LM4140_05

LM4140 High Precision Low Noise Low Dropout Voltage Reference February 2005 LM4140 High Precision Low Noise Low Dropout Voltage Reference General Description The LM4140 series of precision references are designed to combine high accuracy, low drift and noise with low power dissipation in a small package. The LM4140 is the industry’s first reference with output voltage options lower than the bandgap voltage. The key to the advance performance of the LM4140 is the use of EEPROM registers and CMOS DACs for temperature coefficient curvature correction and trimming of the output voltage accuracy of the device during the final production testing. The major advantage of this method is the much higher resolution available with DACs than is available economically with most methods utilized by other bandgap references. The low input and dropout voltage, low supply current and output drive capability of the LM4140 makes this product an ideal choice for battery powered and portable applications. The LM4140 is available in three grades (A, B, C) with 0.1% initial accuracy and 3, 6 and 10 ppm/˚C temperature coefficients. For even lower Tempco, contact National Semiconductor. The device performance is specified over the temperature range (0˚C to +70˚C) and is available in compact 8-pin SO package. For other output voltage options from 0.5V to 4.5V, contact National Semiconductor. Features High initial accuracy: 0.1% Ultra low noise Low Temperature Coefficient: 3 ppm/˚C (A grade) Low voltage operation: 1.8V SO-8 package Low dropout voltage: 20 mV (typ) @ 1mA Supply Current: 230 µA (typ), ≤ 1 µA disable mode Enable pin Output voltage options: 1.024V, 1.250V, 2.048V, 2.500V, and 4.096V n Custom voltages from 0.5V to 4.5V n Temperature range (0˚C to 70˚C) n n n n n n n n n Applications Summary n n n n n n n n n Portable, battery powered equipment Instrumentation and test equipment Automotive Industrial process control Data acquisition systems Medical equipment Precision scales Servo systems Battery charging Typical Application Typical Temperature Coefficient (Sample of 5 Parts) 10107901 COUT, Output bypass capacitor. See text for selection detail. 10107923 Refer to the Ordering Information Table in this Data Sheet for Specific Part Number © 2005 National Semiconductor Corporation DS101079 www.national.com LM4140 Ordering Information (0˚C to 70˚C) Initial Output Voltage Accuracy @ 25˚C and Temperature Coefficient Temperature Range LM4140 Supplied as 95 Units, Tape and Reel LM4140ACM-1.0 LM4140ACM-1.2 LM4140 Supplied as 2500 Units, Tape and Reel LM4140ACMX-1.0 LM4140ACMX-1.2 LM4140ACMX-2.0 LM4140ACMX-2.5 LM4140ACMX-4.1 LM4140BCMX-1.0 LM4140BCMX-1.2 LM4140BCMX-2.0 LM4140BCMX-2.5 LM4140BCMX-4.1 LM4140CCMX-1.0 LM4140CCMX-1.2 LM4140CCMX-2.0 LM4140CCMX-2.5 LM4140CCMX-4.1 0.1%, 3 ppm/˚C max (A grade) LM4140ACM-2.0 LM4140ACM-2.5 LM4140ACM-4.1 LM4140BCM-1.0 LM4140BCM-1.2 0.1%, 6 ppm/˚C max (B grade) LM4140BCM-2.0 LM4140BCM-2.5 LM4140BCM-4.1 LM4140CCM-1.0 LM4140CCM-1.2 0.1%, 10 ppm/˚C max (C grade) LM4140CCM-2.0 LM4140CCM-2.5 LM4140CCM-4.1 Connection Diagram 8-Lead Surface Mount (M) 10107902 Top View See NS Package Number M08A Pin Functions Vref (Pin 6): Input (Pin 2): Ground (Pins 1, 4, 7, 8): Enable (Pin 3): NC (Pin 5): Reference Output. Capable of sourcing up to 8mA. Positive Supply. Negative Supply or Ground Connection. These pins must be connected to ground. Pulled to input for normal operation. Forcing this pin to ground will turn-off the output. This pin must be left open. www.national.com 2 LM4140 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Maximum Voltage on any Input pin Output Short-Circuit Duration Power Dissipation (TA = 25˚C) (Note 2) ESD Susceptibility (Note 3) Human Body Model Machine Model −0.3V to 5.6V Indefinite 345mW 2 kV 200V Lead Temperature: Soldering, (10 sec.) +260˚C Operating Range (Note 1) Storage Temperature Range Ambient Temperature Range Junction Temperature Range −65˚C to +150˚C 0˚C to 70˚C 0˚C to 80˚C LM4140 Electrical Charateristics Unless otherwise specified, VIN = 3.0V for the LM4140-1.024 and LM4140-1.250, VIN = 5.0V for all other voltage options, VEN = VIN. COUT = 1µF (Note 4), ILOAD = 1mA, TA = TJ = 25˚C. Limits with standard typeface are for TA = 25˚C, and limits in boldface type apply over 0˚C to 70˚C temperature range. Symbol Parameter Output Voltage Initial Accuracy (Note 7) LM4140B-1.024 LM4140B-1.250 LM4140B-2.048 LM4140B-2.500 LM4140B-4.096 LM4140C-1.024 LM4140C-1.250 LM4140C-2.048 LM4140C-2.500 LM4140C-4.096 TCVREF/˚C Temperature Coefficient: A Grade B Grade C Grade Line Regulation 1.024V and 1.250V options ∆VREF/∆VIN All other voltage options Load Regulation All other voltage options ∆VREF/∆ILOAD 4.096V Option ∆VREF ∆VREF Long-Term Stability Thermal Hysteresis (Note 8) 1000 Hrs 0˚C ≤ TA ≤ + 70˚C 5 60 20 Vref + 200mV ≤ VIN ≤ 5.5V 1 mA ≤ ILOAD ≤ 8mA 1 20 150 35 150 ppm ppm ppm/mA 20 1.8V ≤ VIN ≤ 5.5V 50 300 350 200 250 ppm/V 0˚C ≤ TA ≤ + 70˚C Conditions Min (Note 6) Typ (Note 5) Max (Note 6) Units ± 0.1 % VREF ± 0.1 3 6 10 ppm/˚C 3 www.national.com LM4140 LM4140 Electrical Charateristics (Continued) Unless otherwise specified, VIN = 3.0V for the LM4140-1.024 and LM4140-1.250, VIN = 5.0V for all other voltage options, VEN = VIN. COUT = 1µF (Note 4), ILOAD = 1mA, TA = TJ = 25˚C. Limits with standard typeface are for TA = 25˚C, and limits in boldface type apply over 0˚C to 70˚C temperature range. Symbol Parameter LM4140-1.024, LM4140-1.250 Dropout Voltage (Note 9) LM4140-2.048, LM4140-2.500 VIN-VREF LM4140-4.096 Conditions IL = 1 mA to 8 mA IL = 1 mA IL = 8 mA IL = 1 mA IL = 8 mA Min (Note 6) 1.8 20 160 20 195 2.2 Typ (Note 5) Max (Note 6) 5.5 40 45 235 400 40 45 270 490 µVPP Units V Operating Voltage mV VN IS(ON) Output Noise Voltage (Note 10) Supply Current All other voltage options 4.096V Option 0.1 Hz to 10 Hz ILOAD = 0 mA 230 265 VEnable < 0.4V 0.8VIN 2 .01 320 375 350 400 1 µA V nA 0.4 V nA 35 40 mA µA IS(OFF) VH IH VL IL ISC Supply Current Logic High Input Voltage Logic High Input Current Logic Low Input Voltage Logic Low Input Current Short Circuit Current 1 8.5 20 Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 2: Without PCB copper enhancements. The maximum power dissipation must be de-rated at elevated temperatures and is limited by TJMAX (maximum junction temperature), θJ-A (junction to ambient thermal resistance) and TA (ambient temperature). The maximum power dissipation at any temperature is: PDissMAX = (TJMAX − TA)/θJ-A up to the value listed in the Absolute Maximum Ratings. The θJ-A for the SO-8 package is 160˚C/W. Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged directly into each pin. Note 4: For proper operation, a 1µF capacitor is required between the output pin and the GND pin of the device. (See Application Section for details) Note 5: Typical numbers are at 25˚C and represent the most likely parametric norm. Note 6: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. The limits are used to calculate National’s Average Outgoing Quality Level (AOQL). Note 7: High temperature and mechanical stress associated with PCB assembly can have significant impact on the initial accuracy of the LM4140 and may create significant shifts in VREF. See Application Hints section regarding accuracy and PCB layout consideration. Note 8: Thermal hysteresis is defined as the changes in +25˚C output voltage before and after the cycling of the device from 0˚C to 70˚C. Note 9: Dropout voltage is defined as the minimum input to output differential voltage at which the output voltage drops by 0.5% below the value measured with VIN = 3.0V for the LM4140-1.024 and LM4140-1.250, VIN = 5.0V for all other voltage options. Note 10: The output noise is based on 1.024V option. Output noise is linearly proportional to VREF. www.national.com 4 LM4140 LM4140 Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, No Load, COUT = 1µF, VIN = 3.0V for LM4140-1.024 and LM4140-1.250, and 5V for all other voltage options. VIN = VEN. Power Up/Down Ground Current Enable Response 10107905 10107906 * The 1µF output capacitor is actively discharged to ground. See ON/OFF Operation section for more details. Line Transient Response Load Transient Response 10107907 10107908 5 www.national.com LM4140 LM4140 Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, No Load, COUT = 1µF, VIN = 3.0V for LM4140-1.024 and LM4140-1.250, and 5V for all other voltage options. VIN = VEN. (Continued) Output Impedance Power Supply Rejection Ratio 10107909 10107910 Dropout Voltage vs Load Current Output Voltage Change vs Sink Current (ISINK) 10107911 10107912 Note: 1.024V and 1.250V options require 1.8V supply. www.national.com 6 LM4140 LM4140 Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, No Load, COUT = 1µF, VIN = 3.0V for LM4140-1.024 and LM4140-1.250, and 5V for all other voltage options. VIN = VEN. (Continued) Total Current (IS(OFF)) vs Supply Voltage Total Current (IS(ON)) vs Supply Voltage 10107913 10107914 Spectral Noise Density (0.1Hz to 10Hz) Spectral Noise Density (10Hz to 100kHz) 10107931 10107932 Ground Current vs Load Current Long Term Drift 10107938 10107939 7 www.national.com LM4140 LM4140 Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, No Load, COUT = 1µF, VIN = 3.0V for LM4140-1.024 and LM4140-1.250, and 5V for all other voltage options. VIN = VEN. (Continued) Load Regulation vs Temperature Output Voltage vs Load Current 10107940 10107941 Line Regulation vs Temperature IQ vs Temperature 10107942 10107943 Short Circuit Current vs Temperature Dropout Voltage vs Load Current (VOUT) = 2.0V 10107944 10107945 www.national.com 8 LM4140 Application Hints INPUT CAPACITORS Although not always required, an input capacitor is recommended. A supply bypass capacitor on the input assures that the reference is working from a source with low impedance, which improves stability. A bypass capacitor can also improve transient response by providing a reservoir of stored energy that the reference can utilize in case where the load current demand suddenly increases. The value used for CIN may be used without limit. Refer to the typical application section for examples of input capacitors. OUTPUT CAPACITORS The LM4140 requires a 1µF (nominally) output capacitor for loop stability (compensation) as well as transient response. During the sudden changes in load current demand, the output capacitor must source or sink current during the time it takes the control loop of the LM4140 to respond. This capacitor must be selected to meet the requirements of minimum capacitance and equivalent series resistance (ESR) range. In general, the capacitor value must be at least 0.2µF (over the actual ambient operating temperature), and the ESR must be within the range indicated in Figure 1, Figure 2 and Figure 3. 10107930 FIGURE 3. 10 µF ESR Range TANTALUM CAPACITORS Surface-mountable solid tantalum capacitors offer a good combination of small physical size for the capacitance value, and ESR in the range needed for by the LM4140. The results of testing the LM4140 stability with surface mount solid tantalum capacitors show good stability with values in the range of 0.1µF. However, optimum performance is achieved with a 1µF capacitor. Tantalum capacitors that have been verified as suitable for use with the LM4140 are shown in Table 1. TABLE 1. Surface-Mount Tantalum Capacitor Selection Guide 1µF Surface-Mount Tantalums Manufacturer Kemet NEC Siemens Nichicon Sprague Kemet NEC Siemens Nichicon Sprague Part Number T491A105M010AS NRU105N10 B45196-E3105-K F931C105MA 293D105X0016A2T T491A225M010AS NRU225M06 B45196/2.2/10/10 F930J225MA 293D225X0010A2T 10107928 2.2µF Surface-Mount Tantalums FIGURE 1. 0.22 µF ESR Range ALUMINUM ELECTROLYTIC CAPACITORS Although probably not a good choice for a production design, because of relatively large physical size, an aluminium electrolytic capacitor can be used in the design prototype for an LM4140 reference. A 1µF capacitor meeting the ESR conditions can be used. If the operating temperature drops below 0˚C, the reference may not remain stable, as the ESR of the aluminium electrolytic capacitor will increase, and may exceed the limits indicated in the figures. 10107929 FIGURE 2. 1 µF ESR Range 9 www.national.com LM4140 Application Hints (Continued) the LM4140 input voltage, but must remain within the Absolute Maximum Rating for the enable pin. OUTPUT ACCURACY Like all references, either series or shunt, the after assembly accuracy is made up of primarily three components: initial accuracy itself, thermal hysteresis and effects of the PCB assembly stress. LM4140 provides an excellent output initial accuracy of 0.1% and temperature coefficient of 6ppm/˚C (B Grade). For best accuracy and precision, the LM4140 junction temperature should not exceed 70˚C. The thermal hysteresis curve on this datasheet are performance characteristics of three typical parts selected at random from a sample of 40 parts. Parts are mounted in a socket to minimize the effect of PCB’s mechnical expansion and contraction. Readings are taken at 25˚C following multiple temperature cycles to 0˚C and 70˚C. The labels on the X axis of the graph indicates the device temperature cycle prior to measurement at 25˚C. MULTILAYER CERAMIC CAPACITORS Surface-mountable multilayer ceramic capacitors may be an attractive choice because of their relatively small physical size and excellent RF characteristics. However, they sometimes have an ESR values lower than the minimum required by the LM4140, and relatively large capacitance change with temperature. The manufacturer’s datasheet for the capacitor should be consulted before selecting a value. Test results of LM4140 stability using multilayer ceramic capacitors show that a minimum of 0.2µF is usually needed. Multilayer ceramic capacitors that have been verified as suitable for use with the LM4140 are shown in Table 2. TABLE 2. Surface-Mount Ceramic Capacitors Selection Guide 2.2µF Surface-Mount Ceramic Manufacturer Tokin Murata Tokin Part Number 1E225ZY5U-C203 GRM42-6Y5V225Z16 1E475ZY5U-C304 4.7µF Surface-Mount Ceramic REVERSE CURRENT PATH The P-channel Pass transistor used in the LM4140 has an inherent diode connected between the VIN and VREF pins (see diagram below). 10107933 10107903 Forcing the output to voltages higher than the input, or pulling VIN below voltage stored on the output capacitor by more than a Vbe, will forward bias this diode and current will flow from the VREF terminal to VIN. No damage to the LM4140 will occur under these conditions as long as the current flowing into the output pin does not exceed 50mA. ON/OFF OPERATION The LM4140 is designed to quickly reduce both VREF and IQ to zero when turned-off. VREF is restored in less than 200µs when turned-on. During the turn-off, the charge across the output capacitor is discharged to ground through internal circuitry. The LM4140 is turned-off by pulling the enable input low, and turned-on by driving the input high. If this feature is not to be used, the enable pin should be tied to the VIN to keep the reference on at all times (the enable pin must not be left floating). To ensure proper operation, the signal source used to drive the enable pin must be able to swing above and below the specified high and low voltage thresholds which guarantee an ON or OFF state (see Electrical Characteristics). The ON/OFF signal may come from either a totem-pole output, or an open-collector output with pull-up resistor to the LM4140 input voltage. This high-level voltage may exceed FIGURE 4. Typical Thermal Hysteresis The mechanical stress due to the PCB’s mechanical and thermal stress can cause an output voltage shift more than the true thermal coefficient of the device. References in surface mount packages are more susceptible to these stresses because of the small amount of plastic molding which support the leads. Following the recommendations on PCB Layout Consideration section can minimize the mechanical stress on the device. PCB LAYOUT CONSIDERATION The simplest ways to reduce the stress related shifts are: 1. Mounting the device near the edges or the corners of the board where mechanical stress is at its minimum. The center of the board generally has the highest mechanical and thermal expansion stress. 2. Mechanical isolation of the device by creating an island by cutting a U shape slot on the PCB for mounting the device. This approach would also provide some thermal isolation from the rest of the circuit. Figure 5 is a recommended printed board layout with a slot cut on three sides of the circuit layout to serve as a strain relief. www.national.com 10 LM4140 Application Hints (Continued) 10107935 10107934 FIGURE 5. Suggested PCB Layout with Slot 11 www.national.com LM4140 Typical Application Circuits Boosted Output Current Voltage Reference with Force and Sense Output 10107920 Precision Programmable Current Source 10107915 Boosted Ouput Current with Current Limiter 10107921 Precision DAC Reference 10107922 Complimentary Outputs 10107936 10107919 * Low Noise Op Amp such as OP-27 www.national.com 12 LM4140 Typical Application Circuits (Continued) Strain Gauge Conditioner for 350Ω Bridge 10107937 10107926 FIGURE 6. 13 www.national.com LM4140 Typical Application Circuits (Continued) 10107927 FIGURE 7. www.national.com 14 LM4140 High Precision Low Noise Low Dropout Voltage Reference Physical Dimensions inches (millimeters) unless otherwise noted SO-8 Package Type M NS Package Number M08A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. 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