ZXCT1010E5 - Zetex Semiconductors

ISSUE 5 - MARCH 2003

SEMICONDUCTORS

ZXCT1010

DESCRIPTION

The ZXCT1010 is a high side current sense monitor.

Using this device eliminates the need to disrupt the

ground plane when sensing a load current.

It is an enhanced version of the ZXCT1009 offering

reduced typical output offset and improved accuracy

at low sense voltage.

The wide input voltage range of 20V down to as low as

2.5V make it suitable for a range of applications. A

minimum operating current of just 4µA, combined

with its SOT23-5 package make suitable for portable

battery equipment.

FEATURES

•Low cost, accurate high-side current sensing.

•Output voltage scaling.

•Up to 2.5V sense voltage.

•2.5V – 20V supply range.

•300nA typical offset current.

•3.5µA quiescent current.

•1% typical accuracy.

•SOT23 -5 package.

APPLICATIONS

•Battery Chargers

•Smart Battery Packs

•DC Motor control

•Over current monitor

•Power Management

•Level translating

•Programmable current source

ENHANCED HIGH-SIDE CURRENT MONITOR

APPLICATION CIRCUIT

ORDERING INFORMATION

PART NUMBER PACKAGE PARTMARKING

ZXCT1010E5 SOT23-5 1010

out

To Loa

out

sense

out

Load

GND

ZXCT1010

ISSUE 5 - MARCH 2003

SEMICONDUCTORS

ZXCT1010

ABSOLUTE MAXIMUM RATINGS

Voltage on any pin -0.6V to 20V (relative to GND)

Continuous output current 25mA

Continuous sense voltage Vin + 0.5V > Vsense†> Vin – 5V

Operating Temperature -40 to 85°C

Storage Temperature -55 to 125°C

Package Power Dissipation (TA= 25°C)

SOT23-5 500mW

ELECTRICAL CHARACTERISTICS

Test Conditions TA= 25°C, Vin = 5V, Rout = 100Ω.

SYMBOL PARAMETER CONDITIONS LIMITS UNIT

Min Typ Max

Vin VCC Range 2.5 20 V

Iout1Output current Vsense =0V

Vsense = 10mV

Vsense = 100mV

Vsense = 200mV

Vsense =1V

0.975

1.95

9.7

0.3

100

1.00

2.00

10.0

115

1.025

2.05

10.3

µA

IqGround pin current Vsense = 0V 3.5 8 µA

Vsense2Sense Voltage 0 2500 mV

Isense Load pin

input current

100 nA

Acc Accuracy Rsense = 0.1Ω

Vsense = 200mV -2.5 2.5 %

Gm Transconductance,

Iout /V

sense

10000 µA/V

BW Bandwidth RF Pin = -20dBm3

Vsense = 10mV dc

Vsense = 100mV dc

300

kHz

MHz

1Includes input offset voltage contribution

2Vsense=Vin-Vload

3-20dBm=63mVp-p into 50Ω

ISSUE 5 - MARCH 2003

SEMICONDUCTORS

ZXCT1010

TYPICAL CHARACTERISTICS

ISSUE 5 - MARCH 2003

SEMICONDUCTORS

ZXCT1010

PIN DESCRIPTION

Pin Name Pin Function

Vin Supply Voltage

Load Connection to load/battery

Iout Output current, proportional to Vin-Vload

GND Ground

SOT23-5

Package Suffix – E5

Top View

CONNECTION DIAGRAM

Load

out

100Ω

SCHEMATIC DIAGRAM

GND

Iout

Load

VIN

ISSUE 5 - MARCH 2003

SEMICONDUCTORS

ZXCT1010

The following lines describe how to scale a load

current to an output voltage.

Vsense = Vin -V

load

Vout = 0.01 x Vsense x Rout1

E.g.

A 1A current is to be represented by a 100mV output

voltage:

1)Choose the value of Rsense to give 50mV > Vsense >

500mV at full load.

For example Vsense = 100mV at 1.0A. Rsense = 0.1/1.0

=> 0.1 ohms.

2)Choose Rout to give Vout = 100mV, when Vsense =

100mV.

Rearranging 1for Rout gives:

Rout =V

out /(Vsense x 0.01)

Rout = 0.1 / (0.1 x 0.01) = 100 Ω

TYPICAL CIRCUIT APPLICATION

POWER DISSIPATION

The maximum allowable power dissipation of the

device for normal operation (Pmax), is a function of

the package junction to ambient thermal resistance

(θja), maximum junction temperature (Tjmax), and

ambient temperature (Tamb), according to the

expression:

Pmax = (Tjmax – Tamb) / θja

The device power dissipation, PDis given by the

expression:

PD=Iout.(Vin-Vout) Watts

Where Rload represents any load including DC motors,

a charging battery or further circuitry that requires

monitoring, Rsense can be selected on specific

requirements of accuracy, size and power rating.

APPLICATIONS INFORMATION

out

sense

out

load

Load

GND

ZXCT1010

ISSUE 5 - MARCH 2003

SEMICONDUCTORS

ZXCT1010

Li-Ion Charger Circuit

The above figure shows the ZXCT1010 supporting

the Benchmarq bq2954 Charge Management IC.

Most of the support components for the bq2954 are

omitted for clarity. This design also uses the Zetex

FZT789A high current Super-␤PNP as the switching

transistor in the DC-DC step down converter and the

FMMT451 as the drive NPN for the FZT789A. The

circuit can be configured to charge up to four Li-Ion

cells at a charge current of 1.25A. Charge can be

terminated on maximum voltage, selectable

minimum current, or maximum time out. Switching

frequency of the PWM loop is approximately 120kHz.

100Ω

0.2Ω

100Ω

FZT789A

BC81725 1kΩ

BAS16

10µH

FMMT451

140µH

ZHCS1000

220Ω

SNS pin

MOD pin

Charger Input To Battery +

bq2954

ZXCT1010

support components omitted for clarity

Vin Load

Iout

APPLICATIONS INFORMATION (Continued) Bi-Directional Current Sensing

The ZXCT1010 can be used to measure current

bi-directionally, if two devices are connected as

shown below.

If the voltage V1 is positive with respect to the

voltage V2 the lower device will be active, delivering

a proportional output current to Rout. Due to the

polarity of the voltage across Rsense, the upper

device will be inactive and will not contribute to the

current delivered to Rout. When V2 is more positive

than V1, current will be flowing in the opposite

direction, causing the upper device to be active

instead.

Non-linearity will be apparent at small values of

Vsense due to offset current contribution. Devices

can use separate output resistors if the current

direction is to be monitored independently.

Bi-directional Transfer Function

Iout

Load 5

Vin

Iout 3

Load

5Vin 4

sense

out

-400 -200 0 200 400

Output Current (mA)

Sense Voltage (mV)

Output Current v Sense Voltage

ISSUE 5 - MARCH 2003

SEMICONDUCTORS

ZXCT1010

PCB trace shunt resistor for low cost

solution.

The figure below shows output characteristics of the

device when using a PCB resistive trace for a low

cost solution in replacement for a conventional

shunt resistor. The graph shows the linear rise in

voltage across the resistor due to the PTC of the

material and demonstrates how this rise in

resistance value over temperature compensates for

the NTC of the device.

The figure opposite shows a PCB layout suggestion.

The resistor section is 25mm x 0.25mm giving

approximately 150mΩusing 1oz copper. The data

for the normalised graph was obtained using a 1A

load current and a 100Ωoutput resistor. An

electronic version of the PCB layout is available at

www.zetex.com/isense

APPLICATIONS INFORMATION (Continued)

Layout shows area of shunt

resistor compared to SOT23-5

package. Not actual size

Actual Size

Zetex plc

Fields New Road

Chadderton

Oldham, OL9 8NP

United Kingdom

Telephone (44) 161 622 4422

Fax: (44) 161 622 4446

Zetex GmbH

Streitfeldstraße19

D-81673 München

Germany

Telefon: (49) 89 45 49 49 0

Fax: (49) 89 45 49 49 49

Zetex Inc

Suite 315

700 Veterans Memorial Highway

Hauppauge, NY 11788

USA

Telephone: (631) 360 2222

Fax: (631) 360 8222

Zetex (Asia) Ltd

3701-04 Metroplaza, Tower 1

Hing Fong Road

Kwai Fong

Hong Kong

Telephone: (852) 26100 611

Fax: (852) 24250 494

These offices are supported by agents and distributors in major countries world-wide.

This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be used, applied or reproduced

for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. The Company

reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service.

For the latest product information, log on to www.zetex.com

ZXCT1010

SEMICONDUCTORS

ISSUE 5 - MARCH 2003

PACKAGE DIMENSIONS SOT23-5

DIM Millimetres Inches

MIN MAX MIN MAX

A 0.90 1.45 0.035 0.057

A1 0.00 0.15 0.00 0.006

A2 0.90 1.3 0.035 0.051

b 0.35 0.50 0.014 0.020

C 0.09 0.20 0.0035 0.008

D 2.80 3.00 0.110 0.118

E 2.60 3.00 0.102 0.118

E1 1.50 1.75 0.059 0.069

e 0.95 REF 0.037 REF

e1 1.90 REF 0.075 REF

L 0.10 0.60 0.004 0.024

a°010010