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OPT3002

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SBOS745A – MAY 2016 – REVISED JUNE 2016

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Copyright © 2016, Texas Instruments Incorporated

7.4 Device Functional Modes

7.4.1 Automatic Full-Scale Setting Mode

The OPT3002 has an automatic full-scale-range setting mode that eliminates the need for a user to predict and

set the optimal range for the device. This mode is entered when the configuration register range number field

(RN[3:0]) is set to 1100b.

The first measurement that the device takes in auto-range mode is a 10-ms range assessment measurement.

The device then determines the appropriate full-scale range to take its first full measurement.

For subsequent measurements, the full-scale range is set by the result of the previous measurement. If a

measurement is towards the low side of full-scale, then the full-scale range is decreased by one or two settings

for the next measurement. If a measurement is towards the upper side of full-scale, then the full-scale range is

increased by one setting for the next measurement.

If the measurement exceeds the full-scale range, resulting from a fast-increasing optical transient event, then the

current measurement is aborted. This invalid measurement is not reported. A 10-ms measurement is taken to

assess and properly reset the full-scale range. Then, a new measurement is taken with this proper full-scale

range. Therefore, during a fast-increasing optical transient in this mode, a measurement can possibly take longer

to complete and report than indicated by the configuration register conversion time field (CT).

7.4.2 Interrupt Reporting Mechanism Modes

There are two major types of interrupt reporting mechanism modes: latched window-style comparison mode and

transparent hysteresis-style comparison mode. The configuration register latch field (L) (see the configuration

register, bit 4) controls which of these two modes is used. An end-of-conversion mode is also associated with

each major mode type. The end-of-conversion mode is active when the two most significant bits of the threshold

low register are set to 11b. The mechanisms report via the flag high and flag low fields, the conversion ready

field, and the INT pin.

7.4.2.1 Latched Window-Style Comparison Mode

The latched window-style comparison mode is typically selected when using the OPT3002 to interrupt an

external processor. In this mode, a fault is recognized when the input signal is above the high-limit register or

below the low-limit register. When the consecutive fault events trigger the interrupt reporting mechanisms, these

mechanisms are latched, thus reporting whether the fault is the result of a high or low comparison. These

mechanisms remain latched until the configuration register is read, which clears the INT pin and flag high and

flag low fields. The SMBus alert response protocol, described in detail in the SMBus Alert Response section,

clears the pin but does not clear the flag high and flag low fields. The behavior of this mode, along with the

conversion ready flag, is summarized in Table 2. Note that Table 2 does not apply when the two threshold low

register MSBs (see the Transparent Hysteresis-Style Comparison Mode section for clarification on the MSBs) are

set to 11b.