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MAX3280 Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX3280 Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 11 page users design equipment that meets Level 3 of IEC 1000- 4-2, without additional ESD-protection components. The main difference between tests done using the Human Body Model and IEC 1000-4-2 is higher peak current in IEC 1000-4-2. Because series resistance is lower in the IEC 1000-4-2 ESD test model (Figure 4a), the ESD-withstand voltage measured to this standard is generally lower than that measured using the Human Body Model. Figure 4b shows the current waveform for the ±8kV IEC 1000-4-2 Level 4 ESD Contact Discharge test. The Air-Gap test involves approaching the device with a charger probe. The Contact Discharge method connects the probe to the device before the probe is energized. Machine Model The Machine Model for ESD testing uses a 200pF stor- age capacitor and zero-discharge resistance. It mimics the stress caused by handling during manufacturing and assembly. All pins (not just the RS-485 inputs) require this protection during manufacturing. Therefore, the Machine Model is less relevant to the I/O ports than are the Human Body Model and IEC 1000-4-2. True Fail-Safe The MAX3280E/MAX3281E/MAX3283E/MAX3284E guarantee a logic-high receiver output when the receiv- er inputs are shorted or open, or when they are connect- ed to a terminated transmission line with all drivers disabled. This guaranteed logic high is achieved by set- ting the receiver threshold between -50mV and -200mV. If the differential receiver input voltage (A-B) is greater than or equal to -50mV, RO is logic high. If (A-B) is less than or equal to -200mV, RO is logic low. In the case of a terminated bus with all transmitters dis- abled, the receiver’s differential input voltage is pulled to ground by the termination. This results in a logic high with a 50mV minimum noise margin. Unlike previous fail-safe devices, the -50mV to -200mV threshold com- plies with the ±200mV EIA/TIA-485 standard. Receiver Enable (MAX3281E and MAX3283E only) The MAX3281E and MAX3283E feature a receiver out- put enable (EN, MAX3281E or EN, MAX3283E) input that controls the receiver. The MAX3281E receiver enable (EN) pin is active high, meaning the receiver outputs are active when EN is high. The MAX3283E receiver enable (EN) pin is active low. Receiver outputs are high impedance when the MAX3281E’s EN pin is low and when the MAX3283E’s EN pin is high. Low-Voltage Logic Levels (MAX3284E only) An increasing number of applications now operate at low-voltage logic levels. To enable compatibility with these low-voltage logic level applications, such as digi- tal FPGAs, the MAX3284E VL pin is a user-defined sup- ply voltage that designates the voltage threshold for a logic high. At lower VL voltages, the data rate will also be lower. A logic-high level of 1.65V will receive data at 20Mbps. Table 2 gives data rates at various voltages at VL. Applications Information Propagation Delay Matching The MAX3280E/MAX3281E/MAX3283E/MAX3284E (VCC = VL) exhibit propagation delays that are closely matched from one device to another, even between devices from different production lots. This feature allows multiple data lines to receive data and clock sig- nals with minimal skew with respect to each other. Figure 5 shows the typical propagation delays. Small receiver skew times, the difference between the low-to- high and high-to-low propagation delay, help maintain a symmetrical ratio (50% duty cycle). The receiver skew time | tPLH - tPHL | is under 2ns for either a 3.3V supply or a 5V supply. Multidrop Clock Distribution Low package-to-package skew (8ns max) makes the MAX3280E/MAX3281E/MAX3283E/MAX3284E (VCC = VL) ideal for multidrop clock distribution. When distributing a clock signal to multiple circuits over long transmission lines, receivers in separate locations, and possibly at two different temperatures, would ideally ±15kV ESD-Protected 52Mbps, 3V to 5.5V, SOT23 RS-485/RS-422 True Fail-Safe Receivers 6 _______________________________________________________________________________________ PART ENABLE = HIGH ENABLE = LOW MAX3281E Active High Z MAX3283E High Z Active Table 1. MAX3281E/MAX3283E Enable Table VCC = 3V TO 5.5V VL MAXIMUM DATA RATE 1.65V 20Mbps 2.2V 33Mbps ≥3.3V 52Mbps Table 2. MAX3284E Data Rate Table |
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