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LTC4307-1 Datasheet(PDF) 9 Page - Linear Technology |
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LTC4307-1 Datasheet(HTML) 9 Page - Linear Technology |
9 / 12 page LTC4307-1 9 43071fa OPERATION Figure 3 shows the LTC4307-1 in a capacitance buffering application. Due to the LTC4307-1’s capacitance buffering feature and sub-10pF input capacitance, this application circuit passes the HDMI 50pF maximum DDC capacitance specification easily when the LTC4307-1 is located right at the HDMI connector interface as shown. The capacitance of the internal bus connected to the SDAIN and SCLIN pins may be much larger than 50pF, but because of the LTC4307-1’s capacitance buffering, the internal bus ca- pacitance is isolated from the HDMI connector. APPLICATIONS INFORMATION In HDMI, the sink device pulls the hot plug detect HPD signal high to tell the source that it is ready to accept commands through the DDC. This signal can be controlled through the READY pin of the LTC4307-1 to prevent the possibility of erroneous attempts by the source to contact the sink before the sink is ready to return its extended display identification data (EDID). The READY pin only goes high after 5V is applied and the LTC4307-1 ENABLE pin is pulled high by the HDMI receiver IC, a controller in the sink, or the 5V line itself. capacitance from 50pF to 150pF results in a tPHL increase from 81ns to 91ns. Larger output capacitances translate to longer delays (up to 125ns). Users must quantify the difference in propagation times for a rising edge versus a falling edge in their systems and adjust setup and hold times accordingly. READY Digital Output This pin provides a digital flag which is low when either ENABLE is low or the start-up sequence described earlier in this section has not been completed. READY goes high when ENABLE is high and the input and output 2-wire busses are connected. The pin is driven by an open-drain pull-down capable of sinking 3mA while holding 0.4V on the pin. Connect a resistor to VCC to provide the pull-up. READY can be used to control the HDMI hot plug detect (HPD) signal to prevent the possibility of erroneous at- tempts by the source to contact the sink before the sink is ready to communicate. ENABLE When the ENABLE pin is driven below 0.8V with respect to the LTC4307-1’s ground, the input 2-wire bus is discon- nected from the output 2-wire bus and the READY pin is internally pulled low. When the pin is driven above 2V, the part waits for data transactions on both 2-wire bus- ses to be complete (as described in the Start-Up section) before connecting the two sides. At this time the internal pull-down on READY releases. LTC4307 and LTC4307-1 Feature Differences The LTC4307-1 HDMI level-shifting 2-wire bus buffer is specifically intended for HDMI applications. Features in the general purpose LTC4307 device that are not required in HDMI systems have been removed. In addition, level- shifting functionality has been added to the LTC4307-1 to allow 3.3V HDMI devices to interface safely to the 5V HDMI DDC bus. See Table 1 for a list of the differences between the LTC4307 and LTC4307 -1. Table 1. Differences Between the LTC4307 and the LTC4307-1 SPECIFICATION LTC4307 LTC4307-1 COMMENTS ON LTC4307-1 Pre-charge Yes No HDMI DDC Lines are Not Hot Swapped Level Shifting No Yes, 2.2V to 5.5V Provides Communication Between 3.3V and 5V DDC Busses, Protects 3.3V Devices from 5V Supply Stuck Bus Disconnect and Recovery Yes No Stuck Busses, Not an Issue in HDMI Systems Rise Time Accelerators Yes No Complies with HDMI Specification Version 1.3 DDC Capacitance Requirement |
Similar Part No. - LTC4307-1_15 |
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Similar Description - LTC4307-1_15 |
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