
Si840x
3. Device Operation
Device behavior during start-up, normal operation, and shutdown is shown in Figure 7, where UVLO+ and UVLO–
are the positive-going and negative-going thresholds respectively. Refer to Table 12 to determine outputs when
power supply (VDD) is not present.
3.1. Device Startup
Outputs are held low during powerup until VDD is above the UVLO threshold for time period tSTART. Following
this, the outputs follow the states of inputs.
3.2. Under Voltage Lockout
Under Voltage Lockout (UVLO) is provided to prevent erroneous operation during device startup and shutdown or
when VDD is below its specified operating circuits range. Both Side A and Side B each have their own under
voltage lockout monitors. Each side can enter or exit UVLO independently. For example, Side A unconditionally
enters UVLO when AVDD falls below AVDD UVLO– and exits UVLO when AVDD rises above AVDD UVLO+ . Side B
operates the same as Side A with respect to its BVDD supply.
UVLO+
UVLO-
AVDD
UVLO+
UVLO-
BVDD
INPUT
tSTART
tSD
tSTART
tSTART
tPH L
tPLH
OUTPUT
Figure 7. Device Behavior during Normal Operation
Rev. 1.6
13