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CM2020-00TR Datasheet(PDF) 4 Page - ON Semiconductor |
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CM2020-00TR Datasheet(HTML) 4 Page - ON Semiconductor |
4 / 9 page 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 VCC5V, VCCLV 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 |
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