PGA302: Datasheet clarification

Ruben Khazhakyan

Prodigy 20 points

Part Number: PGA302

Hello,

I work with pga302 datasheet and have a couple of questions:

Q1. In the datasheet internal voltage reference TC specified as +/- 250 ppm/C.

Is this typo ?

Q2. My project is - design pressure transmitter. The sensor is piezoresistive bridge.

Assume , the sensor is ideal . What could be the best accuracy , that pga302 can achieve ?

On page 68, table 67 the numbers look strange. E.g. VINPP - VINPN = 34.651 mV, VOUT EXPECTED = 0.5 V

VINPP - VINPN = 13.844 mV, VOUT EXPECTED = 2.5 V

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I assume that gain is the same for all rows. Please, explain.

Thank you in advance,

Ruben

over 3 years ago

+1 Scott Cummins over 3 years ago

TI__Mastermind 31655 points

Hi Ruben,

That is not a typo. The voltage reference temperature coefficient is shown there. You can see more information about this kind of specification here: Voltage Reference Selection Basics White Paper (Rev. A)

The methodology for acquiring the data for tables 67 and 68 is described just above the tables in the application data section. PGAIN was set to 40V/V for the test, and a calibration was run. The input used for this test was a sensor emulator, so the inputs were perfectly repeatable, much like an ideal sensor. Given a proper calibration and an ideal sensor, you can expect accuracy similar to what is shown in the tables.

Regards,

Scott

0 Ruben Khazhakyan over 3 years ago in reply to Scott Cummins

Prodigy 20 points

Hello Scott,

For Q2, above table 67 stated , that PGAIN set to 40V/V. Then, not clear how lower (second row vs first) input voltage (13.844 mV) generates higher output (2.5V).

E.g P1: 34.651mV x 40 x A = 0.5 V

P2: 13.844 mV x 40 x A = 2.5 V

where A - some constant, that is the same for P1, P2 and P3

Or I miss something ?

Thank you for response.

Ruben

+1 Scott Cummins over 3 years ago in reply to Ruben Khazhakyan

TI__Mastermind 31655 points

Hi Ruben,

The PGAIN only sets the gain between the input and the ADC. The DAC output is controlled by the internal temperature and nonlinearity compensation algorithm, and is not a direct passthrough of the ADC data unless it is configured that way. In the datasheet example a 3 pressure 3 temperature calibration is done, where the inputs and desired outputs are shown in the table. The details of the compensation algorithm are described in the datasheet in the Digital Compensation and Filter section.

Regards,

Scott

0 Ruben Khazhakyan over 3 years ago in reply to Scott Cummins

Prodigy 20 points

Hi Scott,

Got you. Many thanks.

Regards,

Ruben

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PGA302: Datasheet clarification