49-1184; Rev 0; 12/96 General Description The MAX4172 is a low-cost, precision, high-side current- sense amplifier for portable PCs, telephones, and other systems where battery/DC power-line monitoring is criti- cal, High-side power-line monitoring is especially useful in battery-powered systems, since it does not interfere with the battery chargers ground path. Wide bandwidth and ground-sensing capability make the MAX4172 suitable for closed-loop baitery-charger and general- purpose current-source applications. The OV to 32V input common-mode range is independent of the supply volt- age, which ensures that current-sense feedback remains viable, even when connected to a battery in deep dis- MA AXLAA Low-Cost, Precision, High-Side Current-Sense Amplifier * Low-Cost, High-Side Current-Sense Amplifier @ +0.5% Typical Full-Scale Accuracy Over Temperature @ 3V to 32V Supply Operation @ OV to 32V Input Rangeindependent of Supply Voltage 4 800kHz Bandwidth [VsensE = 100mvV (1C)] 200kHz Bandwidth [Vsense = 6.25mV (C/16)j Available in Space-Saving pMAX and SO Features charge. Packages To provide a high level of flexibility, the MAX4172 func- tions 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 sin- gle resistor, accommodating a wide range of battery voit- Ordering Information ages and currents. __ PART TEMP.RANGE _PIN-PACKAGE An open-collector pawer-good output. (PG) indicates MAX4172ESA -40C to +85C 8SO when the supply voltage reaches an adequate level to MAX4172EUA 40C to 485C 8 uMAX guarantee proper operation of the current-sense amplifi- ~Contact ki rm abil er. The MAX4172 operates with a 3.0V to 32V supply ontact factory for availability. voltage, and is available in a space-saving, 8-pin pMAX or SO package. Applications . Portable PCs: Notebooks/Subnotebooks/Palmtops Typical Oper. ating Circuit Battery-Powered/Portable Equipment Closed-Loop Battery Chargers/Current Sources aires Rs Smart-Battery Packs pe cs - ov TO a2v iy" Vsense ANALOG OR Portable/Cellular Phones REGULATOR SENS LOGIC SUPPLY Portable Test/Measurement Systems - Energy Management Systems RS RS 100k Vt + PA fo Pin Configuration pnanaan | PRERTOB | .010/ MAX4172 BATTERY lour= TOP VIEW our ! Vee / 10002 . GND ase [1 fa] vs FEEDBACK LOOP as. {2 | AAAXIAA 17] 56 Vout = 500mV/A | MAX4172 a Rout ne. [3] re] our 1k nec. Fa] 5] GND 4 pMAX/SO LOW-COST BATTERY CHARGER/CURRENT SOURCE SMAAXIMM Maxim Integrated Products 3-87 For free samples & the latest literature: http:/;www.maxim-ic.com, or phone 1-800-998-8800 For small orders, phone 408-737-7600 ext. 3468. SLEPXVINMAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier ABSOLUTE MAXIMUM RATINGS V+, RS+, RS, PG occ cece crests sce eneneenaees -0.3V to +36V Operating Temperature Range .0.3V to (V+ + 0.3V) MAX4172E_ Av cccccceceeeereeetcetescecsesettteeertees -40C to +85C Differential Input Voltage, Vase - VAS. ee Storage Temperature Range 65C to +150C Current into Any Pin Lead Temperature (soldering, 108C) ...0....c.cc ee +360C Continuous Power Dissipation (TA SO (derate 5.88mW/C above +70C) oe 471mw MAX (derate 4. 10mMW/C above +70C) ue 330mW Stresses beyond those listed under Absoiute Maximum Ratings may cause permanent damage to the device. These are siress 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 extendad periods may affect device reliability. ELECTRICAL CHARACTERISTICS (V+ = +3V to +32V; RS+, RS- = OV to 32V; Ta = Tan to TMA; Unless otherwise noted. Typical values are at V+ = +12V, RS+ = 72V, Ta = +25C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX | UNITS Operating Voltage Range V+ 3 32 Vv Input Voltage Range Vrs- 0 32 Vv Supply Current Iya louT = OmA 0.8 1.6 mA MAX4172ESA 0.1 0.75 V+ = 12V, Vase = 12V = * input Offset Voltage Vos MAX4172EUA +0.2 #16 mV VRS+ $ 2.0V 4 Positive Input Bias Current | Vrs+ > 2.0V, lout = OmA 0 27 425 A OSTENE TNPUE IAS wut AS+ Vass $2.0V, lout = OmA 325 a5 |b Negative input Bias Current ' Vas+ > 2.0V 80 85 A | egatve inputivias RS: [Vass 2.0V 650 a | Maximum VsSeNsE Voltage 150 475 my} VSENSE = 6.25mV, V+ = 12V,| MAX4172ESA 8.0 | A Low-Level Current Error Vass = 12V (Note 1) MAX4172EUA HS U MAX4172ESA, 20 Ta = -40C to OC MAX4172EUA, 50 = ~ Ta = -40C to OC Output Current Error YSENSE 4 oy V+ = 12V, pA RS+ = MAX4172ESA, +10 Ta = OC to +85C MAX4172EUA, 15 Ta = 0C to +85C OUT Power-Supply <3 Ov 0.2 Rejection Ratio AMlouT/ AV+ | BV < V+ $ 32V, Vass > 2. . pA QUT Comman-Mods Alout /AVage| 2.0V < Vrs < 32V 9.03 uAN Rejection Ratio 3-88 PAAXIAALow-Cost, Precision, High-Side Current-Sense Amplifier ELECTRICAL CHARACTERISTICS (continued) (V+ = +3V to +32V; RS+, RS- = QV to 32V; Ta = Tin to TMAX: unless otherwise noted. Typical values are at V+ = +12V, RS+ = 12V, Ta = +26C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX | UNITS Maximum Output Voltage (out) lout s 1.5mA V+-1.2 Vv VSENSE = 100mV B00 Bandwidth kH VSENSE = 6.25mV (Note 1) 200 2 Maximum Output Current fout 15 1.75 mA Gm = lout / (Vs - VRS): Ta = 0C to +85C 9.8 10 10.2 Transconductance Gm VSENSE = 100MV, Vay > 20V [Ta = 40C OC a7 10 103 mAN V+ Threshold for PG Output V+ rising 2.77 V Low (Note 2} V+ falling 2.67 PG Output Low Valtage Vou Igink = tL2mA, V+ = 2.9V, Ta = 425C a4 v Leakage Current into PG V+ = 2.5V, Ta = 425C 1 yA Power-Off input Leakage . _ _ Current (RS+, RS-) V+ = OV, VRs+ = VAS. = 32V 0.4 1 pA, OUT Rise Time VSENSE = OmV to 100mV, 10% to 90% 400 ns OUT Fail Time VSENSE = 100mV to OmV, 90% to 10% 800 ns , . Rising 1.3 OUT Settling Time to 1% VSENSE = SMV to 100rmnV - us Falling 6 OUT Output Resistance VSENSE = 150mV 20 MQ 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. (V+ = +12V, Vase = 12V, Rout = 1kQ, Ta = +25C, unless otherwise noted.) SUPPLY CURRENT vs. SUPPLY VOLTAGE 3 Taz SUPPLY CURRENT (uA) 2822238238 V+ (V) OUTPUT ERROR vs, SUPPLY VOLTAGE 0S = 100mV 0.4 03 02 Zot = So S we ~ 9 a Ta= 85C 02 Tax 425C 03 al Ta=-40C 05 10 20 30 40 V+ V} 15 1.0 05 OS 1.0 15 2.0 2.5 C/16 LOAD OUTPUT ERROR vs. SUPPLY VOLTAGE 10 Vsense = 6.25mV Ta = -40C Ta=+85C Ve WV) 30 Typical Operating Characteristics wate? 40 3-89 MAAXLM = NLow-Cost, Precision, High-Side Current-Sense Amplifier ERROR vs. SENSE VOLTAGE 40 35 30 25 20 15 10 5 Q 5 MAX4172 ERROR (%) 0.1m im 10m 100m 1 Vsense (V) OUTPUT ERROR vs. COMMON-MODE VOLTAGE = 100mV Tae + Tas +85C 0 6 12 18 24 30 40 Vas- (V) OmV to 10mV Vseuse TRANSIENT RESPONSE MAXANTIO, Vout 50mV/div Ch Soames 3-90 ad SOmV/div Vout 500mV/div Typical Operating Characteristics (continued) (V+ = 412V, Vas, = 12V, Rout = 1kQ, Ta = +25C, unless otherwise noted.) POWER-SUPPLY REJECTION RATIO vs. FREQUENCY veg seme (TEL VTL HAE ALA ST CE Trl 0 OTT Tae! | CEST BLN mR aE a 0 ! 0.01 Of 1 10 100 = 1000 POWER-SUPPLY FREQUENCY (kHz) ERROR (%) V+ THRESHOLD FOR PS OUTPUT LOW vs. TEMPERATURE 2.95 2.90 = 2.85 Q 280 RISING VOLTAGE oQ & 2.75 = 2.70 z= & 2.65 & = 2.60 => 2.55 2.50 2.45 V+ FALLING VOL AO 5 10 35 60 85 TEMPERATURE (C) GmV to 100mV Vseuse TRANSIENT RESPONSE GND pale GND 1Ops/div PA MKAMALow-Cost, Precision, High-Side Current-Sense Amplifier Typical Operating Characteristics (continued) (V+ = +12V, VaS+ = 12V, Rout = 1kQ, Ta = +25C, unless otherwise noted.) START-UP DELAY V+ to PG POWER-UP DELAY Mancarra. 1 Vout 6 S0dmVidiv 2Vidiv ~~ Ve V+ 2vidiv Nidiv GND TOpsitiv Veense = 100mV 100kC2 PULL-UP RESISTOR FROM PG TO +4V 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 internai connection. Leave open or connect to GND. 5 GND Ground 6 OUT Current Output. OUT is proportional to the magnitude of the sense voltage (Vas+ - VRS-). A 1kQ resistor from OUT to ground will result in a voltage equal to 10V/V of sense voltage. 7 PE Power Good Open-Collectar 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 node. Current flows through Rai and Q1, and into the The MAX4172 is a unidirectional, high-side current-sense amplifier with an input common-mode range that is inde- pendent of supply voltage. This feature not only allows the monitoring of current flow into a battery in deep dis- charge, but also enables high-side current sensing at voltages far in excess of the supply voltage (V+). The MAX4172 current-sense amplifiers unique topolo- gy 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- 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 A1s inverting input is high impedance, no current flows though Re2 (neglect- ing the input bias current), so A1s negative input is equal to VSOURCE - (ILOAD x RSENSE). A1s open-loop gain forces its positive input to essentially the same voltage level as the negative input. Therefore, the drop across R@i equals ILOAD x RSENSE. Then, since IRG1 3-91 MAAXLIMA = NMAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier flows through Rai, IRG1 x Rai = ILOAD x RSENSE. The internal current mirror multiplies Inq: by a factor of 50 to give louT = 50 x IrG1. Substituting lout / 50 for Ing1. (lout / 50) x Rat = ILOAD x RSENSE, or: lout = 50 x ILoap x (RSENSE / Ra1) The internal current gain of 50 and the factory-trimmed resistor Rai combine to result in the MAX4172 transconductance (Gm) of 10mA/V. Gm is de- fined as being equal to lout / (Vas+ - Vas-). Since (Vas+ - VRS-) = ILQAD X RSENSE, the output current (louT) can be calculated with the following formula: louT = Gm x (VRs+ - VRs-} = (10mA/V) x.(ILOAD x RSENSE) Current Output The output voltage equation for the MAX4172 is given below: Vout = (Gm) x (RSENSE x Rout x ILaan) 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 Gm = MAX4172 transconductance (1OmA/V). The full-scale output voltage range can be set by changing the Rout resistor value, but the output volt- age must be no greater than V+ - 1.2V. The above equation can be modified to determine the Rout required for a particular full-scale range: Rout = (Vout )/ (ILOAD x RSENSE x Gm) QUT is a high-impedance current source that can be integrated by connacting it to a capacitive load. _ PG Output The PG output is an open-collector logic output that indicates the status of the MAX4172s V+ power sup- ply. A logic low on the PG output indicates that V+ is sufficient to power the MAX4172. This level is tempera- ture dependent (see Typical Operating Characteristics graphs), and is typically 2.7V at room temperature. The internal PG comparator has a 100mvV (typical) hystere- sis to prevent possible oscillations caused by repeated toggling of the PG output, making the device ideal for power-management systems lacking soft-start capabili- ty. An internal delay (15s typical) in the PG compara- tor allows adeguate 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 contro! loop have sufficient voltage to operate correctly. 3-92 RSENSE head TO LOAD INPUT > + ~ BATTERY RS+] sense | RS- Rex Rep tras \e/ MAM MAX4172 ai Va | +50 lour = 50 tre: cuRRENT } Et our MIRROR | a Ve - PG + VTH exp 4 Figure 1. Functional Diagram Applications Information Suggested Component Values for Various Applications 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 vari- ous applications required to sense currents from 1OOMA to 10A. Adjust the RSENSE value to monitor higher or lower cur- rent levels. Select RSENSE using the guidelines and for- mulas in the following section. Sense Resistor, Rsense Choose RsSENSE based on the following criteria: * Voltage Loss: A high Rsense value causes the power-source voltage to degrade through iR joss. For minimal voltage loss, use the lowest RSENSE value, MAAXIAALow-Cost, Precision, High-Side Current-Sense Amplifier Table 1. Suggested Component Values = FULL-SCALE CURRENT-SENSE OUTPUT FULL-SCALE SCALE FACT > LOAD CURRENT RESISTOR, RESISTOR, Rout OUTPUT oan FACTOR. ~ (A) Rsense (mQ) (ka) VOLTAGE, Vout (V) ouTfisense (V/A) R 0.1 1000 3.48 3.48 34.8 mall, 1 100 3.48 3.48 3.48 Ni 5 20 3.48 3.48 0.696 Nd 10 10 3.48 3.48 0.348 Accuracy: A high Rsense value allows lower cur- rents to be measured more accurately. This is INPUT LOAD/BATTERY because offsets become less significant when the RSENSE 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 resistors value might crift if it is allowed to heat up excessively. e Inductance: Keep inductance low if ISENSE has a large high-frequency component. Wire-wound resis- tors have the highest inductance, while metal film is somewhat better. Low-inductance metal-film resis- tors are also available. Instead of being spiral wrapped around a core, as in metal-film or wire- wound resistors, they are a straight band of metal and are available in values under 19. * 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 inaccura- cies 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 mea- sured is 10A, and that you have determined a 0.3-inch- wide, 2-aunce copper to be appropriate. The resistivity of 0.1-inch-wide, 2-ounce (70um thickness) copper is 30mOAt. For 10A, you might want RSENSE = 5mQ for a 50mvV drop at full scale. This resistor requires about 2 inches of 0.1-inch-wide copper trace. MA AXIMA O3in. COPPER = g O.1 in, COPPER @ 0.2 in. COPPER ____/ {+ =f Ne VSENSE PAAXLAA VsuPPLY 3V 10 32V LI ns, MAX4I72 ,, | 8 RS- aut [S GND | 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 full- scale IouT determined by RSENSE. OUT's high imped- ance permits using RouT values up to 200kQ with minimal error. QUTs 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 parai- leled to further increase the current-sense limit. As an alternative, PC board traces can be adjusted over a wide range. 3-93MAX4172 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 sys- tems, large voltage drops can develop across the ground plane, which can add to or subtract from Vour. Use a single-point star ground for the highest current- measurement 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 prob- lem, you can place a 1pF 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 ijoad, reducing the current transients. These capacitors are not required for MAX4172 operation or stability. The RS+ and RS- inputs can he filtered by placing a capac- itor (e.g., 1pF) between them to average the sensed current. 3-94 Chip Information TRANSISTOR COUNT: 177 SUBSTRATE CONNECTED TO GND MAAXIMA