ZXCT1020 ZXCT1020 Low offset current output current monitor Description The ZXCT1020 is a precision high-side current sense monitor. Using this type of device eliminates the need to disrupt the ground plane when sensing a load current. The ZXCT1020 uses two external resistors to set the overall voltage gain for applications where improved accuracy at small sense voltages is required. For fixed gain variants Zetex offers the ZXCT1021 (G=10) and ZXCT1022 (G=100). The ZXCT1020 footprint follows that of the ZXCT1021/2 with only 2 additional resistors required: Current output enables the user to set the gain via these external resistors. Using two external resistors to set the gain ensures optimal versatility as the transconductance can be varied to meet the output impedance requirements of the load that the ZXCT1020 has to drive. The very low offset voltage enables a typical accuracy of 3% for sense voltages of only 10mV, giving better tolerances for small sense resistors necessary at higher currents. One resistor between pins 1 and 4 for setting transconductance, and the other between pins 3 and 2 for setting overall gain. 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 25µA, combined with its SOT23-5 package make it suitable for portable battery equipment too. Features Applications • Accurate high-side current sensing • Battery chargers • Versatile current output scaling • Over-current monitor • 2.5V - 20V operating range • Motherboard power supply current measurement • 25µA quiescent current • Level translating • 1% typical accuracy • Programmable current source • SOT23-5 package Pinout information S+ 1 Typical application circuit 5 R SH GND 2 3 4 S(LOAD) 5 VB S+ 1 OUT IL RS S- 4 VB + Top view VOUT RG 3 2 ZXCT1020 GND Ordering information Order reference Package ZXCT1020E5TA SOT23-5 Issue 1 - August 2007 © Zetex Semiconductors plc 2007 Device marking 1020 Status Preview 1 Reel size (inches) 7 Quantity per reel 3000 Tape width (mm) 8 www.zetex.com ZXCT1020 Absolute maximum ratings Voltage on VB with respect to GND pin -0.5V to 20V Voltage on S+(a), S-(b), OUT with respect to GND pin -0.5V to VB+0.5V VSENSE(c) -0.5V to +2.5V(d) Junction temperature Storage temperature Package power dissipation (Tamb = 25°C) SOT23-5 -40°C to125°C -55°C to 150°C 300mW NOTES: (a) Subject to VSENSE+ never going 6V below VB. (b) Subject to absolute maximum VSENSE not being exceeded. (c) VSENSE is defined as the voltage difference across the sense resistor. and is the voltage across resistor RSH plus the voltage between S+ and S-. (d) VSENSE might need to be reduced when used with smaller values of RSH and at larger rails due to increased power dissipation. Pin out information Pin 1 Name S+ Pin function Positive sense input. Should be tied to positive side of sense resistor via resistance (RSH) of the order of 150⍀ to 1.5k⍀. 2 3 GND OUT Ground and substrate connection of device. Current output. A gain setting resistor (RG) referenced to GND should be connected to this pin to set overall voltage gain of: Gain = RG/RSH The resistance, RG, placed on out will set the ZXCT1020 output impedance equal to RG. When driving low impedance loads both RG and RSH should be reduced. 4 VB 5 S- Input voltage pin. Provides bias to current monitor and should be tied to the rail whose current is being monitored. High impedance negative sense voltage input Recommended operating conditions Parameter VSENSE+ Common-mode sense input range VB Bias pin input voltage range (*) Min. 2.5 Max. 20 Units V 2.5 20 V VSENSE Differential sense Input voltage range 0 1.5 V VOUT Output voltage range 0 VSENSE- - 1 V RSH Shunt resistor value 120 2000 ⍀ TA Ambient temperature range -40 85 °C NOTES: (*) For best performance VB and VSENSE+ should be referred to the rail whose current is being measured. Recommended resistor gain setting combinations Gain RSHUNT RGAIN 10 20 50 100 1.5k⍀ 750⍀ 300⍀ 150⍀ 15k⍀ 15k⍀ 15k⍀ 15k⍀ Issue 1 - August 2007 © Zetex Semiconductors plc 2007 2 www.zetex.com ZXCT1020 Electrical characteristics Tamb = 25°C, VSENSE+ = VB = 15V, VSENSE = 100mV, RG = 15k⍀, RSH = 1.5k⍀ unless otherwise stated. Symbol Parameter Conditions Limits Min. VOUT Output voltage VSENSE = 0mV Unit Typ. Max. 3 15 mV VSENSE = 30mV 291 300 309 mV VSENSE = 100mV 0.98 1 1.02 V VSENSE = 150mV 1.47 1.5 1.53 V 50 300 ppm TC[1] Output voltage temperature coefficient IQ Ground pin current VSENSE = 0V 25 35 A IS- S- input current VSENSE = 0V 20 100 nA I S+ S+ input current VSENSE = 0V 100 Acc Accuracy VSENSE = 100mV Gain VOUT /VSENSE VSENSE = 100mV 10 V/V ROUT Output resistance RG not connected 370 M⍀ BW Bandwidth VSENSE (DC) = 10mV 300 kHz VSENSE (DC) = 100mV 2 MHz 80 dB PSRR Power supply rejection ratio Issue 1 - August 2007 © Zetex Semiconductors plc 2007 VSENSE+ = VB = 2.5 to 20V 3 -2 70 nA 2 % www.zetex.com ZXCT1020 Typical characteristics Test conditions unless otherwise stated: TA = 25°C, VB = VSENSE+ (via RSH) =15V, VSENSE = 100mV RSH = 1.5k⍀, RG = 15k⍀. Supply current v Temperature Issue 1 - August 2007 © Zetex Semiconductors plc 2007 4 www.zetex.com ZXCT1020 Test conditions unless otherwise stated: TA = 25°C, VB = VSENSE+ (via RSH) =15V, VSENSE = 100mV Gain = 10, RG = 15k⍀. ° ° ° ° ° ° ° ° ° ° ° ° Issue 1 - August 2007 © Zetex Semiconductors plc 2007 5 ° ° ° www.zetex.com ZXCT1020 Test conditions unless otherwise stated: TA = 25°C, VB = VSENSE+ (via RSH) =15V, VSENSE = 100mV Gain = 20, RG = 15k⍀. ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° Issue 1 - August 2007 © Zetex Semiconductors plc 2007 6 www.zetex.com ZXCT1020 Test conditions unless otherwise stated: TA = 25°C, VB = VSENSE+ (via RSH) =15V, VSENSE = 100mV RG = 15k⍀. ° ° ° ° Gain = 100 VSENSE = 10mV ° ° ° Issue 1 - August 2007 © Zetex Semiconductors plc 2007 7 www.zetex.com ZXCT1020 Typical AC characteristics Test conditions unless otherwise stated: TA = 25°C, VB = VSENSE+ (via RSH) =15V, VSENSE = 100mV, RG = 15k⍀. Gain = 10 Gain = 50 Issue 1 - August 2007 © Zetex Semiconductors plc 2007 8 www.zetex.com ZXCT1020 Test conditions unless otherwise stated: TA = 25°C, RG=15k, VB = VSENSE+ (via RSH) =15V, VSENSE = 100mV unless otherwise stated. Various gains with constant RG Issue 1 - August 2007 © Zetex Semiconductors plc 2007 9 www.zetex.com ZXCT1020 Test conditions unless otherwise stated: TA = 25°C, G=100, RG = 15k, VB = VSENSE+ (via RSH), VSENSE = 100mV. Issue 1 - August 2007 © Zetex Semiconductors plc 2007 10 www.zetex.com ZXCT1020 Application information The ZXCT1020 has a VB pin that is used to provide power to the current monitor. The maximum voltage applied to the ZXCT1020 must be applied to this pin. The S+ and S- pins are used to measure the current flowing to the load through the sense resistor. In normal use, the S+ is tied to VB via a shunt resistor, RH making the ZXCT1020 essentially line powered. The ZXCT1020 has a programmable gain set by the ratio of two external resistors RG and RSH. RS R SH S(LOAD) 5 VB S+ 1 IL 4 + VOUT RG 3 2 ZXCT1020 GND RSH sets the transconductance whereas RG set the gain and results in an output voltage defined as: RG V OUT = ---------- × V SENSE R SH Where VSENSE = RSENSE x IL The ZXCT1020 has been tested to the same conditions as the ZXCT1021 giving an overall voltage gain of 10. The gain of the ZXCT1020 can be adjusted simply by varying RG. So to achieve a gain of 50 RG is increased from 15k⍀ to 75k⍀. An alternative is to decrease RSH from 1.5k⍀ to 300⍀. Decreasing RSH increases the transconductance and, if for any given gain, reducing the RSH will reduce the overall output impedance. To achieve a gain of 100, for example, the following resistor values could be used: RSH = 150 RG = 15k Issue 1 - August 2007 © Zetex Semiconductors plc 2007 11 www.zetex.com ZXCT1020 Intentionally left blank Issue 1 - August 2007 © Zetex Semiconductors plc 2007 12 www.zetex.com ZXCT1020 Package outline - SOT23-5 Dim. A A1 A2 b C D E E1 e e1 L a° Millimeters Min. 0.90 0.00 0.90 0.20 0.09 2.70 2.20 1.30 Inches Max. 1.45 0.15 1.30 0.50 0.26 3.10 3.20 1.80 Min. 0.0354 0.00 0.0354 0.0078 0.0035 0.1062 0.0866 0.0511 0.95 REF 1.90 REF 0.10 0° Max. 0.0570 0.0059 0.0511 0.0196 0.0102 0.1220 0.1181 0.0708 0.0374 REF 0.0748 REF 0.60 30° 0.0039 0° 0.0236 30° Note: Controlling dimensions are in millimeters. Approximate dimensions are provided in inches Issue 1 - August 2007 © Zetex Semiconductors plc 2007 13 www.zetex.com ZXCT1020 Definitions Product change Zetex Semiconductors reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or service. Customers are solely responsible for obtaining the latest relevant information before placing orders. Applications disclaimer The circuits in this design/application note are offered as design ideas. It is the responsibility of the user to ensure that the circuit is fit for the user’s application and meets with the user’s requirements. No representation or warranty is given and no liability whatsoever is assumed by Zetex with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Zetex does not assume any legal responsibility or will not be held legally liable (whether in contract, tort (including negligence), breach of statutory duty, restriction or otherwise) for any damages, loss of profit, business, contract, opportunity or consequential loss in the use of these circuit applications, under any circumstances. Life support Zetex products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the Chief Executive Officer of Zetex Semiconductors plc. As used herein: A. Life support devices or systems are devices or systems which: 1. are intended to implant into the body or 2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labelling can be reasonably expected to result in significant injury to the user. B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. Reproduction The product specifications contained in this publication are 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. Terms and Conditions All products are sold subjects to Zetex’ terms and conditions of sale, and this disclaimer (save in the event of a conflict between the two when the terms of the contract shall prevail) according to region, supplied at the time of order acknowledgement. For the latest information on technology, delivery terms and conditions and prices, please contact your nearest Zetex sales office. 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Samples may be available “Active” Product status recommended for new designs “Last time buy (LTB)” Device will be discontinued and last time buy period and delivery is in effect “Not recommended for new designs” Device is still in production to support existing designs and production “Obsolete” Production has been discontinued Datasheet status key: “Draft version” This term denotes a very early datasheet version and contains highly provisional information, which may change in any manner without notice. “Provisional version” This term denotes a pre-release datasheet. It provides a clear indication of anticipated performance. However, changes to the test conditions and specifications may occur, at any time and without notice. “Issue” This term denotes an issued datasheet containing finalized specifications. However, changes to specifications may occur, at any time and without notice. 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