PGA309: EEPROM combined with PGA309

Hi,

The PGA309 requires a industry standard two-wire (I2C)  EEPROM with at least 1-kb of memory.

The PGA309 minimum digital supply supported by the PGA309 is 2.7V, therefore the EEPROM needs to support the 2.7V supply.

Please refer to the PGA309 User Guide, page 62:

The PGA309 uses an industry standard, Two-Wire, external EEPROM  A 1k-bit minimum EEPROM is needed if all 17 temperature coefficients are used. Larger EEPROMs may be used to provide additional user space for serial number, lot code, or other product data.

Texas Instruments does not produce the EEPROM devices, so you will need to consult with the EEPROM manufacturers to see if they have low power offerings.Most of the standard EEPROM devices I was immediately able to find on the web specify a maximum write/read current of 1mA.

Thank you and Regards,

Luis

Hello Luis,

Just some quick questions related to this matter.

Is an EEPROM mandatory to provide data to the PGA309? Can we use a microcontroller using SPI communication to provide the required registers?

Hi Benjamin,

In the great majority of cases, the PGA309 is used with an EEPROM. The EEPROM stores all the calibration settings, and the device uses the look-up table to load the proper calibration settings over temperature (Stand-Alone mode).

The device has a test pin (pin 9), when set to '1', the device is set in "test mode": the internal PGA309 state machine is stopped, and VOUT is enabled. In this mode, an external micro-controller can modify any of the writable registers using the one-wire or two-wire interface.   If the Test pin is high when the supply becomes valid, the registers stay in the initial (POR) state and output is enabled immediately. An external controller can then modify any of the writable PGA309 registers using either a One-Wire or Two-Wire digital interface. This is described on section 3.4 Test Pin, p70 of the PGA309 User Guide.

In general, the test mode is often used for initial calibration, because the values in the EEPROM are ignored and the PGA309 registers can be individually set as required.  However, it is possible to enable the PGA309 output and manipulate the register settings using a micro-controller using the test mode. The microcontroller controls the device settings in this case, and the PGA309 internal state machine (normal Stand-Alone) routine is disabled.

Thank you and Regards,

Luis

Hello Luis,

Thanks a lot for this detailed answer.
Just to be certain I have understood what you said:

An initial calibration can be performed by setting the pin TEST to state "High".
I can perform this initial calibration with a microcontroller to set the registers and define fixed gain/offset values of the PGA309.
I have to set it back to "normal mode" again after this initial calibration.

Just few more questions then:
Would the PGA309 keep the values set during the initial calibration after switching if off and back on?
If that's so, is the EEPROM gain/offset registers still mandatory to be read in normal mode, if I don't want to change the gain/offset values after this initial calibration?

Hi again,

I found the answer to my question in the user manual chapter 1.11.Power-Up and Normal Operation.

"The PGA309 has circuitry to detect when the power supply is applied to the PGA309, and reset the internal registers and circuitry to an initial state."

Then, is there a way to jump this reset of the registers ?

Last question:

Would it be possible to keep the PGA in TEST mode to keep controlling the gain/offset value with the microcontroller and not use a EEPROM at all?

Hi Benjamin,

On test mode, with test pin high, the internal state machine stops, and the device does not attempt to read the EEPROM.  The PGA309 device does not have internal memory, and relies on the EEPROM to store all calibration and  settings; so all register settings (Gain, Zero DAC, Gain DAC, etc) will need to be re-configured every time after power-up.

It is possible to use the device on this mode since the output of the PGA309 is enabled, but essentially the micro-controller is manually feeding all registers and correction coefficient settings.  Since the internal state machine is not running, the PGA309 stand-alone routine stops.  In general, this mode is intended for debug or during the initial calibration algorithm; but it is possible that you could use the device in this mode.

Another option you could consider is the PGA308.  The PGA308 is similar to the PGA309, except the PGA308 does not require an external EEPROM, it incorporates One-Time-Programmable (OTP) memory cell to store the calibration coefficients.  There are other differences, for example, it does not provide over temperature calibration, and linearization coefficients, but it could be another option to be considered since the EEPROM consumes too much current for your application. 

I also discussed this question on your other E2E thread below...

https://e2e.ti.com/support/amplifiers/f/14/t/931384

Thank you and Regards,

Luis

Hello Luis,

Thanks a lot for all of your replies and sorry to have divided my question into two topics.

I'll take a look on PGA308 and let you know if I have more questions about it :-)