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POWER DISSIPATION

APPLICATION CIRCUITS

T =T +P ´ q

J

A

D

JA

(2)

NOISE PERFORMANCE

R

3

R

2

V

IN

+2.7V

Enable

(1)

OPA333,

OPA363,

OPA369

or

R

66.5

1

W

C

1.5nF

1

C

1 F

2

m

P1.2

VREF

A0+

REF3312

+2.7V

V

CC

V

SS

16-Bit

ADC

MSP430x20x3PW

REF3312,, REF3318

REF3320, REF3325

REF3330, REF3333

SBOS392A – AUGUST 2007 – REVISED SEPTEMBER 2007

The REF33xx family is specified to deliver current

Figure 20 shows a simple application circuit where

loads of ±5mA over the specified input voltage range.

low-power components are used to create a signal

The temperature of the device increases according to

chain. The analog input signal is buffered with either

Equation 2:

a zero-drift OPA333 or zero-crossover OPA363. The

reference voltage created from REF3312 provides a

stable, high-accuracy, low-drift reference voltage to

the MSP430 using much less power than the

Where:

MSP430 internal reference. The reference voltage is

used by the internal, 16-bit analog-to-digital converter

(ADC) to accurately convert the analog input signal.

The configuration in Figure 20 presents an example

of a unipolar signal chain.

An example of a bipolar configuration is illustrated in

(

°C/W)

Figure 21. The analog input signal (±2.5V) is offset

and attenuated so that it matches the analog input of

The REF33xx junction temperature must not exceed

the 16-bit ADC on the MSP430. The negative input of

the absolute maximum rating of +150

°C.

the ADC is offset by 0.62V, creating a digital code

that corresponds to the analog input voltage. In this

configuration, two reference voltages are used. The

Typical 0.1Hz to 10Hz voltage noise for each member

REF3312 creates a 1.25V reference input to the ADC

of the REF33xx family is specified in the Electrical

and is an offset point for the INA159. The same

Characteristics table. The noise voltage increases

voltage is used to create the offset voltage to the

with

output

voltage

and

operating

temperature.

negative input to the ADC. The REF3330 creates a

Additional filtering can be used to improve output

precise analog supply voltage of 3V. In this way, the

noise levels. Special attention should be taken to

high PSRR of the REF3330 helps to filter unwanted

ensure that the output impedance does not degrade

noise from the 3.3V digital supply.

output voltage accuracy.

(1)

Enable is a function of the OPA363 not available on the OPA333.

Figure 20. Unipolar Signal Chain Configuration

Copyright © 2007, Texas Instruments Incorporated

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Product Folder Link(s): REF3312 REF3318 REF3320 REF3325 REF3330 REF3333