MAX4929E for HDMI / DVI low frequency switch
Abstract: The MAX4929E is a low-frequency HDMI / DVI switch designed for monitors or HDTV receivers. The device can handle all low-frequency signals that need to be switched and can be used with the new MAX4886 TMDS switch or TMDS receiver with two inputs.
The basic principles of HDMI / DVI In recent years, the field of video transmission has almost undergone a fundamental transformation from analog to digital. VGA and component video—an analog video connection—are being replaced by HDMI ™ and DVI ™. The requirements of these two digital video transmission standards are almost identical, and a set of high-frequency and low-frequency signals are processed simultaneously. The DVI specification was finalized in 1999. At the time of writing this article, the HDMI specification version 1.3 is in the works. Both standards use the high-frequency (video) part of TMDS® (Minimum Transition Differential Signal) to transmit data. The TMDS signal uses four differential pairs to transmit R, G, B, and clock, occupying 8 pins of the 19-pin connector. HDMI and DVI are designed to be "plug and play", that is, when the monitor (receiver) and the video source are connected together, they are looking for a method to work together with the best performance. Most new TMDS HDTV chips contain two complete sets of TMDS (high frequency) inputs, but cannot process LoF (low frequency) signals.
To achieve the "plug and play" function in HDMI and DVI systems, the source (usually a computer, DVD player or game console) and the receiver (usually a monitor or receiver) must be connected. HDMI and DVI borrow the open standards of VESA (Video Electronics Standards Association), using DDC (Digital Display Channel), a new signal called HPD (Hot Swap Detection), and a channel that can supply 50mA from the source to the sink Standard 5V signal. In the standard VESA method, the source addresses EDID (Extended Display Identification Data) EPROM. The EPROM device contains the brand, type number, and supported resolution mode of the receiving device. The source and sink must have at least one display mode in order for the two to work together. Figure 1 shows a schematic diagram of connecting the source and receiver EDID EPROM through an HDMI / DVI connector.
Figure 1. The schematic shows the EDID EPROM where the HDMI / DVI connector connects the source and sink.
Figure 1 shows the TMDS signals connected as four differential pairs, + 5V, HPD, and DDC signals. The DDC signal is connected to EDID. EDID power is provided internally by the receiver. The figure illustrates the general connection mode of the source and sink. The source and receiver communicate via I²C compatible DDC lines. The I²C specification introduced in 1980 is the + 5V specification. A typical EDID EPROM such as 24LC22 contains a 2kb EPROM for storing required information and can work from 2.5V to 5.5V. When working on a + 3.3V power supply, a typical low-cost EDID EPROM does not have a + 5V withstand voltage. Therefore, the EDID EPROM device must work on a + 5V power supply, or externally with + 5V protection.
In order to switch between two HDMI / DVI sources, the designer must deal with two different signals: the TMDS high-frequency signal and the aforementioned low-frequency signal. Some new HDMI processors already include two sets of inputs that can handle high-frequency TMDS signals, but cannot handle low-frequency signals with high voltage. Maxim's MAX4929E provides maximum flexibility when processing the aforementioned low-frequency signals.
The MAX4929E is used to switch between low-frequency video signal sources. All signals connected to external connectors are protected by ± 15kV HBM (human body model). This high-level ESD protection can usually eliminate the extra protection measures for each pin. The MAX4929E allows access to two sets of DDC signals, and the device selects one of the inputs. This source switching can achieve multiple functions: provide ESD protection for the signal, only gate one source at a time and provide logic level clamping to protect the EDID EPROM terminal from higher voltages than its power supply. The MAX4929E consumes very little current, and the + 5V provided by the source device can meet its power requirements.
The MAX4929E has no special power-on sequence requirements, so designers do not have to worry about what happens when one source device is turned on and other source devices are turned off. The switching function between source devices is necessary for the following reasons: the switching function puts the receiving end under the control of which connectable device; it also prevents the second cable from loading the I²C bus. The latter advantage solves two problems encountered when two source devices are connected to a load at the same time: Possible host conflicts with additional capacitive loads (distributed capacitance of 200pf / m per cable) If the second A 2m long cable connected to the main cable will exceed the specification of 700pf maximum distributed capacitance. By using switches, the I²C drive "sees" only one load at a time. In this way, even two 3m cables do not violate the 700pf specification.
In most systems, the MCU controls various operations. The MCU must determine whether the input is valid, and after the EDID handshake, return a TTL compatible HPD signal. The following functions of the MAX4929E (Figure 2) solve three problems: ESD protection at the HPD output allows the MCU to determine whether the selected HDMI input is connected to provide a logic level conversion function from a low voltage MCU to a 5V TTL compatible signal
Figure 2. The schematic diagram shows the typical circuit connection of the MAX4929E. The device provides the switching, logic level matching, and ESD protection required to implement a complete 2: 1 HDMI or DVI switch.
ESD protection has been discussed earlier. If the HPR signal is at a logic high level (nominal value + 5V), the logic high level will appear on the pin connected to the MCU, and ensure that the logic level of the pin is compatible with the MCU level because MAX4929E The reference pin is connected to the power supply of the MCU. If a + 5V signal appears on the selected input, a logic level compatible signal can be obtained on the MCU. After receiving this signal, the MCU then sends out the HPD signal. The MAX4929E "guids" the HPD signal to the appropriate HDMI device and generates a fully TTL compatible signal on the connected device. The MAX4929E receives a logic 1 or logic 0 from a low-voltage MCU, and generates an in-phase logic 0 or 1 (TTL compatible level) for HPD. Using its input ensures that the signal is logic level compatible because its reference is connected to the same power supply of the MCU.
In addition to working with TMDS devices that include two high-frequency inputs, the MAX4929E can also form a chipset with the MAX4886 HDMI / DVI video switch to integrate and integrate two sets of TMDS into a single device. The MAX4886 / MAX4929E chipset can provide a second set of inputs for single-input devices.
Conclusion The MAX4929E controls the switching of all low-frequency signals in a 2: 1 HDMI / DVI switch. Provide high-level ESD protection for all external leads. The MAX4929E is used in conjunction with the EDID EPROM. Its input can accept a + 5V signal level and clamp the output to a + 3.3V level to match the EDID. In addition, the MAX4929E isolates the capacitance of a cable, so the DDC output has only one set of DDC connections at a time. The MAX4929E has a third input voltage and can be connected to the same power supply of the system MCU. This feature ensures that the SEL, HPR, and HPD signals are compatible with the logic level of the MCU. The MAX4929E can handle all the switching, logic level matching, and ESD protection required to achieve a 2: 1 HDMI or DVI switch. The MAX4929E can also enhance the MAX4886 to achieve a complete single-input device switching function.
To achieve the "plug and play" function in HDMI and DVI systems, the source (usually a computer, DVD player or game console) and the receiver (usually a monitor or receiver) must be connected. HDMI and DVI borrow the open standards of VESA (Video Electronics Standards Association), using DDC (Digital Display Channel), a new signal called HPD (Hot Swap Detection), and a channel that can supply 50mA from the source to the sink Standard 5V signal. In the standard VESA method, the source addresses EDID (Extended Display Identification Data) EPROM. The EPROM device contains the brand, type number, and supported resolution mode of the receiving device. The source and sink must have at least one display mode in order for the two to work together. Figure 1 shows a schematic diagram of connecting the source and receiver EDID EPROM through an HDMI / DVI connector.
Figure 1. The schematic shows the EDID EPROM where the HDMI / DVI connector connects the source and sink.
Figure 1 shows the TMDS signals connected as four differential pairs, + 5V, HPD, and DDC signals. The DDC signal is connected to EDID. EDID power is provided internally by the receiver. The figure illustrates the general connection mode of the source and sink. The source and receiver communicate via I²C compatible DDC lines. The I²C specification introduced in 1980 is the + 5V specification. A typical EDID EPROM such as 24LC22 contains a 2kb EPROM for storing required information and can work from 2.5V to 5.5V. When working on a + 3.3V power supply, a typical low-cost EDID EPROM does not have a + 5V withstand voltage. Therefore, the EDID EPROM device must work on a + 5V power supply, or externally with + 5V protection.
In order to switch between two HDMI / DVI sources, the designer must deal with two different signals: the TMDS high-frequency signal and the aforementioned low-frequency signal. Some new HDMI processors already include two sets of inputs that can handle high-frequency TMDS signals, but cannot handle low-frequency signals with high voltage. Maxim's MAX4929E provides maximum flexibility when processing the aforementioned low-frequency signals.
The MAX4929E is used to switch between low-frequency video signal sources. All signals connected to external connectors are protected by ± 15kV HBM (human body model). This high-level ESD protection can usually eliminate the extra protection measures for each pin. The MAX4929E allows access to two sets of DDC signals, and the device selects one of the inputs. This source switching can achieve multiple functions: provide ESD protection for the signal, only gate one source at a time and provide logic level clamping to protect the EDID EPROM terminal from higher voltages than its power supply. The MAX4929E consumes very little current, and the + 5V provided by the source device can meet its power requirements.
The MAX4929E has no special power-on sequence requirements, so designers do not have to worry about what happens when one source device is turned on and other source devices are turned off. The switching function between source devices is necessary for the following reasons: the switching function puts the receiving end under the control of which connectable device; it also prevents the second cable from loading the I²C bus. The latter advantage solves two problems encountered when two source devices are connected to a load at the same time: Possible host conflicts with additional capacitive loads (distributed capacitance of 200pf / m per cable) If the second A 2m long cable connected to the main cable will exceed the specification of 700pf maximum distributed capacitance. By using switches, the I²C drive "sees" only one load at a time. In this way, even two 3m cables do not violate the 700pf specification.
In most systems, the MCU controls various operations. The MCU must determine whether the input is valid, and after the EDID handshake, return a TTL compatible HPD signal. The following functions of the MAX4929E (Figure 2) solve three problems: ESD protection at the HPD output allows the MCU to determine whether the selected HDMI input is connected to provide a logic level conversion function from a low voltage MCU to a 5V TTL compatible signal
Figure 2. The schematic diagram shows the typical circuit connection of the MAX4929E. The device provides the switching, logic level matching, and ESD protection required to implement a complete 2: 1 HDMI or DVI switch.
ESD protection has been discussed earlier. If the HPR signal is at a logic high level (nominal value + 5V), the logic high level will appear on the pin connected to the MCU, and ensure that the logic level of the pin is compatible with the MCU level because MAX4929E The reference pin is connected to the power supply of the MCU. If a + 5V signal appears on the selected input, a logic level compatible signal can be obtained on the MCU. After receiving this signal, the MCU then sends out the HPD signal. The MAX4929E "guids" the HPD signal to the appropriate HDMI device and generates a fully TTL compatible signal on the connected device. The MAX4929E receives a logic 1 or logic 0 from a low-voltage MCU, and generates an in-phase logic 0 or 1 (TTL compatible level) for HPD. Using its input ensures that the signal is logic level compatible because its reference is connected to the same power supply of the MCU.
In addition to working with TMDS devices that include two high-frequency inputs, the MAX4929E can also form a chipset with the MAX4886 HDMI / DVI video switch to integrate and integrate two sets of TMDS into a single device. The MAX4886 / MAX4929E chipset can provide a second set of inputs for single-input devices.
Conclusion The MAX4929E controls the switching of all low-frequency signals in a 2: 1 HDMI / DVI switch. Provide high-level ESD protection for all external leads. The MAX4929E is used in conjunction with the EDID EPROM. Its input can accept a + 5V signal level and clamp the output to a + 3.3V level to match the EDID. In addition, the MAX4929E isolates the capacitance of a cable, so the DDC output has only one set of DDC connections at a time. The MAX4929E has a third input voltage and can be connected to the same power supply of the system MCU. This feature ensures that the SEL, HPR, and HPD signals are compatible with the logic level of the MCU. The MAX4929E can handle all the switching, logic level matching, and ESD protection required to achieve a 2: 1 HDMI or DVI switch. The MAX4929E can also enhance the MAX4886 to achieve a complete single-input device switching function.
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