ZXCT1012 REDUCED HEIGHT MICRO-POWER CURRENT MONITOR Description Pin Assignments The ZXCT1012 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. (Top View) 5 SENSE- NC 1 The ZXCT1012 takes the voltage developed across a small value resistor and translates it into a proportional output current. A user defined output resistor scales the output current into a ground referenced voltage. GND 2 OUT 3 The ZXCT1012 has the accuracy specification of the ZXCT1010 but in TSOT25. 4 SENSE+ TSOT25 A minimum operating current of just 3.5μA, combined with its TSOT25 package make it suitable for portable battery equipment where size and current consumption are critical. The wide input voltage range down to as low as 2.5V make it suitable for a wide range of applications requiring direct operation from a battery. Features Applications • • • • • • • • • 2.5V to 20V supply range 3.5μA quiescent current Current output - user set gain Thin package - TSOT25 Temperature range -40 to 85°C Battery fuel gauge Battery chargers Overcurrent monitor Power management Typical Application Circuit RSENSE VIN SENSE+ SENSE- ZXCT1012 GND OUT RLOAD VOUT ROUT ZXCT1012 Document number: DS33444 Rev. 2 - 2 1 of 9 www.diodes.com September 2011 © Diodes Incorporated ZXCT1012 REDUCED HEIGHT MICRO-POWER CURRENT MONITOR Pin Descriptions Pin Name 1 N/C No connection 2 GND Ground connection 3 OUT 4 SENSE+ 5 SENSE- Description Output current pin. Current generated due to a difference voltage between VSENSE+ and VSENSE- flows out of this pin. A suitable value resistor connected to ground creates an output voltage. The maximum voltage out of this pin will be VSENSE- - 1.5V. This pin should be connected to the rail whose current is being measured and also provides power to internal circuitry. It is the positive input of the current monitor and has an input range from 20V down to 2.5V. The current through this pin varies with differential sense voltage. This is the negative input of the current monitor and has an input range from 20V down to 2.5V. Absolute Maximum Ratings (TA = 25°C) Description VSENSE+ Max. Voltage on any pin(relative to GND pin) VSENSE (Note 1) Ambient Operating Temperature Range Storage Temperature Maximum Junction Temperature Power Dissipation (TA = 25°C) Package (Note 2) RθJA PDISS @ 25°C TSOT25 250°C/W 500mW Rating Unit 20 -0.6 and VSENSE+ +0.5 -0.15 to 3 -40 to 85 -55 to 150 150 300 (De-rate to 0 at 150°C) V V V °C °C °C mW Recommended Operating Conditions Symbol VIN TA VSENSE VOUT Parameter Sense+ range Ambient temperature range differential Sense voltage Output voltage swing Min. Max. Units 2.5 -40 10 0 20 85 2500 VSENSE- -15 V C mV V Operation above the absolute maximum rating may cause device failure. Operation at the absolute maximum ratings, for extended periods, may reduce device reliability. Notes: 1. VSENSE is defined as the differential voltage between the SENSE+ and SENSE- pins. (VSENSE = VSENSE+ - VSENSE-) 2. Mounted on 30mm x 16mm x1.1mm FR4 board with 1oz copper. ZXCT1012 Document number: DS33444 Rev. 2 - 2 2 of 9 www.diodes.com September 2011 © Diodes Incorporated ZXCT1012 REDUCED HEIGHT MICRO-POWER CURRENT MONITOR Electrical Characteristics (TA = 25°C, VIN = VSENSE+ = 5V; unless otherwise specified) Symbol IOUT Parameter Output Current IQ ISENSEACC Gm Ground Pin Current SENSE- Pin Input Current Accuracy Transconductance,IOUT/VSENSE (Note 3) TC Temperature Coefficient BW Bandwidth CMRR (Note 4) Notes: Common Mode Rejection Ratio Conditions VSENSE = 0V VSENSE = 10mV VSENSE = 40mV VSENSE = 100mV VSENSE = 200mV VSENSE = 0V RSENSE = 0.1V VSENSE = 200mV VSENSE = 200mV TA = 0 to 50°C (Note 3) VSENSE = 10mV CL = 5pF ROUT = 1kΩ VSENSE = 100mV VSENSE = 100mV, ROUT = 1kΩ VIN = 2.5V to 20V Min. 0 85 380 0.975 1.95 Limits Typ. 0.3 100 400 1.00 2.00 3.5 -2.5 Max. 15 115 420 1.025 2.05 8 100 2.5 Unit µA µA µA mA mA µA nA % 10 mA/V 500 ppm/°C 300 2 kHz MHz 80 dB 3. Temperature dependent measurements are extracted from characterisation and simulation results. 4. With the ZXCT1012 using SENSE+ as its power supply pin, common mode rejection cannot be distinguished from power supply rejection. ZXCT1012 Document number: DS33444 Rev. 2 - 2 3 of 9 www.diodes.com September 2011 © Diodes Incorporated ZXCT1012 REDUCED HEIGHT MICRO-POWER CURRENT MONITOR Typical Characteristics 4 10m VIN = 5V TA = 25°C VIN = 5V TA = 25°C OUTPUT CURRENT ERROR (%) IOUT, OUTPUT CURRENT (A) ROUT = 0Ω 1m 100µ 10µ ROUT = 0Ω 3 2 Typical 1 0 1µ -1 100µ 1m 10m 100m VSENSE (V) Typical Output vs. Sense Voltage 3 2% VIN = 5V VSENSE = 0.2V 10m 100m VSENSE (V) Error vs. Sense Voltage 1 VIN = 5V TA = 25° C VSENSE(AC) = 63.2mVpp ROUT = 0Ω 0 GAIN (dB) 0% -2% DC VSENSE = 0.01V -3 VSENSE = 0.1V -6 -4% VSENSE = 1V -9 -6% -40 12 -20 0 20 40 60 TEMPERATURE (°C) Output Current vs. Temperature 10 VIN = 5V -10 VSENSE = 1V ROUT = 0Ω 10 0.1 1 FREQUENCY (MHz) Frequency Response 0 VIN = 5V TA = 25° C IOUT, OUTPUT CURRENT (mA) -12 0.01 80 TA = 25° C VSENSE(AC) = 63.2Vpp -20 VSENSE = 0.8V 8 REJECTION (dB) IOUT, OUTPUT CURRENT (mA) 1m 1 VSENSE = 0.6V 6 VSENSE = 0.4V 4 -40 VSENSE = 0.01V -50 VSENSE = 1V -60 -70 VSENSE = 0.2V 2 VSENSE = 0.1V -30 -80 0 0 1 2 3 4 VIN, SUPPLY VOLTAGE (V) Transfer Characteristics ZXCT1012 Document number: DS33444 Rev. 2 - 2 5 4 of 9 www.diodes.com -90 1 10 100 1k 10k 100k FREQUENCY (Hz) Common Mode Rejection 1M 10M September 2011 © Diodes Incorporated ZXCT1012 REDUCED HEIGHT MICRO-POWER CURRENT MONITOR Applications Information The ZXCT1012 current monitor works by converting the voltage developed across a small sense resistor into a current on the out pin. In reality it is a voltage to current converter. This output current can be converted into a voltage simply by passing it through a resistor (ROUT) to ground. The current monitor has a transconductance of 10mA/V. But the overall amplifying conversion is affected by both the RSENSE and ROUT. The gain equation of the ZXCT1012 is: R VOUT = IL × R SENSE OUT 100 For best performance RSENSE should be connected as close to the SENSE+ (and SENSE-) pins; which minimizes any series resistance with RSENSE and potential for interference pickup. When choosing appropriate values for RSENSE a compromise must be reached between in-line signal loss (including potential power dissipation effects) and small signal accuracy. Higher values for RSENSE gives better accuracy at low load currents by reducing the inaccuracies due to internal offsets. For best operation the ZXCT1012 has been designed to provide best performance with VSENSE of the order of 40mV to 200mV. Current monitors are single supply devices which means they tend to saturate at very low sense voltages. However it does mean the output can never go negative. Also the output can never change direction (monotonic). This is important if the current monitor is used in a control loop. As the sense voltage is reduced the output will tend to saturate as the input offset voltage starts to have greater effect. It is recommended to have a minimum sense voltage of 10mV to minimize linearity errors. Diodes has specified the output voltage at VSENSE of 10mV, 40mV, 100mV and 200mV; which is the recommended sense voltage range. The maximum differential input voltage, VSENSE, is 2.5V; however this will cause large output currents to flow increasing power dissipation in the chip. The sense voltage can be increased further, without damaging the ZXCT1012, by the inclusion of a resistor, RLIM, between SENSE- pin and the load. Typical values around 10kΩ. See figure below. RSENSE CC RLIM ZXCT1012 If large reverse currents are expected then the resistor, RLIM, will provide protection from exceeding absolute maximum ratings. A suitable value for RLIM can be determined from: R LIM = VSENSE(REF) 5mA Where VSENSE(REV) is the maximum expected reverse sense voltage generated. ZXCT1012 Document number: DS33444 Rev. 2 - 2 5 of 9 www.diodes.com September 2011 © Diodes Incorporated ZXCT1012 REDUCED HEIGHT MICRO-POWER CURRENT MONITOR Applications Information (cont.) The following lines describe how to scale a load current to an output voltage. VSENSE = RSENSE * ILOAD equation (1) IOUT = 10mA/V x VSENSE equation (2) VOUT = IOUT x ROUT equation (3) Design example In the circuit below a 1A current is to be represented by a 100mV output voltage (VOUT): A) To be within recommended values choose the value of RSENSE to give: 50mV > VSENSE > 200mV at full load. For example set VSENSE = 100mV at 1.0A. From equation (1) RSENSE = 0.1V/1.0A = 0.1Ω B) Now choose ROUT to give: VOUT = 100mV, when VSENSE = 100mV. From equation (2) IOUT = 10mA/V x 0.1 = 1mA Rearranging equation (3) for ROUT gives: ROUT = VOUT/IOUT = 0.1/0.001 = 100Ω RSENSE VIN SENSE+ SENSE- ZXCT1012 GND OUT RLOAD VOUT ROUT = 0.1 / (0.1 x 0.01) = 100Ω Typical Circuit Application Where RLOAD represents any load including DC motors, a charging battery or further circuitry that requires monitoring, RSENSE can be selected on specific requirements of accuracy, size and power rating. ZXCT1012 Document number: DS33444 Rev. 2 - 2 6 of 9 www.diodes.com September 2011 © Diodes Incorporated ZXCT1012 REDUCED HEIGHT MICRO-POWER CURRENT MONITOR 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 (θJA), maximum junction temperature (TJMAX), and ambient temperature (TA), according to the expression: PMAX = (TJMAX – TA) / θJA The device power dissipation, PD is given by the expression: PD = IOUT.(VIN-VOUT) watts Care must be taken when using this device at large input voltages and large sense voltages to prevent too much power dissipation. 600 500 400 300 200 100 0 0 VIN = 20V 25 50 75 100 125 TA, AMBIENT TEMPERATURE (°C) 150 VSENSE = 2.5V ROUT = 100Ω IOUT = 2.5 x 0.01 = 25mA VOUT = IOUT x ROUT = 25mA x 100Ω = 2.5V PD = 25mA (20 - 2.5)V = 438mW ZXCT1012 Document number: DS33444 Rev. 2 - 2 7 of 9 www.diodes.com September 2011 © Diodes Incorporated ZXCT1012 REDUCED HEIGHT MICRO-POWER CURRENT MONITOR Ordering Information Device Package Marking Reel Size Quantity ZXCT1012ET5TA TSOT25 1012 7 3000 Tape & Reel Package Outline Dimensions (All Dimensions in mm) D e1 E E1 L2 c 4x θ1 e L θ 5x b A A2 A1 TSOT25 Dim Min Max Typ A 1.00 − − A1 0.01 0.10 − A2 0.84 0.90 − D 2.90 − − E 2.80 − − E1 1.60 − − b 0.30 0.45 − c 0.12 0.20 − e 0.95 − − e1 1.90 − − L 0.30 0.50 L2 0.25 − − θ 0° 8° 4° θ1 4° 12° − All Dimensions in mm Suggested Pad Layout C C Dimensions Value (in mm) C 0.950 X 0.700 Y 1.000 Y1 3.199 Y1 Y (5x) X (5x) ZXCT1012 Document number: DS33444 Rev. 2 - 2 8 of 9 www.diodes.com September 2011 © Diodes Incorporated ZXCT1012 REDUCED HEIGHT MICRO-POWER CURRENT MONITOR IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION). 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