The OPT4001-Q1 has the following modes of operation:

• Power-down mode: This mode is a power-down or standby mode where the device enters a low-power state. There is no active light sensing or conversion in this mode. The device still responds to I²C transactions that can be used to bring the device out of this mode. The OPERATING_MODE register is set to 0.
• Continuous mode: In this mode, the OPT4001-Q1 measures and updates the output registers continuously as determined by the conversion time and generates a hardware interrupt on the INT pin for every successful conversion. 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. The OPERATING_MODE register is set to 3.
• One-shot mode: There are two ways in which the OPT4001-Q1 can be used in one-shot mode of operation with one common theme where the OPT4001-Q1 stays in standby mode and a conversion is triggered either by a register write to the configuration register or by a 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 the auto-ranging control logic and a fresh auto-range detection is initiated, ignoring the previous measurements. This mode is particularly useful in situations where lighting conditions are expected to change frequently and the conditions for the one-shot trigger frequency are not expected to change very often. There is a small penalty on conversion time resulting from the auto-ranging logic recovering from a reset state. The full reset cycle on the auto-ranging control logic takes approximately 500 μs, which must be accounted for between measurements when this mode is used. The OPERATING_MODE register is set to 1.
  • Regular auto-range one-shot mode: Auto-range selection logic uses the information from the previous measurements to determine the range for the current trigger. Only use this mode 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 between these modes is that the interval between measurements is determined by the one-shot triggers. The OPERATING_MODE register is set to 2.

  One-shot mode can be triggered by the following:

  • Hardware trigger: The INT pin can be configured as an input to trigger a measurement, setting the INT_DIR register to 0. When the INT pin is used as input, there is no hardware interrupt to indicate completion of measurement. The controller must 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 the next successful measurement. The INT pin can be configured to indicate measurement completion to read out the output registers by setting the INT_DIR register to 1.

  The interval between subsequent triggers must be set to account for all aspects involved in the trigger mechanism, such as 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 the current measurement, the device simply ignores the new request until the previous conversion is completed.

  The device enters standby after each one-shot trigger; therefore, the measurement interval in the one-shot trigger mechanism must account for additional time (t_ss time, as specified in the Specifications section 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 the device not entering standby mode between triggers.

Figure 6-3 illustrates a timing diagram of the various operating modes.

Figure 6-3 Timing Diagrams for Different Operating Modes