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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 4A, 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. 4A quiescent current. 1% typical accuracy. SOT23 -5 package.
APPLICATIONS * * * * * * * Battery Chargers Smart Battery Packs DC Motor control Over current monitor Power Management Level translating Programmable current source
APPLICATION CIRCUIT
Vin
Rsense
To Load
V in
Load
ZXCT1010
GND I out
Vout Rout
ORDERING INFORMATION
PART NUMBER
ZXCT1010E5
PACKAGE
SOT23-5
PARTMARKING
1010
ISSUE 4 - DECEMBER 2001 1
ZXCT1010
ABSOLUTE MAXIMUM RATINGS
Voltage on any pin Continuous output current Continuous sense voltage Operating Temperature Storage Temperature Package Power Dissipation SOT23-5 -0.6V to 20V (relative to GND) 25mA Vin + 0.5V > Vsense> Vin - 5V -40 to 85C -55 to 125C (TA = 25C) 500mW
ELECTRICAL CHARACTERISTICS
Test Conditions TA = 25C, Vin = 5V, Rout = 100. SYMBOL
V in I out 1
PARAMETER
V CC Range Output current
CONDITIONS Min
2.5 V sense = 0V V sense = 10mV V sense = 100mV V sense = 200mV V sense = 1V 0 85 0.975 1.95 9.7 1 0
LIMITS Typ
0.3 100 1.00 2.00 10.0 4
UNIT Max
20 10 115 1.025 2.05 10.3 8 2500 100 V A A mA mA mA A mV nA
Iq V sense 2 I sense Acc Gm BW
Ground pin current Sense Voltage Load pin input current Accuracy Transconductance, I out / V sense Bandwidth
V sense = 0V
R sense = 0.1 V sense = 200mV -2.5 10000 RF P in = -20dBm 3 V sense = 10mV dc V sense = 100mV dc 2.5 % A/V
300 2
kHz MHz
Includes input offset voltage contribution Vsense=Vin-Vload 3 -20dBm=63mVp-p into 50
2
1
ISSUE 4 - DECEMBER 2001 2
ZXCT1010
TYPICAL CHARACTERISTICS
ISSUE 4 - DECEMBER 2001 3
ZXCT1010
PIN DESCRIPTION
Pin Name V in Load I out GND Pin Function Supply Voltage Connection to load/battery Output current, proportional to V in -V load Ground
CONNECTION DIAGRAM SOT23-5 Package Suffix - E5
NC GND Iout
1 2 3
5
Load
4
VIN
Top View
SCHEMATIC DIAGRAM
Vin 100
+ -
Load
Iout
ISSUE 4 - DECEMBER 2001 4
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 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 Vsense = 100mV. Rearranging 1 for Rout gives: Rout = Vout /(Vsense x 0.01) Rout = 0.1 / (0.1 x 0.01) = 100 TYPICAL CIRCUIT APPLICATION
Vin
Rsense
V in
Load
ZXCT1010
GND I out
Vout Rout
Rload
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.
ISSUE 4 - DECEMBER 2001 5
ZXCT1010
APPLICATIONS INFORMATION (Continued)
Bi-Directional Current Sensing
To Battery +
Charger Input BC81725
FZT789A 140H
1k ZHCS1000
0.2
The ZXCT1010 can be used to measure current bi-directionally, if two devices are connected as shown below.
Iout 3
Vin
BAS16
Load
5 Load
100 10H
Vin
4
5V
+MOD pin FMMT451 220 SNS pin 100
Iout
V1
R sense
V2
bq2954
ZXCT1010
4
Iout
Vin
Load
5
Vout R out
support components omitted for clarity
Li-Ion Charger Circuit
The above figure 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. 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
5
Output Current (mA)
4 3 2 1 0
-400
-200
0
3
200
400
Sense Voltage (mV)
Output Current v Sense Voltage
ISSUE 4 - DECEMBER 2001 6
ZXCT1010
APPLICATIONS INFORMATION (Continued)
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 150m using 1oz copper. The data for the normalised graph was obtained using a 1A load current and a 100 output resistor. An electronic version of the PCB layout is available at www.zetex.com/isense
Actual Size
Layout shows area of shunt resistor compared to SOT23-5 package. Not actual size
ISSUE 4 - DECEMBER 2001 7
ZXCT1010
PACKAGE DIMENSIONS SOT23-5
DIM Millimetres MIN A A1 A2 b C D E E1 e e1 L a 0.90 0.00 0.90 0.35 0.09 2.80 2.60 1.50 0.95 REF 1.90 REF 0.10 0 0.60 10 MAX 1.45 0.15 1.3 0.50 0.20 3.00 3.00 1.75 Inches MIN 0.035 0.00 0.035 0.014 0.0035 0.110 0.102 0.059 0.037 REF 0.075 REF 0.004 0 0.024 10 MAX 0.057 0.006 0.051 0.020 0.008 0.118 0.118 0.069
(c) Zetex plc 2001
Zetex plc Fields New Road Chadderton Oldham, OL9 8NP United Kingdom Telephone (44) 161 622 4422 Fax: (44) 161 622 4420 Zetex GmbH Streitfeldstrae 19 D-81673 Munchen Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 Zetex Inc 700 Veterans Memorial Hwy Hauppauge, NY11788 USA Telephone: (631) 360 2222 Fax: (631) 360 8222 Zetex (Asia) Ltd 3701-04 Metroplaza, Tower 1 Hing Fong Road Kwai Fong Hong Kong Telephone: (852) 26100 611 Fax: (852) 24250 494
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 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. For the latest product information, log on to
www.zetex.com
ISSUE 4 - DECEMBER 2001 8

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