The OPT4001 device has the following modes of operation:

• Power-down mode: This is power-down or standby mode where the device enters a low power state. There is no active light sensing or conversion in this mode. Device still responds to I²C transactions which can be utilized to bring the device out of this mode. Register OPERATING_MODE is set to 0.
• Continuous mode: In this mode OPT4001 measures and updates the output registers continuously determined by the conversion time and generates hardware interrupt on pin INT (Only on SOT-5X3 package variant) for every successful conversion. TI recommends to configure the INT pin in output mode using the INT_DIR register. The device active circuits are continuously kept active to minimize the interval between measurements. Register OPERATING_MODE is set to 3.
• One shot mode of operation: There are several ways in which OPT4001 can be used in one shot mode of operation with one common theme where OPT4001 stays in standby mode and a conversion is triggered either by a register write to configuration register or hardware interrupt on the INT pin.

  There are two types of one shot modes.

  • Force auto-range one shot mode: Every one shot trigger forces a full reset on auto-ranging control logic and a fresh auto-range detection is initiated ignoring the previous measurements. This is particularly useful in situations where lighting conditions are expected to change a lot and one shot trigger frequency is not very often. There is small penalty on conversion time due for the auto-ranging logic to recover from reset state. The full reset cycle on the auto-ranging control logic takes around 500 μs which needs to be accounted for between measurements when this mode is used. Register OPERATING_MODE is set to 1.
  • Regular auto-range one shot mode: Auto-range selection logic utilizes the information from the previous measurements to decide the range for the current trigger. This mode is recommended only when the device needs time synchronized measurements with frequent triggers from the controller. In other words, this mode can be used as an alternative to continuous mode the key difference being that the interval between measurements is determined by the one shot triggers. Register OPERATING_MODE is set to 2.

  One Shot can be triggered by the following

  • Hardware trigger (Only on SOT-5X3 variant):INT pin can be configured to be an input to trigger a measurement setting INT_DIR register to 0. Since INT pin is used as input, there is no hardware interrupt to indicate completion of measurement. The controller needs to keep time from the trigger mechanism and read out output registers.
  • Register trigger: An I²C write to the OPERATING_MODE register triggers a measurement (value of 1 or 2). The register value is reset after next successful measurement. INT pin can be configured to indicate measurement completion to read out output registers setting the INT_DIR register to 1.
  TI highly recommends to set the interval between subsequent triggers to account for all the aspects involved in the trigger mechanism like the I²C transaction time, device wake-up time, auto-range time (if used) and device conversion time. If a conversion trigger is received before the completion of current measurement, the device simply ignores the new request until the previous conversion is completed.

  Since the device enters standby after each one shot trigger, measurement interval in the one shot trigger mechanism needs to account for additional time T_ss as specified in the specification table for the circuits to recover from standby state. However setting the quick wake up register QWAKE eliminates the need for this additional T_ss at the cost of not powering down the active circuit with device not entering the standby mode between triggers.