for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maximintegrated.com. max4172 low-cost, precision, high-side current-sense amplifier _______________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 charger? ground path. wide bandwidth and ground-sensing capability make the max4172 suitable for closed-loop battery-charger and general-purpose cur- rent-source applications. the 0 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 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 volt- ages 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 amplifi- er. the max4172 operates with a 3.0v to 32v supply voltage, and is available in a space-saving, 8-pin ?ax 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 ?.5% typical full-scale accuracy over temperature 3v to 32v supply operation high accuracy +2v to +32v common-mode range, functional down to 0v, independent of supply voltage 800khz bandwidth [v sense = 100mv (1c)] 200khz bandwidth [v sense = 6.25mv (c/16)] available in space-saving max and so packages out gnd feedback loop low-cost battery charger/current source v out = 500mv/a r out 1k ? 100k ? analog or logic supply 2a 0 to 32v i out = v sense / 100 ? v+ rs+ r sense 50m ? v sense rs- pg max4172 power good load/ battery low-cost switching regulator unregulated dc supply 3v to 32v __________________pin configuration top view out gnd n.c. 1 + 2 8 7 v+ pg rs- n.c. rs+ max/so 3 4 6 5 max4172 __________typical operating circuit 19-1184; rev 2; 10/12 part max4172esa+ max4172eua+ -40? to +85? -40? to +85? temp. range pin-package 8 so 8 ?ax ______________ordering information + denotes a lead(pb)-free/rohs-compliant package. ?ax is a registered trademark of maxim integrated products, inc.
max4172 low-cost, precision, high-side current-sense amplifier 2 maxim integrated t a = 0? to +85? absolute maximum ratings electrical characteristics (v+ = +3v to +32v; v rs+ , v rs- = 0 to 32v; t a = t min to t max ; unless otherwise noted. typical values are at v+ = +12v, v rs+ = 12v, t a = +25?.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v+, rs+, rs-, pg ...................................................-0.3v to +36v out ..............................................................-0.3v to (v+ + 0.3v) differential input voltage, v rs+ - v rs- ............................?00mv current into any pin..........................................................?0ma continuous power dissipation (t a = +70?) so (derate 5.88mw/? above +70?) ..........................471mw ?ax (derate 4.10mw/? above +70?) .....................330mw operating temperature range max4172e_a ....................................................-40? to +85? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? soldering temperature (reflow) .......................................+260? i out = 0ma 3v v+ 32v, v rs+ > 2.0v v sense = 100mv, v+ = 12v, v rs+ = 12v v sense = 6.25mv, v+ = 12v, v rs+ = 12v (note 1) v+ = 12v, v rs+ = 12v v rs+ 2.0v 2.0v < v rs+ < 32v conditions ?/v 0.03 ? i out / ? v rs+ out common-mode rejection ratio ma 0.8 1.6 i v+ supply current v 032 v rs- v 332 v+ operating voltage range input voltage range ?/v 0.2 ? i out / ? v+ out power-supply rejection ratio ?0 ? ?.0 low-level current error ?.1 ?.75 4 mv 150 175 maximum v sense voltage units min typ max symbol parameter v rs+ > 2.0v, i out = 0ma v rs+ 2.0v, i out = 0ma 0 27 42.5 ? -325 +42.5 i rs+ positive input bias current v rs+ > 2.0v v rs+ 2.0v 05085 ? -650 85 i rs- negative input bias current max4172esa, t a = -40? to 0? max4172esa max4172esa v os input offset voltage mv max4172eua ?.2 ?.6 max4172eua ?5 max4172eua, t a = -40? to 0? ?0 max4172eua, t a = 0? to +85? ? output current error ?5 max4172esa, t a = 0? to +85? ?0
max4172 low-cost, precision, high-side current-sense amplifier 3 maxim integrated electrical characteristics (continued) (v+ = +3v to +32v; v rs+ , v rs- = 0 to 32v; t a = t min to t max ; unless otherwise noted. typical values are at v+ = +12v, v rs+ = 12v, t a = +25?.) 1000 950 500 010 supply current vs. supply voltage 600 650 550 900 850 800 max4172-01 v+ (v) supply current ( a) 20 30 750 700 40 t a = +85 c t a = +25 c t a = -40 c i out = 0ma 0.5 0.4 -0.5 010 output error vs. supply voltage -0.3 -0.4 -0.2 0.3 0.2 0.1 max4172-03 v+ (v) error (%) 20 30 0 -0.1 40 t a = +25 c t a = +85 c t a = -40 c v sense = 100mv 1.5 1.0 -3.0 010 c/16 load output error vs. supply voltage -2.0 -1.5 -2.5 0.5 0 max4172-02 v+ (v) error (%) 20 30 -0.5 -1.0 40 t a = +85 c t a = +25 c t a = -40 c v sense = 6.25mv __________________________________________typical operating characteristics (v+ = +12v, v rs+ = 12v, r out = 1k ? , t a = +25?, unless otherwise noted.) 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. i out 1.5ma conditions v v+ - 1.2 maximum output voltage (out) units min typ max symbol parameter v+ = 2.5v, t a = +25? i sink = 1.2ma, v+ = 2.9v, t a = +25? ? 1 leakage current into pg v 0.4 v ol pg output low voltage v sense = 5mv to 100mv v sense = 0 to 100mv, 10% to 90% ? 6 out settling time to 1% 1.3 ns 400 out rise time v sense = 150mv m ? 20 out output resistance v sense = 100mv to 0mv, 90% to 10% ns 800 out fall time rising falling v+ = 0v, v rs+ = v rs- = 32v ? 0.1 1 power-off input leakage current (rs+, rs-) v sense = 100mv khz 800 bandwidth g m = i out /(v rs+ - v rs- ), v sense = 100mv, v rs+ > 2.0v ma/v 9.8 10 10.2 g m transconductance ma 1.5 1.75 i out maximum output current v+ rising v 2.77 v+ threshold for pg output low (note 2) v sense = 6.25mv (note 1) t a = 0? to +85? v+ falling 2.67 t a = -40? to 0? 9.7 10 10.3 200
0.75 0.55 -0.65 0 6 30 40 output error vs. common-mode voltage -0.45 -0.25 0.35 0.15 max4172-06 v rs- (v) error (%) 12 18 -0.05 24 t a = -40 c t a = +25 c v sense = 100mv t a = +85 c 2.95 2.90 2.45 -40 -15 85 v+ threshold for pg output low vs. temperature 2.50 2.55 2.60 2.85 2.80 2.75 2.70 max4172-07 temperature ( c) v+ trip threshold (v) 10 35 2.65 60 v+ rising voltage v+ falling voltage 40 -5 0.1m 10m 100m 1m 1 error vs. sense voltage 0 max4172-04 v sense (v) error (%) 10 5 15 20 25 30 35 35 0 0.01 0.1 1 10 100 1000 power-supply rejection ratio vs. frequency 5 max4172-05 power-supply frequency (khz) error (%) 15 10 20 30 25 5mv p-p 1.0v p-p 0.5v p-p v sense = 100mv 10 s/div 0 to 10mv v sense transient response gnd v sense 5mv/div v out 50mv/div gnd max4172-08 10 s/div 0 to 100mv v sense transient response gnd v sense 50mv/div v out 500mv/div gnd max4172-09 ____________________________typical operating characteristics (continued) (v+ = +12v, v rs+ = 12v, r out = 1k ? , t a = +25?, unless otherwise noted.) max4172 low-cost, precision, high-side current-sense amplifier 4 maxim integrated
5 s/div startup delay gnd v out 500mv/div v+ 2v/div gnd v sense = 100mv max4172-10 10 s/div v+ to pg power-up delay gnd pg 2v/div v+ 2v/div gnd 100k ? pullup resistor from pg to +4v max4172-11 ______________________________________________________________pin description max4172 low-cost, precision, high-side current-sense amplifier 5 maxim integrated ____________________________typical operating characteristics (continued) (v+ = +12v, v rs+ = 12v, r out = 1k ? , t a = +25?, unless otherwise noted.) current output. out is proportional to the magnitude of the sense voltage (v rs+ - v rs- ). a 1k ? resistor from out to ground will result in a voltage equal to 10v/v of sense voltage. out 6 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. pg 7 supply voltage input for the max4172 v+ 8 ground gnd 5 no connect. no internal connection. leave open or connect to gnd. n.c. 3, 4 pin load-side connection for the external sense resistor. the ??indicates the direction of current flow. rs- 2 power connection to the external sense resistor. the ??indicates the direction of current flow. rs+ 1 function name _______________detailed description 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 amplifier? unique topolo- gy simplifies current monitoring and control. the max4172? amplifier operates as shown in figure 1. the battery/load current flows through the external sense resistor (r sense ), from the rs+ node to the rs- node. current flows through r g1 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? inverting input is high impedance, no current flows though r g2 (neglect- ing the input bias current), so a1? negative input is equal to v source - (i load x r sense ). a1? open-loop gain forces its positive input to essentially the same voltage level as the negative input. therefore, the drop across r g1 equals i load x r sense . then, since i rg1
max4172 low-cost, precision, high-side current-sense amplifier 6 maxim integrated flows through r g1 , i rg1 x r g1 = i load x r sense . the internal current mirror multiplies i rg1 by a factor of 50 to give i out = 50 x i rg1 . substituting i out /50 for i rg1 , (i out /50) x r g1 = i load x r sense , or: i out = 50 x i load x (r sense /r g1 ) 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 de- fined as being equal to i out /(v rs+ - v rs- ). since (v rs+ - v rs- ) = i load x r sense , the output current (i out ) can be calculated with the following formula: i out = g m x (v rs+ - v rs- ) = (10ma/v) x (i load x r sense ) current output the output voltage equation for the max4172 is given below: v out = (g m ) x (r sense x r out x i load ) where v out = the desired full-scale output voltage, i load = the full-scale current being sensed, r sense = the current-sense resistor, r out = the voltage-setting resistor, and g m = max4172 transconductance (10ma/v). the full-scale output voltage range can be set by changing the r out resistor value, but the output volt- age 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: r out = (v out )/(i load x r sense x g m ) out is a high-impedance current source that can be integrated by connecting it to a capacitive load. pg output the pg output is an open-collector logic output that indicates the status of the max4172? 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 100mv (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 (15? typical) in the pg compara- tor 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. __________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 100ma to 10a. adjust the r sense value to monitor higher or lower cur- rent levels. select r sense using the guidelines and for- mulas in the following section. sense resistor, r sense choose r sense 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. r g1 rs+ r sense input r g2 to load/ battery rs- v sense a1 1:50 current mirror max4172 out v th i out = 50 i rg1 i rg1 q1 v+ pg v+ gnd i load figure 1. functional diagram
max4172 low-cost, precision, high-side current-sense amplifier 7 maxim integrated ? accuracy: a high r sense value allows lower cur- rents to be measured more accurately. this is because offsets become less significant when the sense voltage is larger. for best performance, select r sense to provide approximately 100mv of sense voltage for the full-scale current in each application. ? efficiency and power dissipation: at high current levels, the i 2 r losses in r sense can be significant. take this into consideration when choosing the resistor value and its power dissipation (wattage) rating. also, the sense resistor? value might drift if it is allowed to heat up excessively. ? inductance: keep inductance low if i sense 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 1 ? . ? cost: if the cost of r sense is an issue, you might want to use an alternative solution, as shown in figure 2. this solution uses the pcb 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? resis- tance temperature coefficient is fairly high (approxi- mately 0.4%/?). 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-ounce copper to be appropriate. the resistivity of 0.1-inch-wide, 2-ounce (70? thickness) copper is 30m ? /ft. for 10a, you might want r sense = 5m ? for a 50mv drop at full scale. this resistor requires about 2 inches of 0.1-inch-wide copper trace. current-sense adjustment (resistor range, output adjust) choose r out after selecting r sense . choose r out to obtain the full-scale voltage you require, given the full- scale i out determined by r sense . out? high imped- ance permits using r out values up to 200k ? with minimal error. out? load impedance (e.g., the input of an op amp or adc) must be much greater than r out (e.g., 100 x r out ) to avoid degrading measurement accuracy. high-current measurement the max4172 can achieve high-current measurements by using low-value sense resistors, which can be paral- leled to further increase the current-sense limit. as an alternative, pcb traces can be adjusted over a wide range. 3.48 3.48 3.48 100 1 3.48 3.48 output resistor, r out (k ? ) 3.48 0.348 10 10 3.48 3.48 3.48 full-scale output voltage, v out (v) 0.696 20 5 34.8 full-scale load current (a) scale factor, v out /i sense (v/a) 1000 0.1 current-sense resistor, r sense (m ? ) table 1. suggested component values out gnd 1 o.1 in. copper v sense r sense input load/battery v supply r out o.3 in. copper o.3 in. copper 2 8 rs+ rs- v+ 3v to 32v max4172 6 5 figure 2. max4172 connections showing use of pc board
max4172 low-cost, precision, high-side current-sense amplifier 8 maxim integrated ___________________chip information 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 v out . 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 1? 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 capac- itor (e.g., 1?) between them to average the sensed current. substrate connected to gnd package information for the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages . note that a ?? ?? or ??in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing per tains to the package regardless of rohs status. package type package code outline no. land pattern no. so s8+4 21-0041 90-0096 ?ax u8+1 21-0036 90-0092
maxim integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim integr ated product. no circuit patent licenses are implied. maxim integrated reserves the right to change the circuitry and specifications without notice at any time . the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidance. maxim integrated 160 rio robles, san jose, ca 95134 usa 1-408-601-1000 _________________________________ 9 2012 maxim integrated products, inc. maxim integrated and the maxim integrated logo are trademarks of maxim integrated products , inc. max4172 low-cost, precision, high-side current-sense amplifier revision history revision number revision date description pages changed 0 12/96 initial release 1 6/10 clarified 0 to 2v is not a high-accuracy range for the device, removed future product reference, added lead-free options and soldering temperature. 1, 2 2 10/12 revised the package information .8
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