Figure 5. Simplified view of the electrical parameters of the DDC block

5V_OUT

SDA

VDD_IC

SDA_IC

VTdown_IC

T RISE_BUS

Vtup_IC

70%

30%

VTdown_BUS

Vtup_BUS

VHYST_BUS

T FALL_BUS

t

t

Source IC drives

Sink drives through HDMI cable

VDD_5V

The HDMI standard specifies that the max capacitance of the cable can reach up to 700 pF. Knowing that the max

capacitance of the sink input can reach up to 50 pF, this means that the I2C buffer must be able to drive a load

capacitance up to 750 pF. On the other hand, the I2C standard specifies a maximum rise time (30%-70%) of the

signal must be lower than 1µs in order to keep the signal integrity. Taking into account the max cable capacitance

of 750 pF, it is not possible to guarantee a rise time lower than 1µs in the worst case.

Therefore, a dynamic pull-up has been integrated at the output of the SDA and the SCL lines and synchronized

with the I2C driver. This signal booster accelerates for a short period the charging time of the equivalent cable

capacitance, allowing driving any HDMI cable.

The Figure 6. Benefit of the dynamic pull-up on the DDC bus illustrates the benefit of the dynamic pull-up

integrated in the HDMI2C1-6C1 device.

HDMI2C1-6C1

DDC bus description

DS9943 - Rev 4

page 5/22