ZXCT1012
REDUCED HEIGHT MICRO-POWER CURRENT MONITOR
ZXCT1012
Document number: DS33444 Rev. 2 - 2 1 of 9
www.diodes.com September 2011
© Diodes Incorporated
Description
The ZXCT1012 is a high side current sense monitor. Using
this type of device eliminates the need to disrupt the ground
plane when sensing a load cu rrent.
The ZXCT1012 takes the voltage developed across a small
value resistor and translates it into a proportional output
current. A user defined output resistor scales the output
current into a ground referenced voltage.
The ZXCT1012 has the accuracy specification of the
ZXCT1010 but in TS OT25.
A minimum operating current of just 3.5μA, combined with its
TSOT25 package make it suitable for portable battery
equipment where size and cur rent consumption are critical.
The wide input voltage ra nge down to as lo w as 2.5V make it
suitable for a wide range of applications requiring direct
operation from a battery.
Pin Assignments
5
43
2
1
GND
NC
OUT SENSE+
SENSE-
TSOT25
(Top View)
Features
• 2.5V to 20V supply range
• 3.5μA quiescent current
• Current output - user set gain
• Thin package - TSOT25
• Temperature range -40 to 85°C
Applications
• Battery fuel gauge
• Battery chargers
• Overcurrent monitor
• Power management
Typical Application Circuit
ZXCT1012
R
SENSE
V
IN
V
OUT
R
OUT
R
LOAD
SENSE+ SENSE-
OUT
GND
ZXCT1012
REDUCED HEIGHT MICRO-POWER CURRENT MONITOR
ZXCT1012
Document number: DS33444 Rev. 2 - 2 2 of 9
www.diodes.com September 2011
© Diodes Incorporated
Pin Descriptions
Pin Name Description
1 N/C
No connection
2 GND
Ground connection
3 OUT
Output current pin. Current generated due to a difference vol tage
between VSENSE+ and VSENSE- flows out of this pin. A suitable
value resistor connected to ground creates an output voltage. The
maximum voltage out of this pin will be VSENSE- - 1.5V.
4 SENSE+
This pin should be connected to the rail whose current is being
measured and also pr ovides power to internal circuitry. It is the
positive input of the current monitor and h as an in put range from
20V down to 2.5V. The current through this pin varies with
differential sense voltage.
5 SENSE-
This is the negative input of the current monitor and has an input
range from 20V down to 2.5V.
Absolute Maximum Ratings (TA = 25°C)
Description Rating Unit
VSENSE+ Max. 20 V
Voltage on any pin(relative to GND pin) -0.6 and VSENSE+ +0.5 V
VSENSE (Note 1) -0.15 to 3 V
Ambient Operating Temperature Range -40 to 85 °C
Storage Temperature -55 to 150 °C
Maximum Junction Temperatu r e 150 °C
Power Dissipation (TA = 25°C) 300
(De-rate to 0 at 150°C) mW
Package
(Note 2) RθJA PDISS @ 25°C
TSOT25 250°C/W 500mW
Recommended Operating Conditions
Symbol Parameter Min. Max. Units
VIN Sense+ range 2.5 20 V
TA Ambient temperature range differential -40 85 C
VSENSE Sense voltage 10 2500 mV
VOUT Output voltage swing 0 VSENSE- -15 V
Operation above the absolute maximum rating may cause device failure.
Operation at the absolute maximum ratings, for extended periods, may reduce device reliability.
Notes: 1. VSENSE is defined as the differential voltage between the SENSE+ and SENSE- pins. (VSENSE = VSENSE+ - VSENSE-)
2. Mounted on 30mm x 16mm x1.1mm FR4 board with 1oz copper.
ZXCT1012
REDUCED HEIGHT MICRO-POWER CURRENT MONITOR
ZXCT1012
Document number: DS33444 Rev. 2 - 2 3 of 9
www.diodes.com September 2011
© Diodes Incorporated
Electrical Characteristics (TA = 25°C, VIN = VSENSE+ = 5V; unless otherwise specified)
Symbol Parameter Conditions Limits Unit
Min. Typ. Max.
IOUT Output Current
VSENSE = 0V
VSENSE = 10mV
VSENSE = 40mV
VSENSE = 100mV
VSENSE = 200mV
0
85
380
0.975
1.95
0.3
100
400
1.00
2.00
15
115
420
1.025
2.05
µA
µA
µA
mA
mA
IQ Ground Pin Current VSENSE = 0V 3.5 8 µA
ISENSE- SENSE- Pin Input Current 100 nA
ACC Accuracy RSENSE = 0.1V
VSENSE = 200mV
-2.5 2.5 %
Gm Transconductance,IOUT/VSENSE
(Note 3) 10 mA/V
TC Temperature Coefficient VSENSE = 200mV
TA = 0 to 50°C (Note 3) 500 ppm/°C
BW Bandwidth CL = 5pF
ROUT = 1kΩ VSENSE = 10mV
VSENSE = 100mV 300
2 kHz
MHz
CMRR
(Note 4) Common Mod e Rejection Ratio VSENSE = 100mV, ROUT = 1kΩ
VIN = 2.5V to 20V 80 dB
Notes: 3. Temperature dependent measurements are extracted from characterisation and simulation results.
4. With the ZXCT1012 using SENSE+ as its power supply pin, common mode rejection cannot be distinguished from power supply rejection.
ZXCT1012
REDUCED HEIGHT MICRO-POWER CURRENT MONITOR
ZXCT1012
Document number: DS33444 Rev. 2 - 2 4 of 9
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© Diodes Incorporated
Typical Characteristics
100µ 1m 10m 100m 1
V (V)
Typi cal Output vs. Sense Volt age
SENSE
10m
1m
100µ
10µ
1µ
I, OU
T
P
U
T
C
U
R
R
E
N
T
(
A
)
OUT
V = 5V
T = 25°C
R = 0
IN
A
OUT
Ω
1m 10m 100m 1
V (V)
Er ror v s. S ense Voltag e
SENSE
-1
0
1
2
3
4
OUTPUT CURRENT ERROR (%)
Typical
V = 5V
T = 25°C
R = 0
IN
A
OUT
Ω
-40 TEMPERA TURE (°C)
Output Current vs. Tempe r at ur e
-20 0 20 40 60 80
-6%
-4%
-2%
0%
2%
I, OU
T
P
U
T
C
U
R
R
E
N
T
(m
A
)
OUT
V = 5V
V = 0.2V
R = 0
IN
SENSE
OUT
Ω
FREQUENCY (MHz)
Fr equency Response
0.01 0.1 1 10
-12
-9
-6
-3
0
3
G
A
IN (
d
B)
V = 5V
T = 25C
V = 63.2mVpp
IN
A
SENSE(AC)
°
DC V = 0.01V
SENSE
V = 0.1V
SENSE
V = 1V
SENSE
V , SUPPLY VOLTAGE (V)
Transfer Cha ract e risti c s
IN
102345
0
2
4
6
8
10
12
I,
O
U
T
P
U
T
C
U
R
R
E
N
T
(
m
A
)
OUT
V = 5V
T = 25C
R = 0
IN
A
OUT
°
Ω
V = 1V
SENSE
V = 0.8V
SENSE
V = 0.4V
SENSE
V = 0.6V
SENSE
V = 0.2V
SENSE
1 10 100 1k 10k 100k 1M 10M
FREQUENCY (Hz)
Common Mode Reject ion
-90
V = 5V
T = 25C
V = 63.2Vpp
IN
A
SENSE(AC)
°
-80
-70
-60
-50
-40
-30
-20
-10
0
R
E
J
E
C
TI
O
N (
d
B)
V = 0.01V
SENSE
V = 1V
SENSE
V = 0.1V
SENSE
ZXCT1012
REDUCED HEIGHT MICRO-POWER CURRENT MONITOR
ZXCT1012
Document number: DS33444 Rev. 2 - 2 5 of 9
www.diodes.com September 2011
© Diodes Incorporated
Applications Information
The ZXCT1012 current monit or works by converting the voltage de velop ed across a small se nse res istor into a c urrent on th e
out pin. In realit y it is a voltage to current converter. T his output current can be converted into a voltage simply by pa ssing it
through a resistor (ROUT) to ground.
The current monitor has a transconductance of 10mA/V. But the overall amplifying conversion is affected by both the RSENSE
and ROUT.
The gain equat ion of the Z X CT1012 is:
100
OUT
R
SENSE
R
L
I
OUT
V×=
For best performance RSENSE should be connected as clos e to the SENSE+ (and SENSE-) pins; which minimizes any series
resistance with RSENSE and potential for interference pickup.
When choosing appro priate values for RSENSE a compromise must be reac hed between in-lin e signal loss (includi ng potential
power dissipation effects) and small signal accuracy.
Higher values for RSENSE gives better accuracy at low load currents by reducing the inacc uracies due to internal offsets. For
best operation the ZXCT1012 has been designed to provide best performa nce with VSENSE of the order of 40mV to 200mV.
Current monitors are single supply devices which means they tend to saturate at very low sense voltages. However it does
mean the output can never go negative. Also the output can never change direction (monotonic). This is important if the
current monitor is used in a control loop.
As the sense voltage is reduced the output will tend to saturate as the input offset voltage starts to have greater effect. It is
recommended to have a minimum sense voltage of 10mV to minimize linearity errors. Diodes has specified the output voltage
at VSENSE of 10mV, 40mV, 100mV and 200mV; which is the recommended sense voltage range.
The maximum differential input voltage, VSENSE, is 2.5V; however this will cause large output currents to flow increasing po wer
dissipation in the chip. The sense voltage can be increased further, without damaging the ZXCT1012, by the inclusion of a
resistor, RLIM, between SENSE- pin and the load. Typical values around 10kΩ. See figure below.
ZXCT1012
R
SENSE
R
LIM
C
C
If large reverse currents are expected then the resistor, RLIM, will provide protection from exc eeding absolute maximum ratings.
A suitable value for RLIM can be determined from:
mA5
V
R)REF(SENSE
LIM =
Where VSENSE(REV) is the maximum expected reverse sense voltage gen erated.
ZXCT1012
REDUCED HEIGHT MICRO-POWER CURRENT MONITOR
ZXCT1012
Document number: DS33444 Rev. 2 - 2 6 of 9
www.diodes.com September 2011
© Diodes Incorporated
Applications Information (cont.)
The following lines describe how to scale a load current to an output voltage.
VSENSE = RSENSE * ILOAD equation (1)
IOUT = 10mA/V x VSENSE equation (2)
VOUT = IOUT x ROUT equation (3)
Design example
In the circuit below a 1A current is to be represented b y a 100mV outp ut voltage (VOUT):
A) To be within recommended values choos e the value of RSENSE to give:
50mV > VSENSE > 200mV at full load.
For example set VSENSE = 100mV at 1.0A.
From equation (1)
RSENSE = 0.1V/1.0A = 0.1Ω
B) Now choose ROUT to give:
VOUT = 100mV, when VSENSE = 100mV.
From equation (2)
IOUT = 10mA/V x 0.1 = 1mA
Rearranging equati on (3) for ROUT gives:
ROUT = VOUT/IOUT = 0.1/0.001 = 100Ω
ZXCT1012
R
SENSE
V
IN
V
OUT
R
OUT
R
LOAD
SENSE+ SENSE-
OUT
GND
= 0.1 / (0.1 x 0.01) = 100Ω
Typical Circuit Application
Where RLOAD represents any load including DC motors, a charging battery or further circuitry that requires monitoring, RSENSE
can be selected on specific requir ements of accuracy, size and power rating.
ZXCT1012
REDUCED HEIGHT MICRO-POWER CURRENT MONITOR
ZXCT1012
Document number: DS33444 Rev. 2 - 2 7 of 9
www.diodes.com September 2011
© Diodes Incorporated
Power Dissipation
The maximum allo wable power dissipati on of the device for normal operation (P MAX), is a function of the package junction to
ambient thermal resistance (θJA), maximum junction temperature (TJMAX), and ambient temperature (TA), according to the
expression:
PMAX = (TJMAX – TA) / θJA
The device power dissipation, PD is given by the expression:
PD = IOUT.(VIN-VOUT) watts
Care must be taken when using this device at large input voltages and large sense voltages to prevent too much power
dissipation.
0
100
200
300
400
500
600
T , AMBIENT TEMPERA TURE ( C)
A
°
0 25 5075100125150
VIN = 20V VSENSE = 2.5V
ROUT = 100Ω
IOUT = 2.5 x 0.01
= 25mA
VOUT = IOUT x ROUT
= 25mA x 100Ω
= 2.5V
PD = 25mA (20 - 2.5)V
= 438mW
ZXCT1012
REDUCED HEIGHT MICRO-POWER CURRENT MONITOR
ZXCT1012
Document number: DS33444 Rev. 2 - 2 8 of 9
www.diodes.com September 2011
© Diodes Incorporated
Ordering Information
Device Package Marking Reel Size Quantity
ZXCT1012ET5TA TSOT25 1012 7 3000 Tape & Reel
Package Outline Dimensions (All Dimensions in mm)
Suggested Pad Layout
TSOT25
Dim Min Max Typ
A − 1.00 −
A1 0.01 0.10 −
A2 0.84 0.90 −
D − − 2.90
E − − 2.80
E1 − − 1.60
b 0.30 0.45 −
c 0.12 0.20 −
e − − 0.95
e1 − − 1.90
L 0.30 0.50
L2 − − 0.25
θ 0° 8° 4°
θ1 4° 12° −
All Dimensions in mm
Dimensions Value (in mm)
C 0.950
X 0.700
Y 1.000
Y1 3.199
c
A1
L
E1 E
A2
D
e1
e5x b
θ
4x 1
θ
L2
A
Y1
C C
X (5x)
Y (5x)
ZXCT1012
REDUCED HEIGHT MICRO-POWER CURRENT MONITOR
ZXCT1012
Document number: DS33444 Rev. 2 - 2 9 of 9
www.diodes.com September 2011
© Diodes Incorporated
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