ZHCSL07C September 2019 – August 2021 TPS8802
PRODUCTION DATA
The high-bandwidth, low noise photo gain amplifier connects to the output of the photo input stage to further amplify the photodiode signal. The gain amplifier is adjustable on-the-fly using the I2C interface. The gain amplifier has four settings:
The gain stage has the option of being referenced to GND or PREF with the PREF_SEL bit. When PREF_SEL=1, a 5 mV reference offset counteracts the gain stage's input offset voltage to keep the gain stage output above 50 mV. The 5 mV reference offset is amplified by the gain stage, causing the output to change when the gain is changed, even when there is zero photo-current. It is recommended to connect a 470 kΩ resistor from PREF to VINT if the gain is set to 11x, 20x, or 35x. This resistor changes the PREF voltage to 70 mV and prevents the output from dropping below 50 mV in worst-case conditions. Referencing the gain stage to PREF causes the 50 mV reference to change with signal level due to the finite impedance of the reference. Because the reference is changing with the signal level, the gain is slightly less with PREF_SEL=1.