zxct1011 Zetex Semiconductors plc., zxct1011 Datasheet - Page 6

• Manufacturer Part Number: zxct1011
• Description: Zxct1011 - High-side Low Drift Current Monitor
• Manufacturer: Zetex Semiconductors plc.

A 1 ampere load current is to be measured into a battery. The output signal required to an over
current controller needs to be 3.3V. What is a suitable value of R
to the supply current be?
Figure 1 ZXCT1011 to measure a 1.0 A load current
To obtain the highest accuracy, choose the of R
The transconductance using a 120
Choose R
Rearranging equation 1 without the offset error gives:
Now consider the offset error for this resistor:
Issue 1- July 2005
© Zetex Semiconductors plc 2005
V
in
= 5.0V - 9.0V
V
I
Output signal required: 3.3V
load
in
120R
R
= 5.0V - 9.0V
out
shunt
= 1.0A
to give V
out
3
R
= 3.3V, when V
V
shunt
sense+
5
R
ZXCT
1011
I
sense
out
2
V
R
R
R
R
Offset due to supply current = R
sense-
out
sense
out
out
4
resistor will be 10mA/V.
= (V
= 3.3k
sense
= 0.1/1.0 = 0.1
3.3V
out
= 100mV
x R
sense
6
shunt
I
R
load
to give 100mV:
) / (1.2 x I
load
= 1A
Load
out
out
x R
x 4x10
and what will the error due
sense
-6
)
µA = 13.2mV = 0.4%
ZXCT1011
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