2093 - Power Manager 2: Does it allow to read a 1.0 Volt signal from the ADC with attenuator setting 1 (divide by 3) on a PWR6AT6 device?
The POWR6AT6 should be able to read 1.0 Volts from the ADC using either of the attenuator settings (zero or 1). Please insure that the DONE bit (b0 of ADC_MUX) is set to "1" when you read the data or that you have waited the minimum time (Tconvert) for the ADC conversion to complete successfully.
The calculation to convert the register values to the voltage is the same for either attenuator setting.
The 4 most significant bits of the ADC_VALUE_LOW are used (b7 - b4 as shown in the data sheet) and the other 4 bits are ignored. The LSB (b0) should be a 1 to insure that conversion completed successfully when you read the data. The 8 bits of the ADC_VALUE_HIGH are combined with the 4 bits from the ADC_VALUE_LOW to create a 12 bit number [D11:0] as shown below:
Attenuator = 0, ADC VALUE = 0001 1111 0100 = 500 dec. => 500 * 2 = 1.000 Volts
Attenuator = 1, ADC VALUE = 0001 1111 0010 = 498 dec. => 498 * 2 = 0.996 Volts
Please note that the I2C clock speed must be at least 50 kHz (see Fi2c note in the specifications section of the data sheet) to insure that the DONE bit (b0 of ADC_MUX) is set correctly. Otherwise the only way to insure that the ADC conversion has completed successfully is to wait for the Tconvert time shown in the data sheet. This is noted on page 3-21 of the POWR6AT6 data sheet.