PGA308: power-on response time for PGA308

Hi Tess,

The PGA308 and PGA309 are programmable bridge sensor conditioners.   In the standard application, the configuration settings, offset, gain and calibration factors are programmed into memory.  The PGA308 incorporates banks of one-time programmable (OTP) memory to store the calibration settings, while the PGA309  relies on an external EEPROM device to store the configuration settings and calibration coefficients. 

At power-up, in stand-alone mode, the devices read the configuration settings before enabling the output.  The devices only enable the output if they have been programmed with valid memory contents. 

The power-on sequence of the PGA308 is described on the PGA308 User's Guide; and depending on the mode of operation, the device may exhibit different behavior. Assuming the device is used in stand-alone mode, when the power supply voltage becomes valid, the PGA308 waits for approximately 25ms, during which time VOUT is disabled, and then attempts to read the data from the last valid OTP memory bank. If the memory bank has the proper checksum, the PGA308 registers are loaded with the OTP data and VOUT is enabled. However if the checksum is invalid, VOUT is disabled. Section 2.10 of the PGA308 User's Guide discusses the power-on sequence and Figure 5-10 of the PGA308 User's Guide shows the Power-on sequence on Stand-alone mode.  On the PGA308, for applications that require a fast turn-on for VOUT, the NOW bit in the CFG2 Register must be set to '1', which eliminates the 25ms disable of VOUT on power-up.  When NOW=1, the output is enabled 60µs after power is valid.  After the output is enabled, the output settles according to the settling time specification on page 3 of the PGA308 datasheet (~15μs typical to 0.01%, when G=200, no capacitive load).

The PGA309 Power-On Sequence in Normal Stand-Alone Operation is described on Section 3.1, p60 of the PGA309 User's Guide.  After the power supply becomes valid, the PGA309 waits for approximately 33ms and then attempts to read the configuration register data form the EEPROM.  If the EEPROM has been programmed with the flag word 0x5499, and the Checksum1 register values are valid, the device will trigger the Temp ADC conversion (the device takes about 160ms to complete  the 16-bit temperature conversion).  Once the conversion is complete, the PGA309 begins reading the Lookup Table from EEPROM to calculate the settings for the Gain and Zero DACs using the piecewise linear interpolation algorithm. The PGA309 reads the entire Lookup Table and determines if the checksum for the Lookup Table (Checksum2) is correct. Each entry in the Lookup Table requires approximately 500ms to read from the EEPROM. Once Checksum2 is determined to be valid, the calculated value for the Gain and Zero DACs is updated into their respective registers, and the Output Amplifier (VOUT) is enabled.  Once the output is enabled, the output settles to target according to the settling time specification on page 3 of the PGA309 datasheet. 

Please review the PGA308 User's Guide and PGA309 User's Guide documents, they provide a detailed explanation of the power sequences of each device depending of the mode of operation.

Thank you and Regards,

Luis