Sense+ sense, Zxct1081 – Diodes ZXCT1081 User Manual
Page 9
ZXCT1081
ZXCT1081
Document number: DS32102 Rev. 1 - 2
9 of 11
March 2010
© Diodes Incorporated
A Product Line of
Diodes Incorporated
R
SENSE
C
D
R
LIM
ZXCT1081
SENSE+
SENSE-
Figure 2 Protection/Error Sources for ZXCT1081
Capacitor CD provides high frequency transient decoupling when used with R
LIM
; typical values are of the order 10pF.
For best performance R
SENS
E should be connected as close to the SENSE+ (and SENSE ) pins; minimizing any series
resistance with R
SENSE
.
When choosing appropriate values for R
SENSE
a compromise must be reached between in-line signal loss (including
potential power dissipation effects) and small signal accuracy.
Higher values for R
SENSE
gives better accuracy at low load currents by reducing the inaccuracies due to internal offsets. For
best operation the ZXCT1081 has been designed to operate with V
SENSE
of the order of 50mV to 150mV.
Current monitors' basic configuration is that of a unipolar voltage to current to voltage converter powered from a single
supply rail. The internal amplifier at the heart of the current monitor may well have a bipolar offset voltage but the output
cannot go negative; this results in current monitors saturating at very low sense voltages.
As a result of this phenomenon the ZXCT1081 has been specified to operate in a linear manner over a V
SENSE
range of
10mV to 150mV range, however it will still be monotonic down to V
SENSE
of 0V.
It is for this very reason that Zetex has specified an input offset voltage (V
O(10)
) at 10mV. The output voltage for any V
SENSE
voltage from 10mV to 150mV can be calculated as follows:
V
OUT
= (V
SENSE
) xG + V
O(10)
Alternatively the load current can be expressed as:
I
L
=
V
OUT
– V
O(10)
GxR
SENSE