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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 4A, 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. 4A 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
APPLICATION CIRCUIT
Vin
Rsense
To Load
ZXCT 1009 Vout Rout
ORDERING INFORMATION
PART NUMBER
ZXCT1009F ZXCT1009T8
PACKAGE
SOT23 SM8
PARTMARKING
109 ZXCT1009
SM8 due for release May 2001 Sampling April 2001 8 leaded SOT223
ISSUE 3 - APRIL 2001 1
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 85 C -55 to 125 C (TA = 25 C) 450mW 2W
ELECTRICAL CHARACTERISTICS
Test Conditions TA = 25 C, 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 Load pin 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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ZXCT1009
TYPICAL CHARACTERISTICS
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ZXCT1009
PIN DESCRIPTION
Pin Name V in Load I 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
Load N/C
1
1 2 3 4 8 7 6 5
Load
3
N/C N/C N/C N/C
Iout
Vin
Iout
Vin
Top View
2
Top View
SCHEMATIC DIAGRAM
Vin 100
+ -
Load
Iout
ISSUE 3 - APRIL 2001 4
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 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.
SM8
Rearranging 1 for Rout gives: Rout = Vout /(Vsense x 0.01) Rout = 0.1 / (0.1 x 0.01) = 100
SOT23
TYPICAL CIRCUIT APPLICATION
Vin
Rsense
ZXCT1009
Vin Load Iout
Rload Vout
Rout
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 3 - APRIL 2001 5
ZXCT1009
APPLICATIONS INFORMATION (Continued)
Transient Protection
To Battery +
Charger Input FMMT3904
FZT789A 140H
1k ZHCS1000
0.2
Vin
Load
100
FMMD914
10H
5V
+MOD pin FMMT451 220 SNS pin 100
Iout
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
ZXCT1009
Vin
Rsense
To Load
support components omitted for clarity
ZXCT 1009 Rlim R
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
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.
Vout
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. Ref er e n c e : D V S 2 9 54S 1 H Li - I on C har ger Development System.
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
ISSUE 3 - APRIL 2001 6
ZXCT1009
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 150musing 1oz copper. The data for the normalised graph was obtained using a 1A load current and a 100 output resistor. An electronic vers i o n o f th e P C B l a y out i s a v a i l a bl e a t www.zetex.com/isense
ZXCT1009 Vout Vin
ZXCT1009 Vout Vin
Rout
Load GND
Rout
Actual Size
Load GND
Layout shows area of shunt resistor compared to SOT23 package. Not actual size
ISSUE 3 - APRIL 2001 7
ZXCT1009
PACKAGE DIMENSIONS SOT23
DIM Millimetres Min A
N
Inches Max 3.05 1.40 1.10 0.53 0.15 Min 0.105 0.047 - 0.0145 0.0033 NOM 0.075 0.10 2.50 0.0004 0.0825
NOM 0.037
Max 0.120 0.055 0.043 0.021 0.0059
2.67 1.20 - 0.37 0.085 NOM 1.9 0.01 2.10
NOM 0.95
B C D F G K L
0.004 0.0985
PACKAGE DIMENSIONS SM8
N
DIM
Millimetres Min Typ - - 0.7 - - - 4.59 1.53 - - - Max 1.7 0.1 - 0.32 6.7 3.7 - - 7.3 - 15
Inches Min - Typ - Max 0.067 0.004 - 0.013 0.264 0.145 - - 0.287 - 15
A A1 b c D E e1 e2 He Lp
- 0.02 - 0.24 6.3 3.3 - - 6.7 0.9 -
0.0008 - - 0.009 0.248 0.130 - - 0.264 0.035 - 0.028 - - - 0.180 0.060 - - -
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 Streitfeldstrae 19 D-81673 Munchen Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 Zetex Inc. 47 Mall Drive, Unit 4 Commack NY 11725 USA Telephone: (631) 543-7100 Fax: (631) 864-7630 Zetex (Asia) Ltd. 3701-04 Metroplaza, Tower 1 Hing Fong Road, Kwai Fong, Hong Kong Telephone:(852) 26100 611 Fax: (852) 24250 494 These are supported by agents and distributors in major countries world-wide (c) Zetex plc 2000 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.
ISSUE 3 - APRIL 2001 8

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