ZETEX ZXCT1009F

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.
APPLICATIONS
•
Battery Chargers
•
Smart Battery Packs
•
DC Motor control
It takes a high side voltage developed across a current
shunt resistor and translates it into a proportional
output current.
•
Over current monitor
•
Power Management
•
Level translating
A user defined output resistor scales the output
current into a ground-referenced voltage.
•
Programmable current source
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 4µA, combined
with its SOT23 package make it a unique solution,
suitable for portable battery equipment.
APPLICATION CIRCUIT
Vin
To Load
Rsense
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.
ZXCT
1009
Vout
Rout
ORDERING INFORMATION
PART NUMBER
PACKAGE
PARTMARKING
ZXCT1009F
SOT23
109
ZXCT1009T8
SM8
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 = 100Ω.
SYMBOL
PARAMETER
CONDITIONS
LIMITS
Min
V in
V CC Range
I out 1
Output current
V sense
I sense
†
Typ
2.5
UNIT
Max
20
V
V sense =0V
1
4
15
µA
V sense =10mV
90
104
120
µA
V sense =100mV
0.975
1.002
1.025
mA
V sense =200mV
1.95
2.0
2.05
mA
V sense =1V
9.6
9.98
10.2
mA
Sense Voltage
0
Load pin
2500
mV
100
nA
input current
Acc
Accuracy
Gm
Transconductance,
BW
Bandwidth
R sense = 0.1Ω
-2.5
V sense =200mV
2.5
%
10000
µA/V
RF P in = -20dBm‡
V sense = 10mV dc
300
kHz
V sense = 100mV dc
2
MHz
I out / V sense
1
Includes input offset voltage contribution
Vsense=Vin-Vload
‡ -20dBm=63mVp-p into 50Ω
†
ISSUE 3 - APRIL 2001
2
ZXCT1009
TYPICAL CHARACTERISTICS
ISSUE 3 - APRIL 2001
3
ZXCT1009
PIN DESCRIPTION
Pin Name
Pin Function
V in
Supply Voltage
Load
Connection to load/battery
I out
Output current, proportional to V in -V load
CONNECTION DIAGRAMS
SOT23
Package Suffix – F
Load
SM8
Package Suffix – T8
1
Vin
1
8
N/C
N/C
2
7
N/C
Vin
3
6
N/C
Iout
4
5
N/C
Load
3
Iout
2
Top View
Top View
SCHEMATIC DIAGRAM
Vin
Load
100Ω
+
-
Iout
ISSUE 3 - APRIL 2001
4
ZXCT1009
POWER DISSIPATION
APPLICATIONS INFORMATION
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:
The following lines describe how to scale a load
current to an output voltage.
Vsense = Vin - Vload
Vout = 0.01 x Vsense x Rout1
Pmax = (Tjmax – Tamb) / θja
E.g.
The device power dissipation, PD is given by the
expression:
A 1A current is to be represented by a 100mV output
voltage:
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
Rout = 0.1 / (0.1 x 0.01) = 100 Ω
SOT23
TYPICAL CIRCUIT APPLICATION
Vin
Rsense
ZXCT1009
Vin
Load
Rload
Iout
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
Transient Protection
APPLICATIONS INFORMATION (Continued)
FZT789A 140µH
Charger Input
FMMT3904
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.
To Battery +
0.2Ω
ZHCS1000
1kΩ
Vin
Load
100Ω
FMMD914
10µH
+ -
5V
bq2954
MOD pin
Vin
ZXCT1009
To Load
Rsense
FMMT451
220Ω
Iout
SNS pin
ZXCT
1009
100Ω
support components omitted for clarity
Rlim
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
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) =
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 − 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
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.
ZXCT1009
ZXCT1009
Vout
Vin
Vout
Load
Rout
Rout
Vin
GND
The figure opposite shows a PCB layout suggestion.
The resistor section is 25mm x 0.25mm giving
approximately 150mΩusing 1oz copper. The data for
the normalised graph was obtained using a 1A load
current and a 100Ω 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
Actual Size
Load
GND
Layout shows area of shunt
resistor compared to SOT23
package. Not actual size
ISSUE 3 - APRIL 2001
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ZXCT1009
PACKAGE DIMENSIONS SOT23
N
DIM Millimetres
PACKAGE DIMENSIONS SM8
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
F
0.085
0.15
0.0033
G
NOM 1.9
K
0.01
0.10
0.0004
L
2.10
2.50
0.0825
N
NOM 0.95
DIM
0.021
0.0059
NOM 0.075
0.004
0.0985
NOM 0.037
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°
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
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D-81673 München
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
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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
© 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
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