1 issue 6 - august 2003 semiconductors zxct1010 description the zxct1010 is a high side current sense monitor. using this device eliminates the need to disrupt the ground plane when sensing a load current. it is an enhanced version of the zxct1009 offering reduced typical output offset and improved accuracy at low sense voltage. the wide input voltage range of 20v down to as low as 2.5v make it suitable for a range of applications. a minimum operating current of just 4a, combined with its sot23-5 package make suitable for portable battery equipment. features ? low cost, accurate high-side current sensing. ? output voltage scaling. ? up to 2.5v sense voltage. ? 2.5v ? 20v supply range. ? 300na typical offset current. ? 3.5a quiescent current. ? 1% typical accuracy. ? sot23 -5 package. applications ? battery chargers ? smart battery packs ? dc motor control ? over current monitor ? power management ? level translating ? programmable current source enhanced high-side current monitor application circuit ordering information part number package partmarking zxct1010e5 sot23-5 101 v v i in in out to load v out r sense r out load gnd zxct1010
2 issue 6 - august 2003 semiconductors zxct1010 absolute maximum ratings voltage on any pin -0.6v to 20v (relative to gnd) continuous output current 25ma continuous sense voltage v in + 0.5v > v sense ? > v in ? 5v operating temperature -40 to 85 c storage temperature -55 to 125 c package power dissipation (t a = 25 c) sot23-5 500mw electrical characteristics test conditions t a = 25 c, v in = 5v, r out = 100 ? . symbol parameter conditions limits unit min typ max v in v cc range 2.5 20 v i out 1 output current v sense =0v v sense = 10mv v sense = 100mv v sense = 200mv v sense =1v 0 85 0.975 1.95 9.7 0.3 100 1.00 2.00 10.0 10 115 1.025 2.05 10.3 a a ma ma ma i q ground pin current v sense = 0v 3.5 8 a v sense 2 sense voltage 0 2500 mv i sense load pin input current 100 na acc accuracy r sense = 0.1 ? v sense = 200mv -2.5 2.5 % gm transconductance, i out /v sense 10000 a/v bw bandwidth rf p in = -20dbm 3 v sense = 10mv dc v sense = 100mv dc 300 2 khz mhz 1 includes input offset voltage contribution 2 v sense =v in -v load 3 -20dbm=63mvp-p into 50 ?
issue 6 - august 2003 semiconductors zxct1010 3 typical characteristics
4 issue 6 - august 2003 semiconductors zxct1010 pin description pin name pin function v in supply voltage load connection to load/battery i out output current, proportional to v in -v load gnd ground sot23-5 package suffix ? e5 top view connection diagram + - v in load i out 100 ? schematic diagram 1 2 3 4 5 nc gnd i out load v in
issue 6 - august 2003 semiconductors zxct1010 5 the following lines describe how to scale a load current to an output voltage. v sense = v in -v load v out = 0.01 x v sense x r out 1 e.g. a 1a current is to be represented by a 100mv output voltage: 1)choose the value of r sense to give 50mv > v sense > 500mv at full load. for example v sense = 100mv at 1.0a. r sense = 0.1/1.0 => 0.1 ohms. 2)choose r out to give v out = 100mv, when v sense = 100mv. rearranging 1 for r out gives: r out =v out /(v sense x 0.01) r out = 0.1 / (0.1 x 0.01) = 100 ? typical circuit application power dissipation the maximum allowable power dissipation of the device for normal operation (pmax), is a function of the package junction to ambient thermal resistance ( ja), maximum junction temperature (tjmax), and ambient temperature (tamb), according to the expression: p max = (tj max ? t amb ) / ja the device power dissipation, p d is given by the expression: p d =i out .(v in -v out ) watts where r load represents any load including dc motors, a charging battery or further circuitry that requires monitoring, r sense can be selected on specific requirements of accuracy, size and power rating. applications information v v i in in out v out r sense r out r load load gnd zxct1010
issue 6 - august 2003 semiconductors zxct1010 6 li-ion charger circuit the above figure shows the zxct1010 supporting the benchmarq bq2954 charge management ic. most of the support components for the bq2954 are omitted for clarity. this design also uses the zetex fzt789a high current super- pnp as the switching transistor in the dc-dc step down converter and the fmmt451 as the drive npn for the fzt789a. the circuit can be configured to charge up to four li-ion cells at a charge current of 1.25a. charge can be terminated on maximum voltage, selectable minimum current, or maximum time out. switching frequency of the pwm loop is approximately 120khz. 100 ? 0.2 ? 100 ? fzt789a bc81725 1k ? bas16 10h fmmt451 140h zhcs1000 220 ? sns pin mod pin charger input to battery + bq2954 5v zxct1010 support components omitted for clarity + - v in load i out applications information (continued) bi-directional current sensing the zxct1010 can be used to measure current bi-directionally, if two devices are connected as shown below. if the voltage v1 is positive with respect to the voltage v2 the lower device will be active, delivering a proportional output current to rout. due to the polarity of the voltage across rsense, the upper device will be inactive and will not contribute to the current delivered to rout. when v2 is more positive than v1, current will be flowing in the opposite direction, causing the upper device to be active instead. non-linearity will be apparent at small values of vsense due to offset current contribution. devices can use separate output resistors if the current direction is to be monitored independently. bi-directional transfer function iout 3 load 5 vin 4 r iout 3 load 5 vin 4 v 1 v v 2 sense out r out -400 -200 0 200 400 0 1 2 3 4 5 output current (ma) sense voltage (mv) output current v sense voltage
issue 6 - august 2003 semiconductors zxct1010 7 pcb trace shunt resistor for low cost solution. the figure below shows output characteristics of the device when using a pcb resistive trace for a low cost solution in replacement for a conventional shunt resistor. the graph shows the linear rise in voltage across the resistor due to the ptc of the material and demonstrates how this rise in resistance value over temperature compensates for the ntc of the device. the figure opposite shows a pcb layout suggestion. the resistor section is 25mm x 0.25mm giving approximately 150m ? using 1oz copper. the data for the normalised graph was obtained using a 1a load current and a 100 ? output resistor. an electronic version of the pcb layout is available at www.zetex.com/isense applications information (continued) layout shows area of shunt resistor compared to sot23-5 package. not actual size actual size
zxct1010 semiconductors 8 issue 6 - august 2003 europe zetex plc fields new road chadderton oldham, ol9 8np united kingdom telephone (44) 161 622 4444 fax: (44) 161 622 4446 hq@zetex.com zetex gmbh streitfeldstra ? e19 d-81673 m nchen germany telefon: (49) 89 45 49 49 0 fax: (49) 89 45 49 49 49 europe.sales@zetex.com americas zetex inc 700 veterans memorial hwy hauppauge, ny 11788 usa telephone: (1) 631 360 2222 fax: (1) 631 360 8222 usa.sales@zetex.com asia pacific zetex (asia) ltd 3701-04 metroplaza tower 1 hing fong road kwai fong hong kong telephone: (852) 26100 611 fax: (852) 24250 494 asia.sales@zetex.com these offices are supported by agents and distributors in major countries world-wide. this publication is issued to provide outline information only which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. the company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. for the latest product information, log on to www.zetex.com ? zetex plc 2003 package dimensions sot23-5 dim millimetres inches min max min max a 0.90 1.45 0.035 0.057 a1 0.00 0.15 0.00 0.006 a2 0.90 1.3 0.035 0.051 b 0.35 0.50 0.014 0.020 c 0.09 0.20 0.0035 0.008 d 2.80 3.00 0.110 0.118 e 2.60 3.00 0.102 0.118 e1 1.50 1.75 0.059 0.069 e 0.95 ref 0.037 ref e1 1.90 ref 0.075 ref l 0.10 0.60 0.004 0.024 a 010010
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