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TCA9803

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SCPS267B – MARCH 2017 – REVISED FEBRUARY 2020

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9.4 Device Functional Modes

Table 1 shows the TCA980x function table.

Table 1. Enable Function Table

INPUT

EN

FUNCTION

L

Outputs disabled

H

SDAA = SDAB

SCLA = SCLB

Table 2 lists the TCA980x B-Side current source functions.

Table 2. B-Side Current Source Function Table

VCCB

FUNCTION

L

Current sources disabled, weak pull-up is connected with back-power protection

H

Current sources enabled

9.4.1 Device Operation Considerations

9.4.1.1 B-Side Input Low (VIL/IILC/RILC)

The TCA980x family utilizes the current source on the B side to determine whether an external device is driving

the bus low, or if it is driving the bus low itself. As such, there are some parameters that must be met to ensure a

successful transmission of a low from the B-side to the A-side. These parameters are listed in Table 3.

Table 3. B-side Input Low-Level Parameters

PARAMETER

SHORT DESCRIPTION

DETAILED INFORMATION

VIL

Low-level input voltage

The input voltage that is interpreted as a low. On the B-side, IILC must

also be satisfied to maintain a low

See the VILC & IILC section

IILC

Low-level input current

(contention)

The minimum amount of current that an external device must be sinking

from the TCA980x to transmit a low. VIL must also be satisfied

See the VILC & IILC section

RILC

Low-level allowed pull-

down resistance

The maximum allowed pull-down resistance of an external device in

order to successful transmit a low

See the RILC section

9.4.1.1.1

VILC & IILC

The IILC parameter is the minimum amount of current that the external device must sink from the TCA980x in

order for the TCA980x to accept the low on the B-side.

In order for the TCA980x to accept a low on the B-side, both VIL and IILC parameters must be satisfied. In an idle

bus condition (both A and B sides are high), meeting the VIL threshold with an external device pull-down meets

the IILC requirement, since the pull-down has to sink the entire ICS (current source value) current before the

voltage on the pin falls.

In a contention situation (the A-side is being driven low externally, and the B-side is driven low by the TCA980x),

the VIL requirement is already satisfied by the TCA980x alone (Since the output low voltage is less than the VIL

threshold). In order for a device on the B-side to over-drive the A-side, it must sink the IILC value for the TCA980x

to accept that the low is now being driven by the B-side. This helps reduce or eliminate overshoot during the

hand off between a slave an master during a clock-stretching event, or an acknowledge.

External pull-up resistors on the B-side are not allowed for this reason. As the additional current provided by

them may hinder an external device from being able to satisfy the TCA980x's IILC requirement. For more

information on this and allowed external current into the device, see the Input and Output Leakage Current (IEXT-

I/IEXT-O) section.