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general description the max9937 is a tiny automotive grade current-sense amplifier designed for unidirectional high-side current- sense applications. this device addresses major areas of concern for automotive applications including load- dump protection up to +40v, reverse-battery protec- tion, and filtering for emi and transient performance. the max9937 also features a low input offset voltage of ?.2mv (max) at +25? with a low temperature drift of just 1?/? (typ). the max9937 is available in a 5-pin sc70 package and is rated over the -40? to +125? temperature range. applications automotive battery current sense fuse box current sense ecu current monitor features ? reverse battery and load-dump protection -20v to +40v ? +4v to +28v input common-mode range ? flexible emi filtering ? low v os : ?.2mv (max) ? low v os drift: 1?/? (typ) ? 20? supply current ? 350khz, 3db small signal bandwidth max9937 automotive current-sense amplifier with reverse-battery protection ________________________________________________________________ maxim integrated products 1 19-4233; rev 0; 8/08 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. load microcontroller adc r sense gnd out v cc rs+ rs- r rsn 499 r rsp 499 r out 10k 5v rsp rsn bias block v bat = 4v to 28v max9937 gain = v out v sense = r out r rsp typical application circuit ordering information part temp range pin- package top mark max9937axk+t -40? to +125? 5 sc70 +atb + denotes a lead-free/rohs-compliant package. t = tape and reel. pin configuration appears at end of data sheet.
max9937 automotive current-sense amplifier with reverse-battery protection 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = 5v, v bat = v rs+ = 12v, v sense = (v rs+ - v rs- ) = 0, r rsp = r rsn = 500
max9937 automotive current-sense amplifier with reverse-battery protection _______________________________________________________________________________________ 3 parameter symbol conditions min typ max units maximum output current i out r rsn = 500
max9937 automotive current-sense amplifier with reverse-battery protection 4 _______________________________________________________________________________________ typical operating characteristics (v cc = 5v, v bat = v rsp = 12v, v sense = v rs+ - v rs- = 0, r rsp = r rsn = 500 offset voltage vs. temperature max9937 toc02 temperature ( c) offset voltage ( v) 100 400 300 200 600 500 700 800 41216 8 202428 offset voltage vs. common-mode voltage max9937 toc03 common-mode voltage (v) offset voltage ( v) t a = +25 c t a = +125 c t a = -40 c 0 -700 -500 -400 -300 -200 -100 0 3.0 3.5 4.0 4.5 5.0 offset voltage vs. power-supply voltage max9937 toc04 power-supply voltage (v) offset voltage ( v) -600 t a = +125 c t a = -40 c t a = +25 c ac common-mode rejection ratio c in = 220nf max9937 toc05 frequency (hz) cmrr (dbv) 100k 10k 1k 100 10 -100 -80 -60 -40 -20 0 -120 11m c load = 10pf c load = 1nf c load = 100pf ac power-supply rejection ratio c in = 220nf max9937 toc06 frequency (hz) psrr (dbv) 100k 10k 1k 100 10 -120 -100 -80 -60 -40 -20 0 -140 11m c load = 100pf c load = 10pf c load = 1nf 0 10 5 20 15 30 25 35 25 100 175 250 325 400 475 550 offset voltage histogram max9937 toc01 offset voltage ( v) frequency (%)
max9937 automotive current-sense amplifier with reverse-battery protection _______________________________________________________________________________________ 5 typical operating characteristics (continued) (v cc = 5v, v bat = v rsp = 12v, v sense = v rs+ - v rs- = 0, r rsp = r rsn = 500 gain error histogram max9937 toc07 gain error (%) frequency (%) -0.1 -0.2 -0.3 0 0.1 0.2 0.3 0.4 0.5 0.6 -40 40 0 80 120 160 gain error vs. temperature max9937 toc08 temperature ( c) gain error (%) -0.8 -0.2 -0.4 -0.6 0 0.2 0.4 0.6 0.8 1.0 412 8 16202428 gain error vs. common-mode voltage max9937 toc09 common-mode voltage (v) gain error (%) t a = +25 c t a = +125 c t a = -40 c 0 1.0 0.5 2.0 1.5 2.5 3.0 -40 40 0 80 120 160 input bias current vs. temperature max9937 toc10 temperature ( c) input bias current ( a) -1.00 0 -0.50 0.50 1.50 1.00 2.00 -40 40 0 80 120 160 input bias current mismatch vs. temperature max9937 toc11 temperature ( c) input bias current mismatch (%) 2.00 2.04 2.12 2.08 2.16 2.20 41216 8 202428 input bias current vs. common-mode voltage max9937 toc12 common-mode voltage (v) input bias current ( a)
max9937 automotive current-sense amplifier with reverse-battery protection 6 _______________________________________________________________________________________ typical operating characteristics (continued) (v cc = 5v, v bat = v rsp = 12v, v sense = v rs+ - v rs- = 0, r rsp = r rsn = 500 supply current vs. temperature max9937 toc17 temperature ( c) supply current ( a) gain vs. frequency referenced to dc gain (c in = 220nf) max9937 toc18 frequency (hz) gain (db) 100k 10k 1k 100 -30 -20 -10 0 10 -40 10 1m c load = 100nf c load = 10pf c load = 1nf 0 0.4 1.2 0.8 1.6 2.0 41216 8 202428 input bias current mismatch vs. common-mode voltage max9937 toc13 common-mode voltage (v) input bias current mismatch (%) 0 1.0 0.5 2.0 1.5 2.5 3.0 3.0 4.0 3.5 4.5 5.0 input bias current vs. supply voltage max9937 toc14 supply voltage (v) input bias current ( a) 80 1.2 1.6 0.8 0.4 0 3.0 4.0 3.5 4.5 5.0 input bias current mismatch vs. supply voltage max9937 toc15 supply voltage (v) input bias current mismatch (%) 15 17 16 18 19 3.0 3.8 3.6 3.2 3.4 4.0 4.2 4.4 4.6 4.8 5.0 supply current vs. supply voltage max9937 toc16 supply voltage (v) supply current ( a)
max9937 automotive current-sense amplifier with reverse-battery protection _______________________________________________________________________________________ 7 typical operating characteristics (continued) (v cc = 5v, v bat = v rsp = 12v, v sense = v rs+ - v rs- = 0, r rsp = r rsn = 500 output slew rate v sense = -5mv to +5mv out 50mv/div in 10mv/div max9937 toc19 +5 -5 0v 4 s/div output slew rate v sense = 5mv to 200mv out 2v/div in 100mv/div max9937 toc20 100ms/div load-dump protection out 1v/div v cm 10v/div max9937 toc21 4 s/div reverse-battery protection out 2v/div v cm 10v/div max9937 toc22 rsp 5v/div output-voltage nonlinearity vs. sense voltage max9937 toc23 sense voltage (mv) % of full-scale 100 80 60 40 20 -0.05 0 0.05 0.10 0.15 0.20 -0.10 1 120 140 160 180 200 t a = +25 c t a = +125 c t a = -40 c 2.00 1.00 0 3.00 4.00 5.00 6.00 7.00 8.00 9.00 -40 40 0 80 120 160 maximum output current vs. temperature max9937 toc24 temperature ( c) output current (ma) v bat = 28v v bat = 12v v bat = 4v
max9937 detailed description the max9937 unidirectional high-side, current-sense amplifier features a 4v to 28v input common-mode volt- age range that is independent of supply voltage (v cc = 2.7v to 5.5v). the max9937 monitors the current through a current-sense resistor by converting the sense voltage to a current output (out). gain is set by the ratio of an output resistor (r out ) and an input resistor (r rsp ). high- side current monitoring with the max9937 does not inter- fere with the ground path of the load, making it useful for a variety of automotive battery/ecu monitoring. robust input esd structure allows input common-mode voltages to exceed the 28v maximum operating input range for short durations, making the max9937 ideal for applications that need to withstand short-duration load-dump conditions. the max9937 is able to with- stand reverse-battery conditions by a suitable choice of input resistors (r rsn , r rsp ). see the input common- mode voltages > 28v and < 0v section . current-sense amplifier operation the max9937 current-sense amplifier operation is best understood as a specialized op-amp circuit with a p-channel fet in the feedback path. the op amp forces a current through an external gain resistor at rsp (r rsp , see the typical application circuit ) so that its voltage drop equals the voltage drop across the external sense resistor, r sense , making the voltage at rsp the same as rsn. an external resistor at rsn (r rsn ) has the same value as r rsp to minimize input offset voltage due to input bias currents. the current through r rsp is now sourced by the high- voltage p-channel fet into an external resistor (r out ) at out. this produces an output voltage whose magni- tude is given by the following equations: the gain accuracy is primarily determined by the matching of the two gain resistors, r rsp and r out . the voltage gain error of the max9937 is less than 1.5%. total gain = 20v/v with r out = 10k
in this case, r rs = r rsp = r rsn ,
max9937 automotive current-sense amplifier with reverse-battery protection 10 ______________________________________________________________________________________ at frequencies below the output corner frequency, the max9937 itself provides excellent 100db (dc) com- mon-mode rejection. at higher frequencies, as the cmrr of the max9937 degrades, the output filter formed by r out and c out helps boost the common- mode rejection of the circuit. input common-mode voltages > 28v and < 0v short-duration overvoltages on the battery line are iso- lated from the rsp and rsn pins of the max9937 by the use of input resistors r rsp and r rsn . the input esd clamp structure is designed so that the device can withstand short-duration (< 1s) overvoltages up to 40v when using resistors r rsp and r rsn of 500 max9937 sc70 top view 2 34 + pin configuration chip information process: bicmos package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . package type package code document no. 5 sc70 x5+1 21-0076
max9937 automotive current-sense amplifier with reverse-battery protection 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 ____________________ 11 ? 2008 maxim integrated products is a registered trademark of maxim integrated products, inc. package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .) sc70, 5l.eps package outline, 5l sc70 21-0076 1 1 e

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