PCA9507D datasheet(6/20 Pages) NXP

6 / 20 page

PCA9507_1

Product data sheet

Rev. 01 — 7 February 2008

6 of 20

NXP Semiconductors

PCA9507

2-wire serial bus extender for HDMI DDC I2C-bus and SMBus

6.3.2 Port B (SDAB and SCLB)

SDAB and SCLB are standard I2C-bus with static level offset that has no rise time

accelerator. The static level offset produces an output LOW of 0.5 V (typical) at 6 mA. As

with the standard I2C-bus system, pull-up resistors are required to provide the logic HIGH

levels. The size of these pull-up resistors depends on the system requirement, and should

meet the current sinking capability of the device that drives the buffer, as well as that of

the buffer. The minimum and maximum pull-up resistors are determined and the pull-up

resistor’s value is chosen to be within the minimum and maximum range.

Using Equation 1, calculate the minimum pull-up resistor value:

(1)

Where:

RPU(min) is the minimum pull-up resistor value for the open-drain SCLB and SDAB.

VCC(B)(max) is the maximum supply rail of the pull-up resistor.

0.4 V is the maximum VOL of the device that drives the buffer on logic LOW.

IOL(max) at VOL = 0.4 V is the maximum sink current of the device that drives the buffer

on logic LOW.

The maximum pull-up resistor should also be sized such that the RC time constant meets

the standard I2C-bus rise time, which is 1

µs for Standard-mode (100 kHz) or 300 ns for

Fast-mode (400 kHz). DDC bus complies with the I2C-bus Standard-mode and operates

below 100 kHz, and maximum rise time is 1

µs using a simpliﬁed RC equation.

Using Equation 2, calculate the maximum pull-up resistor value:

(2)

Where:

RPU(max) is the maximum allowable pull-up resistor on the SCLB and SDAB in order to

meet the I2C-bus rise time speciﬁcation.

CL(max) is the maximum allowable capacitance load (include the capacitance of driver,

the line, and the buffer) in order to meet the rise time speciﬁcation.

tr is the rise time speciﬁed as 1 µs (for bus speed 100 kHz or lower) and 300 ns (for bus

speed 400 kHz or lower).

The chosen pull-up resistor RPU is: RPU(min) ≤ RPU ≤ RPU(max).

PU min

()

CC B

() max

()

0.4 V

–

OL max

()

-------------------------------------------------

PU max

()

L max

()

1.2

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