VCCB

A-Side

B-Side

ICS

TCA980x

I

2C Slave

PD

OL

OL

R

V

/ I

14

TCA9803

SCPS267B – MARCH 2017 – REVISED FEBRUARY 2020

www.ti.com

Product Folder Links: TCA9803

Submit Documentation Feedback

Copyright © 2017–2020, Texas Instruments Incorporated

9.4.1.1.2

RILC

The RILC parameter describes the maximum allowed pull-down resistance. This parameter comes from the

combination of IILC and ICS, and states the maximum resistance that can satisfy the IILC parameter. Note that

series resistors on the bus are going to affect this, as seen with other types of buffers (voltage delta across the

series resistor. This increases the effective VOL of the external device pulling the bus low).

The calculated resistance of the internal pull-down FET of an external device can be calculated from the VOL and

IOL measurements of the external device in question using Equation 1. Take care to consider any series resistors

placed in the path from the TCA980x to any external device. Note that RPD is the calculated resistance of the

internal pull-down FET, and not a resistor to ground. This is for determining if the external device's output

characteristics meet the TCA980x RILC requirement (150 Ω).

(1)

9.4.1.2 Input and Output Leakage Current (IEXT-I/IEXT-O)

The Input external current (IEXT-I) and output external current (IEXT-O) parameters describe the amount of parasitic

current either injected into the device or pulled from the device (such as leakage from ESD cells) without

affecting device operation as shown in Table 4.

Table 4. B-Side Input and Output Leakage Current

PARAMETER

SHORT DESCRIPTION

DETAILED

INFORMATION

IEXT-I

Input leakage current

Current that is external, but pulled up to supply, leaking current into the TCA980x

B-side. An example is a leaky ESD cell from VCC, or an external pull-up resistor.

See the IEXT-I

section

IEXT-O

Output leakage current

Current that is pulled from the TCA980x B-side. ESD cells are the most common

form of output leakage. Care must be taken not to violate this spec, otherwise the

leakage current can create a false low.

See the IEXT-O

section

9.4.1.2.1

IEXT-I

IEXT-I is a current source that is external to the TCA980x B-side, but leaks current into the device. This type of

input leakage may not exceed the IEXT-I maximum spec, or else the minimum IILC value does not apply.

Figure 13. IEXT-I Example

As shown in Figure 13, IEXT-I is a source of additional current into the device, shown as a leaky ESD cell. The

user must keep IEXT-I as close to 0 as possible, since the TCA980x has a current source as a pull-up internally,

and uses this current source to help detect which side is driving a low. As IEXT-I increases, it increases the

minimum IILC value, requiring that an external device sink more current from the TCA980x in order to transmit a

low. There must be no external pull-up resistor on the B-side to contribute to IEXT-I.