shutdown Supply Current IIN 1.25V < VIN < 5.5V 5 Quiescent BIAS Current IQ 4.5V < VBIAS < 5.5V 250 µA Shutdown BIAS Current I SHDN 5 µA VOUT Input Bias Current 4.5V < VBIAS < 5.5V MAX1982: VIN = open, VOUT = 1.20V 30 MAX1983: VIN = open, 0.8V < VOUT < 2.0V 2 µA REGULATOR CHARACTERISTICS ΔVOUT/ ΔVIN Line Regulation MAX1982 1.20V Output Voltage Accuracy VOUT ILOAD = 10mA, 1.5V < VIN < 5.5V IOUT = 1mA to 300mA, VOUT + 0.5V < VIN < 5.5V -0.15 +0.15 %/V -3 +3 % _______________________________________________________________________________________ 3 MAX1982/MAX1983 ELECTRICAL CHARACTERISTICS (continued) ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 3, VIN = 1.8V, VOUT = 1.2V, ILOAD = 1mA, CLOAD = 10µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL MAX1983 0.80V Output Voltage Accuracy VOUT Dropout Voltage VDO Current Limit ILIM CONDITIONS IOUT = 1mA to 300mA, VOUT + 0.5V < VIN < 5.5V MIN MAX UNITS -3 +3 % ILOAD = 300mA 350 ILOAD = 150mA 175 VIN - VOUT = 1.3V mV 330 1400 mA -12.5 -6 % PGOOD COMPARATOR Comparator Threshold % of regulated output voltage LOGIC AND I/O SHDN Input High Voltage VIH SHDN Input Low Voltage VIL 2.4 SHDN Input Current V -1 0.8 V +1 µA 0.1 V PGOOD Output Low Voltage PGOOD sinking 1mA PGOOD Output High Leakage Current 0 < VPGOOD < VIN -1 +1 µA Rising edge within 5% of regulation level 1 4 ms DYNAMICS PGOOD Propagation Delay tPD Note 1: Specifications over temperature are guaranteed by design, not production tested. Note 2: VOUT is 1.2V for MAX1982. For MAX1983 VOUT is set to 1.2V with circuit of Figure 4. Typical Operating Characteristics (Circuit of Figure 3, TA = +25°C, unless otherwise noted.) BIAS INPUT CURRENT vs. INPUT VOLTAGE 28 27 26 25 140 135 170 165 160 VBIAS = 5V VIN = 1.8V VBIAS = 5V 130 2.5 175 MAX1982/83 toc03 145 VBIAS = 5V 1.5 3.5 INPUT VOLTAGE (V) 4 GROUND CURRENT vs. OUTPUT CURRENT MAX1982/83 toc02 29 150 BIAS INPUT CURRENT (μA) MAX1982/83 toc01 30 GROUND CURRENT (μA) INPUT CURRENT vs. INPUT VOLTAGE INPUT CURRENT (μA) MAX1982/MAX1983 Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply 4.5 5.5 155 1.5 2.5 3.5 INPUT VOLTAGE (V) 4.5 5.5 0 50 100 150 200 OUTPUT CURRENT (mA) _______________________________________________________________________________________ 250 300 Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply BIAS SUPPLY CURRENT vs. TEMPERATURE 27.5 VBIAS = 5V 145 140 IBIAS (μA) 26.5 26.0 130 125 25.5 VBIAS = 5V 150 100 50 120 115 25.0 -15 10 35 0 -40 85 60 -15 10 35 60 85 0 100 150 200 250 TEMPERATURE (°C) OUTPUT CURRENT (mA) OUTPUT VOLTAGE ERROR vs. OUTPUT CURRENT OUTPUT VOLTAGE ERROR vs. TEMPERATURE SHORT-CIRCUIT CURRENT LIMIT vs. INPUT VOLTAGE 0.50 0.25 0 -0.25 -0.50 VIN = 1.8V 0.75 0.50 0.25 ILOAD = 300mA 0 -0.25 ILOAD = 200mA -0.50 ILOAD = 0mA -0.75 -0.75 800 150 200 250 -40 300 600 500 400 300 200 100 -15 10 35 60 1.50 85 2.50 SHORT-CIRCUIT CURRENT LIMIT vs. TEMPERATURE 650 4.50 5.50 POWER-SUPPLY REJECTION RATIO (VIN) vs. FREQUENCY 0 MAX1982/83 toc10 700 3.50 INPUT VOLTAGE (V) TEMPERATURE (°C) OUTPUT CURRENT (mA) MAX1982/83 toc11 100 VIN = 2.1V VP-P = 0.6V ILOAD = 0 -10 -20 -30 PSRR (dB) SHORT-CIRCUIT CURRENT LIMIT (mA) 50 700 0 -1.00 -1.00 300 MAX1982/83 toc09 0.75 1.00 SHORT-CIRCUIT CURRENT LIMIT (mA) VBIAS = 5V VIN = 1.8V RELATIVE VOUT ERROR (%) 1.00 0 50 TEMPERATURE (°C) MAX1982/83 toc07 -40 VOUT ERROR (%) 135 MAX1982/83 toc08 IIN (μA) 27.0 DROPOUT VOLTAGE vs. OUTPUT CURRENT 200 MAX1982/83 toc06 VBIAS = 5V MAX1982/83 toc05 MAX1982/83 toc04 150 DROPOUT VOLTAGE (mV) INPUT CURRENT vs. TEMPERATURE 28.0 600 -40 -50 -60 -70 550 -80 -90 500 -100 -40 -15 10 35 TEMPERATURE (°C) 60 85 10 100 1k 10k 100k 1M FREQUENCY (Hz) _______________________________________________________________________________________ 5 MAX1982/MAX1983 Typical Operating Characteristics (continued) (Circuit of Figure 3, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (Circuit of Figure 3, TA = +25°C, unless otherwise noted.) POWER-SUPPLY REJECTION RATIO (VBIAS) vs. FREQUENCY 0 -20 -40 -40 PSRR (dB) -30 -50 -60 -70 -80 -90 -90 -100 -100 1k 10k 100k IL = 200mA IL = 100mA -60 -80 100 IL = 300mA -50 -70 10 VIN = 3V VP-P = 0.4V -10 -30 MAX1982/83 toc13 VBIAS = 5V VP-P = 0.6V ILOAD = 0 -20 RIPPLE REJECTION RATIO (VIN) vs. FREQUENCY MAX1982/83 toc12 0 -10 PSRR (dB) MAX1982/MAX1983 Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply 1M 10 FREQUENCY (Hz) 100 1k 10k 100k 1M FREQUENCY (Hz) LINE TRANSIENT (NO LOAD) LOAD TRANSIENT (1mA TO 300mA) MAX1982/83 toc14 MAX1982/83 toc15 2.4V VIN 1.8V 500mV/ div 1mV/ div VOUT 300mA ILOAD 200mA/ div 10mV/ div VOUT 1mV/div 100μs/div 10μs/div LOAD TRANSIENT (300mA TO 1mA) LOAD TRANSIENT IN DROPOUT MAX1982/83 toc16 300mA ILOAD 200mA/ div 10mV/ div VOUT 10μs/div 6 MAX1982/83 toc17 300mA ILOAD 200mA/ div 50mV/ div VOUT 20μs/div _______________________________________________________________________________________ Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply SHUTDOWN RESPONSE UNDERVOLTAGE LOCKOUT MAX1982/83 toc19 MAX1982/83 toc18 5V 5V VBIAS 2V/ div VSHDN 2V/ div 1.2V 500mV/ div 500mV/ div VOUT VOUT ILOAD = 300mA ILOAD = 300mA 100μs/div 100μs/div PGOOD RESPONSE MAX1982/83 toc20 2V/ div VOUT 500mV/ div VPGOOD 1ms/div _______________________________________________________________________________________ 7 MAX1982/MAX1983 Typical Operating Characteristics (continued) (Circuit of Figure 3, TA = +25°C, unless otherwise noted.) MAX1982/MAX1983 Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply Pin Description PIN NAME FUNCTION MAX1982 MAX1983 1 1 BIAS Bias Voltage. Input voltage to the control circuitry. BIAS powers all control blocks and the gate of the pass transistor. Bypass BIAS to GND with a 0.1µF ceramic capacitor. 2 2 GND Ground 3 3 SHDN 4 — PGOOD Power-Good Output. The open-drain PGOOD output goes high at least 1ms after the output voltage has attained regulation. PGOOD asserts low 10µs after the output falls by 10%. — 4 ADJ Feedback for Adjustable Output. Connect ADJ to the midpoint of a resistor-divider between OUT and GND for an adjustable output voltage between 0.8V and 2.0V. 5 5 OUT Regulator Output. Bypass OUT to GND with a 10µF to 22µF low-ESR ceramic capacitor. 6 6 IN Shutdown Control Input. Drive SHDN low to enter the low-power shutdown state. Connect SHDN to BIAS for normal operation. Internal Pass Transistor Input. IN connects to the drain of the internal power switch. Bypass IN to GND with a 10µF ceramic capacitor. Detailed Description The MAX1982/MAX1983 are low-voltage, low-dropout linear regulators with an external bias supply input (see Figures 1 and 2). BIAS is powered by a 4.5V to 5.5V supply that is commonly available in laptop and desktop computers. The 5V bias supply drives the gate of the internal pass transistor, while a lower voltage input at the drain of the transistor (IN) is regulated to provide VOUT. Separating the bias input voltages yields higher efficiency. These devices are ideal for applications that require low-voltage outputs from low-voltage inputs. The MAX1982 delivers 1.2V (±3%) at 300mA from an input voltage of 1.25V to 5.5V. The MAX1983 delivers an adjustable output voltage from 0.8V to 2V. The MAX1982 features an open-drain PGOOD output that transitions high 1ms after the output reaches regulation. PGOOD goes low within 10µs of the output falling out of regulation by 120mV. Both devices feature current- and thermal-limiting circuitry that protect the MAX1982/MAX1983 from damage during fault conditions. Bias Supply Input The BIAS input powers the control circuitry and provides the pass transistor gate drive. Power BIAS from a well-regulated 5V (±10%) supply. Current drawn from the BIAS supply remains relatively constant with variations in VIN and load current (see the Typical Operating Characteristics). Bypass BIAS with a 0.1µF or greater 8 capacitor as close to the device as possible. The bias supply current remains low (250µA) when the MAX1982/MAX1983 are in dropout. Power-Supply Input IN connects to the drain of the internal N-channel power transistor. IN may be as low as 1.25V, minimizing power dissipation. Bypass IN with a 10µF or greater capacitor as close to the device as possible. Shutdown The MAX1982/MAX1983 feature a low-power shutdown mode that reduces quiescent current drawn to 1µA (typ), and BIAS current consumption to less than 1µA (typ). Driving SHDN low disables the voltage reference, error amplifier, gate-drive circuitry, and pass transistor (see Figure 2), and the device output enters a highimpedance state. Connect SHDN to BIAS for normal operation. PGOOD Output The MAX1982 provides an open-drain PGOOD output that goes high 1ms (min) after the output attains regulation (within 10% of the nominal output voltage). PGOOD transitions low 10µs after the output falls out of regulation by 120mV, or when the device enters shutdown. Connect a pullup resistor from PGOOD to BIAS for a logic-level output. Use a 100kΩ resistor to minimize current consumption. _______________________________________________________________________________________ Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply MAX1982/MAX1983 PGOOD MAX1982 SHDN 1ms DELAY BIAS UVLO SHUTDOWN OVERTEMP IN CURRENT SENSE BIAS 0.8V REFERENCE OUT GND Figure 1. MAX1982 Functional Diagram MAX1983 SHDN BIAS UVLO SHUTDOWN OVERTEMP IN CURRENT SENSE BIAS 0.8V REFERENCE GM OUT AV R1 ADJ R2 GND Figure 2. MAX1983 Functional Diagram _______________________________________________________________________________________ 9 MAX1982/MAX1983 Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply Current Limit The MAX1982/MAX1983 limit the output current to 600mA (typ) in the event of an overload or output short circuit. The current limit prevents damage to the internal power transistor, but the device can enter thermal shutdown if the power dissipation is great enough to increase the die temperature above +160°C (see the Thermal-Overload Protection section). Thermal-Overload Protection Thermal-overload protection limits the power dissipation in the MAX1982/MAX1983. When the die temperature exceeds +160°C, the pass transistor turns off, allowing the device to cool. Normal operation resumes when the die temperature cools by 20°C. A continuous thermal-overload condition results in a pulsed output. For continuous operation, do not exceed a junction temperature of +150°C. Applications Information Output Voltage Selection The MAX1982 output is fixed at 1.2V. The MAX1983 provides an adjustable output (0.8V to 2.0V). Connect ADJ to a resistive voltage-divider between OUT and 4.5V TO 5.5V 1.25V TO 5.5V IN BIAS 10μF 0.1μF MAX1982 GND 1.2V OUT 10μF ON SHDN PGOOD OFF 100kΩ Figure 3. MAX1982 Typical Application Circuit 4.5V TO 5.5V IN BIAS 1.5V TO 5.5V 10μF MAX1983 0.1μF GND 1.2V OUT R1 20kΩ ON SHDN Figure 4. MAX1983 Typical Application Circuit 10 10μF ADJ OFF R2 40kΩ GND as shown in Figure 4. Set the output voltage using the following equation: ⎛ R1 ⎞ VOUT = 0.8V ⎜1 + ⎟ ⎝ R2 ⎠ Set R2 at 40kΩ and choose R1 to achieve the desired output voltage. Set VIN to higher than (VOUT + 400mV) to meet the dropout voltage requirement (see the Input/Output (Dropout) Voltage section). To ensure stability over the specified input voltage range, the minimum output capacitance must be 10µF with a maximum ESR of 35mΩ. Operating Region and Power Dissipation The maximum power dissipation of the MAX1982/ MAX1983 depends on the thermal resistance of the 6-pin SOT23 package and the circuit board, the temperature difference between the die and ambient air, and the rate of airflow. The power dissipated in the device is: PD = IOUT × ( VIN − VOUT ) The resulting maximum power dissipation is: PDISS(MAX) = TJ(MAX) − TA θ JC + θCA where TJ(MAX) is the maximum junction temperature (+150°C) and TA is the ambient temperature, θJC is the thermal resistance from the die junction to the package case, and θCA is the thermal resistance from the case through the PC board, copper traces, and other materials to the surrounding air. For optimum power dissipation, use a large ground plane with good thermal contact to GND, and use wide input and output traces. When 1 square inch of copper is connected to the device, the maximum allowable power dissipation of a 6-pin SOT23 package is 696mW. The maximum power dissipation is derated by 8.7mW/°C above TA = +70°C. Extra copper on the PC board increases thermal mass, and reduces thermal resistance of the board. Refer to the MAX1982/MAX1983 EV kit for a layout example. The MAX1982/MAX1983 deliver up to 300mA and operate with input voltages up to 5.5V, but not simultaneously. High output currents can only be achieved when the input-output differential voltages are low (Figure 5). Undervoltage Lockout (UVLO) The undervoltage lockout (UVLO) circuit ensures that the regulator starts up with adequate voltage for the gate-drive circuitry to bias the internal pass transistor. The UVLO circuitry monitors V BIAS ______________________________________________________________________________________ Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply TYPICAL DROPOUT VOLTAGE LIMIT 250 200 150 100 50 TA = +25°C TYPICAL SUPPLY VOLTAGE LIMIT MAXIMUM OUTPUT CURRENT (mA) MAXIMUM CONTINUOUS CURRENT 300 TA = +50°C TA = +70°C TJ = +150°C 0 0 1 2 3 4 5 INPUT-OUTPUT DIFFERENTIAL VOLTAGE (V) Figure 5. Power Operating Region—Maximum Output Current vs. Supply Voltage only. The UVLO threshold is 4.2V, and V BIAS must remain above this level for proper operation, regardless of the level of VIN. Input Capacitor Bypass IN to ground with a 10µF or greater ceramic capacitor. Bypass BIAS to ground with a 0.1µF ceramic capacitor for normal operation in most applications. Output Capacitor Bypass OUT to ground with a low-ESR ceramic capacitor greater than 10µF. The ESR must be less than 35mΩ. Choose an output capacitor to maintain the required output voltage tolerance during a load step. The change in output voltage is, ⎡ Δt ⎤ ΔV = I ⎢ESR + ⎥ COUT ⎥⎦ ⎢⎣ where I is the load current, COUT is the output capacitance, and Δt is the duration of the load step. Noise, PSRR, and Transient Response The MAX1982/MAX1983 operate with low-dropout voltage and low quiescent current in notebook computers while maintaining good noise, transient response, and AC rejection specifications. See the Typical Operating Characteristics for a graph of Power-Supply Rejection Ratio (PSRR) vs. Frequency. Improved supply-noise rejection and transient response can be achieved by increasing the values of the input and output capacitors and use passive filtering techniques when operating from noisy sources. The MAX1982/MAX1983 load-transient response graphs (see the Typical Operating Characteristics) show two components of the output response: a DC shift from the output impedance due to the load current change and the transient response. A typical transient response for a step change in the load current from 1mA to 300mA is 20mV. Increasing the output capacitor’s value and decreasing the ESR attenuate the overshoot. Input/Output (Dropout) Voltage A regulator’s minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, the dropout voltage determines the useful end-of-life battery voltage. Because the MAX1982/MAX1983 use an N-channel pass transistor, the dropout voltage is a function of the drain-to-source on-resistance (RDS(ON) = 1Ω max) multiplied by the load current (see the Typical Operating Characteristics): VDROPOUT = VIN − VOUT = RDS(ON) × IOUT PC Board Layout Guidelines The MAX1982/MAX1983 require proper layout to achieve the intended output power level, high efficiency, and low noise. Proper layout involves the use of a ground plane, appropriate component placement, and correct routing of traces using appropriate trace widths. 1) Minimize high-current ground loops. Connect the ground of the device, the input capacitor, and the output capacitor together at one point. 2) To optimize performance, a ground plane is essential. Use all available copper layers in applications where the device is located on a multilayer board. 3) Connect the input filter capacitor less than 10mm from IN. The connecting copper trace carries large currents and must be at least 2mm wide, preferably 5mm wide. 4) Use as much copper as necessary to increase the thermal resistance of the device. In general, more copper provides better heatsinking capabilities. ______________________________________________________________________________________ 11 MAX1982/MAX1983 350 MAX1982/MAX1983 Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply Package Information Chip Information TRANSISTOR COUNT: 430 PROCESS: BiCMOS 12 For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 6SOT23 U16-1 21-0058 ______________________________________________________________________________________ Low-Voltage, Low-Dropout Linear Regulators with External Bias Supply REVISION NUMBER REVISION DATE 0 7/02 1 10/08 DESCRIPTION PAGES CHANGED Initial release Added lead-free parts 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 ____________________ 13 © 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. MAX1982/MAX1983 Revision History