A Product Line of
Diodes Incorporated
ZXCT1107/1109/1110
LOW POWER HIGH-SIDE CURRENT MONITORS
Application Information (cont.)
Alternatively, the ZXCT1110 may be used with a reduced sense voltage if desired. From Equation 3, with ε=4%,
0.082
VSENSE
=
= 0.082/(4-1.8) = 37.2mV
ε −1.8
Equation 4 gives
RSENSE = 37.2mV/2A = 18.6mΩ
A suitable preferred value is 20mꢀ. Then the sense voltage will be 2A * 20mꢀ = 40mV.
Equation 5 gives
2
RGAIN
=
= 12500ꢀ
0.004 * 0.04
A suitable preferred value is 13kꢀ.
The alternative example circuit using the ZXCT1110 with a sense voltage of 40mV is shown in Figure 3, giving the required
overall accuracy of ±6%.
20mΩ
ILOAD
VSUPPLY
S+
S-
ZXCT1110
LOAD
GND
OUT
OUTPUT
VOUT
13k
GND
Figure 3. Example Circuit using ZXCT1110
Protection Against Load Short Circuit
In the event of a load short circuit or overload, a large proportion of the supply voltage may appear between the sense
terminals. The supply may be current limited, but there is normally a large reservoir capacitor which can deliver enough
energy to damage the ZXCT11xx before the supply voltage falls to a safe level due to current limit activation.
The ZXCT11xx is rated for a maximum sense voltage of +0.8V, but is safe if the input current is limited to ±8.5mA. In Figure
4, the resistor RPROT limits the current and therefore protects the current monitor device against load short circuit without
introducing significant current measurement error.
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MARCH 2011
© Diodes Incorporated
ZXCT1107/1109/1110
Document number: DS35033 Rev. 1 - 2