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general description the MAX9934** high-precision, low-voltage, high-side current-sense amplifier is ideal for both bidirectional (charge/discharge) and unidirectional current measure- ments in battery-powered portable and laptop devices. input offset voltage (v os ) is a low 10? (max) at +25? across the -0.1v to 5.5v input common-mode voltage range, and is independent of v cc . its precision input specification allows the use of very small sense volt- ages (typically ?0mv full-scale) for minimally invasive current sensing. the output of the MAX9934 is a current proportional to input v sense and is available in either 25?/mv or 5?/mv gain options (g m ) with gain accuracy better than 0.25% (max) at +25?. a chip select (cs) allows multiplexing of several MAX9934 current outputs to a single microcontroller adc channel (see the typical operating circuit ). cs is compatible with 1.8v and 3.3v logic systems. the MAX9934 is designed to operate from a 2.5v to 3.6v v cc supply, and draws just 120? (typ) quiescent current. when powered down (v cc = 0), rs+ and rs- draw less than 0.1na (typ) leakage current to reduce battery load. the MAX9934 is robust and protected from input faults of up to ?v input differential voltage between rs+ and rs-. the MAX9934 is specified for operation over the -40? to +125? temperature range and is available in 8-pin ?ax , 6-pin ?fn (2mm x 2mm x 0.8mm), or a 6- bump ucsp (1mm x 1.5mm x 0.6mm), making it ideal for space-sensitive applications. applications pdas and smartphones mp3 players sensor instrumentation amplifiers notebook pcs and ultra-mobile pcs portable current monitoring features input offset voltage: 10 v (max) gain error less than 0.25% -0.1v to +5.5v input common-mode voltage range chip select allows multiplexing several MAX9934 current monitors to one adc current output allows r out selection for gain flexibility single supply operation: 2.5v to 3.6v two gain options: g m of 25 a/mv (MAX9934t) and 5 a/mv (MAX9934f) bidirectional or unidirectional operation small, 6-bump ucsp (1mm x 1.5mm x 0.6mm), 6-pin dfn (2mm x 2mm x 0.6mm), and 8-pin max packages MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing ________________________________________________________________ maxim integrated products 1 19-5011; rev 0; 10/09 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available ordering information part gain pin- package top mark MAX9934falt+t* 5?/mv 6 ?fn acp MAX9934fart+t* 5?/mv 6 ucsp aag MAX9934faua+t 5?/mv 8 ?ax MAX9934talt+t* 25?/mv 6 ?fn aco MAX9934tart+t* 25?/mv 6 ucsp aaf MAX9934taua+t 25?/mv 8 ?ax note: all devices are specified over the -40? to +125? extended temperature range. + denotes a lead(pb)-free/rohs-compliant package. t = tape and reel. * future product?ontact factory for availability. ?ax is a registered trademark and ucsp is a trademark of maxim integrated products, inc. **patent pending. i load r sense rs- rs+ -0.1v v cm 5.5v v cc = 3.3v v cc cs gnd MAX9934 out r out 10k ? v out to adc from c chip select 1000pf 0.1 f typical operating circuit
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = 3.3v, v rs+ = v rs- = 3.0v, v sense = 0, v cm = (v rs+ + v rs- )/2, v cs = 3.3v, r out = 10k ? to gnd for unidirectional operation, r out = 10k ? to v cc /2 for bidirectional operation. t a = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) (note 2) 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. rs+, rs- to gnd......................................................-0.3v to +6v v cc to gnd ..............................................................-0.3v to +4v cs, out to gnd (v cc = 0, or cs < v il )..................-0.3v to +4v out to gnd (cs > v ih )................................-0.3v to v cc + 0.3v differential input voltage (rs+ - rs-) ....................................?v output short-circuit current duration out to gnd or v cc ...............................................continuous continuous input current into any terminal.....................?0ma continuous power dissipation (t a = +70?) 8-pin ?ax (derate multilayer 4.8mw/? above +70?).............................................................388mw junction-to-ambient thermal resistance ( ja ) (note 1) ....................................................................206?/w junction-to-case thermal resistance ( jc ) (note 1) ......................................................................42?/w 6-pin ?fn (derate multilayer 4.5mw/? above +70?)..........................................................357.8mw junction-to-ambient thermal resistance ( ja ) (note 1 ) ................................................................223.6?/w junction-to-case thermal resistance ( ja ) (note 1) ....................................................................122?/w 6-bump ucsp (derate multilayer 3.9mw/? above +70?).............................................................308mw junction-to-ambient thermal resistance ( ja ) (note 1) ....................................................................260?/w operating temperature range .........................-40? to +125? junction temperature ......................................................+150? storage temperature range .............................-65? to +160? lead temperature (soldering, 10s) .................................+300? reflow soldering temperature (ucsp, ?fn, and ?ax) ..........................................................................+260? parameter symbol conditions min typ max units dc characteristics t a = +25? ?0 MAX9934t -40? t a +125? ?4 t a = +25? ?0 input offset voltage (note 3) v os MAX9934f -40? t a +125? ?0 ? MAX9934t ?0 input offset voltage drift (note 3) v os /dt MAX9934f ?0 nv/? common-mode input voltage range (average of v rs + and v rs - ) (note 3) cmvr guaranteed by cmrr2 -0.1 +5.5 v t a = +25? 128 134 0 v cm v cc - 0.2v (MAX9934f) -40? t a +125? 112 t a = +25? 128 135 cmrr1 0 v cm v cc - 0.2v (MAX9934t) -40? t a +125? 109 t a = +25? 119 125 -0.1 v cm 5.5v (MAX9934f) -40? t a +125? 104 t a = +25? 98 113 common-mode rejection ratio (note 3) cmrr2 -0.1 v cm 5.5v (MAX9934t) -40? t a +125? 98 db note 1: package thermal resistances were obtained using the method described in jedec specification jesd51-7, using a four- layer board. for detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial .
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing _______________________________________________________________________________________ 3 parameter symbol conditions min typ max units MAX9934t 25 current gain (transconductance) g m MAX9934f 5 ?/mv t a = +25? ?.25 MAX9934t -40? t a +125? ?.0 t a = +25? ?.25 current gain error (note 4) g me MAX9934f -40? t a +125? ?.4 % MAX9934t ?00 gain error drift g me /dt MAX9934f ?40 ppm/? input-bias current for rs+ i brs+ v rs + = v rs - = 5.5v 0.1 100 na v rs + = v rs - v cc - 0.2v 0.1 100 na input-bias current for rs- i brs- v rs + = v rs - = 5.5v 35 60 ? input leakage current i lek v cc = 0, v rs+ = v rs - = 5.5v 0.1 100 na dc characteristics minimum current for output low i ol unidirectional, v ol = i ol x r out 1 100 na v oh i out = +600?, v oh = v cc - v out 0.1 0.25 output-voltage range (MAX9934t) v ol i out = -600?, bidirectional 0.15 0.25 v v oh i out = +375?, v oh = v cc - v out 0.18 0.30 output-voltage range (MAX9934f) v ol i out = -375?, bidirectional 0.18 0.26 v deselected amplifier output leakage i olk v cs = 0, v out = 3.6v, and 0 v cc 3.6v 0.1 100 na logic i/o (cs) input voltage low cs v il 0.54 v input voltage high cs v ih 1.26 v input current cs i il ,i ih 0 v cs v cc 0.1 100 na power supply supply-voltage range v cc guaranteed by psrr 2.5 3.6 v power-supply rejection ratio psrr 2.5v v cc 3.6v, v rs+ = v rs- = 2v (note 3) 110 120 db supply current i cc v cc = 3.3v, r out = 10k ? to 3.3v, v rs+ = v rs- = 3.1v 120 230 ? supply current, output deselected i cc , des v cs = 0, r out = 10k ? to 3.3v, v rs+ = v rs- = 3.1v 120 210 ? ac characteristics (c l = 1000pf) MAX9934t g m = 25?/mv, v sense = 5mv 1.5 amplifier bandwidth bw MAX9934f g m = 5?/mv, v sense = 25mv 5 khz electrical characteristics (continued) (v cc = 3.3v, v rs+ = v rs- = 3.0v, v sense = 0, v cm = (v rs+ + v rs- )/2, v cs = 3.3v, r out = 10k ? to gnd for unidirectional operation, r out = 10k ? to v cc /2 for bidirectional operation. t a = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) (note 2)
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 4 _______________________________________________________________________________________ parameter symbol conditions min typ max units 0.1% final value, figure 1, MAX9934t 670 output settling time t s 0.1% final value, figure 1, MAX9934f 220 ? output to 0.1% final value, figure 2, MAX9934t 150 output select time t zh output to 0.1% final value, figure 2, MAX9934f 80 ? output deselect time t hz output step of 100mv, c l = 10pf, figure 2 2s power-down time t pd output step of -100mv, c l = 10pf, v cc > 2.5v 2s 0.1% final value, figure 3, MAX9934t 300 power-up time t pu 0.1% final value, figure 3, MAX9934f 200 ? electrical characteristics (continued) (v cc = 3.3v, v rs+ = v rs- = 3.0v, v sense = 0, v cm = (v rs+ + v rs- )/2, v cs = 3.3v, r out = 10k ? to gnd for unidirectional operation, r out = 10k ? to v cc /2 for bidirectional operation. t a = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) (note 2) note 2: all devices are 100% production tested at t a = +25?. unless otherwise noted, specifications overtemperature are guaran- teed by design. note 3: guaranteed by design. thermocouple, contact resistance, rs- input-bias current, and leakage effects preclude measure- ment of this parameter during production testing. devices are screened during production testing to eliminate defective units. note 4: gain error tested in unidirectional mode: 0.2v v out 3.1v for the MAX9934t; 0.25v v out 2.5v for the MAX9934f.
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing _______________________________________________________________________________________ 5 typical operating characteristics (v cc = 3.3v, v rs+ = v rs- = 3.0v, v sense = 0, c l = 1000pf, r out = 10k ? to gnd for unidirectional operation, r out = 10k ? to v cc /2 for bidirectional operation. t a = +25?, unless otherwise noted.) MAX9934t v os histogram m ax9934 toc01 v os ( f v) n (%) -8 -6 -4 -2 0 2 4 6 8 5 10 15 20 25 30 35 40 0 -10 10 offset voltage vs. common-mode voltage m ax9934 toc04 co mm on- m ode voltage (v) offset voltage ( f v) 4 . 8 4 . 1 2 . 7 3 . 4 1 . 3 2 . 0 0 . 6 -8 -6 -4 -2 0 2 4 6 8 10 -10 -0 . 15 . 5 v cc = 3 . 3v v cc = 3 . 6v v cc = 2 . 5v MAX9934t drift v os histogram m ax9934 toc02 tcv os (nv/ n c) n (%) 6 1218243036424854 5 10 15 20 25 30 0 060 offset voltage vs. common-mode voltage m ax9934 toc03 co mm on- m ode voltage (v) offset voltage ( f v) 4 . 8 4 . 1 2 . 7 3 . 4 1 . 3 2 . 0 0 . 6 -8 -6 -4 -2 0 2 4 6 8 10 -10 -0 . 15 . 5 t a = +125 n c t a = +25 n c t a = -40 n c 0 0.5 1.5 1.0 2.5 3.0 2.0 3.5 02030 10 40 50 60 70 80 v out vs . v sense v ref = gnd MAX9934 toc09 v sense (mv) v out (v) gain = 25 a/mv gain = 5 a/mv unidirectional 5 10 15 20 25 30 0 -0 . 16 -0 . 12 -0 . 08 -0 . 04 0 0 . 04 0 . 08 0 . 12 0 . 16 -0 . 20 0 . 20 MAX9934t gain error histogram m ax9934 toc05 ge (%) n (%) 5 10 15 20 25 30 35 0 -160 -120 -80 -40 0 40 80 120 160 -200 200 MAX9934t gain error drift histogram m ax9934 toc06 tc ge (pp m / n c) n (%) 5 10 15 20 25 30 35 40 0 -0 . 16 -0 . 12 -0 . 08 -0 . 04 0 0 . 04 0 . 08 0 . 12 0 . 16 -0 . 20 0 . 20 MAX9934f gain error histogram m ax9934 toc07 ge (%) n (%) -160 -120 -80 -40 0 40 80 120 160 -200 200 MAX9934f gain error drift histogram m ax9934 toc08 tc ge (pp m /c) n (%) 5 10 15 20 25 0
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 6 _______________________________________________________________________________________ typical operating characteristics (continued) (v cc = 3.3v, v rs+ = v rs- = 3.0v, v sense = 0, c l = 1000pf, r out = 10k ? to gnd for unidirectional operation, r out = 10k ? to v cc /2 for bidirectional operation. t a = +25?, unless otherwise noted.) -2.0 -0.5 -1.0 -1.5 0.5 0 1.5 1.0 2.0 v out vs . v sense v ref = 1 . 65v MAX9934 toc10 v sense (mv) v out - v ref (v) -40 -20 0 20 40 gain = 25 a/mv gain = 5 a/mv bidirectional v out vs. v sense (v out < 5mv) m ax9934 toc11 v sense + v os ( f v) v out (mv) 80 60 40 20 1 2 3 4 5 0 0100 g = 25 f a/mv g = 5 f a/mv 0 100 50 200 150 250 300 0 200 300 100 400 500 600 v oh vs . i oh MAX9934 toc12 i oh ( a) v oh (mv) MAX9934f MAX9934t 40 80 60 120 100 140 160 -40 -10 5 20 -25 35 50 65 80 95 110 125 supply current vs . temperature (v cs = 0) MAX9934 toc13 temperature ( c) supply current ( a) v cm = 0v v cm = 5.5v 40 80 60 120 100 140 160 -40 -10 5 20 -25 3550658095110125 supply current vs . temperature MAX9934 toc14 temperature ( c) supply current ( a) v cm = 0v v cm = 5.5v 1pa 10pa 100pa 1na 10na -0.1 1.3 2.7 4.1 0.6 2.0 3.4 4.8 5.5 rs+ bias current vs . v rs+ MAX9934 toc15 v rs+ (v) rs+ bias current t a = +125 c t a = +25 c and -40 c
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing _______________________________________________________________________________________ 7 typical operating characteristics (continued) (v cc = 3.3v, v rs+ = v rs- = 3.0v, v sense = 0, c l = 1000pf, r out = 10k ? to gnd for unidirectional operation, r out = 10k ? to v cc /2 for bidirectional operation. t a = +25?, unless otherwise noted.) 1pa 10pa 1na 100pa 10na 100na -0.1 0.9 0.4 1.4 1.9 2.4 2.9 3.4 rs- bias current vs . v rs- (-0 . 1v v rs- v cc ) MAX9934 toc16 v rs- (v) rs- bias current (pa) t a = +125 c t a = +25 c and -40 c 0 15 10 5 20 25 30 35 40 45 50 3.0 4.0 3.5 4.5 5.0 5.5 rs- bias current vs . v rs- ( 3v v rs_ 5 . 5v) MAX9934 toc17 v rs- (v) rs- bias current ( a) t a = +125 c t a = +25 c t a = -40 c 100fa 1pa 100pa 10pa 1na 10na 0 1.0 1.5 0.5 2.0 2.5 3.0 3.5 4.0 output leakage current vs . v out (v cs = 0) MAX9934 toc18 v out (v) output leakage current t a = +125 c t a = +25 c t a = -40 c 1pa 10pa 100pa 1na 10na 0 1.0 2.0 3.0 0.5 1.5 2.5 3.5 4.0 output leakage current vs . v out (v cc = 0, v cs = 0) MAX9934 toc19 v out (v) output leakage current t a = +125 c t a = +25 c t a = -40 c normalized gain vs. frequency m ax9934 toc20 frequency (hz) nor m alized gain (db) 10k 1k 100 10 -30 -20 -10 0 10 -40 1 100k g = 5 f a/mv g = 25 f a/mv common-mode rejection ratio vs. frequency m ax9934 toc21 frequency (khz) c m rr (db) 10 1 . 0 0 . 1 -120 -100 -80 -60 -40 -20 0 -140 0 . 01 100
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 8 _______________________________________________________________________________________ typical operating characteristics (continued) (v cc = 3.3v, v rs+ = v rs- = 3.0v, v sense = 0, c l = 1000pf, r out = 10k ? to gnd for unidirectional operation, r out = 10k ? to v cc /2 for bidirectional operation. t a = +25?, unless otherwise noted.) power-supply rejection ratio vs. frequency m ax9934 toc22 frequency (khz) psrr (db) 10 1 . 0 0 . 1 -100 -80 -60 -40 -20 0 -120 0 . 01 100 output setting time vs . percentage of final value MAX9934 toc23 percentage of final value ( % ) setting time (ms) 0.10 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 1.00 0.01 1v v out step MAX9934t MAX9934f 100 s/div large-signal input step response (MAX9934f) v sense 20mv/div v out 500mv/div MAX9934 toc24 0.01 % final value 1 % final value 2v 1v 400 s/div large-signal input step response (MAX9934t) v sense 5mv/div v out 500mv/div MAX9934 toc25 0.01 % final value 1 % final value 2v 1v m ax9934 toc26 1v 1v 40 f s/d i v v cs 2v/d i v v out 500mv/d i v v out 500mv/d i v 1% final value 0 . 1% final value 0 . 1% final value m ax9934t m ax9934f 1% final value output select time 4 s/div cs disabled transient response c out = 10pf (MAX9934t) v cs 2v/div v out 1v/div MAX9934 toc27 c l = 0
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing _______________________________________________________________________________________ 9 typical operating characteristics (continued) (v cc = 3.3v, v rs+ = v rs- = 3.0v, v sense = 0, c l = 1000pf, r out = 10k ? to gnd for unidirectional operation, r out = 10k ? to v cc /2 for bidirectional operation. t a = +25?, unless otherwise noted.) power-up time m ax9934 toc28 1v 1v 100 f s/d i v v cs 2v/d i v v out 500mv/d i v v out 500mv/d i v m ax9934t m ax9934f 1% final value 0 . 1% final value c bypass = 0 . 1f 1% final value 0 . 1% final value saturation recovery time v out = v ol to 1v (MAX9934t) m ax9934 toc29 1mv 0v 1v unidirectional 400 f s/d i v v sense 5mv/d i v v out 500mv/d i v 400 s/div saturation recovery time v out = v oh to 1v (MAX9934t) v sense 10mv/div v out 1v/div MAX9934 toc30 1v unidirectional
MAX9934 detailed description the MAX9934 high-side, current-sense amplifier moni- tors current through an external current-sense resistor by amplifying the voltage across the resistor (v sense ) to create an output current (i out ). an output voltage (v out ) then develops across the external output resis- tor (r out ). see the typical operating circuit . the MAX9934 uses precision amplifier design tech- niques to achieve a low-input offset voltage of less than 10?. these techniques also enable extremely low-input offset voltage drift over time and temperature and achieve gain error of less than 0.25%. the precision v os specification allows accurate current measurements with a low-value current-sense resistor, thus reducing power dissipation in battery-powered systems, as well as load- regulation issues in low-voltage dc power supplies. the MAX9934 high-side current-sense amplifier fea- tures a -0.1v to +5.5v input common-mode range that is independent of supply voltage (v cc ). this ability to sense at voltages beyond the supply rail allows the monitoring of currents out of a power supply even in a shorted condition, while also enabling high-side current sensing at voltages greater than the MAX9934 supply high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 10 ______________________________________________________________________________________ pin description pin/bump ucsp ?ax ?fn name function a1 1 1 v cc power supply a2 2 2 out current output. out provides an output current proportional to input v sense . connect an external resistor (r out ) from out to gnd for unidirectional sensing or to an external reference voltage for bidirectional sensing. a3 3 3 gnd ground b1 8 6 rs+ sense resistor power side connection b2 7 5 rs- sense resistor load side connection b3 6 4 cs chip-select input. drive cs high to enable out, drive cs low to put out in a high- impedance state. 4, 5 n.c. no connection. not internally connected. % final value v out 1v step t s 2v 1v t s % final value v sense figure 1. output settling time cs out gnd rs- rs+ v cc *r gain g m MAX9934 g m *r gain = 40 ? for the MAX9934t and r gain = 200 ? for the MAX9934f. functional diagram
voltage. further, when v cc = 0, the amplifier maintains an extremely high impedance on both its inputs and output, up to the maximum operating voltages (see the absolute maximum ratings section). the MAX9934 features a cs that can be used to dese- lect its output current-source. this allows multiple cur- rent-sense amplifier outputs to be multiplexed into a single adc channel with a single r out . see the chip select functionality for multiplexed systems section for more details. the functional diagram shows the internal operation of the MAX9934. at its core is the indirect current-feed- back architecture. this architecture uses two matched transconductance amplifiers to convert their input dif- ferential voltages into an output current. a high-gain feedback amplifier forces the voltage drop across r gain to be the same as the input differential voltage. the internal resistor (r gain ) sets the transconductance gain of the device. both input and output transconduc- tance amplifiers feature excellent common-mode rejec- tion characteristics, helping the MAX9934 to deliver industry-leading precision specifications over the full common-mode range. applications information advantages of current-output architecture the transconductance transfer function of the MAX9934 converts input differential voltage to an output current. an output termination resistor, r out , then converts this current to a voltage. in a large circuit board with multi- ple ground planes and multiple current-measurement rails spread across the board, traditional voltage-output current-sense amplifiers become susceptible to ground-bounce errors. these errors occur because the local ground at the location of the current-sense amplifi- er is at a slightly different voltage than the local ground voltage at the adc that is sampling the voltage. the MAX9934 allows accurate measurements to be made even in the presence of system ground noise. this is achieved by sending the output information as a cur- rent, and by terminating to the adc ground. a further advantage of current-output systems is the flexibility in setting final voltage gain of the device. since the final voltage gain is user-controlled by the choice of output termination resistor, it is easy to opti- mize the monitored load current range to the adc input voltage range. it is no longer necessary to increase the size of the sense resistor (also increasing power dissi- pation) as necessary with fixed-gain, voltage-output current-sense amplifiers. MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing ______________________________________________________________________________________ 11 100mv t hz % final value t zh v out 0v 1.8v v cs figure 2. output select and deselect time 100mv t pd % final value t pu v cc v out 0v 3.3v 2.5v figure 3. output power-up and power-down time
MAX9934 chip-select functionality for multiplexed systems the MAX9934 features a cs that can be used to dese- lect the output current - source achieving a high-imped- ance output with 0.1na leakage current. thus, different supply voltages can be used to power different MAX9934 devices that are multiplexed on the same bus. this technique makes it possible for advanced current monitoring and power-management schemes to be implemented when a limited number of adc chan- nels are available. in a multiplexed arrangement, each MAX9934 is typi- cally placed near the load being monitored and all amplifier outputs are connected in common to a single load resistor located adjacent to the monitoring adc. this resistor is terminated to the adc ground reference as shown in figure 4 for unidirectional applications. figure 5 shows a bidirectional multiplexed application. terminating the external resistor at the ground refer- ence of the adc minimizes errors due to ground shift as discussed in the advantages of current-output architecture section. the MAX9934 is capable of both sourcing and sinking current from out, and thus can be used as a precision bidirectional current-sense amplifier. to enable this functionality, terminate r out to a midrail voltage v bias . high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 12 ______________________________________________________________________________________ v cc = 3.3v v cc = 3.3v v cc = 3.3v r sense -0.1v v cm 5.5v r sense -0.1v v cm 5.5v r sense -0.1v v cm 5.5v MAX9934 MAX9934 MAX9934 10k ? (optional) adc cs3 cs2 cs1 microcontroller v in1 v in2 v in3 i load3 i load2 i load1 v out 0.1 f 0.1 f 0.1 f out3 out2 out1 unidirectional operation figure 4. typical application circuit showing chip-select multiplexing
in figure 5, v out is equal to v bias when the sum of all outputs is zero. for positive input-sense voltages, the MAX9934 sources current causing its output voltage to rise above v bias . for negative input-sense voltages, the MAX9934 sinks current causing its output voltage to be lower than v bias , thus allowing bidirectional current sensing. since the adc reference voltage, v ref , determines the full-scale reading, a common choice for v bias is v ref /2. the current output makes it possible to use a simple resistor-divider from v ref to gnd to generate v bias . the output resistance for gain calculation is the parallel combination of the two resistors. for example, if two equal value resistors, r, are used to generate a v bias = v ref /2, the output termination resistance for gain calculation is r out = r/2. see figure 5. MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing ______________________________________________________________________________________ 13 v cc = 3.3v v cc = 3.3v v cc = 3.3v r sense -0.1v v cm 5.5v r sense -0.1v v cm 5.5v r sense -0.1v v cm 5.5v MAX9934 MAX9934 MAX9934 r 10k ? adc v ref cs2 cs1 microcontroller cs cs cs to external reference voltage 10k ? r cs3 (optional) v in1 v in2 v in3 i load3 i load2 i load1 v out out3 out2 out1 r out = r 2 figure 5. bidirectional multiplexed operation
MAX9934 a MAX9934 can be deselected by either forcing v cs low as shown in figures 4 and 5, or by making v cc = 0 as shown in figure 6. in all these conditions, the MAX9934 maintains a high-impedance output with 0.1na (typ) leakage current. in this state, out can rise above v cc if necessary. thus, different supply voltages can be used to power different MAX9934 devices that are multiplexed on the same out bus. multiplexing by forcing the MAX9934 to be powered down (v cc = 0) reduces its supply current to zero to help extend bat- tery life in portable applications. choosing r sense and r out in the current-sense application, the monitored load current (i load ) develops a sense voltage (v sense ) across a current-sense resistor (r sense ). the MAX9934 sources or sinks an output current that is pro- portional to v sense . finally, the MAX9934 output cur- rent is provided to an output resistor (r out ) to develop an output voltage across r out that is proportional to the sensed load current. high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 14 ______________________________________________________________________________________ v cc = 3.3v r sense -0.1v v cm 5.5v MAX9934 r out 10k ? (optional) adc cs2 cs1 microcontroller cs cs3 v cc = 3.3v r sense -0.1v v cm 5.5v MAX9934 cs v cc = 3.3v r sense -0.1v v cm 5.5v MAX9934 cs 1/4 max4737 1/4 max4737 1/4 max4737 v in1 v in2 v in3 i load1 out3 out2 out1 0.1 f 0.1 f 0.1 f i load3 i load2 figure 6. multiplexed amplifiers with power saving
three components are to be selected to optimize the current-sense system: r sense , r out , and the MAX9934 gain option (g m = 25?/mv or 5?/mv). tables 1 and 2 are gain tables for unidirectional and bidirectional operation, respectively. they offer a few examples for both MAX9934 options having an output range of 3.1v unidirectional and ?.65v bidirectional. note that the output current of the MAX9934 adds to its quiescent current. this can be calculated as follows: i out,max = v out,max /r out when selecting r sense , consider the expected magni- tude of i load and the required v sense to manage power dissipation in r sense : r sense = v sense,max /i load,max r sense is typically a low-value resistor specifically designed for current-sense applications. finally, in selecting the appropriate MAX9934 gain option (g m ), consider both the required v sense and i out : g m = i out,max /v sense,max once all three component values have been selected in the current-sense application, the system performance is represented by: v sense = r sense x i load and v out = v sense x g m x r out accuracy in a first-order analysis of accuracy there are two MAX9934 specifications that contribute to output error, input offset (v os ) and gain error (ge). the MAX9934 has a maximum v os of 10? and a maximum ge of 0.25%. note that the tolerance and temperature coefficient of the chosen resistors directly affect the precision of any measurement system. 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 drifts if it is allowed to self-heat excessively. the precision v os of the MAX9934 allows the use of a small sense resistor to reduce power dissipation and eliminate hot spots. kelvin contacts due to the high currents that flow through r sense , take care to prevent trace resistance in the load current path from causing errors in the sense voltage. use a four ter- minal current-sense resistor or kelvin contacts (force and sense) pcb layout techniques. interfacing the MAX9934 to sar adcs since the MAX9934 is essentially a high-output imped- ance current-source, its output termination resistor, r out , acts like a source impedance when driving an adc channel. most successive approximation register (sar) architecture adcs specify a maximum source resistance to avoid compromising the accuracy of their readings. choose the output termination resistor r out such that it is less than that required by the adc speci- fication (10k ? or less). if the r out is larger than the source resistance specified, the adc internal sampling capacitor can momentarily load the amplifier output and cause a drop in the voltage reading. if r out is larger than the source resistance specified, consider using a ceramic capacitor from adc input to gnd. this input capacitor supplies momentary charge to the internal adc sampling capacitor, helping hold v out constant to within ?/2 lsb during the acquisition period. use of this capacitor reduces the noise in the output signal to improve sensitivity of measurement. MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing ______________________________________________________________________________________ 15 part v sense (mv) output current (?) r out (k ? ) gain (v/v) 12.4 310 10 250 MAX9934t 24.8 620 5 125 62 310 10 50 MAX9934f 75 375 8 40 table 1. unidirectional gain table* * all calculations were made with v cc = 3.3v and v out(max) = v cc - v oh = 3.1v. part v sense (mv) output current (?) r out (k ? ) gain (v/v) ?.8 ?45 10 250 ?1.6 ?90 5 125 MAX9934t ?4 ?00 2.4 60 ?9 ?45 10 50 ?8 ?90 5 25 MAX9934f ?2 ?60 4 20 table 2. bidirectional gain table* * all calculations were made with v cc = 3.3v, v out(max) = v cc - v oh = 3.1v, v out(min) = v ol , and out connected to an exter- nal reference voltage of v ref = 1.65v through r out .
MAX9934 effect of input-bias currents the MAX9934 has extremely low cmos input-bias cur- rents at both rs+ and rs- (0.1na) when the input com- mon-mode voltage is less than the supply voltage. when the input common-mode voltage becomes higher than the supply voltage, it draws the input stage operat- ing current from rs-, 35? (typ). rs+ maintains its cmos input characteristics. low-input-bias currents are extremely useful in design of input filters for current-sense amplifiers. input differ- ential filters are sometimes required to average out rapidly varying load currents. an example of such load currents are those consumed by a processor, or switching power supply. large bias and offset currents can interact with resistors used in these external filters to generate large input offset voltages and gain errors. for more detailed information, see application note an3888: performance of current-sense amplifiers with input series resistors . due to the low-input-bias currents, resistors as large as 10k ? can be easily used without impact on error speci- fications with the MAX9934. for applications where the input common-mode voltage is below v cc , a balanced differential filter can be used. for applications where the input common-mode voltage extends above v cc , use a one-sided filter with a capacitor between rs+ and rs-, and a filter resistor in series with rs+ to main- tain the excellent performance of the MAX9934. see figure 7. pcb layout for applications where the input common-mode voltage extends above v cc , trace resistance between r sense and rs- influences the effective v os error due to the voltage drop developed across the trace resistance by the 35? input bias current at rs-. monitoring very low currents the accuracy of the MAX9934 leads to a wide dynamic range. this applies to both unidirectional mode and bidirectional mode. this is made possible in the unidi- rectional mode because the output maintains gain accuracy below 1mv as shown in the v out vs. v sense (v out < 5mv) graph in the typical operating char- acteristics . extending the useful output below 1mv makes it possible for the MAX9934 to accurately moni- tor very low currents. use as precision instrumentation amplifier when the input common-mode voltage is below v cc , the input bias current of the rs- input drops to the 10pa range, the same range as the rs+ input. this low-input-bias current in combination with the rail-to-rail common-mode input range, the extremely high com- mon-mode rejection, and low v os of the MAX9934 make it ideally suited for use as a precision instrumen- tation amplifier. in addition, the MAX9934 is stable into an infinite capacitive load, allowing filtering flexibility. figure 8 shows the MAX9934 in a multiplexed arrange- ment of strain-gauge amplifiers. ucsp applications information for the latest application details on ucsp construction, dimensions, tape carrier information, printed circuit board techniques, bump-pad layout, and recommend- ed reflow temperature profile, as well as the latest infor- mation on reliability testing results go to the maxim website at www.maxim-ic.com/ucsp for the application note 1891: understanding the basics of the wafer-level chip-scale package (wl-csp). high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 16 ______________________________________________________________________________________ buck controller rs+ rs- MAX9934 asic figure 7. one-sided input filter
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing ______________________________________________________________________________________ 17 cs3 cs1 cs2 microcontroller to external reference voltage v ref cs r r out1 v out v cc = 3.3v 0.1 f v in1 MAX9934 cs out2 v cc = 3.3v 0.1 f v in2 cs out3 v cc = 3.3v 0.1 f v in3 MAX9934 MAX9934 r out = r/2 10k ? (optional) 10k ? adc figure 8. multiplexed, strain-gauge amplifier operation
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 18 ______________________________________________________________________________________ chip information process: bicmos rs+ rs- cs top view (bumps on bottom) b2 a2 b3 a3 b1 a1 v cc out gnd ++ ucsp 16 v cc rs+ 25 out rs- 34 gnd cs dfn MAX9934t/f MAX9934t/f cs n.c. n.c. 1 2 8 7 rs+ rs- out gnd v cc max top view 3 4 6 5 MAX9934t/f + pin configurations
MAX9934 package information for the latest package outline information and land patterns, go to www.maxim-ic.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 th e package regardless of rohs status. ucsp.eps package type package code document no. 2x3 ucsp r61a1+1 21-0228 6 ?fn l622+1 21-0164 8 ?ax u8+1 21-0036 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing ______________________________________________________________________________________ 19
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 20 ______________________________________________________________________________________ package information (continued) for the latest package outline information and land patterns, go to www.maxim-ic.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 th e package regardless of rohs status. 6, 8, 10l udfn.eps even terminal l c odd terminal l c l e l a e e d pin 1 index area b e a b n solder mask coverage a a 1 pin 1 0.10x45 l l1 (n/2 -1) x e) sample marking a1 a2 7 package outline, 6, 8, 10l udfn, 2x2x0.80 mm 21-0164 b 1 2 aaa aaa
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing ______________________________________________________________________________________ 21 package information (continued) for the latest package outline information and land patterns, go to www.maxim-ic.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 th e package regardless of rohs status. common dimensions symbol min. nom. a 0.70 0.75 a1 d 1.95 2.00 e 1.95 2.00 l 0.30 0.40 pkg. code n e b package variations l1 6 l622-1 0.65 bsc 0.300.05 0.250.05 0.50 bsc 8 l822-1 0.200.03 0.40 bsc 10 l1022-1 2.05 0.80 max. 0.50 2.05 0.10 ref. (n/2 -1) x e 1.60 ref. 1.50 ref. 1.30 ref. a2 - 0.15 0.20 0.25 0.020 0.025 0.035 package outline, 6, 8, 10l udfn, 2x2x0.80 mm 21-0164 b 2 2
MAX9934 high-precision, low-voltage, current-sense amplifier with current output and chip select for multiplexing 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. 22 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2009 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. package information (continued) for the latest package outline information and land patterns, go to www.maxim-ic.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 th e package regardless of rohs status.

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