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 4µA, combined with a SOT23
package make it a unique solution for portable battery
equipment. The SM8 device offers an alternative package
option.
Pin Assignments
SOT23
Package Suffix - F
V
SENSE-
3
1
I
OUT
V
SENSE+
2
(Top View)
Features
•
•
•
•
•
•
•
•
Low cost, accurate high-side current sensing
Output voltage scaling
Up to 2.5V sense voltage
2.5V to 20V supply range
4μA quiescent current
1% typical accuracy
SOT23 and SM8 packages
AEC-Q100.3 qualified; ZXCT1009FTA only
SM8
Package Suffix – T8
V
SENSE-
N/C
V
SENSE+
I
OUT
1
2
3
4
8
7
6
5
N/C
N/C
N/C
N/C
(Top View)
Applications
•
•
•
•
•
•
•
•
Battery chargers
Smart battery packs
DC motor control
Over current monitor
Power management
Level translating
Programmable current source
Application Circuit
V
IN
R
SENSE
To load
2
V
SENSE+
3
V
SENSE-
ZXCT1009
I
OUT
1
V
OUT
R
OUT
ZXCT1009
Document number: DS33441 Rev. 12 - 2
1 of 8
www.diodes.com
April 2011
© Diodes Incorporated
ZXCT1009
HIGH-SIDE CURRENT MONITOR
Pin Descriptions
Pin Name
V
SENSE+
V
SENSE-
I
OUT
Pin Function
Connection to supply voltage
Connection to load
Output current, proportional to measured current
Absolute Maximum Ratings
(T
A
= 25°C)
Description
Voltage on any pin
(relative to IOUT)
Continous output current, I
OUT
Continuous sense voltage,
Operating temperature, T
A
Storage temperature
Package power
SOT23
dissipation @ T
A
= 25°C
SM8
(Derate to zero @ 125°C)
†
V
SENSE
Rating
-0.6 to 20
25
-0.5 to +5
-40 to 85
-55 to 125
450
2
Unit
V
mA
V
°C
°C
mW
W
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
(T
A
= 25°C, V
IN
= 5V, R
OUT
= 100Ω)
Symbol
V
IN
Parameter
V
CC
range
V
SENSE
= 0V
V
SENSE
= 10mV
V
SENSE
= 100mV
V
SENSE
= 200mV
V
SENSE
= 1V
Conditions
Limits
Typ
4
104
1.002
2.0
9.98
Units
V
µA
µA
mA
mA
mA
mV
nA
Min
2.5
1
90
0.975
1.95
9.6
0
Max
20
15
120
1.025
2.05
10.2
2500
100
I
OUT
1
Output Current
V
SENSE
†
Sense Voltage
V
SENSE -
Input Current
Accuracy
Transconductance,
I
OUT
/V
SENSE
Bandwidth
V
SENSE(DC)
= 10mv, RF P
IN
= -40dBm
‡
‡
I
SENSE-
A
CC
R
SENSE
= 0.1Ω
V
SENSE
= 200mV
-2.5
10000
300
2
2.5
%
µA/V
kHz
MHz
G
M
BW
Notes:
V
SENSE(DC)
= 100mv, RF P
IN
= -20dBm
1. Includes input offset voltage contribution
†. VSENSE is defined as the differential voltage between VSENSE+ and VSENSE-
.
VSENSE = VSENSE+ - VSENSE-
= VIN - VLOAD
= ILOAD x RSENSE
‡ -20dBm=63mVPP into 50Ω
ZXCT1009
Document number: DS33441 Rev. 12 - 2
2 of 8
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April 2011
© Diodes Incorporated
ZXCT1009
HIGH-SIDE CURRENT MONITOR
Typical Characteristics
ZXCT1009
Document number: DS33441 Rev. 12 - 2
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ZXCT1009
HIGH-SIDE CURRENT MONITOR
Typical Characteristics
(cont.)
Power Dissipation
The maximum allowable power dissipation of the device for
normal operation (P
MAX
), is a function of the package junction to
ambient thermal resistance (θ
JA
), maximum junction temperature
(T
JMAX
), and ambient temperature (T
AMB
), according to the
expression:
P
MAX
= (T
JMAX
– T
AMB
) /
θ
JA
The device power dissipation, P
D
is given by the expression:
P
D
= I
OUT
(V
IN
-V
OUT
) W
Application Information
The following text describes how to scale a load current
to an output voltage.
V
SENSE
= V
IN
- V
LOAD
1
V
OUT
= 0.01 x V
SENSE
x R
OUT
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 => 0.1Ω.
2) Choose R
OUT
to give V
OUT
= 100mV, when
V
SENSE
= 100mV.
Rearranging
1
for Rout gives:
R
OUT
= V
OUT
/(V
SENSE
x 0.01)
R
OUT
= 0.1 / (0.1 x 0.01) = 100Ω
ZXCT1009
Document number: DS33441 Rev. 12 - 2
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April 2011
© Diodes Incorporated
ZXCT1009
HIGH-SIDE CURRENT MONITOR
Application Information
(cont.)
Li-Ion Charger Circuit
Transient Protection
An additional resistor, R
LIM
can be added in series with R
OUT
(as below), to limit the current from I
OUT
. Any circuit
connected to V
OUT
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.
V
IN
R
SENSE
To load
2
V
SENSE+
3
V
SENSE-
ZXCT1009
I
OUT
1
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 Diodes FZT789A high current
Super-ß 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.
R
LIM
V
OUT
R
OUT
ZXCT1009 with additional current limiting Resistor R
LIM
.
Assuming the worst case condition of V
OUT
= 0V; providing a
low impedance to a transient, the minimum value of R
LIM
is
given by:-
R
LIM(min)
= (V
PK
– V
MAX
)/I
PK
V
PK
= Peak transient voltage to be withstood
V
MAX
= Maximum working voltage = 20V
I
PK
= Peak output current = 40mA
The maximum value of R
LIM
is set by V
IN(MIN)
, V
OUT(MAX)
and
the dropout voltage (see transfer characteristic on page 3) of
the ZXCT1009 :-
R
LIM(MAX)
= R
OUT
[V
IN(MIN)
– (V
DP
+ V
OUT(MAX)
)]/V
OUT(MAX)
V
IN(MIN)
= Minimum Supply Operating Voltage
V
DP
= Dropout Voltage
V
OUT(MAX)
= Maximum Operating Output Voltage
ZXCT1009
Document number: DS33441 Rev. 12 - 2
5 of 8
www.diodes.com
April 2011
© Diodes Incorporated
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