PGA309: Usage in "TEST mode" only for direct microcontroller application

Hi Benjamin,

When using test mode (Test, pin 9 set to high), the internal state machine of the device stops, and the device does not attempt to read the EEPROM contents.

The microcontroller has access to write the internal registers of the PGA309 and change the Gain settings, mux settings, Gain DAC adjustments and Zero DAC adjustments (microcontroller has access to the PGA309 internal writable registers). 

On test mode, the device is unable to store any settings after power-down, so when the device supply powers on, and the test pin is high, the device defaults to POR register values and needs to be re-configured by the microcontroller every time at power-up. All the settings and correction coefficients need to be re-configured.  In general, this test mode is used during initial calibration of the device, or for debug purposes.

The difference to stand-alone mode, is that the PGA309 is 'manually' set up by the microcontroller. On test mode, the state machine power-on sequence shown on Figure 3-1 of the PGA309 User Guide is not running, therefore, on test mode, the device does not attempt to access the eeprom, and does not monitor the temperature to select the correct EEPROM calibration settings.

To answer your question, the micro-controller is able to modify/write registers on test mode, and the PGA309 output of the device is active, so it is possible to configure the device in this fashion, as long as the device Gain settings and Gain calibration and offset calibrations and all registers are set correctly by the microcontroller.

Thank you and Regards,

Luis

Hi Benjamin,

If you are not interested in the temperature coefficients, and you can't afford the current consumption of the external EEPROM on the PGA309 application, you could consider the PGA308.

The PGA308 is very similar to the PGA309, except it incorporates One-Time-Programmable (OTP) memory cells to store settings.

The PGA308 device offers offset and Gain calibration (very similar to PGA309) and similar functions to the PGA309.   The main differences is that the PGA308 uses the internal OTPs instead of external EEPROM, it does not offer over temperature compensation, or sensor linearization circuitry;and some of the PGA gain settings and DAC calibration ranges are slightly different.

Thank you and Regards,

Luis

Hello Luis,

Thanks for all of these information!

As I said in the other topic, I'm going to think about this solution.

The idea I actually have in mind is to allow the user, thanks to a HMI, to take control of the PGA30x to configure it him/herself (exactly like your own application for the evaluation board PGA309EVM-USB, but for the gain/offset only) with a calibration everytime it is switched off and back on.

The reason for that is that I don't know which sensor will be used and there could be up to 8 sensor connected to the board I develop, so I'd rather like not using that much EEPROM, for consumption matter as you mentionned.

Hello Luis,
I did not come back to you on this one.
Could you please confirm that I can program the gain/offset of the PGA308 without using the POR memory?
The POR memory won't do with my application, since I'd like to be able to program the PGA308 with different configurations an unlimited number of times.
Thanks for your help.

Hello Benjamin,

You are correct, the PGA308 contains seven one-time programmable (OTP) user memory banks. All seven of these banks can be independently programmed. However, the default register bank at POR can be set only four times. Therefore, the OTP memory will not work for unlimited number of times.

In your application, using the 'Software Lock Mode', the microcontroller is able to control the PGA308 RAM directly by enabling the One-Wire interface, disabling any One-Wire timeouts, (and disabling the OTP checksum check).  This mode is used for PGA308 control through a microcontroller UART interface. It allows the PGA308 to be controlled as a flexible data acquisition front-end; and allows you to program the gain/offset of the device.  

The PGA308 "Virtual Software Lock Mode" is also supported in applications where the 1W is connected to VOUT.   The PGA308 contains an output enable counter configured by the OENC Register that enables VOUT for a programmed period of time so that voltage readings can be taken, and then disables VOUT so that One-Wire communication can occur.  After the One-Wire interface is enabled, it stays enabled as long as valid One-Wire communications take place.

Please review section 2.10 "Power Sequence of the PGA308" on p.17 and section 5.6 "1 W connected to Vout Program Mode, Virtual Software Mode" on page 70 of the PGA308 User Guide.  Figure 5-12, p. 70 shows the flow of the Virtual software lock mode of operation controlling the PGA308 RAM on applications where 1W is connected to VOUT.

Thank you and Regards,

Luis