LMV7291 Single 1.8V Low Power Comparator with Rail-to-Rail Input General Description Features The LMV7291 is a rail-to-rail input low power comparator, characterized at supply voltage 1.8V, 2.7V and 5.0V. It consumes only 9uA supply current per channel while achieving a 800ns propagation delay. The LMV7291 is available in SC70 package. With this tiny package, the PC board area can be significantly reduced. It is ideal for low voltage, low power and space critical designs. The LMV7291 features a push-pull output stage which allows operation with minimum power consumption when driving a load. The LMV7291 is built with National Semiconductor’s advance submicron silicon-gate BiCMOS process. It has bipolar inputs for improved noise performance and CMOS outputs for rail-to-rail output swing. (VS = 1.8V, TA = 25˚C, Typical values unless specified). n Single Supply n Ultra low supply current 9µA per channel n Low input bias current 10nA n Low input offset current 200pA n Low guaranteed VOS 4mV n Propagation delay 880ns (20mV overdrive) n Input common mode voltage range 0.1V beyond rails Applications n n n n Mobile communications Laptops and PDA’s Battery powered electronics General purpose low voltage applications Typical Circuit 20080024 FIGURE 1. Threshold Detector © 2004 National Semiconductor Corporation DS200800 www.national.com LMV7291 Single 1.8V Low Power Comparator with Rail-to-Rail Input March 2004 LMV7291 Absolute Maximum Ratings (Note 1) Wave Soldering (10 sec.) 260˚C If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Storage Temperature Range ESD Tolerance Operating Ratings (Note 1) 2KV (Note 2) 200V (Note 6) ± Supply Voltage VIN Differential Supply Voltage (V+ - V−) Voltage at Input/Output pins −65˚C to +150˚C Junction Temperature (Note 4) 5.5V V+ +0.1V, V− −0.1V +150˚C Operating Temperature Range (Note 3) −40˚C to +85˚C Package Thermal Resistance (Note 3) SC-70 Soldering Information Infrared or Convection (20 sec.) 265˚C/W 235˚C 1.8V Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = 1.8V, V− = 0V. Boldface limits apply at the temperature extremes. Symbol Parameter VOS Input Offset Voltage Condition TC VOS Input Offset Temperature Drift IB Input Bias Current IOS Input Offset Current IS Supply Current LMV7291 ISC Output Short Circuit Current Sourcing, VO = 0.9V VCM = 0.9V (Note 7) VOL Output Voltage High Output Voltage Low Typ (Note 4) Max (Note 5) Units 0.3 4 6 mV 10 uV/C 10 nA 200 9 3.5 6 4 6 IO = 0.5mA 1.7 1.74 IO = 1.5mA 1.58 1.63 Sinking, VO = 0.9V VOH Min (Note 5) pA 12 14 µA mA V IO = −0.5mA 52 70 IO = −1.5mA 166 220 mV Input Common Mode Voltage Range CMRR > 45 dB CMRR Common Mode Rejection Ratio 0 < VCM < 1.8V 47 78 dB PSRR Power Supply Rejection Ratio V+ = 1.8V to 5V 55 80 dB ILEAKAGE Output Leakage Current VO = 1.8V 2 pA VCM 1.9 −0.1 V V 1.8V AC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = 1.8V, V− = 0V, VCM = 0.5V, VO = V+/2 and RL > 1MΩ to V−. Boldface limits apply at the temperature extremes. Symbol tPHL tPLH Parameter Propagation Delay (High to Low) Propagation Delay (Low to High) www.national.com Condition Min (Note 5) Typ (Note 4) Max (Note 5) Units Input Overdrive = 20mV Load = 50pF//5kΩ 880 ns Input Overdrive = 50mV Load = 50pF//5kΩ 570 ns Input Overdrive = 20mV Load = 50pF//5kΩ 1100 ns Input Overdrive = 50mV Load = 50pF//5kΩ 800 ns 2 Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = 2.7V, V− = 0V. Boldface limits apply at the temperature extremes. Symbol Parameter VOS Input Offset Voltage Conditions Min (Note 5) Max (Note 5) Units 0.3 4 6 mV TC VOS Input Offset Temperature Drift IB Input Bias Current IOS Input offset Current IS Supply Current LMV7291 ISC Output Short Circuit Current Sourcing, VO = 1.35V 12 15 Sinking, VO = 1.35V 12 15 IO = 0.5mA 2.63 2.66 IO = 2.0mA 2.48 2.55 VOH VOL VCM Output Voltage High Output Voltage Low Input Common Voltage Range VCM = 1.35V (Note 7) Typ (Note 4) 10 µV/C 10 nA 200 9 pA 13 15 mA V IO = −0.5mA 50 70 IO = −2mA 155 220 CMRR > 45dB µA 2.8 −0.1 mV V V CMRR Common Mode Rejection Ratio 0 < VCM < 2.7V 47 78 dB PSRR Power Supply Rejection Ratio V+ = 1.8V to 5V 55 80 dB ILEAKAGE Output Leakage Current VO = 2.7V 2 pA 2.7V AC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = 2.7V, V− = 0V, VCM = 0.5V, VO = V+/2 and RL > 1MΩ to V−. Boldface limits apply at the temperature extremes. Symbol tPHL tPLH Parameter Propagation Delay (High to Low) Propagation Delay (Low to High) Condition Min (Note 5) Typ (Note 4) Max (Note 5) Units Input Overdrive = 20mV Load = 50pF//5kΩ 1200 ns Input Overdrive = 50mV Load = 50pF//5kΩ 810 ns Input Overdrive = 20mV Load = 50pF//5kΩ 1300 ns Input Overdrive = 50mV Load = 50pF//5kΩ 860 ns 5V Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = 5V, V− = 0V. Boldface limits apply at the temperature extremes. Symbol Parameter VOS Input Offset Voltage Conditions Min (Note 5) VCM = 2.5V (Note 7) Typ (Note 4) Max (Note 5) Units 0.3 4 6 mV TC VOS Input Offset Temperature Drift IB Input Bias Current 10 µV/C 10 nA IOS Input Offset Current IS Supply Current LMV7291 ISC Output Short Circuit Current Sourcing, VO = 2.5V 28 34 Sinking, VO = 2.5V 28 34 200 10 3 pA 14 16 µA mA www.national.com LMV7291 2.7V Electrical Characteristics LMV7291 5V Electrical Characteristics (Continued) Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = 5V, V− = 0V. Boldface limits apply at the temperature extremes. Symbol VOH VOL VCM Parameter Output Voltage High Output Voltage Low Input Common Voltage Range Conditions Min (Note 5) Typ (Note 4) IO = 0.5mA 4.93 4.96 IO = 4.0mA 4.70 4.77 Max (Note 5) Units V IO = −0.5mA 27 70 IO = −4.0mA 225 300 CMRR > 45dB 5.1 −0.1 mV V CMRR Common Mode Rejection Ratio 0 < VCM < 5.0V 47 78 dB PSRR Power Supply Rejection Ratio V+ = 1.8V to 5V 55 80 dB ILEAKAGE Output Leakage Current VO = 5V 2 pA 5.0V AC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = 5.0V, V− = 0V, VCM = 0.5V, VO = V+/2 and RL > 1MΩ to V−. Boldface limits apply at the temperature extremes. Symbol tPHL tPLH Parameter Propagation Delay (High to Low) Propagation Delay (Low to High) Condition Min (Note 5) Typ (Note 4) Max (Note 5) Units Input Overdrive = 20mV Load = 50pF//5kΩ 2100 ns Input Overdrive = 50mV Load = 50pF//5kΩ 1380 ns Input Overdrive = 20mV Load = 50pF//5kΩ 1800 ns Input Overdrive = 50mV Load = 50pF//5kΩ 1100 ns 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 specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics. Note 2: Human body model, 1.5kΩ in series with 100pF. Note 3: The maximum power dissipation is a function of TJ(MAX), θJA, and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ(MAX) - TA)/θJA. All numbers apply for packages soldered directly into a PC board. Note 4: Typical values represent the most likely parametric norm. Note 5: All limits are guaranteed by testing or statistical analysis. Note 6: Machine Model, 0Ω in series with 200pF. Note 7: Offset Voltage average drift determined by dividing the change in VOS at temperature extremes into the total temperature change. Note 8: Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very limited self-heating of the device such that TJ = TA. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond which the device may be permanently degraded, either mechanically or electrically. www.national.com 4 LMV7291 Connection Diagram 5-Pin SC70 20080023 Top View Ordering Information Package 5-Pin SC70 Part Number LMV7291MG LMV7291MGX Package Marking Transport Media 1k Units Tape and Reel C36 3k Units Tape and Reel 5 NSC Drawing MAA05A www.national.com LMV7291 Typical Performance Characteristics (TA = 25˚C, Unless otherwise specified). VOS vs. VCM VOS vs. VCM 20080028 20080029 VOS vs. VCM Short Circuit vs. Supply Voltage 20080030 20080001 Supply Current vs. Supply Voltage Supply Current vs. Supply Voltage 20080002 www.national.com 20080031 6 Supply Current vs. Supply Voltage (Continued) Output Positive Swing vs. VSUPPLY 20080032 20080033 Output Negative Swing vs. VSUPPLY Output Positive Swing vs. ISOURCE 20080035 20080034 Output Negative Swing vs. ISINK Output Positive Swing vs. ISOURCE 20080036 20080037 7 www.national.com LMV7291 Typical Performance Characteristics (TA = 25˚C, Unless otherwise specified). LMV7291 Typical Performance Characteristics (TA = 25˚C, Unless otherwise specified). Output Negative Swing vs. ISINK (Continued) Output Negative Swing vs. ISINK 20080039 20080038 Output Positive Swing vs. ISOURCE Propagation Delay (tPLH) 20080014 20080040 Propagation Delay (tPHL) Propagation Delay (tPLH) 20080018 www.national.com 20080015 8 Propagation Delay (tPHL) (Continued) Propagation Delay (tPLH) 20080020 20080016 Propagation Delay (tPHL) tPHL vs. Overdrive 20080022 20080050 tPLH vs. Overdrive 20080049 9 www.national.com LMV7291 Typical Performance Characteristics (TA = 25˚C, Unless otherwise specified). LMV7291 Application Notes BASIC COMPARATOR VIN is less than VREF, the output (VO) is low. However, if VIN is greater than VREF, the output voltage (VO) is high. A comparator is often used to convert an analog signal to a digital signal. As shown in Figure 2, the comparator compares an input voltage (VIN) to a reference voltage (VREF). If LMV7291 20080025 20080017 FIGURE 2. LMV7291 Basic Comparator HYSTERESIS It is a standard procedure to use hysteresis (positive feedback) around a comparator, to prevent oscillation, and to avoid excessive noise on the output because the comparator is a good amplifier of its own noise. RAIL-TO-RAIL INPUT STAGE The LMV7291 has an input common mode voltage range (VCM) of −0.1V below the V− to 0.1V above V+. This is achieved by using paralleled PNP and NPN differential input pairs. When the VCM is near V+, the NPN pair is on and the PNP pair is off. When the VCM is near V−, the NPN pair is off and the PNP pair is on. The crossover point between the NPN and PNP input stages is around 950mV from V+. Since each input stage has its own offset voltage (VOS), the VOS of the comparator becomes a function of the VCM. See curves for VOS vs. VCM in Typical Performance Characteristics section. In application design, it is recommended to keep the VCM away from the crossover point to avoid problems. The wide input voltage range makes LMV7291 ideal in power supply monitoring circuits, where the comparators are used to sense signals close to gnd and power supplies. Inverting Comparator with Hysteresis The inverting comparator with hysteresis requires a three resistor network that are referenced to the supply voltage VCC of the comparator (Figure 3). When VIN at the inverting input is less than VA, the voltage at the non-inverting node of the comparator (VIN < VA), the output voltage is high (for simplicity assume VO switches as high as VCC). The three network resistors can be represented as R1||R3 in series with R2. The lower input trip voltage VA1 is defined as OUTPUT STAGE The LMV7291 has a push-pull output stage. This output stage keeps the total system power consumption to the absolute minimum. The only current consumed is the low supply current and the current going directly into the load. When output switches, both PMOS and NMOS at the output stage are on at the same time for a very short time. This allows current to flow directly between V+ and V− through output transistors. The result is a short spike of current (shoot-through current) drawn from the supply and glitches in the supply voltages. The glitches can spread to other parts of the board as noise. To prevent the glitches in supply lines, power supply bypass capacitors must be installed. See section for supply bypassing in the Application Notes for details. When VIN is greater than VA (VIN > VA), the output voltage is low and very close to ground. In this case the three network resistors can be presented as R2//R3 in series with R1. The upper trip voltage VA2 is defined as The total hysteresis provided by the network is defined as ∆VA = VA1 - VA2 A good typical value of ∆VA would be in the range of 5 to 50 mV. This is easily obtained by choosing R3 as 1000 to 100 times (R1||R2) for 5V operation, or as 300 to 30 times (R1||R2) for 1.8V operation. www.national.com 10 LMV7291 Application Notes (Continued) 20080042 FIGURE 3. Inverting Comparator with Hysteresis When VIN is high, the output is also high. To make the comparator switch back to its low state, VIN must equal VREF before VA will again equal VREF. VIN can be calculated by: Non-Inverting Comparator with Hysteresis A non-inverting comparator with hysteresis requires a two resistor network, and a voltage reference (VREF) at the inverting input (Figure 4). When VIN is low, the output is also low. For the output to switch from low to high, VIN must rise up to VIN1, where VIN1 is calculated by The hysteresis of this circuit is the difference between VIN1 and VIN2. ∆VIN = VCCR1/R2 11 www.national.com LMV7291 Application Notes low inductive ground connection. Make sure ground paths are low-impedance where heavier currents are flowing to avoid ground level shift. Preferably there should be a ground plane under the component. (Continued) 4. The output trace should be routed away from inputs. The ground plane should extend between the output and inputs to act as a guard. 5. When the signal source is applied through a resistive network to one input of the comparator, it is usually advantageous to connect the other input with a resistor with the same value, for both DC and AC consideration. Input traces should be laid out symmetrically if possible. 6. All pins of any unused comparators should be tied to the negative supply. Typical Applications 20080044 POSITIVE PEAK DETECTOR A positive peak detect circuit is basically a comparator operated in a unity gain follower configuration, with a capacitor as a load to maintain the highest voltage. A diode is added at the output to prevent the capacitor from discharging through the output, and a 1MΩ resistor added in parallel to the capacitor to provide a high impedance discharge path. When the input VIN increases, the inverting input of the comparator follows it, thus charging the capacitor. When it decreases, the cap discharges through the 1MΩ resistor. The decay time can be modified by changing the resistor. The output should be accessed through a follower circuit to prevent loading. 20080043 FIGURE 4. Non-Inverting Comparator with Hysteresis CIRCUIT TECHNIQUES FOR AVOIDING OSCILLATIONS IN COMPARATOR APPLICATIONS Feedback to almost any pin of a comparator can result in oscillation. In addition, when the input signal is a slow voltage ramp or sine wave, the comparator may also burst into oscillation near the crossing point. To avoid oscillation or instability, PCB layout should be engineered thoughtfully. Several precautions are recommended: 1. Power supply bypassing is critical, and will improve stability and transient response. Resistance and inductance from power supply wires and board traces increase power supply line impedance. When supply current changes, the power supply line will move due to its impedance. Large enough supply line shift will cause the comparator to mis-operate. To avoid problems, a small bypass capacitor, such as 0.1uF ceramic, should be placed immediately adjacent to the supply pins. An additional 6.8µF or greater tantalum capacitor should be placed at the point where the power supply for the comparator is introduced onto the board. These capacitors act as an energy reservoir and keep the supply impedance low. In dual supply application, a 0.1µF capacitor is recommended to be placed across V+ and V− pins. 2. Keep all leads short to reduce stray capacitance and lead inductance. It will also minimize any unwanted coupling from any high-level signals (such as the output). The comparators can easily oscillate if the output lead is inadvertently allowed to capacitively couple to the inputs via stray capacitance. This shows up only during the output voltage transition intervals as the comparator changes states. Try to avoid a long loop which could act as an inductor (coil). 3. It is a good practice to use an unbroken ground plane on a printed circuit board to provide all components with a www.national.com 20080054 FIGURE 5. Positive Peak Detector NEGATIVE PEAK DETECTOR For the negative detector, the output transistor of the comparator acts as a low impedance current sink. Since there is no pull-up resistor, the only discharge path will be the 1MΩ resistor and any load impedance used. Decay time is changed by varying the 1MΩ resistor. 12 (Continued) To analyze the circuit, consider it when the output is high. That implies that the inverted input (VC) is lower than the non-inverting input (VA). This causes the C1 to get charged through R4, and the voltage VC increases till it is equal to the non-inverting input. The value of VA at this point is If R1 = R2 = R3 then VA1 = 2VCC/3 At this point the comparator switches pulling down the output to the negative rail. The value of VA at this point is 20080055 FIGURE 6. Negative Peak Detector SQUARE WAVE GENERATOR A typical application for a comparator is as a square wave oscillator. The circuit below generates a square wave whose period is set by the RC time constant of the capacitor C1and resistor R4. The maximum frequency is limited by the large signal propagation delay of the comparator, and by the capacitive loading at the output, which limits the output slew rate. If R1 = R2 = R3 then VA2 = VCC/3 The capacitor C1 now discharges through R4, and the voltage VC decreases till it is equal to VA2, at which point the comparator switches again, bringing it back to the initial stage. The time period is equal to twice the time it takes to discharge C1 from 2VCC/3 to VCC/3, which is given by R4C1.ln2. Hence the formula for the frequency is: F = 1/(2.R4.C1.ln2) 20080056 20080057 FIGURE 7. Squarewave Oscillator 13 www.national.com LMV7291 Typical Applications LMV7291 Single 1.8V Low Power Comparator with Rail-to-Rail Input Physical Dimensions inches (millimeters) unless otherwise noted 5-Pin SC70 NS Package Number MAA05A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. 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