Diodes ZXCT1107/1109/1110 - Manual (Page 11)

ZXCT1107/1109/1110
LOW POWER HIGH-SIDE CURRENT MONITORS
ZXCT1107/1109/1110
Document number: DS35033 Rev. 3 - 2
11 of 16
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JULY 2011
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Application Information (cont.)
The ZXCT1110 is highly linear and has a transconductance of 4mA/V ±1.8% and an output of 40µA ±4µA at V
SENSE
=10mV.
The output current can therefore be calculated (Standard International Units) as:
I
OUT
= (40 +/-4)*10
-6
+ (V
SENSE
-0.01)*(0.004 +/- 0.000072) Amp
The worst-case current error is then
I
OUTERROR
= I
OUT
– I
OUTIDEAL
= +/- { 4*10
-6
+ (V
SENSE
-0.01) * 0.000072 } Amp
or I
OUTERROR
= +/- { 3.28*10
-6
+ V
SENSE
* 0.000072 } A
The percentage error is
% 100 *
004 . 0 * V
I
% 100 *
I
I
SENSE
OUTERROR
OUTIDEAL
OUTERROR = = ε
Then
004 . 0 * V
0072 . 0 * V 10 * 28 . 3
SENSE
SENSE
4 +
± = ε
−
%
or % 8 . 1
V
082 . 0
SENSE
± ± = ε
Equation 2
This shows that the error is reduced with increasing V
SENSE
. Then the minimum V
SENSE
required to give the error ± ε % is
8 . 1
082 . 0
V
SENSE − ε
=
V [only for ZXCT1110] Equation 3
In the application, the effect of the external resistor tolerances must also be taken into account.
Table 1: ZXCT1107/ZXCT1109 Error
V
SENSE
Mean I
OUT
Error Band Percent Error
10mV 45.5 µA ±8.5µA ±18.7%
30mV 124.5 µA ±9.5µA ±7.6%
100mV 408 µA ±14µA ±3.4%
200mV 809.5 µA ±22.5µA ±2.8%
Table 2: ZXCT1110 Error
V
SENSE
Mean I
OUT
Error Band Percent Error
10mV 40µA ±4µA ±10%
30mV 120µA ±5.44µA ±4.53%
100mV 400µA ±10.48µA ±2.62%
200mV 800µA ±17.68µA ±2.21%