OPT4048 has output registers which are always available to readout to get measurements, the measurements themselves are updated based on the device mode of operation listed below. The OPT4048 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.
• Continuous mode: In this mode OPT4048 measures all 4 channels in a round robin fashion continuously and updates their corresponding output registers. The conversion time register CONVERSION_TIME determines the time between each channel conversion and a hardware interrupt on pin INT is generated for every successful conversion on each channel or all 4 channels depending on INT_CFG register value. 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.
• One shot mode of operation: There are several ways in which OPT4048 can be used in one shot mode of operation with one common theme which is that OPT4048 stays in standby mode and a conversion is triggered by a register write either by a register write to configuration register or hardware interrupt on the INT pin. Every trigger generates one measurement for 4 channels, effectively taking four times the time set by the CONVERSION_TIME register

  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 in initiated ignoring the previous measurements. This is particularly useful in situation 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.
  • Regular auto-range one shot mode: Auto-range selection logic utilizes the information from the previous measurements to decide on 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 in determined by the one shot triggers.

  One Shot can be triggered using by the following:

  • Hardware trigger: INT pin can be configured to be an input to trigger a measurement using INT_DIR register. 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 M register triggers a measurement. The register value is reset after a successful measurement. INT pin can be configured to indicate measurement completion to read out output registers using the INT_DIR register.
  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 4 times the device conversion time.

  Since the device enters standby after each one shot trigger, measurement interval on 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.