5

Standby mode

The STSAFE-A120 supports a standby mode, with a dedicated attribute. This attribute can be either set to none

or to standby with the PUT_ATTRIBUTE[LOW POWER MODE] command.

When the STSAFE-A120 is in standby mode (ICC-STDBY), it NACKs the incoming I²C START condition until tWAKE-

STDBY.

Figure 13. STSAFE-A120 wake up from STANDBY

STSAFE-A120

Power State

I²C

communication

I²C bus activity

STSAFE-A120

Power State

I²C

communication

ACK

IDLE BUS TIME TO STANDBY

ICC-PROC

ICC-STDBY

Command

Idle

Command processing time

STANDBY entry after last activity on I²C bus

STANDBY entry after command processing

IDLE

IDLE BUS TIME TO STANDBY

ICC-PROC

ICC-STDBY

Table 1. STSAFE-A120 wake up time from standby

Name

Description

Min

Typ

Max

Units

tWAKE-STDBY

Wake-up time from STANDBY

-

60

-

µs

If LOW POWER MODE is enabled, the STSAFE-A120 automatically enters in standby mode after IDLE BUS

TIME TO STANDBY milliseconds following the scheme illustrated in Figure 14.

Figure 14. STSAFE-A120 standby entry

STSAFE-A120

Power State

I²C

communication

ICC-STDBY

SOF

NACK

ACK

Command

ICC-PROC (Wake-up)

2nd

SOF

Idle

Idle

Start Of Frame (SOF) or any other

activity on the I²C lines

tWAKE-STBY

ICC-PROC (Detect I²C SOF)

The polling time from the host shall be greater than tWAKE-STDBY, and lower than IDLE BUS TIME TO STANDBY

to avoid a dead loop.

IDLE BUS TIME TO STANDBY is adjustable, starting at 50 ms, and up to 1600 ms with 50 ms steps.

In case of power optimization, disabling the standby mode is not recommended when the bus is shared with other

I²C devices.

STSAFE-A120

Standby mode

DS14609 - Rev 1

page 18/38