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ZXCT1009
HIGH-SIDE CURRENT MONITOR
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 4 A, combined with its SOT23 package make it a unique solution for portable battery equipment.
APPLICATIONS
* Battery chargers * Smart battery packs * DC motor control * Over current monitor * Power management * Level translating * Programmable current source
APPLICATION CIRCUIT
FEATURES
* Low cost, accurate high-side current sensing * Output voltage scaling * Up to 2.5V sense voltage * 2.5V - 20V supply range * 4A quiescent current * 1% typical accuracy * SOT23 and SM8 packages
ORDERING INFORMATION
DEVICE
ZXCT1009FTA ZXCT1009T8TA
REEL SIZE
7" 7"
TAPE WIDTH
8mm 12mm
QUANTITY PER REEL
3,000 units 1,000 units
PARTMARKING
109 ZXCT1009
PACKAGE
SOT23 SM8
ISSUE 9 - OCTOBER 2005 1
SEMICONDUCTORS
ZXCT1009
ABSOLUTE MAXIMUM RATINGS
Voltage on any pin Continuous output current Continuous sense voltage Operating temperature Storage temperature Package power dissipation SOT23 SM8 -0.6V to 20V (relative to Iout) 25mA Vin + 0.5V > Vsense> Vin - 5V -40 to 85C -55 to 125C (TA = 25C) 450mW - derate to zero at 125C 2W
Operation above the absolute maximum rating may cause device failure. Operation at the absolute maximum ratings for extended periods may reduce device reliability.
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 1 90 0.975 1.95 9.6 0
LIMITS Typ
4 104 1.002 2.0 9.98
UNIT Max
20 15 120 1.025 2.05 10.2 2500 100 V A A mA mA mA mV nA
V sense I sense Acc Gm BW
Sense voltage V sense input current Accuracy Transconductance, I out / V sense Bandwidth RF P in = -20dBm V sense = 10mV dc V sense = 100mV dc R sense = 0.1 V sense =200mV
-2.5 10000
2.5
% A/V
300 2
kHz MHz
1
Includes input offset voltage contribution Vsense=Vin-Vload -20dBm=63mVp-p into 50
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SEMICONDUCTORS
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ZXCT1009
TYPICAL CHARACTERISTICS
5 10m
IOUT - Output Current (A)
Output Current Error (%)
1m
VIN = 5V Tamb = 25C ROUT = 0W
4 3 2 1 0 -1 -2 10m 100m
Typical
VIN = 5V Tamb = 25C ROUT = 0W
100
10 100 1m 10m 100m 1
1
VSENSE (V)
VSENSE (V)
Typical Output v Sense Voltage
3 10.2
VIN = 5V VSENSE = 1V ROUT = 0W
Error v Sense Voltage
IOUT - Output Current (mA)
VIN = 5V, Tamb = 25C, RF PIN = -20dBm
0 -3
DC VSENSE = 0.01V
10.0
9.8
Gain (dB)
-6 -9 -12 0.01
DC VSENSE = 0.1V DC VSENSE = 1V
9.6
9.4 -40
-20
0
20
40
60
80
0.1
1
10
Temperature (C)
Frequency (MHz)
Output Current v Temperature
12 0
VIN = 5V Tamb = 25C ROUT = 0W VSENSE = 1V VSENSE = 0.8V VSENSE = 0.6V VSENSE = 0.4V VSENSE = 0.2V
Frequency Response
IOUT - Output Current (mA)
-10 -20
10 8 6 4 2 0 0
VIN = 5V Tamb = 25C RF PIN = -20dBm
VSENSE = 1V
Rejection (dB)
-30 -40 -50 -60 -70 -80 -90
VSENSE = 0.1V VSENSE = 0.01V
1
2
3
4
5
1
10
100
1k
10k
100k
1M
10M
VIN - Supply Voltage (V)
Frequency (Hz)
Transfer Characteristic
ISSUE 9 - OCTOBER 2005 3
Common Mode Rejection
SEMICONDUCTORS
ZXCT1009
TYPICAL CHARACTERISTICS (Cont.) SCHEMATIC DIAGRAM
PIN DESCRIPTION
Pin Name V sense+ V senseI out Pin Function Supply voltage Connection to load/battery Output current, proportional to V in -V load
CONNECTION DIAGRAMS SOT23 Package Suffix - F SM8 Package Suffix - T8
Top View
Top View
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SEMICONDUCTORS
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ZXCT1009
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 E.g. The device power dissipation, PD is given by the expression: PD=Iout.(Vin-Vout) Watts 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)
SM8
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
A 1A current is to be represented by a 100mV output voltage:
Rout = 0.1 / (0.1 x 0.01) = 100
SOT23
TYPICAL CIRCUIT APPLICATION
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 9 - OCTOBER 2005 5
SEMICONDUCTORS
ZXCT1009
APPLICATIONS INFORMATION (Continued)
Charger input FMMT3904 FZT789A ZHCS100 Vin FMMD914 5V Load To battery +
Transient Protection
An additional resistor, Rlim can be added in series with Rout (figure 1.0), to limit the current from Iout. 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.
bq2954
MOD pin
FMMT451 Iout
ZXCT1009
SNS pin
Support components omitted for clarity
Li-Ion Charger Circuit
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- 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. 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.
Figure 1.0 ZXCT1009 with additional current limiting Resistor Rlim. Assuming the worst case condition of Vout = 0V; providing a low impedance to a transient, the minimum value of Rlim is given by:Rlim(min) = Vpk - Vmax Ipk
Vpk = Peak transient voltage to be withstood Vmax = Maximum working Voltage = 20V Ipk = Peak output current = 40mA
The maximum value of Rlim is set by Vin(min), Vout(max) and the dropout voltage (see transfer characteristic on page 3) of the ZXCT1009 :Rlim(max) = Rout [Vin(min) - (Vdp + Vout (max))] Vout (max)
Vin(min) = Minimum Supply Operating Voltage Vdp =Dropout Voltage Vout (max)= Maximum Operating Output Voltage
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SEMICONDUCTORS
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APPLICATIONS INFORMATION (Continued)
ZXCT1009
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.
ZXCT1009 Vout Vin
Rout
ZXCT1009 Vout Vin
Load
GND
Actual Size
Load GND
Layout shows area of shunt resistor compared to SOT23 package. Not actual size
1.4
Normalised Voltage
Voltage across Copper Sense Resistor
1.2
VOUT with Copper Sense Resistor
1.0
VOUT with Ideal Sense Resistor
0.8 -40 -20 0 20
40
60
80
100 120 140
Temperature (C)
Effect of Sense Resistor Material on Temperature Performance
ISSUE 9 - OCTOBER 2005 7
SEMICONDUCTORS
Rout
ZXCT1009
PACKAGE DIMENSIONS SOT23
DIM Millimeters Min A
N
Inches Min 0.105 0.047 - 0.0145 0.0033 Max 0.120 0.055 0.043 0.021 0.0059
Max 3.05 1.40 1.10 0.53 0.15
2.67 1.20 - 0.37 0.085
B C D F G K L N
NOM 1.9 0.01 2.10 0.10 2.50
NOM 0.075 0.0004 0.0825 0.004 0.0985
NOM 0.95
NOM 0.037
PACKAGE DIMENSIONS SM8
DIM Millimeters Min A A1 b c D E e1 e2 He Lp - 0.02 - 0.24 6.3 3.3 - - 6.7 0.9 - - Typ - - 0.7 - - - 4.59 1.53 - - - 10 Max 1.7 0.1 - 0.32 6.7 3.7 - - 7.3 - 15 - Min - 0.0008 - 0.009 0.248 0.130 - - 0.264 0.035 - - Inches Typ - - 0.028 - - - 0.180 0.060 - - - 10 Max 0.067 0.004 - 0.013 0.264 0.145 - - 0.287 - 15 -
(c) Zetex Semiconductors plc 2005
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 Hwy 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
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 9 - OCTOBER 2005
SEMICONDUCTORS
8

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