ZXCT1080 datasheet(9/12 Pages) ZETEX

9 / 12 page

ZXCT1080

Issue 1 - November 2007

www.zetex.com

Figure 2

Protection/error sources for ZXCT1080

Capacitor CD provides high frequency transient decoupling when used with RLIM; typical values

are of the order 10pF

For best performance RSENSE should be connected as close to the S+ (and SENSE ) pins;

minimizing any series resistance with RSENSE.

When choosing appropriate values for RSENSE a compromise must be reached between in-line

signal loss (including potential power dissipation effects) and small signal accuracy.

Higher values for RSENSE gives better accuracy at low load currents by reducing the inaccuracies

due to internal offsets. For best operation the ZXCT1080 has been designed to operate with

VSENSE 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 ZXCT1080 has been specified to operate in a linear manner

over a VSENSE range of 10mV to 150mV range, however it will still be monotonic down to VSENSE

of 0V.

It is for this very reason that Zetex has specified an input offset voltage (VO(10)) at 10mV. The

output voltage for any VSENSE voltage from 10mV to 150mV can be calculated as follows:

Alternatively the load current can be expressed as:

R SENSE

C D

R LIM

ZXCT1080

S+

S-

OUT

SENSE

()xG V

O10

()

OUT

O10

()

–

()

GxR

SENSE

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