A Product Line of
Diodes Incorporated
ZXCT1107/1109/1110
LOW POWER HIGH-SIDE CURRENT MONITORS
Application Information (cont.)
Note that in order to avoid additional error, VSUPPLY must be at least 1.5V greater than VOUT. This margin depends on the
value of VSENSE. For VSENSE = 100mV, this margin can be reduced to 1.0V.
RSENSE is chosen based on the threshold VSENSET of sense voltage selected as above, for the chosen threshold load current,
ILOADT
.
VSENSET
RSENSE
=
Equation 4
ILOADT
RGAIN is chosen to give the required threshold output voltage, VOUTT. From Equation 1, the threshold output current is
IOUTT = 0.004 * VSENSET
Equation 1a
Equation 5
VOUTT
RGAIN
=
=
IOUTT
VOUTT
0.004 * VSENSET
or
RGAIN
Design Example
A current monitor is required to provide an output voltage of 2V ±6% when the load current of a 12V supply is 2A. Resistors
are available with 1% tolerance.
The sense and output resistors will contribute a total possible error of 2%, so the ZXCT11xx error must not exceed 4%. From
Table 1, the error of ZXCT1107/1109 will be 3.4% if the sense voltage is 100mV. This satisfies the total error requirement of
6%.
Equation 4 gives
RSENSE = 100mV/2A = 50mΩ
Equation 5 gives
2
RGAIN
=
= 5kΩ
0.004 * 0.1
A suitable preferred value is 5.1kꢀ. This gives a systematic error of +2%, which can be compensated elsewhere in the
system if desired. Figure 2 shows the resulting schematic.
Figure 2. Example Circuit using ZXCT1107/ZXCT1109
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MARCH 2011
© Diodes Incorporated
ZXCT1107/1109/1110
Document number: DS35033 Rev. 1 - 2
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