CM2020−00TR

http://onsemi.com

4

BACKDRIVE PROTECTION

Below, two scenarios are discussed to illustrate what can

happen when a powered device is connected to an

unpowered device via a HDMI interface, substantiating the

need for backdrive protection on this type of interface.

In the first example a DVD player is connected to a TV via

an HDMI interface. If the DVD player is switched off and

the TV is left on, there is a possibility of reverse current flow

back into the main power supply rail of the DVD player.

Typically, the DVD’s power supply has some form of bulk

supply capacitance associated with it. Because all CMOS

logic exhibits a very high impedance on the power rail node

when “off”, if there may be very little parasitic shunt

resistance, and even with as little as a few milliamps of

“backdrive” current flowing into the power rail, it is possible

over time to charge that bulk supply capacitance to some

intermediate level. If this level rises above the

power−on−reset (POR) voltage level of some of the

integrated circuits in the DVD player, these devices may not

reset properly when the DVD player is turned back on.

In a more serious scenario, if any SOC devices are

incorporated in the design which have built−in level shifter

and DRC diodes for ESD protection, there is even a risk for

permanent damage. In this case, if there is a pullup resistor

(such as with DDC) on the other end of the cable, then that

resistance will pull the SOC chips “output” up to a high

level. This will forward bias the upper ESD diode in the

DRC and charge the bulk capacitance in a similar fashion as

described in the first example. If this current flow is high

enough, even as little as a few milliamps, it could destroy

one of the SOC chip’s internal DRC diodes, as they are not

designed for passing DC.

To avoid either of these situations, the CM2020−00TR

was designed to block backdrive current, guaranteeing no

more than 5 mA on any I/O pin when the I/O pin voltage is

greater than the CM2020−00TR supply voltage.

Figure 1. Backdrive Protection Diagram.

SPECIFICATIONS

Table 2. ABSOLUTE MAXIMUM RATINGS

Parameter

Rating

Units

6.0

V

DC Voltage at any Channel Input

6.0

V

Storage Temperature Range

−65 to +150

°C

Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the

Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect

device reliability.

Table 3. STANDARD (RECOMMENDED) OPERATING CONDITIONS

Symbol

Parameter

Min

Typ

Max

Units

5V_SUPPLY Operating Supply Voltage

GND

5

5.5

V

LV_SUPPLY Bias Supply Voltage

1

3.3

5.5

V

−

Operating Temperature Range

–40

−

85

°C