ZXCT1009T8

ZXCT1009 ZETEX | Alldatasheet

Document overview

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Technical content

DESCRIPTION

The ZXCT1009 is a high side current sense monitor. Using this device eliminates the need to disrupt the ground plane when sensing a load current. It takes a high side 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. 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 4µA, combined with its SOT23 package make it a unique solution, 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.
• 4µA quiescent current.
• 1% typical accuracy.
• SOT23 & SM8 † packages.

APPLICATIONS

• Battery Chargers
• Smart Battery Packs
• DC Motor control
• Over current monitor
• Power Management
• Level translating
• Programmable current source HIGH-SIDE CURRENT MONITOR APPLICATION CIRCUIT Vin To Load Vout Rsense Rout ZXCT 1009 † 8 leaded SOT223

ORDERING INFORMATION

PART NUMBER PACKAGE PARTMARKING ZXCT1009F SOT23 109 ZXCT1009T8 SM8 ZXCT1009 SM8 due for release May 2001 Sampling April 2001

Voltage on any pin -0.6V to 20V (relative to I out) Continuous output current 25mA Continuous sense voltage V in + 0.5V > Vsense†> Vin – 5V Operating Temperature -40 to 85 °C Storage Temperature -55 to 125 °C Package Power Dissipation (T A = 25°C) SOT23 450mW SM8 2W

ELECTRICAL CHARACTERISTICS

Test Conditions TA = 25°C, Vin = 5V, Rout = 100Ω . SYMBOL PARAMETER CONDITIONS LIMITS UNIT Min Typ Max Vin VCC Range 2.5 20 V Iout 1 Output current V sense =0V Vsense =10mV Vsense =100mV Vsense =200mV Vsense =1V 0.975 1.95 9.6 104 1.002 2.0 9.98 120 1.025 2.05 10.2 µA µA mA mA mA V sense † Sense Voltage 0 2500 mV Isense Load pin input current 100 nA Acc Accuracy Rsense = 0.1 Ω Vsense =200mV -2.5 2.5 % Gm Transconductance, Iout /V sense 10000 µA/V BW Bandwidth RF P in= -20dBm ‡ Vsense = 10mV dc Vsense = 100mV dc 300 kHz MHz

1 Includes input offset voltage contribution

†Vsense=Vin-Vload ‡ -20dBm=63mVp-p into 50Ω

Load Connection to load/battery I out Output current, proportional to V in-Vload SM8 Package Suffix – T8 Top View SOT23 Package Suffix – F Top View Iout Load Vin Iout Load N/C Vin N/C N/C N/C N/C CONNECTION DIAGRAMS + - Vin Load Iout 100Ω SCHEMATIC DIAGRAM

The following lines describe how to scale a load current to an output voltage. Vsense = Vin - Vload Vout = 0.01 x Vsense x Rout1 E.g. A 1A current is to be represented by a 100mV output voltage: 1)Choose the value of Rsense to give 50mV > Vsense > 500mV at full load. For example Vsense = 100mV at 1.0A. Rsense = 0.1/1.0 => 0.1 ohms. 2)Choose Rout to give Vout = 100mV, when V sense = 100mV. Rearranging 1 for Rout gives: Rout = Vout /(Vsense x 0.01) Rout = 0.1 / (0.1 x 0.01) = 100 Ω Vin Vin Iout Load Vout Rsense Rload Rout ZXCT1009 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 (θja), maximum junction temperature (Tjmax), and ambient temperature (Tamb), according to the expression: P max = (Tjmax – Tamb) / θja The device power dissipation, P D is given by the expression: PD=Iout.(Vin-Vout) Watts SM8 SOT23 Where Rload 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

The above figure shows the ZXCT1009 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-/H9252PNP 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. The ZXCT1009 is intended as a direct functional replacement for the ZDS1009, which is featured in a complete design from Unitrode/Texas Instruments on the Li-Ion charger circuit shown above. Reference: DVS2954S1H Li-Ion Charger Development System. 100Ω 0.2Ω 100Ω FZT789A FMMT3904 1kΩ FMMD914 10µH FMMT451 140µH ZHCS1000 220Ω SNS pin MOD pin Charger Input To Battery + bq2954 ZXCT1009 support components omitted for clarity + - Vin Load Iout APPLICATIONS INFORMATION (Continued) Transient Protection An additional resistor, Rlim can be added in series with Rout (figure 1.0), to limit the current from I out. Any circuit connected to Vout will be protected from input voltage transients. This can be of particular use in automotive applications where load dump and other common transients need to be considered. Figure 1.0 ZXCT1009 with additional current limiting Resistor Rlim. Assuming the worst case condition of V out = 0V; providing a low impedance to a transient, the minimum value of R lim is given by:- R( m i n ) VV Ilim pk max pk Vpk = Peak transient voltage to be withstood V max = Maximum working Voltage = 20V Ipk = Peak output current = 40mA The maximum value of R lim is set by V in(min), Vout(max) and the dropout voltage (see transfer characteristic on page 3) of the ZXCT1009 :- R R [V V V (max) Vlim out in dp out out (max) (min) ( )] (max)= Vin(min) = Minimum Supply Operating Voltage V dp =Dropout Voltage Vout (max)= Maximum Operating Output Voltage Vin To Load Vout Rsense R Rlim ZXCT 1009

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 150mΩ using 1oz copper. The data for the normalised graph was obtained using a 1A load current and a 100 Ω output resistor. An electronic version of the PCB layout is available at www.zetex.com/isense Vout Vin GND Load Rout ZXCT1009 APPLICATIONS INFORMATION (Continued) Layout shows area of shunt resistor compared to SOT23 package. Not actual size Vout Vin GND Load Rout ZXCT1009 Actual Size

N PACKAGE DIMENSIONS SOT23 DIM Millimetres Inches Min Max Min Max A 2.67 3.05 0.105 0.120 B 1.20 1.40 0.047 0.055 C – 1.10 – 0.043 D 0.37 0.53 0.0145 0.021 F 0.085 0.15 0.0033 0.0059 G NOM 1.9 NOM 0.075 K 0.01 0.10 0.0004 0.004 L 2.10 2.50 0.0825 0.0985 N NOM 0.95 NOM 0.037 DIM Millimetres Inches Min Typ Max Min Typ Max A –– 1.7 –– 0.067 A1 0.02 – 0.1 0.0008 – 0.004 b – 0.7 –– 0.028 – c 0.24 – 0.32 0.009 – 0.013 D 6.3 – 6.7 0.248 – 0.264 E 3.3 – 3.7 0.130 – 0.145 He 6.7 – 7.3 0.264 – 0.287 Lp 0.9 –– 0.035 –– α –– 15°– – 15° PACKAGE DIMENSIONS SM8 Zetex plc. Fields New Road, Chadderton, Oldham, OL9-8NP, United Kingdom. Telephone: (44)161 622 4422 (Sales), (44)161 622 4444 (General Enquiries) Fax: (44)161 622 4420 Zetex GmbH Zetex Inc. Zetex (Asia) Ltd. These are supported by Streitfeldstraße 19 47 Mall Drive, Unit 4 3701-04 Metroplaza, Tower 1 agents and distributors in D-81673 München Commack NY 11725 Hing Fong Road, major countries world-wide Germany USA Kwai Fong, Hong Kong © Zetex plc 2000 Telefon: (49) 89 45 49 49 0 Telephone: (631) 543-7100 Telephone:(852) 26100 611 Fax: (49) 89 45 49 49 49 Fax: (631) 864-7630 Fax: (852) 24250 494 Internet:http://www.zetex.com 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.