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| ZXCT1011 High-side low drift current monitor Description The ZXCT1011 is a high side current sense monitor. Using this type of device eliminates the need to disrupt the ground plane when sensing a load current. The ZXCT1011 takes the voltage developed across a current shunt resistor and translates it into a proportional output current. A user defined output resistor scales the output current into a ground referenced voltage. A current reference resistor, external to the IC, results in an improved temperature coefficient compared to the ZXCT1009. The wide input voltage range of 20V down to as low as 2.5V make it suitable for a range of applications. With a minimum operating current of just 4uA, combined with its SOT23-5 package make it suitable for portable battery equipment too. Features Accurate high-side current sensing 2.5V to 20V supply range 4 A quiescent current 1% typical accuracy Package SOT23-5 Temperature range -40 to 125C Applications Automotive current measurement Battery management DC motor and solenoid control Over current monitor Power management Typical application circuit Vin R sense Load Pin connections N/C Rshunt 120 3 5 Vsense+ Vsense+ 4 Vsense- Iout Rshunt V ZXCT1011 I out 2 Rout Vsense- GND Ordering information Order code ZXCT1011E5TA Pack SOT23-5 Part mark 1011 Reel Size inches (mm) 7 (180) Tape width 8mm Quantity Per reel 3,000 Issue 1- July 2005 (c) Zetex Semiconductors plc 2005 1 www.zetex.com ZXCT1011 Absolute maximum ratings Vsense+ Voltage on any pin Vsense+ to VsenseOperating temperature Storage temperature Maximum junction temperature Package power dissipation 20 V 0.6V and Vsense+ +0.5V 2.5V -40 to 125C -55 to 150C 150C 300mW at TA = 25C (De-rate to zero at 150C) Operation above the absolute maximum rating may cause device failure. Operation at the absolute maximum ratings, for extended periods, may reduce device reliability. Electrical characteristics Test conditions TA = 25C, Vin = 5V, Rshunt = 120 . Vsense=100mV. Unless otherwise stated. Symbol Parameter Vin* Iout Supply range Output current Conditions Vsense = 0V =10mV =30mV =100mV =200mV =500mV Min 2.5 1 84 273 0.97 1.95 4.85 0 -3 Typ. 4 116 320 1.00 2.00 5.00 10 30 400 1.5 Max 20 15 124 330 1.03 2.05 5.15 500 100 3 150 Units V A A A mA mA mA mV nA % mA/V ppm/ C kHz MHz Vsense Isense Acc gm Tc BW** Sense voltage Vsense- input current Accuracy Transconductance Iout/Vsense Rsense = 0.1 Vsense = 100mV Rshunt = 120 Temperature coefficient Bandwidth Vsense = 10mV CL = 5pF, Rout = 1k Vsense = 100mV CL = 5pF, Rout = 1k Vsense = 200mV, Rout=1k PSSR Supply rejection - 68 - dB NOTES: * Vsense+ relative to Iout. Vsense = (Vsense+) - (Vsense-). Temperature dependent measurements are extracted from characterization and simulation results. ** Where CL is the capacitance across Rout. Issue 1- July 2005 (c) Zetex Semiconductors plc 2005 2 www.zetex.com ZXCT1011 Typical characteristics TA=25C, Rshunt = 120 unless otherwise stated. Issue 1- July 2005 (c) Zetex Semiconductors plc 2005 3 www.zetex.com ZXCT1011 Typical characteristics TA=25C, Rshunt = 120 unless otherwise stated. Issue 1- July 2005 (c) Zetex Semiconductors plc 2005 4 www.zetex.com ZXCT1011 Pin description Pin no. 1 2 Pin name N/C Iout Rshunt VsensePin function No connection Output current - follows transconductance of sense voltage gm = 10mA/V for Rshunt=120 Trimming resistor Input. - used to trim gain value 60 Rshunt 240 3 4 Low side current sense input. - connect to load/battery etc. Must be lower than Vsense+ for correct operation. Cannot be grounded without additional series resistor. High side current sense input. - Connect to supply rail. Must be higher than Vsense+ for correct operation. 5 Vsense+ Application information Design example The following lines describe how to scale a load current to an output voltage. Vsense = (Vsense+) - (Vsense-) = Iload x Rsense Defining then since Iout = Iq + Vsense x gm gm= 1.2 / Rshunt Iout = Iq + [ (Vsense x 1.2) / Rshunt ] = Iq + [ (1.2 x Iload x Rsense / Rshunt) ] Note: Iq is embedded into the specification of the ZXCT1011 and therefore appears an offset error. out = (Rout x Ioffset) + [(1.2 x Rout x Iload x Rsense) / Rshunt] V The output current of the ZXCT1011 is directly related to the size of the trimming resistor used. It is important to ensure the tolerance of Rshunt is considered. A 1% change in Rshunt will cause a 1% change in output. Consider the following: - Issue 1- July 2005 (c) Zetex Semiconductors plc 2005 5 www.zetex.com ZXCT1011 A 1 ampere load current is to be measured into a battery. The output signal required to an over current controller needs to be 3.3V. What is a suitable value of Rout and what will the error due to the supply current be? Vin = 5.0V - 9.0V Iload = 1.0A Output signal required: 3.3V Vin = 5.0V - 9.0V R sense Rshunt 120R 3 5 Vsense+ 4 V sense- Iload = 1A ZXCT R shunt 1011 I out 2 R load 3.3V R out Figure 1 ZXCT1011 to measure a 1.0 A load current To obtain the highest accuracy, choose the of Rsense to give 100mV: Rsense = 0.1/1.0 = 0.1 The transconductance using a 120 resistor will be 10mA/V. Choose Rout to give Vout = 3.3V, when Vsense = 100mV Rearranging equation 1 without the offset error gives: Rout = (Vout x Rshunt) / (1.2 x ILoad x Rsense) Rout = 3.3k Now consider the offset error for this resistor: Offset due to supply current = Rout x 4x10-6A = 13.2mV = 0.4% Issue 1- July 2005 (c) Zetex Semiconductors plc 2005 6 www.zetex.com ZXCT1011 Application information (cont.) Minimum operating voltage The minimum operating voltage of the ZXCT1011 is 2.5V and is defined as the difference between Vsense+ and the Iout pin. It must be ensured that sufficient headroom is given for the operation of the device when considering Rout. Vin = 10V R sense To load Rshunt 120R 3 5 V sense+ R shunt 4 V sense- ZXCT 1011 I out 2 R Vout 3.3K Figure 2 Considerations for supply rail Voltage across device 2.5V Vin - Vout 2.5V Where Vout = Iout x Rout At low supply voltages and high Vsense measurements, special care must be taken to ensure the correct operation. The circuit in figure 2.0 shows a ZXCT1011 operating from 10V supply rail. The minimum operating voltage of the ZXCT1011 is 2.5V. This allows a maximum output voltage of 7.5V to be set at Vout. A 3k resistor on the output would draw a maximum 2.5mA from Iout. - See minimum usable supply voltage graph on page 4. Issue 1- July 2005 (c) Zetex Semiconductors plc 2005 7 www.zetex.com ZXCT1011 Packaging details - SOT23-5 Europe Zetex GmbH Streitfeldstrae 19 D-81673 Munchen 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 Highway 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 Corporate Headquarters Zetex Semiconductors plc Zetex Technology Park, Chadderton Oldham, OL9 9LL United Kingdom Telephone (44) 161 622 4444 Fax: (44) 161 622 4446 hq@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 contact 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. Issue 1- July 2005 (c) Zetex Semiconductors plc 2005 8 www.zetex.com |
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