ZXCT1109 datasheet(12/17 Pages) DIODES

12 / 17 page

ZXCT1107/1109/1110

LOW POWER HIGH-SIDE CURRENT MONITORS

ZXCT1107/1109/1110

Document number: DS35033 Rev. 1 - 2

12 of 17

www.diodes.com

MARCH 2011

A Product Line of

Diodes Incorporated

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.

LOADT

SENSET

SENSE

Equation 4

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

OUTT

GAIN

SENSET

OUTT

GAIN

004

Equation 5

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

004

GAIN =

= 5k

Ω

A suitable preferred value is 5.1k

Ω. 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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