SI88240ED-IS Datasheet, PDF (25/48 Pages) Silicon Laboratories – QUAD DIGITAL ISOLATORS WITH DC-DC CONVERTER

3. Digital Isolator Device Operation
Si88x4x
VI Input
VDDI^1,2,3,4
Table 11. Si88xx Logic Operation
VDDO^1,2,3,4
VO Output
Comments
H
P
L
P
X
UP
X
P
P
H
Normal operation.
P
L
P
L⁴
Upon transition of VDDI from unpow-
H⁴
ered to powered, V_O returns to the
same state as V_I.
UP
Undetermined Upon transition of VDDO from
unpowered to powered, V_O returns
to the same state as V_I.
Notes:
1. VDDI and VDDO are the input and output power supplies. VI and VO are the respective input and output terminals.
2. P = powered; UP = unpowered.
3. Note that an I/O can power the die for a given side through an internal diode if its source has adequate current. This
situation should be avoided. We recommend that I/O's not be driven high when primary side supply is turned off or
when in dc-dc shutdown mode.
4. See "5. Ordering Guide" on page 38 for details. This is the selectable fail-safe operating mode (ordering option). When
VDDB is powered via the primary side and the integrated dc-dc, the default outputs are undetermined as secondary
side power is not available when primary side power shuts off.
3.1. Device Startup
Outputs are held low during power up until VDDx is above the UVLO threshold for time period t_SU. Following this,
the outputs follow the states of inputs.
3.2. Undervoltage Lockout
Undervoltage Lockout (UVLO) is provided to prevent erroneous operation during device startup and shutdown or
when VDDx is below its specified operating circuits range. Both Side A and Side B each have their own
undervoltage lockout monitors. Each side can enter or exit UVLO independently. For example, Side A
unconditionally enters UVLO when VDDA falls below V_DDUV– and exits UVLO when VDDA rises above V_DDUV+.
Side B operates the same as Side A with respect to its VDD supply.
3.3. Layout Recommendations
To ensure safety in the end user application, high voltage circuits (i.e., circuits with >30 V_AC) must be physically
separated from the safety extra-low voltage circuits (SELV is a circuit with <30 V_AC) by a certain distance
(creepage/clearance). If a component, such as a digital isolator, straddles this isolation barrier, it must meet those
creepage/clearance requirements and also provide a sufficiently large high-voltage breakdown protection rating
(commonly referred to as working voltage protection). Table 4 and Table 6 detail the working voltage and
creepage/clearance capabilities of the Si88xx. These tables also detail the component standards (UL1577,
VDE0884-10, CSA 5A), which are readily accepted by certification bodies to provide proof for end-system
specifications requirements. Refer to the end-system specification (61010-1, 60950-1, 60601-1, etc.) requirements
before starting any design that uses a digital isolator.
Preliminary Rev. 0.6
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