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 Applications ■ Accurate high-side current sensing ■ Automotive current measurement ■ 2.5V to 20V supply range ■ Battery management ■ 4 µA quiescent current ■ DC motor and solenoid control ■ 1% typical accuracy ■ Over current monitor ■ Package SOT23-5 ■ Power management ■ Temperature range -40 to 125°C Typical application circuit R sense Vin Pin connections Load N/C Rshunt 120 Ω Vsense+ 3 Vsense+ 4 5 Iout Vsense- ZXCT1011 Rshunt Vsense- I out 2 V Rout GND Ordering information Order code Pack Part mark Reel Size inches (mm) Tape width Quantity Per reel ZXCT1011E5TA SOT23-5 1011 7 (180) 8mm 3,000 Issue 1- July 2005 © Zetex Semiconductors plc 2005 1 www.zetex.com ZXCT1011 Absolute maximum ratings Vsense+ 20 V Voltage on any pin 0.6V and Vsense+ +0.5V Vsense+ to Vsense- 2.5V Operating temperature -40 to 125°C Storage temperature -55 to 150°C Maximum junction temperature 150°C Package power dissipation 300mW at TA = 25°C (De-rate to zero at 150°C) 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 = 25°C, Vin = 5V, Rshunt = 120⍀. Vsense=100mV. Unless otherwise stated. Symbol Parameter Conditions Min Typ. Max Units Supply range - 2.5 - 20 V Iout Output current Vsense 1 84 273 0.97 1.95 4.85 4 116 320 1.00 2.00 5.00 15 124 330 1.03 2.05 5.15 µA µA µA mA mA mA Vsense Sense voltage† - 0 - 500 mV Isense - Vsense- input current - - - 100 nA Acc Accuracy Rsense = 0.1⍀ Vsense = 100mV -3 - 3 % gm Transconductance Iout/Vsense Rshunt = 120⍀ - 10 - mA/V Tc Temperature coefficient‡ - - 30 150 ppm/° C BW** Bandwidth Vsense = 10mV CL = 5pF, Rout = 1k⍀ Vsense = 100mV CL = 5pF, Rout = 1k⍀ - 400 - kHz Vsense = 200mV, Rout=1k⍀ - Vin* PSSR Supply rejection = 0V =10mV =30mV =100mV =200mV =500mV 1.5 68 MHz - 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 © Zetex Semiconductors plc 2005 2 www.zetex.com ZXCT1011 Typical characteristics TA=25°C, Rshunt = 120 Issue 1- July 2005 © Zetex Semiconductors plc 2005 unless otherwise stated. 3 www.zetex.com ZXCT1011 Typical characteristics TA=25°C, Rshunt = 120 Issue 1- July 2005 © Zetex Semiconductors plc 2005 unless otherwise stated. 4 www.zetex.com ZXCT1011 Pin description Pin no. Pin name Pin function 1 N/C No connection 2 Iout Output current - follows transconductance of sense voltage gm = 10mA/V for Rshunt=120⍀ 3 Rshunt Trimming resistor Input. - used to trim gain value 60⍀ ⱕ Rshunt ⱕ 240⍀ 4 Vsense- 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. 5 Vsense+ High side current sense input. – Connect to supply rail. Must be higher than Vsense+ for correct operation. 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 Iout = Iq + Vsense x gm since 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. ∴Vout = (Rout x Ioffset) + [(1.2 x Rout x Iload x Rsense) / Rshunt] 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 © 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 5 Vsense+ 3 Iload = 1A 4 V sense- ZXCT R shunt 1011 I out R load 2 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 4x10-6µA = 13.2mV = 0.4% Issue 1- July 2005 © 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. R sense Vin = 10V Rshunt 120R 5 4 V sense- V sense+ 3 R shunt To load ZXCT 1011 I out R 2 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 © Zetex Semiconductors plc 2005 7 www.zetex.com ZXCT1011 Packaging details - SOT23-5 Europe Americas Asia Pacific Corporate Headquarters Zetex GmbH Streitfeldstraße 19 D-81673 München Germany Zetex Inc 700 Veterans Memorial Highway Hauppauge, NY 11788 USA Zetex (Asia Ltd) 3701-04 Metroplaza Tower 1 Hing Fong Road, Kwai Fong Hong Kong Zetex Semiconductors plc Zetex Technology Park, Chadderton Oldham, OL9 9LL United Kingdom Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 [email protected] Telephone: (1) 631 360 2222 Fax: (1) 631 360 8222 [email protected] Telephone: (852) 26100 611 Fax: (852) 24250 494 [email protected] Telephone (44) 161 622 4444 Fax: (44) 161 622 4446 [email protected] 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 © Zetex Semiconductors plc 2005 8 www.zetex.com