1
ISSUE 3 - APRIL 2001
ZXCT1009
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.
Thewideinputvoltagerangeof20Vdowntoaslowas
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
V
in
To Load
V
out
R
sense
R
out
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
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ZXCT1009
ABSOLUTE MAXIMUM RATINGS
Voltage on any pin -0.6V to 20V (relative to Iout)
Continuous output current 25mA
Continuous sense voltage Vin + 0.5V > Vsense†> Vin – 5V
Operating Temperature -40 to 85°C
Storage Temperature -55 to 125°C
Package Power Dissipation (TA= 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
Iout1Output current Vsense=0V
Vsense=10mV
Vsense=100mV
Vsense=200mV
Vsense=1V
1
90
0.975
1.95
9.6
4
104
1.002
2.0
9.98
15
120
1.025
2.05
10.2
µA
µA
mA
mA
mA
Vsense†Sense Voltage 0 2500 mV
Isense Load pin
input current 100 nA
Acc Accuracy Rsense = 0.1Ω
Vsense=200mV -2.5 2.5 %
Gm Transconductance,
Iout /V
sense
10000 µA/V
BW Bandwidth RF Pin= -20dBm‡
Vsense = 10mV dc
Vsense = 100mV dc 300
2kHz
MHz
1Includes input offset voltage contribution
†Vsense=Vin-Vload
‡ -20dBm=63mVp-p into 50Ω
ISSUE 3 - APRIL 2001
ZXCT1009
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TYPICAL CHARACTERISTICS
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ZXCT1009
PIN DESCRIPTION
Pin Name Pin Function
Vin Supply Voltage
Load Connection to load/battery
Iout Output current, proportional to Vin-Vload
SM8
Package Suffix –T8
Top View
SOT23
Package Suffix –F
Top View
I
out
Load
V
in
3
2
1
Iout
Load
N/C
Vin N/C
N/C
N/C
N/C
5
6
7
8
4
3
2
1
CONNECTION DIAGRAMS
+
-
V
in
Load
I
out
100Ω
SCHEMATIC DIAGRAM
ISSUE 3 - APRIL 2001
ZXCT1009
5
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 1for 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:
Pmax = (Tjmax – Tamb) / θja
The device power dissipation, PDis 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, Rsense can be selected on specific
requirements of accuracy, size and power rating.
APPLICATIONS INFORMATION
ISSUE 3 - APRIL 2001
ZXCT1009
6
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
frequencyofthePWMloopisapproximately120kHz.
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
5V
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 Iout.
Anycircuitconnectedto Vout will be protectedfrom
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 Vout = 0V;
providing a low impedance to a transient, the
minimum value of Rlim is given by:-
R(min) VV
I
lim pk max
pk
=−
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 :-
RR [V V V (max)
V
lim out in dp out
out
(max) (min) ( )]
(max)
=−+
Vin(min) = Minimum Supply Operating
Voltage
Vdp =Dropout Voltage
Vout (max)= Maximum Operating Output
Voltage
Vin To Load
Vout
Rsense
R
Rlim
ZXCT
1009
ISSUE 3 - APRIL 2001
ZXCT1009
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PCB trace shunt resistor for low cost
solution.
Thefigure below showsoutput characteristics ofthe
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.
Thefigureopposite showsaPCBlayoutsuggestion.
The resistor section is 25mm x 0.25mm giving
approximately150mΩusing1ozcopper.Thedatafor
the normalised graph was obtained using a 1A load
current and a 100Ωoutput 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
ISSUE 3 - APRIL 2001
ZXCT1009
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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
NNOM 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
e1 –4.59 ––0.180 –
e2 –1.53 ––0.060 –
He 6.7 –7.3 0.264 –0.287
Lp 0.9 ––0.035 ––
α––15°– – 15°
PACKAGE DIMENSIONS SM8
Zetex plc.
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