ZXCT1041 EV1
Zdb341R2. 26-Feb-07
4/8
ZXCT1041 EV1 User Guide Rev2
Configuration table for ZXCT1041EV1
LOAD CURRENT
(A)
R
sense
(m
Ω
Ω
Ω
Ω
)
VOUT
(V)
SOLDER LINK
CONFIGURATION
1.5
100
1.5
Short SL1
6.0
25
1.5
Short SL2
7.5
20
1.5
Short SL1 & SL2
FLAG
The direction of current flow can be determined from the flag output pin. The flag output of the device is an open
collector output. On board the ZXCT1041EV1 is a 30k
Ω
resistor which is connected to V1, it may be connected to a
lower voltage eg 3V3 if that is appropriate in the application.
If current is flowing from V1 to V2, the FLAG pin will be High, at the same potential as V1 or the supply connected to
the collector resistor on the Flag output.
If current is flowing in the reverse direction, i.e. from V2 to V1, the FLAG pin will be Low, typically 60mV.
Configuration for different LOAD currents.
The board can be configured for different load currents by changing the smd resistors or fitting a suitable wire ended
resistor and opening both solder links. It is important to ensure an appropriate value of R
sense
is selected to obtain the
desired accuracy for a given output current.
The value of Vout is 10 times the voltage dropped across the sensing resistor, (providing that the input Voltage is
more than 2.7V higher than the Vout.)
Choosing a larger value for R
sense
gives a higher output voltage for a given current resulting in better resolution but at
the expense of increased voltage drop and higher dissipation in R
sense
. It also reduces the minimum voltage at which
the device will be linear as Vout +2.7V is the minimum input voltage for accurate results.
The ZXCT1041 is optimized for values of V
sense
of either polarity between 0 and 800mV.
Example: Scaling for 1.5A load current and a 500mV output.
The ZXCT1041 has a fixed gain of 10.
V
out
= 10 x V
sense
To obtain a 500mV output, 50mV is required between V
sense+
and V
sense-.
The value for R
sense
is thus 50mV /1.5A = 33m
Ω
.
Accuracy
The ZXCT1041 current monitor IC is a 2%
2
accurate device. The accuracy of the output voltage will be influenced by
the tolerance of the external sense used. The ZXCT1041EV1 utilizes 1% accurate sense resistors.
2
Total error at +100mV sense voltage
COMPONENTS LIST
Ref
Value
Package
Part Number
Manufacturer
Notes
R1
100m
Ω
1206
LR1206-R10FI
Welwyn
SMD Sense Resistor 1%
R2
25m
Ω
2512
LRF2512-R025FW
Welwyn
SMD Sense Resistor 1%
R3
30k
Ω
0805
Generic
SMD 1% 0.125W
ZXCT
SOT235
ZXCT1041E5
ZETEX
