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 accura- cy, 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 amplifiers have a voltage output and are offered in three gain ver- sions: 25v/v (MAX9938t), 50v/v (MAX9938f), and 100v/v (MAX9938h). the three 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) and 5-pin sot23 packages, specified for operation over the -40c to +85c extend- ed temperature range. applications cell phones pdas power management systems portable/battery-powered systems notebook computers features ultra-low supply current of 1? (max) low 500? (max) input offset voltage low < 0.5% (max) gain error input common mode: +1.6v to +28v voltage output three gain versions available 25v/v (MAX9938t) 50v/v (MAX9938f) 100v/v (MAX9938h) tiny 1mm x 1mm x 0.6mm, 4-bump ucsp or 5-pin sot23 package MAX9938 1a, 4-bump ucsp/sot23, precision current-sense amplifier ________________________________________________________________ maxim integrated products 1 MAX9938t/f/h MAX9938t/f/h 54 13 2 rs+ rs- gnd out gnd sot23 ucsp top view (bumps on bottom) b1 b2 a1 gnd rs+ out rs- a2 pin configurations 19-4110; rev 0; 4/08 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. ucsp is a trademark of maxim integrated products, inc. ordering information + denotes a lead-free package. note: all devices are specified over the -40c to +85c extended temperature range. part pin- package gain (v/v) top mark MAX9938tebs+ 4 ucsp 25 +agd MAX9938febs+ 4 ucsp 50 +age MAX9938hebs+ 4 ucsp 100 +agf MAX9938teuk+ 5 sot23 25 +affb MAX9938feuk+ 5 sot23 50 +affc MAX9938heuk+ 5 sot23 100 +affd
MAX9938 1a, 4-bump ucsp/sot23, precision current-sense amplifier 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (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) stresses beyond those listed under absolute 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. 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. 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. parameter symbol conditions min typ max units v rs+ = 5v, t a = +25c 0.5 0.85 v rs+ = 5v, -40c < t a < +85c 1.1 v rs+ = 28v, t a = +25c 1.1 1.8 supply current (note 2) i cc v rs+ = 28v, -40c < t a < +85c 2.5 a 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, -40c < t a < +85c 94 130 db t a = +25c 100 500 input offset voltage (note 3) v os -40c < t a < +85c 600 v MAX9938t 25 MAX9938f 50 gain g MAX9938h 100 v/v t a = +25c 0.1 0.5 gain error (note 4) ge -40c < t a < +85c 0.6 % output resistance r out (note 5) 7.0 10 13.2 k gain = 25 1.5 15 gain = 50 3 30 out low voltage v ol gain = 100 6 60 mv out high voltage v oh v oh = v rs- - v out (note 6) 0.1 0.2 v v sense = 50mv, gain = 25 125 v sense = 50mv, gain = 50 60 small-signal bandwidth (note 5) bw v sense = 50mv, gain = 100 30 khz output settling time t s 1% final value, v sense = 50mv 100 s power-up time t on 1% final value, v sense = 50mv 200 s 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 operating temperature range ...........................-40c to +85c junction temperature ......................................................+150c storage temperature range ............................-65c to +150c bump temperature (soldering) reflow............................+235c lead temperature (soldering, 10s) .................................+300c
MAX9938 1a, 4-bump ucsp/sot23, precision current-sense amplifier _______________________________________________________________________________________ 3 0 10 5 20 15 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 (%) 0 10 5 20 15 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 (%) supply current vs. temperature MAX9938 toc03 temperature ( c) supply current ( a) 10 -15 35 60 0.4 0.2 0.6 0.8 1.0 1.2 1.4 28v 3.6v 1.8v 0 -40 85 input offset vs. common-mode voltage MAX9938 toc04 supply voltage (v) input offset ( v) 25 20 10 515 -50 -45 -40 -35 -30 -55 030 input offset vs. temperature MAX9938 toc05 input offset ( v) 20 10 30 40 50 60 0 temperature ( c) 10 -15 35 60 -40 85 supply current vs. common-mode voltage MAX9938 toc06 supply voltage (v) supply current ( a) 15 20 10 30 525 1.0 0.8 0.6 0.4 0.2 1.2 1.4 0 0 -0.5 -0.3 -0.4 -0.1 -0.2 0 0.1 01015 5 202530 gain error vs. common-mode voltage MAX9938 toc07 voltage (v) gain error (%) gain error vs. temperature MAX9938 toc08 temperature ( c) gain error (%) 10 60 85 35 -15 0.06 0.05 0.04 0.03 0.02 0.01 0.07 0.08 0 -40 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 0150 g = 100 g = 25 g = 50 typical operating characteristics (v rs+ = v rs- = 3.6v, t a = +25c, unless otherwise noted.)
MAX9938 1a, 4-bump ucsp/sot23, precision current-sense amplifier 4 _______________________________________________________________________________________ typical operating characteristics (continued) (v rs+ = v rs- = 3.6v, t a = +25c, unless otherwise noted.) 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 0100 g = 100 g = 50 g = 25 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 cmrr vs. frequency MAX9938 toc12 frequency (khz) gain (db) 100khz 10hz 1mhz 100hz 10khz 1khz -40 -60 -80 -100 -120 -140 -20 0 -160 1hz g = 25 g = 50 g = 100 small-signal pulse response (g = 100) MAX9938 toc13a 20 s/div v out v sense 1v 1.5v 10mv 15mv small-signal pulse response (g = 50) MAX9938 toc13b 25 s/div v out v sense 1v 1.5v 20mv 30mv small-signal pulse response (g = 25) MAX9938 toc13c 25 s/div v out v sense 1v 1.5v 40mv 60mv
MAX9938 1a, 4-bump ucsp/sot23, precision current-sense amplifier _______________________________________________________________________________________ 5 typical operating characteristics (continued) (v rs+ = v rs- = 3.6v, t a = +25c, unless otherwise noted.) large-signal pulse response (g = 100) MAX9938 toc14a 20 s/div v out v sense 1v 3v 10mv 30mv large-signal pulse response (g = 50) MAX9938 toc14b 25 s/div v out v sense 0.5v 3v 10mv 60mv large-signal pulse response (g = 25) MAX9938 toc14c 25 s/div v out v sense 0.5v 3v 20mv 120mv pin description pin ucsp sot23 name function a1 5 rs+ external sense resistor power-side connection a2 4 rs- external sense resistor load-side connection b1 1, 2 gnd ground b2 3 out output voltage. v out is proportional to v sense = v rs+ - v rs- .
MAX9938 1a, 4-bump ucsp/sot23, precision current-sense amplifier 6 _______________________________________________________________________________________ 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, and 100v/v for the MAX9938h. the output is protected from input overdrive by use of an output current limiting circuit of 7ma (typical) and a 6v clamp protection circuit. applications information choosing the sense resistor choose 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. gain (v/v) r 1 ( ) r out (k ) 100 100 10 50 200 10 25 400 10 table 1. internal gain setting resistors (typical values) 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
MAX9938 1a, 4-bump ucsp/sot23, precision current-sense amplifier _______________________________________________________________________________________ 7 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 minimum voltage at rs+. v out (max) = v rs+ (min) - v sense (max) - v oh and 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 approxi- mately 120mv (gain of 25v/v), 60mv (gain of 50v/v), or 30mv (gain of 100v/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 off- sets are less significant when the sense voltage is larger. 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 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. r v gi sense out load = (max) (max)
MAX9938 1a, 4-bump ucsp/sot23, precision current-sense amplifier 8 _______________________________________________________________________________________ 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 1). 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 reliability testing results, refer to the application note ucspa wafer-level chip-scale package available on maxims website at www.maxim-ic.com/ucsp . chip information process: bicmos 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 figure 1. bidirectional application
MAX9938 1a, 4-bump ucsp/sot23, precision current-sense amplifier maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 _____________________ 9 ? 2008 maxim integrated products is a registered trademark of maxim integrated products, inc. package information for the latest package outline information, go to www.maxim-ic.com/packages . package type package code document no. 2 x 2 ucsp b4-1 21-0117 5 sot23 u5-2 21-0057
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