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MAX4815 Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX4815 Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 17 page Detailed Description The MAX4815/MAX4816/MAX4817 are high-bandwidth, low-on-resistance, quad-SPST analog switches targeted to serve as integrated T1/E1 analog protection switches for 1+1 and N+1 line-card redundancy applications. These devices are designed to replace electromechani- cal relays to save board space, reduce power consump- tion, and simplify PC board routing. The devices allow the user to live insert the boards with no adverse effects. The MAX4815/MAX4816/MAX4817 support ±3.3V or ±5V dual-supply operation, which is required for E1/T1 signal switching in the line-side of the interface trans- former. Internal voltage multipliers supply the switches yielding excellent linearity and low on-resistance, typi- cally 3.7 Ω, within the E1/T1 analog signal range. This high-bandwidth, typically 550MHz, family of devices is optimized for low return loss and matched pulse tem- plate performance in E1/T1 short-haul and long-haul applications. Analog Signal Levels The on-resistance of the MAX4815/MAX4816/MAX4817 is very low and stable as the analog signals are swept from V- to V+ (see the Typical Operating Characteristics). Fault Protection The fault protection of the MAX4815/MAX4816/ MAX4817 allows the devices to handle input signals of more than twice the supply voltage without clamping the signal, latching up, or disturbing other cards in the system. The device detects when the input voltage drops below the negative supply. As soon as a fault condition is detected, the switch is immediately turned off for 128 clock cycles (typically 128µs). At the end of the 128µs timeout, the switch is turned back on for one clock cycle. At the end of the one clock cycle, if the sig- nal is within the operating range, the switch will remain on. Otherwise, the device will turn the switch off again for 128 clock cycles. This will repeat until the signal is within the operating range. In T1/E1 redundancy appli- cations, this can happen when the load resistor (RL) is removed or disconnected for any reason, as shown in Figure 1. Without a load resistor, the output voltage when using a 1:2 transformer can be as high as ±11V. Hot Insertion The MAX4815/MAX4816/MAX4817 tolerate hot inser- tions, thus are not damaged when inserted into a live backplane. Competing devices can exhibit low imped- ance when plugged into a live backplane that can cause high power dissipation leading to damage of the device itself. The MAX4815/MAX4816/MAX4817 have relatively high input impedance when V+ and V- are unconnected or connected to GND. Therefore, the devices are not destroyed by a hot insertion. In order to guarantee data integrity, the V+ and V- supplies must be properly biased. Applications Information T1/E1 N+1 Redundancy The MAX4815/MAX4816/MAX4817 are designed for adjacent line-card protection applications. Figures 6 and 7 show a basic architecture for twisted-pair interface (120 Ω E1, or 100Ω T1). Coaxial cable interface (75Ω E1) can be illustrated with the same figures but without the single-ended-to-differential conversion stage. A single protection card can replace up to N line cards in a N+1 redundancy scheme. Figure 6 shows the MAX4815/ MAX4816/MAX4817 sitting in the line cards where they can reroute any of the input/output signals to a protection line card. Figure 7 shows the MAX4815/MAX4816/ MAX4817 sitting in a protection-switching card where the switches are always powered. These figures do not show the surge protection elements and resistors for line termi- nation/impedance matching. The low on-resistance and high bandwidth of the MAX4815/MAX4816/MAX4817 yield good pulse tem- plate and return-loss performance (see the Typical Operating Characteristics). The pulse template tests for E1 (twisted pair interface 120 Ω and coaxial interface 75 Ω) and T1 (twisted pair interface 100Ω) were tested using the Dallas DS2155 single-chip transceiver evalu- ation board, and twelve switches in parallel with one switch closed and the other eleven open. The internal transmit termination feature must be disabled when using this circuit. To use the same transmit resistors for E1 twisted pair and coaxial cables, the transmit line build out control register (TLBC) is set to the value 6Ah. This sets the driver voltage so the output pulse has the right amplitude for both 120 Ω (twisted pair) and 75Ω (coaxial) loads. The analog switches were powered with dual power supplies at ±5V. High-Bandwidth, T1/E1, SPST Analog Switches _______________________________________________________________________________________ 9 MAX4815 MAX4816 MAX4817 5V ±10% LIU Tx TRING TTIP 10V ±10% 1:2 + - Vo RL NC_ COM_ Figure 1. Fault Protection |
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