TCA9802 Datasheet, PDF (13/36 Pages) Texas Instruments – Level-Translating I2C Bus Buffer/Repeater

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TCA9802
SCPS266 – MARCH 2017
9.4 Device Functional Modes
Table 1 shows the TCA980x function table.
INPUT
EN
L
H
Table 1. Enable Function Table
FUNCTION
Outputs disabled
SDAA = SDAB
SCLA = SCLB
Table 2 lists the TCA980x B-Side current source functions.
VCCB
L
H
Table 2. B-Side Current Source Function Table
FUNCTION
Current sources disabled, weak pull-up is connected with back-power protection
Current sources enabled
9.4.1 Device Operation Considerations
9.4.1.1 B-Side Input Low (V_IL/I_ILC/R_ILC)
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.
PARAMETER
V_IL
Low-level input voltage
I_ILC
Low-level input current
(contention)
R_ILC
Low-level allowed pull-
down resistance
Table 3. B-side Input Low-Level Parameters
SHORT DESCRIPTION
DETAILED INFORMATION
The input voltage that is interpreted as a low. On the B-side, I_ILC must
also be satisfied to maintain a low
See the V_ILC & I_ILC section
The minimum amount of current that an external device must be sinking
from the TCA980x to transmit a low. V_IL must also be satisfied
The maximum allowed pull-down resistance of an external device in
order to successful transmit a low
See the V_ILC & I_ILC section
See the R_ILC section
9.4.1.1.1 V_ILC & I_ILC
The I_ILC 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 V_IL and I_ILC parameters must be satisfied. In an idle
bus condition (both A and B sides are high), meeting the V_IL threshold with an external device pull-down meets
the I_ILC requirement, since the pull-down has to sink the entire I_CS (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 V_IL requirement is already satisfied by the TCA980x alone (Since the output low voltage is less than the V_IL
threshold). In order for a device on the B-side to over-drive the A-side, it must sink the I_ILC 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 I_ILC requirement. For more
information on this and allowed external current into the device, see the Input and Output Leakage Current (I_EXT-
I^/IEXT-O^{) section.}
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