CM2020−01TR
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, 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 CM2020−01TR
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 CM2020−01TR supply voltage.
Figure 1. Backdrive Protection Diagram.
SPECIFICATIONS
Table 2. ABSOLUTE MAXIMUM RATINGS
Parameter Rating Units
V
CC5V
, V
CCLV
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
