Low-Cost, SOT23, Voltage-Output, High-Side Current-Sense Amplifier MAX4173T/F/H

Transcription

1 19-13; Rev 5; /11 Low-Cost, SOT23, Voltage-Output, General Description The MAX173 low-cost, precision, high-side currentsense amplifier is available in a tiny SOT23-6 package. It features a voltage output that eliminates the need for gain-setting resistors and it is ideal for today s notebook computers, cell phones, and other systems where current monitoring is critical. High-side current monitoring is especially useful in battery-powered systems, since it does not interfere with the ground path of the battery charger. The input common-mode range of to +28V is independent of the supply voltage and ensures that the current-sense feedback remains viable even when connected to a battery in deep discharge. The MAX173 s wide 1.7MHz bandwidth makes it suitable for use inside battery charger control loops. The combination of three gain versions and a userselectable external sense resistor sets the full-scale current reading. This feature offers a high level of integration, resulting in a simple and compact currentsense solution. The MAX173 operates from a single +3V to +28V supply, typically draws only 2µA of supply current over the extended operating temperature range (- C to +85 C), and is offered in the space-saving SOT23 package. Applications Notebook Computers Portable/Battery-Powered Systems Smart Battery Packs/Chargers Cell Phones Power-Management Systems General System/Board-Level Current Monitoring PA Bias Control Precision Current Sources Features Low-Cost, Compact Current-Sense Solution High Accuracy +2V to +28V Common-Mode Range, Functional Down to V, Independent of Supply Voltage Three Gain Versions Available +2V/V () +5V/V () +1V/V () ±.5% Full-Scale Accuracy ±3mV Input Offset Voltage () Wide 1.7MHz Bandwidth () 2µA Supply Current Available in Space-Saving SOT23 Package TO +28V VSENSE R SENSE +3V TO +28V RS+ RS-.1µF A/D CONVERTER Typical Operating Circuit /F/H I LOAD LOAD/ BATTERY /F/H Ordering Information PART EUT+T ESA+ GA (V/V) 2 2 TEMP RANGE - C to +85 C - C to +85 C P-PACKAGE 6 SOT23 8 SO SOT TOP MARK AABN EUT+T 5 - C to +85 C 6 SOT23 AABO ESA+ 5 - C to +85 C 8 SO EUT+T 1 - C to +85 C 6 SOT23 AABP ESA+ 1 - C to +85 C 8 SO +Denotes a lead(pb)-free/rohs-compliant package. T = Tape and reel. Pin Configurations appear at end of data sheet. Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at , or visit Maxim s website at

2 /F/H ABSOLUTE MAXIMUM RATGS, RS+, RS- to V to +3V to V to ( +.3V) Output Short-Circuit to or... Continuous Differential Input Voltage (V RS+ - V RS- )... ±.3V Current into Any Pin... ±2mA 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 Continuous Power Dissipation (T A = +7 C) 8-Pin SO (derate 5.88mW/ C above +7 C)... 71mW SOT23-6 (derate 8.7mW/ C above +7 C) mW Operating Temperature Range... - C to +85 C Storage Temperature Range C to +15 C Lead Temperature (soldering, 1s) C Soldering Temperature (reflow) C (V RS+ = to +28V, = +3V to +28V, V SENSE = V, T A = T M to T MAX, R LOAD = unless otherwise noted. Typical values are at T A = +25 C.) (Note 1) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS Operating Voltage Range Guaranteed by PSR test 3 28 V Common-Mode Input Range V CMR (Note 2) 28 V Common-Mode Rejection CMR V RS+ > +2.V 9 db Supply Current I CC V RS+ > +2.V, > 12V.2 1. ma Leakage Current I RS+, I RS- = V, V RS+ = 28V.3 3 µa Input Bias Current V RS+ > +2.V 5 I RS+ V RS+ +2.V V RS+ > +2.V 1 I RS- V RS+ +2.V -7 1 µa Full-Scale Sense Voltage V SENSE V SENSE = V RS+ - V RS- 15 mv Total Voltage Error (Note 3) Out High Voltage (Note 5) ( - V OH ) V SENSE = +1mV, = +12V, V RS+ = +12V ± V SENSE = +1mV, = +12V, V RS+ = +12V, T A = +25 C V SENSE = +1mV, = +28V, V RS+ = +28V V SENSE = +1mV, = +12V, V RS+ = +.1V -9 ±2 = +12V, V RS+ = +12V, V SENSE = +6.25mV (Note ) ±7.5, = +3.V, V RS+ = 28V, V SENSE = 25mV, = +7.5V, V RS+ = 28V, V SENSE = 25mV, = +15V, V RS+ = 28V, V SENSE = 25mV % V Low Voltage V OL = +5V, V RS+ =.89V, EUT, T A = +25 C V SENSE = mv T A = - C to +85 C mv 2

3 ELECTRICAL CHARACTERISTICS (continued) (V RS+ = to +28V, = +3V to +28V, V SENSE = V, T A = T M to T MAX, R LOAD = unless otherwise noted. Typical values are at T A = +25 C.) (Note 1) Bandwidth PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS BW V RS+ = +12V, = +12V, C LOAD = 5pF, V SENSE = +1mV, V SENSE = +1mV, V SENSE = +1mV V SENSE = +6.25mV (Note ) 2 Gain A V MHz V/V /F/H Gain Accuracy Input Offset Voltage (Note 6) Settling Time to 1% of Final Value A V +1mV to +15mV, /F V SENSE = T A = +25 C.5 ±2.5 = V RS+ = 12V T A = - C to +85 C. A V +1mV to +1mV, V SENSE = T A = +25 C.5 ±2.5 = V RS+ = 12V T A = - C to +85 C. V OS EUT, T A = +25 C.3 ±3 V RS+ = 12V T A = - C to +85 C ±5 = +12V, V RS+ = 12V, C LOAD = 5pF V SENSE = +6.25mV to +1mV V SENSE = +1mV to +6.25mV Output Resistance R 12 kω Power-Supply Rejection Power-Up Time to 1% of Final Value PSR, V SENSE = 8mV, V RS+ +2V 6 8 Note 1: All devices are 1% production tested at T A = +25 C. All temperature limits are guaranteed by design. Note 2: Guaranteed by Total Output Voltage Error Test. Note 3: Total Voltage Error is the sum of gain and offset voltage errors. Note : +6.25mV = 1/16 of +1mV full-scale voltage. Note 5: V SENSE such that output stage is in saturation. Note 6: V OS is extrapolated from the Gain Accuracy tests. Note 7: The device does not experience phase reversal when overdriven. 8, V SENSE = 32mV, V RS+ +2V 6 91, V SENSE = 16mV, V RS+ +2V 6 95 V SENSE = +1mV, C LOAD = 5pF 1 µs Saturation Recovery Time = +12V, V RS+ = 12V (Note 7) 1 µs % mv ns db 3

4 /F/H Typical Operating Characteristics ( = +12V, V RS+ = +12V, V SENSE = +1mV, T A = +25 C, unless otherwise noted.) SUPPLY CURRENT (µa) SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX173 TOC1 SUPPLY CURRENT (µa) SUPPLY CURRENT vs. TEMPERATURE MAX173 toc2 SUPPLY CURRENT (ma) SUPPLY CURRENT vs. RS+ VOLTAGE MAX173 toc SUPPLY VOLTAGE (V) TEMPERATURE ( C) V RS+ (V) TOTAL PUT ERROR (%) TOTAL PUT ERROR vs. SUPPLY VOLTAGE V SENSE = 1mV SUPPLY VOLTAGE (V) MAX173 toc TOTAL PUT ERROR (%) TOTAL PUT ERROR vs. SUPPLY VOLTAGE V SENSE = 6.25mV SUPPLY VOLTAGE (V) MAX173 toc5 TOTAL PUT ERROR (%) TOTAL PUT ERROR vs. FULL-SCALE SENSE VOLTAGE = 28V V SENSE (mv) MAX173 toc6 PSR (db) POWER-SUPPLY REJECTION vs. FREQUENCY MAX173 toc7 TOTAL PUT ERROR (%) TOTAL PUT ERROR vs. COMMON-MODE VOLTAGE MAX173 toc8 GA ACCURACY (%) GA ACCURACY vs. TEMPERATURE MAX173 toc k 1k 1k 1M 1M FREQUENCY (Hz) COMMON-MODE VOLTAGE (V) TEMPERATURE ( C)

5 ( = +12V, V RS+ = +12V, V SENSE = +1mV, T A = +25 C, unless otherwise noted.) TOTAL PUT ERROR (%) TOTAL PUT ERROR vs. TEMPERATURE Typical Operating Characteristics (continued) MAX173 toc1 (5mV/div) (5mV/div) LARGE-SIGNAL TRANSIENT RESPONSE (V SENSE = 6mV to 1mV) MAX173 toc11 1mV 6mV 2V /F/H V TEMPERATURE ( C) LARGE-SIGNAL TRANSIENT RESPONSE (V SENSE = 6mV to 1mV) LARGE-SIGNAL TRANSIENT RESPONSE (V SENSE = 6mV to 1mV) MAX173 toc12 1mV MAX173 toc13 1mV (5mV/div) 6mV (5mV/div) 6mV 1V (2V/div) 5V.3V (3V/div).6V SMALL-SIGNAL TRANSIENT RESPONSE (V SENSE = 95mV TO 1mV) SMALL-SIGNAL TRANSIENT RESPONSE (V SENSE = 95mV TO 1mV) (5mV/div) MAX173 toc1 1mV 95mV (5mV/div) MAX173 toc16 1mV 95mV (5mV/div) 2.V 1.9V (1mV/div) 5V.75V 5

6 /F/H ( = +12V, V RS+ = +12V, V SENSE = +1mV, T A = +25 C, unless otherwise noted.) (5mV/div) (2mV/div) SMALL-SIGNAL TRANSIENT RESPONSE (V SENSE = 95mV to 1mV) MAX173 toc15 Typical Operating Characteristics (continued) 1mV 95mV 1V 9.5V (2V/div) (1V/div) START-UP DELAY ( = to V) (V SENSE = 1mV) MAX173 toc17 V V 2V V 5µs/div Pin Description SOT23 P SO NAME FUNCTION 1, Ground 1 Supply Voltage Input. Bypass to with a.1µf capacitor. 8 RS+ Power-Side Connection to the External Sense Resistor 6 RS- Load-Side Connection for the External Sense Resistor 6 Voltage Output. V is proportional to V SENSE ( V RS+ - V RS- ). Output impedance is approximately 12kΩ. 2, 5, 7 N.C. No Connection. Not internally connected. 6

7 Detailed Description The MAX173 high-side current-sense amplifier features a to +28V input common-mode range that is independent of supply voltage. This feature allows the monitoring of current out of a battery in deep discharge and also enables high-side current sensing at voltages greater than the supply voltage ( ). The MAX173 operates as follows: Current from the source flows through R SENSE to the load (Figure 1). Since the internal-sense amplifier s inverting input has high impedance, negligible current flows through RG2 (neglecting the input bias current). Therefore, the sense amplifier s inverting-input voltage equals V SOURCE - (I LOAD )(R SENSE ). The amplifier s open-loop gain forces its noninverting input to the same voltage as the inverting input. Therefore, the drop across RG1 equals (ILOAD)(RSENSE). Since IRG1 flows through RG1, IRG1 = (I LOAD )(R SENSE ) / RG1. The internal current mirror multiplies I RG1 by a current gain factor, β, to give I RGD = β I RG1. Solving I RGD = β (I LOAD )(R SENSE ) / RG1. Assuming infinite output impedance, V = (IRGD) (RGD). Substituting in for IRGD and rearranging, V = β (RGD / RG1)(R SENSE I LOAD ). The parts gain equals β RGD / RG1. Therefore, V = (GA) (R SENSE ) (I LOAD ), where GA = 2 for, GA = 5 for, and GA = 1 for. V SOURCE TO +28V +3V TO +28V I RG1 RS+ R G1 CURRENT MIRROR R SENSE RGD = 12k Figure 1. Functional Diagram A1 MAX173 I RGD I LOAD RS- R G2 TO LOAD BATTERY V Set the full-scale output range by selecting R SENSE and the appropriate gain version of the MAX173. Applications Information Recommended Component Values The MAX173 senses a wide variety of currents with different sense resistor values. Table 1 lists common resistor values for typical operation of the MAX173. Choosing RSENSE To measure lower currents more accurately, use a high value for R SENSE. The high value develops a higher sense voltage that reduces offset voltage errors of the internal op amp. In applications monitoring very high currents, R SENSE must be able to dissipate the I 2 R losses. If the resistor s rated power dissipation is exceeded, its value may drift or it may fail altogether, causing a differential voltage across the terminals in excess of the absolute maximum ratings. If ISENSE has a large high-frequency component, minimize the inductance of RSENSE. Wire-wound resistors have the highest inductance, metal-film resistors are somewhat better, and low-inductance metal-film resistors are best suited for these applications. Using a PCB Trace as RSENSE If the cost of R SENSE is an issue and accuracy is not critical, use the alternative solution shown in Figure 2. This solution uses copper PC board traces to create a sense resistor. The resistivity of a.1-inch-wide trace of 2-ounce copper is approximately 3mΩ/ft. The resistance-temperature coefficient of copper is fairly high (approximately.%/ C), so systems that experience a wide temperature variance must compensate for this effect. In addition, do not exceed the maximum power dissipation of the copper trace. For example, the (with a maximum load current of 1A and an R SENSE of 5mΩ) creates a full-scale VSENSE of 5mV that yields a maximum V of 1V. RSENSE in this case requires about 2 inches of.1 inchwide copper trace. Output Impedance The output of the MAX173 is a current source driving a 12kΩ resistance. Resistive loading added to reduces the output gain of the MAX173. To minimize output errors for most applications, connect to a high-impedance input stage. When output buffering is required, choose an op amp with a common-mode input range and an output voltage swing that includes ground when operating with a single supply. The op /F/H 7

8 /F/H Table 1. Recommended Component Values FULL-SCALE LOAD CURRENT I LOAD (A).1 CURRENT-SENSE RESISTOR R SENSE (mω) GA FULL-SCALE PUT VOLTAGE (FULL-SCALE V SENSE = 1mV) V (V) PUT.3 in. COPPER + R SENSE.1 in. COPPER V SENSE _ LOAD/BATTERY.3 in. COPPER V LOW-COST SWITCHG REGULATOR TO +28V V SENSE R SENSE I LOAD RS+ +3V TO +28V.1µF +3V TO +28V.1µF RS+ RS- RS- MAX173 LOAD/ BATTERY Figure 2. MAX173 Connections Showing Use of PC Board Figure 3. Current Source amp s supply voltage range should be at least as high as any voltage the system may encounter. The percent error introduced by output loading is determined with the following formula: R % ERROR = 1 LOAD 12k Ω + RLOAD 1 Current Source Circuit Figure 3 shows a block diagram using the MAX173 with a switching regulator to make a current source. where RLOAD is the external load applied to. 8

9 TOP VIEW MAX RS- 3 RS+ SOT23 N.C Pin Configurations 8 RS+ MAX173 7 N.C. 6 5 RS- N.C. SO /F/H Package Information For the latest package outline information and land patterns (footprints), go to Note that a +, #, or - in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE LE NO. LAND PATTERN NO. 8 SO S SOT23 U

10 /F/H REVISION NUMBER REVISION DATE 6/1 DESCRIPTION Clarified V to 2V is not a high-accuracy range for the device, added lead-free options and soldering temperature Revision History PAGES CHANGED 5 /11 Updated V RS+ conditions to synchronize with tested material 2, 3 1, 2 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. 1 Maxim Integrated Products, 12 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.