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ZXCT1010 Enhanced high-side current monitor
Description
The ZXCT1010 is a high side current sense monitor. Using this device eliminates the need to disrupt the ground plane when sensing a load current. It is an enhanced version of the ZXCT1009 offering reduced typical output offset and improved accuracy at low sense 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 4 A, combined with its SOT23-5 package make 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 300nA typical offset current 3.5 A quiescent current 1% typical accuracy SOT23-5 package
Applications
* * * * * * Battery chargers Smart battery packs DC motor control Over current monitor Power management Programmable current source
Pinout information
NC 1 GND 2 IOUT 3
4 VIN 5 Load
Typical application circuit
Pinout - top view
Ordering information
Device ZXCT1010E5TA Issue 9 - July 2006
(c) Zetex Semiconductors plc 2006
Package SOT23-5
Device marking 101 1
Reel size (inches) 7
Tape width (mm) 8
Quantity per reel 3000
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ZXCT1010
Pin information
Pin 1 2 3 4 5 Name N/C GND IOUT Description Not connection Ground connection Output current, proportional to VIN - VLOAD
VSENSE+ Supply voltage VSENSE- Connection to load/battery
Absolute maximum ratings
Voltage on any pin (relative to GND pin) Continuous output current Continous sense voltage Ambient operating temperature range Storage temperature Package power dissipation SOT23-5 -0.6 to 20V (relative to GND) 25mA VIN + 0.5V > VSENSE > VIN - 5V -40 to 85C -55 to 150C Tamb= 25C 300mW
Operation above the absolute maximum rating may cause device failure. Operation at the absolute maximum ratings, for extended periods, may reduce device reliability.
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ZXCT1010
Electrical characteristics
Test conditions Tamb = 25C, VIN = 5V, ROUT = 100 Symbol VIN IOUT(a) Parameter VCC range Output current VSENSE = 0V VSENSE = 10mV VSENSE = 100mV VSENSE = 200mV VSENSE = 1V IQ ISENSEAcc Gm BW Ground pin current VSENSE = 0V 0 VSENSE- input current Accuracy Transconductance, IOUT/VSENSE Bandwidth RF PIN = -20dBm(c) VSENSE = 10mV DC VSENSE = 100mV DC
NOTES: (a) Includes input offset voltage contribution (b) VSENSE = VIN-VLOAD (c) -20dBm = 63mVp-p into 50
Conditions Min. 2.5 0 85 0.975 1.95 9.7
Limits Typ. 0.3 100 1.00 2.00 10.0 3.5
Unit Max. 20 10 115 2.05 10.3 8 2500 100 V A A mA mA A mV nA
1.025 mA
VSENSE(b) Sense voltage
RSENSE = 0.1 VSENSE = 200mV
-2.5 10000
2.5
% A/V
300 2
kHz MHz
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ZXCT1010
Typical characteristics
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ZXCT1010
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 ( ja), maximum junction temperature (Tjmax), and ambient temperature (Tamb), according to the expression: Pmax = (Tjmax - Tamb) /
ja
The device power dissipation, PD is given by the expression: PD=IOUT.(VIN-VOUT) Watts
Applications information
The following lines describe how to scale a load current to an output voltage. VSENSE = VIN - VLOAD VOUT = 0.01 x VSENSE x ROUT(1) For example: 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 . 2 Choose ROUT to give VOUT = 100mV, when VSENSE = 100mV. Rearranging (1) for ROUT gives: ROUT = VOUT /(VSENSE x 0.01) ROUT = 0.1 / (0.1 x 0.01) = 100 Schematic diagram
SENSE+ SENSE-
100
+
GND
OUT
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ZXCT1010
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.
Li-Ion charger circuit
The figure below shows the ZXCT1010 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- PNP 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.
Charger Input BC81725
FZT789A 140H
1k ZHCS1000
0.2
To Battery +
Vin
BAS16
Load
100 10H
5V
+MOD pin FMMT451 220 SNS pin 100
Iout
bq2954
ZXCT1010
support components omitted for clarity
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ZXCT1010
Bi-directional current sensing
The ZXCT1010 can be used to measure current bidirectionally, if two devices are connected as shown opposite. If the voltage V1 is positive with respect to the voltage V2 the lower device will be active, delivering a proportional output current to ROUT. Due to the polarity of the voltage across Rsense, the upper device will be inactive and will not contribute to the current delivered to ROUT. When V2 is more positive than V1, current will be flowing in the opposite direction, causing the upper device to be active instead. Non-linearity will be apparent at small values of VSENSE due to offset current contribution. Devices can use separate output resistors if the current direction is to be monitored independently.
Bi-directional transfer function
Bidirectional Transfer Function
5
Output Current (mA)
4 3 2 1 0
-400
-200
0
200
400
Sense Voltage (mV)
Output Current v Sense Voltage
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ZXCT1010
PCB trace shunt resistor for low cost solution The figure opposite 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 below shows a PCB layout suggestion. The resistor section is 25mm x 0.25mm giving approximately 150mW using 1oz copper. The data for the normalised graph was obtained using a 1A load current and a 100W output resistor. An electronic version of the PCB layout is available at www.zetex.com/isense
Layout shows area of shunt resistor compared to ZSOT23-5 package (not actual size).
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ZXCT1010
Intentionally left blank
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ZXCT1010
Package outline - SOT23-5
DIM A A1 A2 b C D E E1 e e1 L a Min. 0.90 0.00 0.90 0.20 0.09 2.70 2.20 1.30
Millimeters Max. 1.45 0.15 1.30 0.50 0.26 3.10 3.20 1.80 0.95 REF 1.90 REF 0.10 0 0.60 30 0.0039 0 Min. 0.0354 0.00 0.0354 0.0078 0.0035 0.1062 0.0866 0.0511
Inches Max. 0.0570 0.0059 0.0511 0.0196 0.0102 0.1220 0.1181 0.0708 0.0374 REF 0.0748 REF 0.0236 30
Note: Controlling dimensions are in millimeters. Approximate dimensions are provided in inches
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
For international sales offices visit www.zetex.com/offices Zetex products are distributed worldwide. For details, see www.zetex.com/salesnetwork 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.
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