1
ZXCT1008
ISSUE 2 - JULY 2004
AUTOMOTIVE HIGH-SIDE CURRENT MONITOR
DESCRIPTION
The ZXCT1008 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. The
ability to withstand high voltage transients and
reverse polarity connection, makes this part very
suitable for automotive and other transient rich
environments.
FEATURES
Low cost, accurate high-side current sensing
-40 to +125
C temperature range
Up to 500mV sense voltage
2.5V 20V supply range
4A quiescent current
1% typical accuracy
SOT23
DEVICE MARKING
108
APPLICATIONS
Automotive current measurement
DC motor and solenoid control
Over current monitor
Power management
APPLICATION CIRCUIT
DEVICE
REEL
SIZE
TAPE
WIDTH
QUANTITY PER
REEL
ZXCT1008FTA
7"
8mm
3,000 units
ORDERING INFORMATION
ZXCT1008
ISSUE 2 - JULY 2004
2
ABSOLUTE MAXIMUM RATINGS
Voltage on any pin
-0.6V to 20V (relative to Iout)
Continuous output current
10mA
Continuous sense voltage
Vin + 0.5V > Vsense
> Vin 5V
Operating temperature
-40 to 125
C
Storage temperature
-55 to 150
C
Package power dissipation (TA = 25
C)
450mW Derate to zero at 150
C
Operation above the absolute maximum rating may cause device failure. Operation at the absolute maximum
ratings, for extented periods, may reduce device reliability.
ELECTRICAL CHARACTERISTICS
Test Conditions TA = 25
C, Vin = 5V, Rout = 100.
SYMBOL
PARAMETER
CONDITIONS
LIMITS
UNIT
Min
Typ
Max
V
in
V
CC
range
2.5
20
V
I
out
1
Output current
V
sense
=0V
V
sense
=10mV
V
sense
=100mV
V
sense
=200mV
V
sense
=500mV
1
90
0.975
1.95
4.8
4
104
1.0
2.0
5.0
15
120
1.025
2.05
5.2
A
A
mA
mA
mA
V
sense
Sense voltage
0
500
mV
I
sense
-
V
sense
-
input current
100
nA
Acc
Accuracy
R
sense
= 0.1
V
sense
=200mV
-2.5
2.5
%
Gm
Transconductance,
I
out
/ V
sense
10000
A/V
BW
Bandwidth
RF P
in
= -20dBm
V
sense
= 10mV dc
V
sense
= 100mV dc
300
2
kHz
MHz
1
Includes input offset voltage contribution
Vsense=Vin-Vload
-20dBm=63mVp-p into 50
ZXCT1008
ISSUE 2 - JULY 2004
3
TYPICAL CHARACTERISTICS
ZXCT1008
ISSUE 2 - JULY 2004
4
PIN DESCRIPTION
Pin Name
Pin Function
V
sense
+
Supply voltage
V
sense
-
Connection to load/battery
I
out
Output current, proportional to V
in
-V
load
SOT23
Package Suffix F
Top View
CONNECTION DIAGRAM
SCHEMATIC DIAGRAM
TYPICAL CHARACTERISTICS (Cont.)
ZXCT1008
ISSUE 2 - JULY 2004
5
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
E.g.
A 1A current is to be represented by a 100mV output
voltage:
1) Choose the value of R
sense
to give 50mV >
V
sense
> 500mV at full load.
For example V
sense
= 100mV at 1.0A.
R
sense
= 0.1/1.0 => 0.1
2) Choose R
out
to give V
out
= 100mV,
when V
sense
= 100mV.
Rearranging
1
for Rout gives:
Rout = Vout /(Vsense x 0.01)
Rout = 0.1 / (0.1 x 0.01) = 100
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
ZXCT1008
ISSUE 2 - JULY 2004
6
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.
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
a n d o t h e r c o m m o n t r a n s i e n t s n e e d t o b e
considered. The zener Z1 provides additional
protection for local dump, reverse battery and high
voltage transient incidents.
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)
V
V
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 :-
R
R
[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
Figure 1.0
ZXCT1009 with additional current limiting Resistor
Rlim and zener Z1
TYPICAL AUTOMOTIVE CIRCUIT APPLICATION
ZXCT1008
ISSUE 2 - JULY 2004
7
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
-40
-20
0
20
40
60
80
100 120 140
0.8
1.0
1.2
1.4
Effect of Sense Resistor Material
on Temperature Performance
V
OUT
with Ideal
Sense Resistor
V
OUT
with Copper
Sense Resistor
Voltage across
Copper Sense
Resistor
Norma
l
ised
Voltage
Temperature (C)
Vout
Vin
GND
Load
Rout
ZXCT1009
APPLICATIONS INFORMATION
Layout shows area of shunt
resistor compared to SOT23
package. Not actual size
Vout
Vin
GND
Load
Rout
ZXCT1009
Actual Size
ZXCT1008
8
ISSUE 2 - JULY 2004
Europe
Zetex GmbH
Streitfeldstrae 19
D-81673 Mnchen
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
Lansdowne Road, Chadderton
Oldham, OL9 9TY
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
Zetex Semiconductors plc 2004
PACKAGE OUTLINE
DIM
Millimeters
Inches
DIM
Millimeters
Inches
Min
Max
Min
Max
Min
Max
Max
Max
A
2.67
3.05
0.105
0.120
H
0.33
0.51
0.013
0.020
B
1.20
1.40
0.047
0.055
K
0.01
0.10
0.0004
0.004
C
1.10
0.043
L
2.10
2.50
0.083
0.0985
D
0.37
0.53
0.015
0.021
M
0.45
0.64
0.018
0.025
F
0.085
0.15
0.0034
0.0059
N
0.95 NOM
0.0375 NOM
G
1.90 NOM
0.075 NOM
PACKAGE DIMENSIONS
Controlling dimensions are in millimeters. Approximate conversions are given in inches
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