3. Device Operation

Table 3.1. Truth Table Summary

VDD

Input, Ax/AHx

Output, Bx/BHx

P1

ON

High

P

OFF

Low

UP2

X

Low

1. P = powered (> UVLO).

2. UP = Unpowered (< UVLO).

3.1 Device Start-up

During start-up, Output Bx/BHx are held low until the VDD is above the UVLO threshold for a time period of at least tSTART. Following

this, the output is high when the current flowing from anode to cathode is > IF(ON). Device startup, normal operation, and shutdown

behavior is shown in the figure below.

Output:

Bx, BHx

Figure 3.1. Device Start-up

3.2 Undervoltage Lockout

Undervoltage Lockout (UVLO) is provided to prevent erroneous operation during device startup and shutdown or when VDD is below its

3.3 Layout Recommendations

To ensure safety in the end user application, high voltage circuits (i.e., circuits with >30 VAC) must be physically separated from the

safety extra-low voltage circuits (SELV is a circuit with <30 VAC) 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 4.4 Insulation and Safety-Related

Specifications1 on page 15 and Table 4.6 VDE 0884-10 Insulation Characteristics1 on page 16 detail the creepage/clearance and

working voltage capabilities of the Si838x. These tables also detail the component standards (UL1577, VDE 0884, CSA 5A), which are

readily accepted by certification bodies to provide proof for end-system specifications requirements. Refer to the end-system specifica-

tion (60950-1, etc.) requirements before starting any design that uses a digital isolator.

Si838x Data Sheet

Device Operation

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