19-1184; Rev 0; 12/96 Low-Cost, Precision, High-Side Current-Sense Amplifier The MAX4172 is a low-cost, precision, high-side currentsense amplifier for portable PCs, telephones, and other systems where battery/DC power-line monitoring is critical. High-side power-line monitoring is especially useful in battery-powered systems, since it does not interfere with the battery charger’s ground path. Wide bandwidth and ground-sensing capability make the MAX4172 suitable for closed-loop battery-charger and generalpurpose current-source applications. The 0V to 32V input common-mode range is independent of the supply voltage, which ensures that current-sense feedback remains viable, even when connected to a battery in deep discharge. To provide a high level of flexibility, the MAX4172 functions with an external sense resistor to set the range of load current to be monitored. It has a current output that can be converted to a ground-referred voltage with a single resistor, accommodating a wide range of battery voltages and currents. An open-collector power-good output (PG) indicates when the supply voltage reaches an adequate level to guarantee proper operation of the current-sense amplifier. The MAX4172 operates with a 3.0V to 32V supply voltage, and is available in a space-saving, 8-pin µMAX or SO package. ________________________Applications Portable PCs: Notebooks/Subnotebooks/Palmtops Battery-Powered/Portable Equipment Closed-Loop Battery Chargers/Current Sources Smart-Battery Packs Portable/Cellular Phones Portable Test/Measurement Systems Energy Management Systems ____________________________Features ♦ Low-Cost, High-Side Current-Sense Amplifier ♦ ±0.5% Typical Full-Scale Accuracy Over Temperature ♦ 3V to 32V Supply Operation ♦ 0V to 32V Input Range—Independent of Supply Voltage ♦ 800kHz Bandwidth [VSENSE = 100mV (1C)] 200kHz Bandwidth [VSENSE = 6.25mV (C/16)] ♦ Available in Space-Saving µMAX and SO Packages ______________Ordering Information PART MAX4172ESA MAX4172EUA TEMP. RANGE PIN-PACKAGE -40°C to +85°C -40°C to +85°C 8 SO 8 µMAX* *Contact factory for availability. __________Typical Operating Circuit UNREGULATED DC SUPPLY 3V TO 32V RSENSE 50mΩ LOW-COST SWITCHING REGULATOR 0V TO 32V VSENSE RS+ ANALOG OR LOGIC SUPPLY RS- V+ 100k PG __________________Pin Configuration POWER GOOD MAX4172 TOP VIEW OUT 8 V+ 7 PG N.C. 3 6 OUT N.C. 4 5 GND RS+ 1 RS- 2 MAX4172 µMAX/SO 2A LOAD/ BATTERY IOUT = VSENSE / 100Ω GND FEEDBACK LOOP VOUT = 500mV/A ROUT 1k LOW-COST BATTERY CHARGER/CURRENT SOURCE ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 MAX4172 _______________General Description MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier ABSOLUTE MAXIMUM RATINGS V+, RS+, RS-, PG ...................................................-0.3V to +36V OUT ..............................................................-0.3V to (V+ + 0.3V) Differential Input Voltage, VRS+ - VRS- ............................±700mV Current into Any Pin..........................................................±50mA Continuous Power Dissipation (TA = +70°C) SO (derate 5.88mW/°C above +70°C) ..........................471mW µMAX (derate 4.10mW/°C above +70°C) .....................330mW Operating Temperature Range MAX4172E_A ....................................................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10sec) .............................+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 (V+ = +3V to +32V; RS+, RS- = 0V to 32V; TA = TMIN to TMAX; unless otherwise noted. Typical values are at V+ = +12V, RS+ = 12V, TA = +25°C.) PARAMETER Operating Voltage Range Input Voltage Range Supply Current Input Offset Voltage SYMBOL MAX UNITS V+ 3 32 V VRS- 0 32 V mA IV+ VOS CONDITIONS MIN IOUT = 0mA V+ = 12V, VRS+ = 12V 0.8 1.6 MAX4172ESA ±0.1 ±0.75 MAX4172EUA ±0.2 ±1.6 VRS+ ≤ 2.0V Positive Input Bias Current IRS+ Negative Input Bias Current IRS- 0 VRS+ ≤ 2.0V, IOUT = 0mA -325 VRS+ > 2.0V 0 VRS+ ≤ 2.0V -650 150 VSENSE = 100mV, V+ = 12V, VRS+ = 12V Output Current Error OUT Common-Mode Rejection Ratio 2 27 ∆IOUT / ∆V+ 3V ≤ V+ ≤ 32V, VRS+ > 2.0V ∆IOUT / ∆VRS+ 2.0V < VRS+ < 32V 42.5 42.5 50 85 85 175 VSENSE = 6.25mV, V+ = 12V, MAX4172ESA VRS+ = 12V (Note 1) MAX4172EUA Low-Level Current Error mV 4 VRS+ > 2.0V, IOUT = 0mA Maximum VSENSE Voltage OUT Power-Supply Rejection Ratio TYP µA µA mV ±8.0 ±15 MAX4172ESA, TA = -40°C to 0°C ±20 MAX4172EUA, TA = -40°C to 0°C ±50 MAX4172ESA, TA = 0°C to +85°C ±10 MAX4172EUA, 0°Cto to+85°C +85°C TTAA==0°C ±15 µA µA 0.2 µA/V 0.03 µA/V _______________________________________________________________________________________ Low-Cost, Precision, High-Side Current-Sense Amplifier MAX4172 ELECTRICAL CHARACTERISTICS (continued) (V+ = +3V to +32V; RS+, RS- = 0V to 32V; TA = TMIN to TMAX; unless otherwise noted. Typical values are at V+ = +12V, RS+ = 12V, TA = +25°C.) PARAMETER SYMBOL Maximum Output Voltage (OUT) CONDITIONS MIN TYP IOUT ≤ 1.5mA Bandwidth Maximum Output Current IOUT Transconductance Gm PG Output Low Voltage VOL UNITS V+ - 1.2 VSENSE = 100mV 800 VSENSE = 6.25mV (Note 1) 200 Gm = IOUT / (VRS+ - VRS-), VSENSE = 100mV, VRS+ > 2.0V V+ Threshold for PG Output Low (Note 2) MAX kHz 1.5 1.75 TA = 0°C to +85°C 9.8 10 10.2 TA = -40°C to 0°C 9.7 10 10.3 V+ rising 2.77 V+ falling 2.67 V mA mA/V V ISINK = 1.2mA, V+ = 2.9V, TA = +25°C 0.4 V 1 µA 1 µA Leakage Current into PG V+ = 2.5V, TA = +25°C Power-Off Input Leakage Current (RS+, RS-) V+ = 0V, VRS+ = VRS- = 32V 0.1 OUT Rise Time VSENSE = 0mV to 100mV, 10% to 90% 400 ns OUT Fall Time VSENSE = 100mV to 0mV, 90% to 10% 800 ns OUT Settling Time to 1% VSENSE = 5mV to 100mV OUT Output Resistance VSENSE = 150mV Rising 1.3 Falling 6 µs 20 MΩ Note 1: 6.25mV = 1/16 of typical full-scale sense voltage (C/16). Note 2: Valid operation of the MAX4172 is guaranteed by design when PG is low. __________________________________________Typical Operating Characteristics (V+ = +12V, VRS+ = 12V, ROUT = 1kΩ, TA = +25°C, unless otherwise noted.) OUTPUT ERROR vs. SUPPLY VOLTAGE 0.4 900 1.5 750 TA = -40°C 0.1 0 TA = +85°C -0.1 650 -0.2 600 -0.3 550 TA = +25°C 10 20 V+ (V) 30 40 -0.5 -1.0 TA = +25°C -2.0 -2.5 TA = -40°C -0.5 0 TA = -40°C 0 -1.5 -0.4 IOUT = 0mA 500 ERROR (%) 800 700 0.5 0.2 TA = +25°C VSENSE = 6.25mV 1.0 0.3 850 ERROR (%) SUPPLY CURRENT (µA) VSENSE = 100mV MAX4172-02 TA = +85°C 950 0.5 MAX4172-01 1000 C/16 LOAD OUTPUT ERROR vs. SUPPLY VOLTAGE MAX4172-03 SUPPLY CURRENT vs. SUPPLY VOLTAGE 0 10 20 V+ (V) TA = +85°C -3.0 30 40 0 10 20 30 40 V+ (V) _______________________________________________________________________________________ 3 ____________________________Typical Operating Characteristics (continued) (V+ = +12V, VRS+ = 12V, ROUT = 1kΩ, TA = +25°C, unless otherwise noted.) POWER-SUPPLY REJECTION RATIO vs. FREQUENCY ERROR vs. SENSE VOLTAGE 35 MAX4172-05 35 MAX4172-04 40 VSENSE = 100mV 30 30 25 ERROR (%) ERROR (%) 25 20 15 20 0.5Vp-p 15 10 1.0Vp-p 10 5 5mVp-p 5 0 -5 0 0.1m 1m 10m 100m 1 0.01 0.1 1 10 100 POWER-SUPPLY FREQUENCY (kHz) OUTPUT ERROR vs. COMMON-MODE VOLTAGE V+ THRESHOLD FOR PG OUTPUT LOW vs. TEMPERATURE V+ TRIP THRESHOLD (V) 2.90 0.35 0.15 TA = -40°C -0.05 TA = +25°C -0.25 MAX4172-07 2.95 MAX4172-06 VSENSE = 100mV 0.55 TA = +85°C 2.85 2.80 V+ RISING VOLTAGE 2.75 2.70 2.65 2.60 V+ FALLING VOLTAGE 2.55 -0.45 2.50 -0.65 2.45 0 6 12 18 24 30 40 -40 VRS- (V) -15 10 35 MAX4172-09 VSENSE 50mV/div GND GND VOUT 50mV/div VOUT 500mV/div GND GND 10µs/div 85 0mV to 100mV VSENSE TRANSIENT RESPONSE MAX4172-08 VSENSE 5mV/div 60 TEMPERATURE (°C) 0mV to 10mV VSENSE TRANSIENT RESPONSE 4 1000 VSENSE (V) 0.75 ERROR (%) MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier 10µs/div _______________________________________________________________________________________ Low-Cost, Precision, High-Side Current-Sense Amplifier V+ to PG POWER-UP DELAY START-UP DELAY MAX4172-10 MAX4172-11 PG 2V/div VOUT 500mV/div GND GND V+ 2V/div V+ 2V/div GND GND 10µs/div 100kΩ PULL-UP RESISTOR FROM PG TO +4V 5µs/div VSENSE = 100mV ______________________________________________________________Pin Description PIN NAME FUNCTION 1 RS+ Power connection to the external sense resistor. The “+” indicates the direction of current flow. 2 RS- Load-side connection for the external sense resistor. The “-” indicates the direction of current flow. 3, 4 N.C. No Connect. No internal connection. Leave open or connect to GND. 5 GND Ground 6 OUT Current Output. OUT is proportional to the magnitude of the sense voltage (VRS+ - VRS-). A 1kΩ resistor from OUT to ground will result in a voltage equal to 10V/V of sense voltage. 7 PG Power Good Open-Collector Logic Output. A low level indicates that V+ is sufficient to power the MAX4172, and adequate time has passed for power-on transients to settle out. 8 V+ Supply Voltage Input for the MAX4172 _______________Detailed Description The MAX4172 is a unidirectional, high-side current-sense amplifier with an input common-mode range that is independent of supply voltage. This feature not only allows the monitoring of current flow into a battery in deep discharge, but also enables high-side current sensing at voltages far in excess of the supply voltage (V+). The MAX4172 current-sense amplifier’s unique topology simplifies current monitoring and control. The MAX4172’s amplifier operates as shown in Figure 1. The battery/load current flows through the external sense resistor (RSENSE), from the RS+ node to the RS- node. Current flows through RG1 and Q1, and into the current mirror, where it is multiplied by a factor of 50 before appearing at OUT. 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. Since A1’s inverting input is high impedance, no current flows though RG2 (neglecting the input bias current), so A1’s negative input is equal to VSOURCE - (ILOAD x RSENSE). A1’s open-loop gain forces its positive input to essentially the same voltage level as the negative input. Therefore, the drop across RG1 equals ILOAD x RSENSE. Then, since IRG1 _______________________________________________________________________________________ 5 MAX4172 ____________________________Typical Operating Characteristics (continued) (V+ = +12V, VRS+ = 12V, ROUT = 1kΩ, TA = +25°C, unless otherwise noted.) MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier flows through RG1, IRG1 x RG1 = ILOAD x RSENSE. The internal current mirror multiplies IRG1 by a factor of 50 to give IOUT = 50 x IRG1. Substituting IOUT / 50 for IRG1, (IOUT / 50) x RG1 = ILOAD x RSENSE, or: IOUT = 50 x ILOAD x (RSENSE / RG1) The internal current gain of 50 and the factory-trimmed resistor R G1 combine to result in the MAX4172 transconductance (G m ) of 10mA/V. G m is defined as being equal to IOUT / (VRS+ - VRS-). Since (VRS+ - VRS-) = ILOAD x RSENSE, the output current (IOUT) can be calculated with the following formula: IOUT = Gm x (VRS+ - VRS-) = TO LOAD/ BATTERY INPUT RS+ VSENSE RSRG2 RG1 IRG1 A1 (10mA/V) x (ILOAD x RSENSE) MAX4172 Q1 Current Output The output voltage equation for the MAX4172 is given below: VOUT = (Gm) x (RSENSE x ROUT x ILOAD) 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 G m = MAX4172 transconductance (10mA/V). The full-scale output voltage range can be set by changing the ROUT resistor value, but the output voltage must be no greater than V+ - 1.2V. The above equation can be modified to determine the R OUT required for a particular full-scale range: ROUT = (VOUT ) / (ILOAD x RSENSE x Gm) ILOAD RSENSE V+ 1:50 CURRENT MIRROR IOUT = 50 IRG1 OUT V+ PG VTH GND Figure 1. Functional Diagram OUT is a high-impedance current source that can be integrated by connecting it to a capacitive load. PG Output __________Applications Information The PG output is an open-collector logic output that indicates the status of the MAX4172’s V+ power supply. A logic low on the PG output indicates that V+ is sufficient to power the MAX4172. This level is temperature dependent (see Typical Operating Characteristics graphs), and is typically 2.7V at room temperature. The internal PG comparator has a 100mV (typical) hysteresis to prevent possible oscillations caused by repeated toggling of the PG output, making the device ideal for power-management systems lacking soft-start capability. An internal delay (15µs typical) in the PG comparator allows adequate time for power-on transients to settle out. The PG status indicator greatly simplifies the design of closed-loop systems by ensuring that the components in the control loop have sufficient voltage to operate correctly. Suggested Component Values for Various Applications 6 The Typical Operating Circuit is useful in a wide variety of applications. Table 1 shows suggested component values and indicates the resulting scale factors for various applications required to sense currents from 100mA to 10A. Adjust the RSENSE value to monitor higher or lower current levels. Select RSENSE using the guidelines and formulas in the following section. Sense Resistor, RSENSE Choose RSENSE based on the following criteria: • Voltage Loss: A high R SENSE value causes the power-source voltage to degrade through IR loss. For minimal voltage loss, use the lowest R SENSE value. _______________________________________________________________________________________ Low-Cost, Precision, High-Side Current-Sense Amplifier MAX4172 Table 1. Suggested Component Values FULL-SCALE LOAD CURRENT (A) CURRENT-SENSE RESISTOR, RSENSE (mΩ) OUTPUT RESISTOR, ROUT (kΩ) FULL-SCALE OUTPUT VOLTAGE, VOUT (V) SCALE FACTOR, VOUT/ISENSE (V/A) 0.1 1000 3.48 3.48 34.8 1 100 3.48 3.48 3.48 5 20 3.48 3.48 0.696 10 10 3.48 3.48 0.348 • Accuracy: A high RSENSE value allows lower currents to be measured more accurately. This is because offsets become less significant when the sense voltage is larger. For best performance, select RSENSE to provide approximately 100mV of sense voltage for the full-scale current in each application. • Efficiency and Power Dissipation: At high current levels, the I2R losses in RSENSE can be significant. Take this into consideration when choosing the resistor value and its power dissipation (wattage) rating. Also, the sense resistor’s value might drift if it is allowed to heat up excessively. • Inductance: Keep inductance low if ISENSE has a large high-frequency component. Wire-wound resistors have the highest inductance, while metal film is somewhat better. Low-inductance metal-film resistors are also available. Instead of being spiral wrapped around a core, as in metal-film or wirewound resistors, they are a straight band of metal and are available in values under 1Ω. • Cost: If the cost of RSENSE is an issue, you might want to use an alternative solution, as shown in Figure 2. This solution uses the PC board traces to create a sense resistor. Because of the inaccuracies of the copper resistor, the full-scale current value must be adjusted with a potentiometer. Also, copper’s resistance temperature coefficient is fairly high (approximately 0.4%/°C). In Figure 2, assume that the load current to be measured is 10A, and that you have determined a 0.3-inchwide, 2-ounce copper to be appropriate. The resistivity of 0.1-inch-wide, 2-ounce (70µm thickness) copper is 30mΩ/ft. For 10A, you might want RSENSE = 5mΩ for a 50mV drop at full scale. This resistor requires about 2 inches of 0.1-inch-wide copper trace. INPUT LOAD/BATTERY RSENSE O.3 in. COPPER O.3 in. COPPER O.1 in. COPPER VSENSE 1 2 RS+ MAX4172 V+ 8 VSUPPLY 3V TO 32V RSOUT GND 6 5 ROUT Figure 2. MAX4172 Connections Showing Use of PC Board Current-Sense Adjustment (Resistor Range, Output Adjust) Choose ROUT after selecting RSENSE. Choose ROUT to obtain the full-scale voltage you require, given the fullscale IOUT determined by RSENSE. OUT’s high impedance permits using R OUT values up to 200kΩ with minimal error. OUT’s load impedance (e.g., the input of an op amp or ADC) must be much greater than ROUT (e.g., 100 x ROUT) to avoid degrading measurement accuracy. High-Current Measurement The MAX4172 can achieve high-current measurements by using low-value sense resistors, which can be paralleled to further increase the current-sense limit. As an alternative, PC board traces can be adjusted over a wide range. _______________________________________________________________________________________ 7 MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier Power-Supply Bypassing and Grounding In most applications, grounding the MAX4172 requires no special precautions. However, in high-current systems, large voltage drops can develop across the ground plane, which can add to or subtract from VOUT. Use a single-point star ground for the highest currentmeasurement accuracy. The MAX4172 requires no special bypassing and responds quickly to transient changes in line current. If the noise at OUT caused by these transients is a problem, you can place a 1µF capacitor at the OUT pin to ground. You can also place a large capacitor at the RS terminal (or load side of the MAX4172) to decouple the load, reducing the current transients. These capacitors are not required for MAX4172 operation or stability. The RS+ and RS- inputs can be filtered by placing a capacitor (e.g., 1µF) between them to average the sensed current. ___________________Chip Information TRANSISTOR COUNT: 177 SUBSTRATE CONNECTED TO GND ________________________________________________________Package Information DIM C α A 0.101mm 0.004 in e B A1 L A A1 B C D E e H L α INCHES MAX MIN 0.044 0.036 0.008 0.004 0.014 0.010 0.007 0.005 0.120 0.116 0.120 0.116 0.0256 0.198 0.188 0.026 0.016 6° 0° MILLIMETERS MIN MAX 0.91 1.11 0.10 0.20 0.25 0.36 0.13 0.18 2.95 3.05 2.95 3.05 0.65 4.78 5.03 0.41 0.66 0° 6° 21-0036D E H 8-PIN µMAX MICROMAX SMALL-OUTLINE PACKAGE D 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. 8 ___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.