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general description the max9938 high-side current-sense amplifier offers precision accuracy specifications of v os less than 500v (max) and gain error less than 0.5% (max). quiescent supply current is an ultra-low 1a. the max9938 fits in a tiny, 1mm x 1mm ucsp? package size or a 5-pin sot23 package, making the part ideal for applications in notebook computers, cell phones, pdas, and all battery- operated portable devices where accuracy, low quiescent current, and small size are critical. the max9938 features an input common-mode voltage range from 1.6v to 28v. these current-sense ampli - fiers have a voltage output and are offered in four gain versions: 25v/v (max9938t), 50v/v (max9938f), 100v/v (max9938h), and 200v/v (max9938w). the four gain selections offer flexibility in the choice of the external current-sense resistor. the very low 500v (max) input offset voltage allows small 25mv to 50mv full-scale v sense voltage for very low voltage drop at full-current measurement. the max9938 is offered in tiny 4-bump, ucsp (1mm x 1mm x 0.6mm footprint), 5-pin sot23, and 6-pin dfn (2mm x 2mm x 0.8mm) packages specified for operation over the -40c to +85c extended temperature range. applications cell phones pdas power management systems portable/battery-powered systems notebook computers features ultra-low supply current of 1a (max) low 500v (max) input offset voltage low < 0.5% (max) gain error input common mode: +1.6v to +28v voltage output four gain versions available ? +25v/v (max9938t) ? 50v/v (max9938f) ? 100v/v (max9938h) ? 200v/v (max9938w) tiny 1mm x 1mm x 0.6mm, 4-bump ucsp, 5-pin sot23, or 2mm x 2mm x 0.8mm, 6-pin dfn packages 19-4110; rev 6; 1/11 ucsp is a trademark of maxim integrated products, inc. + denotes a lead(pb)-free/rohs-compliant package. g45 indicates protective die coating.note: all devices are specified over the -40c to +85c extended temperature range. max9938 1a, 4-bump ucsp/sot23, precision current-sense amplifier pin conigurations ordering information part pin- package gain (v/v) top mark max9938tebs+g45 4 ucsp 25 +agd max9938febs+g45 4 ucsp 50 +age max9938hebs+g45 4 ucsp 100 +agf max9938webs+g45 4 ucsp 200 +agi max9938teuk+ 5 sot23 25 +affb max9938feuk+ 5 sot23 50 +affc max9938heuk+ 5 sot23 100 +affd max9938weuk+ 5 sot23 200 +afgz MAX9938FELT+ 6 dfn 50 +acm max9938tmax9938f max9938h max9938w max9938tmax9938f max9938h max9938w 5 4 1 3 2 rs+ rs- gnd out gnd sot23 ucsp top view (bumps on bottom) b1 b2 a1 gnd rs+ out rs- a2 1 2 3 6 5 4 rs- n.c.rs+ MAX9938FELT dfn top view (pads on bottom) out n.c. gnd drawings not to scale evaluation kit available downloaded from: http:///
rs+, rs- to gnd .................................................. -0.3v to +30v out to gnd ............................................................ -0.3v to +6v rs+ to rs- .......................................................................... 30v short-circuit duration: out to gnd ......................... continuous continuous input current (any pin) ................................. 20ma continuous power dissipation (t a = +70c) 4-bump ucsp (derate 3.0mw/c above +70c) ........ 238mw 5-pin sot23 (derate 3.9mw/c above +70c) .......... 312mw 6-pin dfn (derate 4.5mw/c above +70c) ............ 358mw operating temperature range ........................... -40c to +85c junction temperature ...................................................... +150c storage temperature range ............................ -65c to +150c lead temperature (excluding ucsp, soldering, 10s) ..... +300c soldering temperature (reflow) ....................................... +260c (v rs+ = v rs- = 3.6v, v sense = (v rs+ - v rs- ) = 0v, t a = -40c to +85c, unless otherwise noted. typical values are at t a = +25c.) (note 1) max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier www.maximintegrated.com maxim integrated 2 absolute maximum ratings 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 parameter symbol conditions min typ max units supply current (note 2) i cc v rs+ = 5v, t a = +25c 0.5 0.85 a v rs+ = 5v, -40c < t a < +85c 1.1 v rs+ = 28v, t a = +25c 1.1 1.8 v rs+ = 28v, -40c < t a < +85c 2.5 common-mode input range v cm guaranteed by cmrr , -40c < t a < +85c 1.6 28 v common-mode rejection ratio cmrr 1.6v < v rs+ < 28v, -40 c < t a < +85c 94 130 db input offset voltage (note 3) v os t a = +25c 100 500 v -40c < t a < +85c 600 gain g max9938t 25 v/v max9938f 50 max9938h 100 max9938w 200 gain error (note 4) ge max9938t/max9938f/ max9938h t a = +25c 0.1 0.5 % -40 c < t a < +85 c 0.6 max9938w t a = +25c 0.1 0.7 -40 c < t a < +85 c 0.8 output resistance r out (note 5) max9938t/f/h 7.0 10 13.2 k? max9938w 14.0 20 26.4 out low voltage v ol gain = 25 1.5 15 mv gain = 50 3 30 gain = 100 6 60 gain = 200 12 120 out high voltage v oh v oh = v rs- - v out (note 6) 0.1 0.2 v small-signal bandwidth(note 5) bw v sense = 50mv, gain = 25 125 v v sense = 50mv, gain = 50 60 khz v sense = 50mv, gain = 100 30 v sense = 50mv, gain = 200 15 output settling time t s 1% inal value, v sense = 50mv 100 s downloaded from: http:///
(v rs+ = v rs- = 3.6v, v sense = (v rs+ - v rs- ) = 0v, t a = -40c to +85c, unless otherwise noted. typical values are at t a = +25c.) (note 1) note 1: all devices are 100% production tested at t a = +25c. all temperature limits are guaranteed by design. note 2: v out = 0. i cc is the total current into rs+ plus rs- pins. note 3: v os is extrapolated from measurements for the gain-error test. note 4: gain error is calculated by applying two values of v sense and calculating the error of the slope vs. the ideal: gain = 25, v sense is 20mv and 120mv. gain = 50, v sense is 10mv and 60mv. gain = 100, v sense is 5mv and 30mv. gain = 200, v sense is 2.5mv and 15mv. note 5: the device is stable for any external capacitance value. note 6: v oh is the voltage from v rs- to v out with v sense = 3.6v/gain. (v rs+ = v rs- = 3.6v, t a = +25c, unless otherwise noted.) max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier www.maximintegrated.com maxim integrated 3 electrical characteristics (continued) 0 10 5 2015 25 30 -0.4 -0.3 -0.2 -0.1 0 0.2 0.3 0.1 0.4 input offset voltage histogram max9938 toc01 input offset voltage (mv) n (%) input offset vs. common-mode voltage max9938 toc04 supply voltage (v) input offset (v) 25 20 10 5 15 -50 -45 -40 -35 -30-55 0 30 supply current vs. temperature max9938 toc03 temperature (c) supply current (a) 10 -15 35 60 0.40.2 0.6 0.8 1.0 1.2 1.4 28v 3.6v1.8v 0 -40 85 supply current vs. common-mode voltage max9938 toc06 supply voltage (v) supply current (a) 15 20 10 30 5 25 1.00.8 0.6 0.4 0.2 1.2 1.4 0 0 0 10 5 2015 25 30 -0.4 -0.3 -0.2 -0.1 0 0.2 0.3 0.1 0.4 gain error histogram max9938 toc02 gain error (%) n (%) input offset vs. temperature max9938 toc05 input offset (v) 2010 30 40 50 60 0 temperature (c) 10 -15 35 60 -40 85 typical operating characteristics downloaded from: http:///
(v rs+ = v rs- = 3.6v, t a = +25c, unless otherwise noted.) max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier maxim integrated 4 www.maximintegrated.com typical operating characteristics (continued) v out vs. v sense (supply = 1.6v) max9938 toc10 v sense (mv) v out (v) 80 60 40 20 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0 0 100 g = 100 g = 50 g = 25 -0.5 -0.3-0.4 -0.1-0.2 0 0.1 0 10 15 5 20 25 30 gain error vs. common-mode voltage max9938 toc07 voltage (v) gain error (%) small-signal pulse response (gain = 100) max9938 toc13a 20s/div v out v sense 1v 1.5v 10mv 15mv small-signal pulse response (gain = 50) max9938 toc13b 25s/div v out v sense 1v 1.5v 20mv 30mv cmrr vs. frequency max9938 toc12 frequency (khz) cmrr (db) 100khz 10hz 1mhz 100hz 10khz 1khz -40-60 -80 -100-120 -140 -20 0 -160 1hz g = 25 g = 50 g = 100 v out vs. v sense (supply = 3.6v) max9938 toc09 v sense (mv) v out (v) 100 50 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 0 150 g = 100 g = 25 g = 50 small signal gain vs. frequency max9938 toc11 frequency (khz) gain (db) 100khz 10hz 1mhz 100hz 10khz 1khz -5 -10-15 -20 -25 0 5 -30 1hz a v = 25v/v a v = 100v/v a v = 50v/v gain error vs. temperature max9938 toc08 temperature (c) gain error (%) 10 60 85 35 -15 0.060.05 0.04 0.03 0.02 0.01 0.07 0.08 0 -40 downloaded from: http:///
(v rs+ = v rs- = 3.6v, t a = +25c, unless otherwise noted.) max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier maxim integrated 5 www.maximintegrated.com typical operating characteristics (continued) pin description pin name function ucsp sot23 dfn a1 5 4 rs+ external sense resistor power-side connection a2 4 6 rs- external sense resistor load-side connection b1 1, 2 3 gnd ground b2 3 1 out output voltage. v out is proportional to v sense = v rs+ - v rs- . 2, 5 n.c. no connection. not internally connected. small-signal pulse response (gain = 25) max9938 toc13c 25s/div v out v sense 1v 1.5v 40mv 60mv large-signal pulse response (gain = 100) max9938 toc14a 20s/div v out v sense 1v 3v 10mv 30mv large-signal pulse response (gain = 50) max9938 toc14b 25s/div v out v sense 0.5v 3v 10mv 60mv large-signal pulse response (gain = 25) max9938 toc14c 25s/div v out v sense 0.5v 3v 20mv 120mv downloaded from: http:///
detailed description the max9938 unidirectional high-side, current-sense amplifier features a 1.6v to 28v input common-mode range. this feature allows the monitoring of current out of a battery with a voltage as low as 1.6v. the max9938 monitors current through a current-sense resistor and amplifies the voltage across that resistor. the max9938 is a unidirectional current-sense amplifier that has a well-established history. an op amp is used to force the current through an internal gain resistor at rs+, which has a value of r 1 , such that its voltage drop equals the voltage drop across an external sense resis - tor, r sense . there is an internal resistor at rs- with the same value as r 1 to minimize offset voltage. the cur - rent through r 1 is sourced by a high-voltage p-channel fet. its source current is the same as its drain current, which flows through a second gain resistor, r out . this produces an output voltage, v out , whose magnitude is i load x r sense x r out /r 1 . the gain accuracy is based on the matching of the two gain resistors r 1 and r out (see table 1 ). total gain = 25v/v for the max9938t, 50v/v for the max9938f, 100v/v for the max9938h, and 200v/v for the max9938w. the output is protected from input overdrive by use of an output current limiting circuit of 7ma (typical) and a 6v clamp protection circuit. table 1. internal gain setting resistors (typical values) max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier www.maximintegrated.com maxim integrated 6 typical operating circuit v batt = 1.6v to 28v r sense r 1 i load r out r 1 gnd out p max9938 rs+ rs- adc load c v dd = 3.3v 10k ? gain (v/v) r 1 (?) r out (k?) 200 100 20 100 100 10 50 200 10 25 400 10 downloaded from: http:///
applications information choosing the sense resistorchoose r sense based on the following criteria: voltage loss a high r sense value causes the power-source voltage to drop due to ir loss. for minimal voltage loss, use the lowest r sense value. out swing vs. v rs+ and v sense the max9938 is unique since the supply voltage is the input common-mode voltage (the average voltage at rs+ and rs-). there is no separate v cc supply voltage pin. therefore, the out voltage swing is limited by the mini - mum voltage at rs+. v out (max) = v rs+ (min) - v sense (max) - v oh and out sense load v (max) r g i (max) = v sense full scale should be less than v out /gain at the minimum rs+ voltage. for best performance with a 3.6v supply voltage, select r sense to provide approximately 120mv (gain of 25v/v), 60mv (gain of 50v/v), 30mv (gain of 100v/v), or 15mv (gain of 200v/v) of sense voltage for the full-scale current in each application. these can be increased by use of a higher minimum input voltage. accuracy in the linear region (v out < v out (max)), there are two components to accuracy: input offset voltage (v os ) and gain error (ge). for the max9938, v os = 500v (max) and gain error is 0.5% (max). use the linear equation: v out = (gain ge) x v sense (gain x v os ) to calculate total error. a high r sense value allows lower currents to be measured more accurately because offsets are less significant when the sense voltage is larger. eficiency 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 resistors value might drift if it is allowed to heat up excessively. the precision v os of the max9938 allows the use of small sense resistors to reduce power dissipation and reduce hot spots. kelvin connections because of the high currents that flow through r sense , take care to eliminate parasitic trace resistance from causing errors in the sense voltage. either use a four- terminal current-sense resistor or use kelvin (force and sense) pcb layout techniques. optional output filter capacitor when designing a system that uses a sample-and-hold stage in the adc, the sampling capacitor momentarily loads out and causes a drop in the output voltage. if sampling time is very short (less than a microsecond), consider using a ceramic capacitor across out and gnd to hold v out constant during sampling. this also decreases the small-signal bandwidth of the current- sense amplifier and reduces noise at out. input filters some applications of current-sense amplifiers need to measure currents accurately even in the presence of both differential and common-mode ripple, as well as a wide variety of input transient conditions. for example, high- frequency ripple at the output of a switching buck or boost regulator results in a common-mode voltage at the inputs of the max9938. alternatively, fast load-current tran - sients, when measuring at the input of a switching buck or boost regulator, can cause high-frequency differential sense voltages to occur at the inputs of the max9938, although the signal of interest is the average dc value. such high-frequency differential sense voltages may result in a voltage offset at the max9938 output. max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier www.maximintegrated.com maxim integrated 7 downloaded from: http:///
the max9938 allows two methods of filtering to help improve performance in the presence of input common - mode voltage and input differential voltage transients. figure 1 shows a differential input filter. the capacitor c in between rs+ and rs- along with the resistor r in between the sense resistor and rs- helps filter against input differential voltages and prevents them from reaching the max9938. the corner frequency of this filter is determined by the choice of r in , c in , and the value of the input resistance at rs- (r 1 ). see table 1 for r 1 values at the different gain options. the value of r in should be chosen to minimize its effect on the input offset voltage due to the bias current at rs-. r in x i bias contributes to the input voltage offset. i bias is typically 0.2a. placing r in at the rs- input does not affect the gain error of the device because the gain is given by the ratio between r out and r 1 at rs+. figure 2 shows the input common-mode filter. again, the corner frequency of the filter is determined by the choice of r in , c in and is affected by r 1 . in this case r in affects both gain error and input offset voltage. r in should be smaller than r 1 so that it has neg - ligible effect on the device gain. if, for example, a filter with r in = 10 and c in = 1f is built, then depending upon the gain selection, the gain error is affected by either 2.5% (g = 25v/v, r 1 = 400) or 5% (g = 50v/v, r 1 = 200) or 10% (g = 100v/v, r 1 = 100) or 10% (g = 200v/v, r 1 = 100). figure 1. differential input filter figure 2. input common-mode filter max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier www.maximintegrated.com maxim integrated 8 r sense c in r in rs- out gnd rs+ max9938 load r sense c in c in r in r in rs- out gnd rs+ max9938 load downloaded from: http:///
bidirectional application battery-powered systems may require a precise bidi- rectional current-sense amplifier to accurately monitor the batterys charge and discharge currents. measurements of the two separate outputs with respect to gnd yields an accurate measure of the charge and discharge currents respectively ( figure 3 ). ucsp applications information for the latest application details on ucsp construction, dimensions, tape carrier information, pcb techniques, bump-pad layout, and recommended reflow tempera - ture profile, as well as the latest information on reliabil - ity testing results, refer to the application note 1891: wafer-level packaging (wlp) and its applications available on maxims website at www.maximintegrated. com/ucsp . figure 3. bidirectional application max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier www.maximintegrated.com maxim integrated 9 v batt = 1.6v to 28v r sense r 1 i load r out r 1 gnd p max9938 r 1 r out r 1 gnd p out out to wall-cube/charger max9938 rs+ rs- rs- rs+ adc adc load c v dd = 3.3v 10k ? 10k ? chip information process: bicmos downloaded from: http:///
max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier www.maximintegrated.com maxim integrated 10 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 pertains to the package regardless of rohs status. package type package code outline no. land pattern no. 2 x 2 ucsp b4+1 21-0117 5 sot23 u5-2 21-0057 90-0174 6 dfn l622+1 21-0164 90-0004 downloaded from: http:///
max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier www.maximintegrated.com maxim integrated 11 package information (continued) 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 pertains to the package regardless of rohs status. sot-23 5l .eps downloaded from: http:///
max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier www.maximintegrated.com maxim integrated 12 package information (continued) 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 pertains to the package regardless of rohs status. downloaded from: http:///
max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier www.maximintegrated.com maxim integrated 13 package information (continued) 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 pertains to the package regardless of rohs status. downloaded from: http:///
maxim integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim integrated product. no circuit patent licenses are implied. maxim integrated reserves the right to change the circuitry and speciications without n otice 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 and the maxim integrated logo are trademarks of maxim integrated products, inc. max9938 1a, 4-bump ucsp/sot23, precision current-sense ampliier ? 2011 maxim integrated products, inc. 14 revision history revision number revision date description pages changed 0 4/08 initial release 1 9/08 added dfn package information 1, 2, 4, 5, 9 2 2/09 added g45 designation to part number 1 3 10/09 added input filters section and max9938w to the data sheet 1, 2, 6C9 4 2/10 updated ec table and input filters section 2, 8 5 8/10 removed power-up time parameter 2 6 1/11 corrected error on figure 2 8 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim integrateds website at www.maximintegrated.com. downloaded from: http:///

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