20 Rev. 1.6
Si8650/51/52/55
3. Device Operation
Device behavior during start-up, normal operation, and shutdown is shown in Figure 8, 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. Additionally, refer to Table 13 for logic conditions when enable pins are used.
Table 12. Si865x Logic Operation
V
I
Input
1,2
EN
Input
1,2,3,4
VDDI
State
1,5,6
VDDO
State
1,5,6
V
O
Output
1,2
Comments
H H or NC P P H Enabled, normal operation.
LH or NC P P L
X
7
L P P Hi-Z
8
Disabled.
X
7
H or NC UP P
L
9
H
9
Upon transition of VDDI from unpowered to pow-
ered, V
O
returns to the same state as V
I
in less
than 1 µs.
X
7
L UP P Hi-Z
8
Disabled.
X
7
X
7
P UP Undetermined Upon transition of VDDO from unpowered to pow-
ered, V
O
returns to the same state as V
I
within
1 µs, if EN is in either the H or NC state. Upon tran-
sition of VDDO from unpowered to powered, V
O
returns to Hi-Z within 1 µs if EN is L.
Notes:
1. VDDI and VDDO are the input and output power supplies. V
I
and V
O
are the respective input and output terminals. EN
is the enable control input located on the same output side.
2. X = not applicable; H = Logic High; L = Logic Low; Hi-Z = High Impedance.
3. It is recommended that the enable inputs be connected to an external logic high or low level when the Si865x is
operating in noisy environments.
4. No Connect (NC) replaces EN1 on Si8650. No Connects are not internally connected and can be left floating, tied to
VDD, or tied to GND.
5. “Powered” state (P) is defined as 2.5 V < VDD < 5.5 V.
6. “Unpowered” state (UP) is defined as VDD = 0 V.
7. Note that an I/O can power the die for a given side through an internal diode if its source has adequate current.
8. When using the enable pin (EN) function, the output pin state is driven into a high-impedance state when the EN pin is
disabled (EN = 0).
9. See "6. Ordering Guide" on page 28 for details. This is the selectable fail-safe operating mode (ordering option). Some
devices have default output state = H, and some have default output state = L, depending on the ordering part number
(OPN). For default high devices, the data channels have pull-ups on inputs/outputs. For default low devices, the data
channels have pull-downs on inputs/outputs.
