ZXCT1050 データシートの表示（PDF） - Diodes Incorporated.

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ZXCT1050

Precision wide input range current monitor

Diodes Incorporated. 

ZXCT1050

Applications information

The ZXCT1050 is a current output version of the ZXCT1051 and as such uses a separate power

supply pin. All biasing for the internal amplifiers comes from its separate VCC input and is not ‘line

powered’, unlike the ZXCT1021.

This means that at very small sense voltages the ZXCT1050 draws very little current (<1␮A) from

the lines being sensed.

The separate VCC pin enables the ZXCT1050 to be operated at sense line voltages down to 0V,

where the ZXCT1021 would switch off. This feature enables the ZXCT1050 to be used to sense the

currents flowing through lines that have been shorted to ground.

VRAIL

R SENSE

R SH

SENSE+ (4)

IL

VCC

(5) SENSE-

(1)

Q1

Out

(3)

Load

ZXCT1050

RG

GND

GND (2)

Basic operation

Load current, IL, from VRAIL is drawn through RSENSE developing a voltage VSENSE across the

sense inputs of the ZXCT1050.

The internal amplifier forces VSENSE across external resistance RSH (internal on the ZXCT1051)

causing a current to flow through transistor Q1 and out of the output pin, OUT. This current is then

converted to a voltage by a resistor, RG, between OUT and GND.

The overall gain of the ZXCT1050 is determined by the following expression:

GAIN

=

20 × --R----G----

RSH

A ratio of 1:2 between RSH and RG creates the fixed gain of 10 with an output impedance equal to

RG (see electrical characteristics for output current-voltage characteristics).

The ZXCT1050 has both RG and RSH external. This allows RG and RSH to be varied so that the

required gain can be achieved at the required output impedance.

For low power applications both RG and RSH can be increased whereas for driving low impedance

RG and RSH can be decreased.

The maximum recommended value for RG is 40k⍀ and the maximum recommended value for

RSH is 10k⍀. Large values of RSH start increasing the effective input offset error, while large values

of RG can created load errors and reduce bandwidths.

The maximum differential input voltage, VSENSE, is 150mV (IL * RSENSE); however voltages up to

500mV will not damage it. This can be increased further by the inclusion of a resistor, RLIM,

between the SENSE+ pin and the rail being sensed, VRAIL.

For best performance RSENSE should be connected as close to the SENSE+ and SENSE- pins thus

minimizing any series resistance with RSENSE.

Issue 1 - June 2007

7

© Zetex Semiconductors plc 2007

www.zetex.com

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