2

2

2

2

2

VREF Total

Error

Accuracy

TempCo

TempHyst

LongTerm Drift

1/ f Noise

REF3425-Q1

OUT

2.5V VREF

IN

GND

ADS7828-Q1

AIN0

AIN1

VREF+

VREF-

VDD

3V VDD

AIN2

AIN3

TDA2 (MCU)

I2C

3.3V VDD

I2C

GPIOx

VDD

Copyright © 2017, Texas Instruments Incorporated

EN

GPIO0

20

REF3425-Q1, REF3430-Q1, REF3433-Q1, REF3440-Q1, REF3450-Q1

SBAS901 – JULY 2018

www.ti.com

Product Folder Links: REF3425-Q1 REF3430-Q1 REF3433-Q1 REF3440-Q1 REF3450-Q1

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Copyright © 2018, Texas Instruments Incorporated

10.2.2 Advanced Driver Assistance Systems (ADAS) Microcontroller Connection

10.2.2.1 Basic Voltage Reference Connection

The circuit shown in Figure 31 shows the basic configuration for the REF34xx-Q1 references.

Figure 31. ADAS Microcontroller Application

10.2.2.2 Design Requirements

In ADAS applications it is common to use an ADC with a MCU to monitor the voltage rails to the

MCU/DSP/FPGAs. In figure Figure 31 the automotive TI Jacinto™ TDA2 MCU is using a ADS7828-Q1 to

monitor several analog input signals and in ADAS these signals will be the system power rails. It is important to

monitor these power rails because tighter rail requirements allow for further system monitoring and optimization.

The REF3425-Q1 is used in this application to provide the precise voltage reference signal. In these systems it is

not typical to have calibration and such the most precise low power voltage reference is necessary to be able to

measure down to 1% accuracy on key power rails.

For this design example, use the parameters listed in Table 3 as the input parameters and desired output

parameters.

Table 3. Typical Core Voltage Rail Monitoring

Specification

Requirement

3V

Output Voltage

2.5V

Voltage Power Rail

1V

Max Error on Voltage Power Rail

1%

Temperature Range

-40C to 125C

10.2.2.3 Detailed Design Procedure

It is important to keep track of the error margin in this system to make sure that the total error of the voltage

reference and ADC are less than the maximum 1% error allowed. To calculate the total RSS error of a voltage

reference use Equation 5.

(5)

With the RSS error of the voltage reference, the ADC error needs also needs to be calculated using the RSS

method as seen in Equation 6. Equation 7 can then be used to sum both errors. It is important to make sure that

only the applicable voltage reference error in relation to the measured signal is used.