MAX472CSA

___________General Description The MAX471/MAX472 are complete, bidirectional, high- side current-sense amplifiers for portable PCs, tele- phones, and other systems where battery/DC power-line monitoring is critical. High-side power-line monitoring is especially useful in battery-powered sys- tems, since it does not interfere with the ground paths of the battery chargers or monitors often found in “smart” batteries. The MAX471 has an internal 35mΩ current-sense resis- tor and measures battery currents up to ±3A. For appli- cations requiring higher current or increased flexibility, the MAX472 functions with external sense and gain-set- ting resistors. Both devices have a current output that can be converted to a ground-referred voltage with a single resistor, allowing a wide range of battery volt- ages and currents. An open-collector SIGN output indicates current-flow direction, so the user can monitor whether a battery is being charged or discharged. Both devices operate from 3V to 36V, draw less than 100µA over tempera- ture, and include a 18µA max shutdown mode. ______________________Applications Portable PCs: Notebooks/Subnotebooks/Palmtops Smart Battery Packs Cellular Phones Portable Phones Portable Test/Measurement Systems Battery-Operated Systems Energy Management Systems __________________________Features ' Complete High-Side Current Sensing ' Precision Internal Sense Resistor (MAX471) ' 2% Accuracy Over Temperature ' Monitors Both Charge and Discharge ' 3A Sense Capability with Internal Sense Resistor (MAX471) ' Higher Current-Sense Capability with External Sense Resistor (MAX472) ' 100µA Max Supply Current ' 18µA Max Shutdown Mode ' 3V to 36V Supply Operation ' 8-Pin DIP/SO Packages ___________Ordering Information M A X 4 7 1 /M A X 4 7 2 Precision, High-Side Current-Sense Amplifiers __________________________________________________________ Maxim Integrated Products 1 1 2 3 4 8 7 6 5 OUT RS- RS- SIGNGND RS+ RS+ SHDN MAX471 DIP/SO TOP VIEW _____________Pin Configurations MAX471 RS+ RS+ RS- RS- SIGN OUT GNDSHDN 3V TO 36V 100k ILOAD 200 2k ILOAD TO LOAD or CHARGER LOGIC SUPPLY DISCHARGE/CHARGE VOUT (1V/A) _______Typical Operating Circuit 19-0335; Rev 2; 12/96 PART MAX471CPA MAX471CSA MAX471EPA -40°C to +85°C 0°C to +70°C 0°C to +70°C TEMP. RANGE PIN-PACKAGE 8 Plastic DIP 8 SO 8 Plastic DIP MAX471ESA -40°C to +85°C 8 SO MAX472CPA 0°C to +70°C 8 Plastic DIP MAX472CSA 0°C to +70°C 8 SO MAX472EPA -40°C to +85°C 8 Plastic DIP MAX472ESA -40°C to +85°C 8 SO MAX472 Pin Configuration continued on last page. For free samples & the latest literature: http://ww.maxim-ic.com, or phone 1-800-998-8800 M A X 4 7 1 /M A X 4 7 2 Precision, High-Side Current-Sense Amplifiers 2 _______________________________________________________________________________________ ABSOLUTE MAXIMUM RATINGS ELECTRICAL CHARACTERISTICS—MAX471 (RS+ = +3V to +36V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°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. Supply Voltage, RS+, RS-, VCC to GND....................-0.3V, +40V RMS Current, RS+ to RS- (MAX471 only)..........................±3.3A Peak Current, (RS+ to RS-) ......................................see Figure 5 Differential Input Voltage, RG1 to RG2 (MAX472 only) .....±0.3V Voltage at Any Pin Except SIGN MAX471 only ...........................................-0.3V to (RS+ - 0.3V) MAX472 only ..........................................-0.3V to (VCC + 0.3V) Voltage at SIGN......................................................-0.3V to +40V Current into SHDN, GND, OUT, RG1, RG2, VCC................±50mA Current into SIGN.................................................+10mA, -50mA Continuous Power Dissipation (TA = +70°C) MAX471 (Note 1): Plastic DIP (derate 17.5mW/°C above +70°C) ..................1.4W SO (derate 9.9mW/°C above +70°C).............................791mW MAX472 : Plastic DIP (derate 9.09mW/°C above +70°C) ..............727mW SO (derate 5.88mW/°C above +70°C)...........................471mW Operating Temperature Ranges MAX47_C_A........................................................0°C to +70°C MAX47_E_A .....................................................-40°C to +85°C Junction Temperature Range ............................-60°C to +150°C Storage Temperature Range .............................-60°C to +160°C Lead Temperature (soldering, 10sec) .............................+300°C VSHDN = 2.4V ILOAD = 0A, excludes ISIGN VSHDN = 0V VSHDN = 2.4V; VCC = 3V to 20V VSIGN = 0.3V VSIGN = 36V ILOAD = 30mA, RS+ = 10V MAX471E MAX471C ILOAD = 0A, RS+ = 10V ILOAD = 1A, RS+ = 10V 3V ≤ RS+ ≤ 36V, ILOAD = 1A CONDITIONS V0 VRS+ - 1.5VOUTOUT Output Voltage Range µA1.0IIHSHDN Input High Current V2.4VIHSHDN Input High Voltage µA1.0IILSHDN Input Low Current V0.3VILSHDN Input Low Voltage µA1.5 18.0IRS+(SHDN)Shutdown Supply Current mA0.1IOLSIGN Sink Current µA1.0SIGN Output Leakage Current mA ±4.0 ±6.0SIGN Threshold (ILOAD required to switch SIGN) %/V0.1PSRRPower-Supply Rejection Ratio ARMS±3ILOADSense Current V 50 113IRS+ 3 36VRS+Supply Voltage Supply Current µA ±3.0 Low-Level OUT Error ±2.5 µA 3.0 No-Load OUT Error mΩ35 70RSENSESense Resistor 0.490 0.500 0.510 mA/A 0.4875 0.500 0.5125 IOUT/ ILOAD Current-Sense Ratio 2.5 UNITSMIN TYP MAXSYMBOLPARAMETER OUT Output Resistance ROUT ILOAD = 3.0A, VOUT = 0V to (VRS+ - 1.5V) 1 3 MΩ OUT Rise, Fall Time tR, tF ILOAD = 50mA to 3.0A, ROUT = 2kΩ, COUT = 50pF, 10% to 90% 4 µs OUT Settling Time to 1% of Final Value ts ILOAD = 100mA to 3.0A, ROUT = 2kΩ, COUT = 50pF 15 µs MAX471C MAX471C MAX471C MAX471E MAX471E MAX471E ±7.0 µA Note 1: Due to special packaging considerations, MAX471 (DIP, SO) has a higher power dissipation rating than the MAX472. RS+ and RS- must be soldered to large copper traces to achieve this dissipation rating. M A X 4 7 1 /M A X 4 7 2 Precision, High-Side Current-Sense Amplifiers _______________________________________________________________________________________ 3 ELECTRICAL CHARACTERISTICS—MAX472 (VCC = +3V to +36V, RG1 = RG2 = 200Ω, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) Note 2: VOS is defined as the input voltage (VSENSE) required to give minimum IOUT. Note 3: VSENSE is the voltage across the sense resistor. VSHDN = 2.4V MAX472C VSHDN = 0V ILOAD = 0A, excludes ISIGN; VCC = 3V to 20V VSHDN = 2.4V; VCC = 3V to 20V VSIGN = 0.3V VSIGN = 36V VCC = 10V, VSENSE = 3mV VCC = 10V MAX472E IRG1 - IGR2 3V ≤ VCC ≤ 36V, VSENSE = 100mV CONDITIONS V0 VCC - 1.5VOUTOUT Output Voltage Range µA1.0IIHSHDN Input High Current V2.4VIHSHDN Input High Voltage µA1.0IILSHDN Input Low Current V0.3VILSHDN Input Low Voltage µA1.5 18.0ICC(SHDN)Shutdown Supply Current mA0.1SIGN Output Sink Current µA1.0SIGN Output Leakage Current µV 60 140 SIGN Threshold (VSENSE required to switch SIGN) 60 120 %/V0.1PSRRPower-Supply Rejection Ratio 120 µA20 48ICC V3 36VCCSupply Voltage Supply Current µA ±3.0 Low-Level OUT Error ±2.5 µA 2.5 µV 140 VOS Input Offset Voltage (Note 2) µA20 35IRG1, IRG2Input Bias Current µA±0.4 ±3.0IOSInput Bias-Current Matching UNITSMIN TYP MAXSYMBOLPARAMETER OUT Output Resistance ROUT IOUT = 1.5mA 1 3 MΩ OUT Rise, Fall Time tR, tF VSENSE = 5mV to 150mV, ROUT = 2kΩ, COUT = 50pF, 10% to 90% 4 µs OUT Settling Time to 1% of Final Value ts VSENSE = 5mV to 150mV, ROUT = 2kΩ, COUT = 50pF 15 µs Maximum Output Current IOUT 1.5 mA MAX472C MAX472E MAX472C MAX472E VCC = 10V, VSENSE = 0V 3 No-Load OUT Error MAX472C MAX472E VSENSE = 100mV, VCC = 10V (Note 3) IRG/IOUTOUT Current Accuracy MAX472C % ±2 MAX472E ±2.5 M A X 4 7 1 /M A X 4 7 2 Precision, High-Side Current-Sense Amplifiers 4 _______________________________________________________________________________________ __________________________________________Typical Operating Characteristics (Typical Operating Circuit (MAX471) or circuit of Figure 4, RG1 = RG2 = 200Ω, ROUT = 2kΩ (MAX472), TA = +25°C, unless otherwise noted.) 65 35 SUPPLY CURRENT vs. SUPPLY VOLTAGE 40 M AX 14 71 -0 1 VRS+ (V) SU PP LY C UR RE NT (µ A) 21 2415 189 123 6 27 30 33 36 45 50 55 60 TA = +85°C TA = +25°C TA = -40°C 2.5 0 0.5 2.0 M AX 14 71 -0 2 I S HD N (µ A) 1.5 1.0 SHUTDOWN CURRENT vs. SUPPLY VOLTAGE VRS+(V) 21 2415 189 123 6 27 30 33 36 TA = +85°C TA = -40°C TA = +25°C 4 -2 SIGN THRESHOLD vs. SUPPLY VOLTAGE -1 M AX 14 71 -0 3 SI GN T HR ES HO LD (m A) 21 2415 189 123 6 27 30 33 36 0 1 2 3 TA = +85°C TA = +25°C TA = -40°C VRS+ (V) 0.6 M AX 14 71 -0 4 OF FS ET C UR RE NT (µ A) MAX471 NO-LOAD OFFSET CURRENT vs. SUPPLY VOLTAGE VRS+ (V) 21 2415 189 123 6 27 30 33 36 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 VS+ = VS- TA = -40°C TA = +85°C TA = +25°C 28 -40 80 TEMPERATURE (°C) RE SI ST AN CE (m Ω ) 20 30 -20 0 6040 M AX 14 71 -0 7 MAX471 RS+ TO RS- RESISTANCE vs. TEMPERATURE 32 34 36 38 40 -12 0.01 0.10 MAX471 ERROR vs. LOAD CURRENT M AX 47 1- 05 ILOAD (A) ER RO R (% ) 1 10 -15 -6 -9 -3 0 3 6 9 12 15 ILOAD FROM RS+ TO RS- ILOAD FROM RS- TO RS+ 40 0.01 10 1000 MAX471 POWER-SUPPLY REJECTION RATIO vs. FREQUENCY M AX 47 1- 06 POWER-SUPPLY FREQUENCY (kHz) PS RR (% ) 1 100 35 30 25 20 15 10 5 0 0.10 V = 0mV TO 50mV V = 0V TO 1V V = 0V TO 0.5V ILOAD = 1A 5V RS+ OUT GND RS– A 1µF 5ΩV 3.0 0 MAX472 NO-LOAD OUTPUT ERROR vs. SUPPLY VOLTAGE 0.5 M AX 14 71 -0 8 VCC (V) I O UT (µ A) 21 2415 189 123 6 27 30 33 36 1.0 1.5 2.0 2.5 TA = +85°C TA = -40°C TA = +25°C RG1 = RG2 = 0Ω 0.70 M AX 14 71 -0 9 ER RO R (% ) MAX472 ERROR vs. SUPPLY VOLTAGE VCC (V) 21 2415 189 123 6 27 30 33 36 VRG1-VRG2 = 60mV, RG1 = RG2 = 200Ω 0.80 0.90 1.00 1.10 TA = -40°C TA = +25°C TA = +85°C M A X 4 7 1 /M A X 4 7 2 Precision, High-Side Current-Sense Amplifiers _______________________________________________________________________________________ 5 25 -25 0.1 10 1000 MAX472 ERROR vs. SENSE VOLTAGE M AX 47 1- 10 VSENSE (mV) ER RO R (% ) 15 5 0 -5 -15 1 100 VRG1-VRG2 VRG2-VRG1 1mA 10mA 100mA 1A 0.1 0 0.2 0.3 0.4 0.5 MAX471 NOISE vs. LOAD CURRENT ISENSE I O UT N OI SE (µ A R M S) M AX 47 1- 15 ____________________________Typical Operating Characteristics (continued) (Typical Operating Circuit (MAX471) or circuit of Figure 4, RG1 = RG2 = 200Ω, ROUT = 2kΩ (MAX472), TA = +25°C, unless otherwise noted.) 100µs/div VCC = 10V, ROUT = 2kΩ 1%, SIGN PULL-UP = 50kΩ 1% LOAD CURRENT 50mA/div VOUT 50mV/div MAX471 0mA to 100mA TRANSIENT RESPONSE 0A 10µs/div ILOAD = 1A, ROUT = 2kΩ 1% VOUT 500mV/div MAX471 START-UP DELAY VSHDN 5V/div 10µs/div ROUT = 2kΩ 1% ILOAD 1A/div MAX471 0A TO 3A TRANSIENT RESPONSE VOUT 10mV/div 100µs/div VCC = 10V, ROUT = 2kΩ 1%, SIGN PULL-UP = 50kΩ 1% LOAD CURRENT 100mA/div 50mA/div50mA/div VOUT 50mV/div MAX471 -100mA to +100mA TRANSIENT RESPONSE SIGN 50mV/div 0A M A X 4 7 1 /M A X 4 7 2 _______________Detailed Description The MAX471 and MAX472 current-sense amplifier’s unique topology allows a simple design to accurately monitor current flow. The MAX471/MAX472 contain two amplifiers operating as shown in Figures 1 and 2. The battery/load current flows from RS+ to RS- (or vice versa) through RSENSE. Current flows through either RG1 and Q1 or RG2 and Q2, depending on the sense- resistor current direction. Internal circuitry, not shown in Figures 1 and 2, prevents Q1 and Q2 from turning on at the same time. The MAX472 is identical to the MAX471, except that RSENSE and gain-setting resistors RG1 and RG2 are external (Figure 2). To analyze the circuit of Figure 1, assume that current flows from RS+ to RS- and that OUT is connected to GND through a resistor. In this case, amplifier A1 is active and output current IOUT flows from the emitter of Q1. Since no current flows through RG2 (Q2 is off), the negative input of A1 is equal to VSOURCE - (ILOAD x RSENSE). The open-loop gain of A1 forces its positive input to essentially the same level as the negative input. Therefore, the drop across RG1 equals ILOAD x RSENSE. Then, since IOUT flows through Q1 and RG (ignoring the extremely low base currents), IOUT x RG1 = ILOAD x RSENSE, or: IOUT = (ILOAD x RSENSE) / RG1 Current Output The output voltage equation for the MAX471/MAX472 is given below. In the MAX471, the current-gain ratio has been preset to 500µA/A so that an output resistor (ROUT) of 2kΩ yields 1V/A for a full-scale value of +3V at ±3A. Other full-scale voltages can be set with differ- ent ROUT values, but the output voltage can be no greater than VRS+ - 1.5V for the MAX471 or VRG_ - 1.5V for the MAX472. VOUT = (RSENSE x ROUT x ILOAD) / RG where VOUT = the desired full-scale output voltage, ILOAD = the full-scale current being sensed, RSENSE = the current-sense resistor, ROUT = the voltage-setting resistor, and RG = the gain-setting resistor (RG = RG1 = RG2). The above equation can be modified to determine the ROUT required for a particular full-scale range: ROUT = (VOUT x RG) / (ILOAD x RSENSE) For the MAX471, this reduces to: ROUT = VOUT / (ILOAD x 500µA/A) OUT is a high-impedance current-source output that can be connected to other MAX471/MAX472 OUT pins Precision, High-Side Current-Sense Amplifiers 6 _______________________________________________________________________________________ ______________________________________________________________Pin Description Load side of the internal current-sense resistor. The “-” indicates direction of flow for SIGN output only. Connect pins 6 and 7 together at the package. RS-6, 7 Gain Resistor. Connect to load side of current-sense resistor through the gain resistor.RG2— Power input for MAX472. Connect to sense resistor (RSENSE) junction with RG1.VCC— Current output that is proportional to the magnitude of the sensed current flowing through RSENSE. A 2kΩ resistor from this pin to ground will result in a voltage equal to 1V/Amp of sensed current in the MAX471. OUT8 Gain Resistor. Connect to battery side of current-sense resistor through the gain resistor.RG1— Ground or Battery Negative TerminalGND4 An open-collector logic output. For the MAX471, a low level indicates current is flowing from RS- to RS+. For the MAX472, a low level indicates a negative VSENSE (see Figure 2). SIGN is high impedance when SHDN is high. Leave open if SIGN is not needed. SIGN5 No Connect—no internal connectionN.C.— Battery (or power) side of the internal current-sense resistor. The “+” indicates direction of flow for SIGN output only. Connect pins 2 and 3 together at the package. RS+2, 3 Shutdown. Connect to ground for normal operation. When high, supply current is less than 5µA. SHDN1 FUNCTION MAX471 NAME — 6 7 8 3 4 5 2 — PIN 1 MAX472 M A X 4 7 1 /M A X 4 7 2 Precision, High-Side Current-Sense Amplifiers _______________________________________________________________________________________ 7 MAX471 Q2 8 5 OUT SIGN 6, 7 RS-2, 3RS+ Q1 COMP A2 RG2RG1 A1 RSENSE MAX472 Q2 8 5 OUT SIGN TO LOAD/CHARGERPOWER SOURCE OR BATTERY Q1 COMP A2 RG2RG1 A1 RSENSE 3 6 VSENSE VCC 7 Figure 1. MAX471 Functional Diagram Figure 2. MAX472 Functional Diagram M A X 4 7 1 /M A X 4 7 2 for current summing. A single scaling resistor is required when summing OUT currents from multiple devices (Figure 3). Current can be integrated by con- necting OUT to a capacitive load. SIGN Output The current at OUT indicates magnitude. The SIGN out- put indicates the current’s direction. Operation of the SIGN comparator is straightforward. When Q1 (Figures 1 and 2) conducts, the output of A1 is high while A2’s output is zero. Under this condition, a high SIGN output indicates positive current flow (from RS+ to RS-). In bat- tery-operated systems, this is useful for determining whether the battery is charging or discharging. The SIGN output may not correctly indicate if the load cur- rent is such that IOUT is less than 3.5µA. The MAX471’s SIGN output accurately indicates the direction of cur- rent flow for load currents greater than 7mA. SIGN is an open-collector output (sinks current only), allowing easy interface with logic circuits powered from any voltage. Connect a 100kΩ pull-up resistor from SIGN to the logic supply. The convention chosen for the polarity of the SIGN output ensures that it draws no current when the battery is being discharged. If current direction is not needed, float the SIGN pin. Shutdown When SHDN is high, the MAX471/MAX472 are shut down and consume less than 18µA. In shutdown mode, SIGN is high impedance and OUT turns off. __________Applications Information MAX471 The MAX471 obtains its power from the RS- pin. This includes MAX471 current consumption in the total sys- tem current measured by the MAX471. The small drop across RSENSE does not affect the MAX471’s perfor- mance. Resistor Selection Since OUT delivers a current, an external voltage gain- setting resistor (ROUT to ground) is required at the OUT pin in order to get a voltage. RSENSE is internal to the MAX471. RG1 and RG2 are factory trimmed for an out- put current ratio (output current to load current) of 500µA/A. Since they are manufactured of the same material and in very close proximity on the chip, they provide a high degree of temperature stability. Choose ROUT for the desired full-scale output voltage up to RS- - 1.5V (see the Current Output section). Precision, High-Side Current-Sense Amplifiers 8 _______________________________________________________________________________________ MAX471 RS+ RS+ RS- RS- SIGN OUT GND TO LOAD/ CHARGER 3V TO 36V MAX471 RS+ RS+ RS- RS- SIGN OUT GND 1k 100k LOGIC SUPPLY VOUT 3V TO 36V RSENSE 1 2 3 4 8 7 6 5 MAX472 RG2 100k RG1 POWER SOURCE OR BATTERY TO LOAD/CHARGER RG1 N.C. SHDN SIGN OUT VCC GND RG2 ROUT LOGIC SUPPLY Figure 3. Paralleling MAX471s to Sense Higher Load Current Figure 4. MAX472 Standard Application Circuit Peak Sense Current The MAX471’s maximum sense current is 3ARMS. For power-up, fault conditions, or other infrequent events, larger peak currents are allowed, provided they are short—that is, within a safe operating region, as shown in Figure 5. MAX472 RSENSE, RG1, and RG2 are externally connected on the MAX472. VCC can be connected to either the load/charge or power-source/battery side of the sense resistor. Connect VCC to the load/charge side of RSENSE if you want to include the MAX472 current drain in the measured current. Suggested Component Values for Various Applications The general circuit of Figure 4 is useful in a wide variety of applications. It can be used for high-current applica- tions (greater than 3A), and also for those where the full- scale load current is less than the 3A of the MAX471. Table 1 shows suggested component values and indi- cates the resulting scale factors for various applications required to sense currents from 100mA to 10A. Higher or lower sense-current circuits can also be built. Select components and calculate circuit errors using the guidelines and formulas in the following section. RSENSE Choose RSENSE based on the following criteria: a) Voltage Loss: A high RSENSE value wi