HDMI2C1-14HD Datasheet, PDF (5/32 Pages) STMicroelectronics – HPD pull down and signal conditioning

HDMI2C1-14HD
2
Application information
Application information
2.1
CEC line description
The CEC bus is described in the HDMI™ standards as the consumer electronics control. It
provides control functions between all the various audiovisual equipments chained in the
user's environment.
The CEC block integrated in the HDMI2C1-14HD implements a level shifter, shifting the
cable CEC +3.3 V voltage (V_{DD_CEC}) down to the ASIC power supply voltage (V_{DD_CEC_IC})
that can be as low as 1.8 V. The Figure 3 shows the functional diagram of the integrated
CEC block.
VDD_CEC_IC
Figure 3. CEC link functional diagram
VDD_CEC
VDD_CEC_IC
decoupling
capacitance
CEC
driver
CEC_IC
UVLO
Enable
Ctrl
circuit
VDD_CEC
CEC
HDMI
connector
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
In case of no activity on the CEC bus, or if the CEC driver is off (V_{DD_CEC_IC} = 0), the CEC
pin is put in high impedance mode (open circuit) protecting the circuitry and the application
against hazardous back drive.
The Figure 4 illustrates the normal operating mode of the CEC block when the IC from the
source and when the sink drives the communication.
Figure 4. Simplified view of the electrical parameters of the CEC block
V_{DD_CEC_IC}
CEC_IC
V_{IL_CEC_IC}
CEC
V_{DD_CEC}
Block in high
impedance
t_{FALL_CEC}
V_{IH_CEC_IC}
90%
10%
Level shifting
Source IC drives
V_{DD_CEC_IC}
CEC_IC
t
t
t
Block in high
impedance
t_{RISE_CEC}
CEC
V_{DD_CEC}
V_{Tdown_CEC}
V_{HYST_CEC}
Block in high
impedance
Level shifting
Sink drives through HDMI cable
V_{Tup_CEC}
t
Block in high
impedance
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