zxct1012 Zetex Semiconductors plc., zxct1012 Datasheet - Page 5

• Manufacturer Part Number: zxct1012
• Description: Zxct1012 - Reduced Height Micro-power Current Monitor
• Manufacturer: Zetex Semiconductors plc.

Applications information
The ZXCT1012 current monitor works by converting the voltage developed across a small sense
resistor into a current on the out pin. In reality it is a voltage to current converter. This output
current can be converted into a voltage simply by passing it through a resistor (R
The current monitor has a transconductance of 10mA/V. But the overall amplifying conversion is
affected by both the R
The gain equation of the ZXCT1012 is:
For best performance R
which minimizes any series resistance with R
When choosing appropriate values for R
signal loss (including potential power dissipation effects) and small signal accuracy.
Higher values for R
due to internal offsets. For best operation the ZXCT1012 has been designed to provide best
performance with V
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. Zetex has specified the output voltage at V
200mV; which is the recommended sense voltage range.
The maximum differential input voltage, V
currents to flow increasing power dissipation in the chip. The sense voltage can be increased
further, without damaging the ZXCT1012, by the inclusion of a resistor, R
and the load. Typical values around 10k . See figure below.
If large reverse currents are expected then the resistor, R
exceeding absolute maximum ratings.
A suitable value for R
Where V
Issue 1 - December 2006
© Zetex Semiconductors plc 2006
R
LIM
ZXCT1012
»
V
V
---------------------------------- -
OUT
SENSE REF
SENSE(REV)
SENSE
C
5mA
C
=
I
(
L
×
R
R
)
SENSE
is the maximum expected reverse sense voltage generated.
SENSE
LIM
SENSE
LIM
SENSE
SENSE
can be determined from:
gives better accuracy at low load currents by reducing the inaccuracies
of the order of 40mV to 200mV.
R
-------------- -
100
OUT
and R
should be connected as close to the SENSE+ (and SENSE-) pins;
OUT
.
SENSE
SENSE
SENSE
a compromise must be reached between in-line
5
, is 2.5V; however this will cause large output
and potential for interference pickup.
SENSE
LIM
, will provide protection from
of 10mV, 40mV, 100mV and
LIM
, between SENSE- pin
ZXCT1012
www.zetex.com
OUT
) to ground.