ZN423 - Zarlink Semiconductor, Inc.

THIS DOCUMENT IS FOR MAINTENANCE

PURPOSES ONLY AND IS NOT

RECOMMENDED FOR NEW DESIGNS

ZN423

PRECISION VOLTAGE REFERENCE SOURCE

DS2347 - 3.0

Fig.1 Pin connections (bottom view)

The ZN423 is a monolithic integrated circuit using the

energy bandgap voltage of a base-emitter junction to produce

a precise, stable, reference source of 1.26V. This is derived

via an external dropping resistor for supply voltages of 1.5V

upwards. The temperature coefficient of the ZN423, unlike

conventional Zener diodes, remains constant with reference

current. the noise figure associated with breakdown

mechanisms is also considerably reduced.

FEATURES

■Low Voltage

■Low Temperature Coefficient

■Very Good Long Term Stability

■Low Slope Resistance

■Low RMS Noise

■Tight Tolerance

■High Power Supply Rejection Ratio

■2-Lead TO-18 Metal Can Package

ABSOLUTE MAXIMUM RATINGS

Reference current, IREF 20mA

Operating temperature range: -55°C to +125°C

Storage temperature range: -65°C to +165°C

ORDERING INFORMATION

Fig.2 Circuit diagram

ELECTRICAL CHARACTERISTICS

Test conditions (unless otherwise stated):

Tamb = 25°C, Shaping capacitor, CS = 0.1µF

Output voltage

Slope resistance

Reference current

Temperature coefficient

External resistor

RMS noise voltage

Power supply ratio

IREF = 5mA

REXT = (VCC-VREF)/IREF

1Hz to 10kHz

PSRR = REXT/RREF, VREF = 1.26V,

IREF = 2.5mA, VCC = 5.0V

VREF

RREF

IREF

REXT

PSRR

1.2

1.5

100

1.26

0.5

1.32

1.5

Ω

ppm/°C

Ω

µV

Symbol

Characteristic Unit Conditions

Value

Min. Typ. Max.

ZN423 (CM-2)

Device Type

ZN423

Operating Temperature

-55°C to +125°C

Package

CM2

ZN423

Reference current IREF (max.) v operating temperature.

Fig.3 Derating curve

Fig.4 Slope resistance v frequency (I

REF

= 5mA)

ZN423

Fig.5 5V, 0.5A power supply

APPLICATIONS

5V, 0.5A Power Supply

The circuit shown in Fig.5 is essentially a constant current

source modified by the feedback components R2 and R3 to

give a constant voltage output.

The output of the ZN424P need only be 2V above the

negative rail, by placing the load in the collector of the output

transistor TR2. Current control is achieved by TR1 and R5.

The simple circuit has the following performance

characteristics:

Output noise and ripple (full load) = 1mV rms

Load regulation (0 to 0.5A) = 0.1%

Temperature coefficient = ±100ppm/°C

Current limit = 0.65A

5V, 1.0A Power Supply

The circuit detailed in Fig.6 provides improved

performance over that in Fig.5. This is achieved by feeding the

ZN423 reference and the ZN424P error amplifier from a more

stable source, derived from the emitter-follower stage (TR1).

The supply rejection ratio is improved by the factor R1/R5,

where R5 is the slope resistance of the ZN423.

The output voltage is given by:

(R3 + R4)

and may be adjusted by replacing R3 with a 220 and a 500Ω

preset potentiometer.

The output is protected against short circuits by TR2

setting a current limit of 1.6A.

VREF

Fig.6 5V, 1.0A power supply

ZN423

Fig.7 0V to 12V, 1A power supply

0V to 12V, 1A Power Supply

The circuit of Fig.7 provides a continuously variable, highly

stable voltage for load currents up to 1A. The output voltage

is given by:

(VR5 + VR6)

and is controlled by VR5 and VR6 which should be high

quality components (preferably wire wound).

The emitter follower stages TR1 and TR2 buffer the

bias and reference from the output stages. The negative

rail allows the output to operate down to 0V.

The current limit stage monitors output current through

R15. As the potential across R15 increases due to load

current, TR4 conducts and supplies base current for TR3,

thus diverting part of the output from the ZN424P via TR3

to TR5.

Shaping is achieved by the network C5, R8 together

with the output decoupling capacitors which also maintain

low output resistance at frequencies above 100kHz.

The power supply has the following performace

characteristics:

Output noise and ripple (full load) <100µV rms

Output resistance (0 to 1A) 1MΩ

Temperature coefficient ± 100ppm/°C

Variable 100mA to 2A Current Source

In the circuit of Fig.8 the output current is set by the resistor

R in the collector of TR2, which may be switched to offer a

range of output currents from 100mA to 2A with fine control by

means of VR3 which varies the reference voltage to the non-

inverting input of the ZN424P.

The feedback path from the output to the inverting input of

the ZN424P maintains a constant voltage across R, equal to

(VCC - VIN) and hence a constant current to the load given by

(VCC - VIN)/R.

VO = VREF

ZN423

Fig.8 Variable current sources

ZN423

HEADQUARTERS OPERATIONS

GEC PLESSEY SEMICONDUCTORS

Cheney Manor, Swindon,

Wiltshire SN2 2QW, United Kingdom.

Tel: (0793) 518000

Fax: (0793) 518411

GEC PLESSEY SEMICONDUCTORS

P.O. Box 660017

1500 Green Hills Road,

Scotts Valley, California 95067-0017,

United States of America.

Tel: (408) 438 2900

Fax: (408) 438 5576

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publication are subject to change by Mitel without notice. No warranty or guarantee express or implied is made regarding the capability, performance or suitability of any product or

service. Information concerning possible methods of use is provided as a guide only and does not constitute any guarantee that such methods of use will be satisf actory in a speciﬁc

piece of equipment. It is the user’s responsibility to fully determine the performance and suitability of any equipment using such information and to ensure that any publication or

data used is up to date and has not been superseded. Manufacturing does not necessarily include testing of all functions or parameters. These products are not suitable for use in

any medical products whose failure to perform may result in signiﬁcant injury or death to the user. All products and materials are sold and services provided subject to Mitel’s

conditions of sale which are available on request.