SI1141(2011) 데이터 시트보기 (PDF) - Silicon Laboratories

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SI1141
(Rev.:2011)

PROXIMITY/AMBIENT LIGHT SENSOR IC WITH I2C INTERFACE

Silicon Laboratories 

Si1141/42/43

3. Operational Modes

The Si1141/42/43 can be in one of many operational modes at any one time. It is important to consider the

operational mode since the mode has an impact on the overall power consumption of the Si1141/42/43. The

various modes are:

 Off Mode

 Initialization Mode

 Standby Mode

 Forced Conversion Mode

 Autonomous Mode

3.1. Off Mode

The Si1141/42/43 is in the Off Mode when VDD is either not connected to a power supply or if the VDD voltage is

below the stated VDD_OFF voltage described in the electrical specifications. As long as the parameters stated in

Table 2, “Absolute Maximum Ratings,” on page 4 are not violated, no current will flow through the Si1141/42/43. In

the Off Mode, the Si1141/42/43 SCL and SDA pins do not interfere with other I2C devices on the bus. The LED pins

will not draw current through the infrared diodes. Keeping VDD less than VDD_OFF is not intended as a method of

achieving lowest system current draw. The reason is that the ESD protection devices on the SCL, SDA and INT

pins also from a current path through VDD. If VDD is grounded for example, then, current flow from system power to

system ground through the SCL, SDA and INT pull-up resistors and the ESD protection devices.

Allowing VDD to be less than VDD_OFF is intended to serve as a hardware method of resetting the Si1141/42/43

without a dedicated reset pin.

The Si1141/42/43 can also reenter the Off Mode upon receipt of either a general I2C reset or if a software reset

sequence is initiated. When one of these software methods is used to enter the Off Mode, the Si1141/42/43

typically proceeds directly from the Off Mode to the Initialization Mode.

3.2. Initialization Mode

When power is applied to VDD and is greater than the minimum VDD Supply Voltage stated in Table 1,

“Recommended Operating Conditions,” on page 4, the Si1141/42/43 enters its Initialization Mode. In the

Initialization Mode, the Si1141/42/43 performs its initial startup sequence. Since the I2C may not yet be active, it is

recommended that no I2C activity occur during this brief Initialization Mode period. The “Start-up time” specification

in Table 1 is the minimum recommended time the host needs to wait before sending any I2C accesses following a

power-up sequence. After Initialization Mode has completed, the Si1141/42/43 enters Standby Mode. The host

must write 0x17 to the HW_KEY register for proper operation.

3.3. Standby Mode

The Si1141/42/43 spends most of its time in Standby Mode. After the Si1141/42/43 completes the Initialization

Mode sequence, it enters Standby mode. While in Standby Mode, the Si1141/42/43 does not perform any Ambient

Light measurements or Proximity Detection functions. However, the I2C interface is active and ready to accept

reads and writes to the Si1141/42/43 registers. The internal Digital Sequence Controller is in its sleep state and

does not draw much power. In addition, the INT output retains its state until it is cleared by the host.

I2C accesses do not necessarily cause the Si1141/42/43 to exit the Standby Mode. For example, reading Si1141/

42/43 registers is accomplished without needing the Digital Sequence Controller to wake from its sleep state.

3.4. Forced Conversion Mode

The Si1141/42/43 can operate in Forced Conversion Mode under the specific command of the host processor. The

Forced Conversion Mode is entered if either the ALS_FORCE or the PS_FORCE command is sent. Upon

completion of the conversion, the Si1141/42/43 can generate an interrupt to the host if the corresponding interrupt

is enabled. It is possible to initiate both an ALS and multiple PS measurements with one command register write

access by using the PSALS_FORCE command.

14

Preliminary Rev. 0.5

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