Figure 8. Driver Propagation Times
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Figure 9. Driver Enable and Disable Times (t PZH , t PSH , t PHZ )大香蕉性
Figure 10. Driver Enable and Disable Times (t PZL , t PSL , t PLZ )
MAX3483E/MAX3485E/
MAX3486E/MAX3488E/
MAX3490E/MAX3491E
3.3V-Powered, ±15kV ESD-Protected, 12Mbps and Slew-Rate-Limited True RS-485/RS-422 Transceivers
Driver Output Protection
Excessive output current and power dissipation caud by faults or by bus contention are prevented by two mechanisms. A foldback current limit on the output stage provides immediate protection against short circuits over the whole common-mode voltage range (e Typical Operating Characteristics ). In addition, a thermal shut-down circuit forces the driver outputs into a high-imped-ance state if the die temperature ris excessively.Propagation Delay
Figures 15–18 show the typical propagation delays. Skew time is simply the difference between the low-to-high and high-to-low propagation delay. Small driver/receiver skew times help maintain a symmetrical mark-space ratio (50% duty cycle).职场高手
The receiver skew time, |t
PRLH - t PRHL |, is under 10ns 20ns for the MAX3483E/MAX3488E). The driver skew times are 8ns for the MAX3485E/MAX3490E/MAX3491E, 12ns for the MAX3486E, and typically under 50ns for the MAX3483E/MAX3488E.
Line Length vs. Data Rate香酥排骨的做法
The RS-485/RS-422 standard covers line lengths up to 4000 feet. For line lengths greater than 4000 feet, e Figure 21 for an example of a line repeater.
Figures 19 and 20 show the system differential voltage for parts driving 4000 feet of 26AWG twisted-pair wire at 125kHz into 120Ω loads.
For faster data rate transmission, plea consult the factory.
±15kV ESD Protection As with all Maxim devices, ESD-protection structures are incorporated on all pins to protect against electrostatic discharges encountered during handling and asmbly. The driver outputs and receiver inputs of the MAX3483E family of devices have extra protection against static electricity. Maxim’s engineers have developed state-of-the-art structures to protect the pins against ESD of ±15kV without damage. The ESD structures withstand high ESD in all states: normal operation, shutdown, and powered down. After an ESD event, Maxim’s E versions keep working without latchup or damage.ESD protection can be tested in various ways; the trans-mitter outputs and receiver inputs of this product family are characterized for protection to the following limits:1)±15kV using the Human Body Model 2)±8kV using the Contact-Discharge method specified in IEC 1000-4-23)±15kV using IEC 1000-4-2’s Air-Gap method.ESD Test Conditions ESD performan感染名词解释
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ce depends on a variety of conditions. Contact Maxim for a reliability report that documents test tup, test methodology, and test results.Human Body Model Figure 22a shows the Human Body Model and Figure 22b shows the current waveform it generates when dis-charged into a low impedance. This model consists of a 100pF capacitor charged to the ESD voltage of interest, which is then discharged into the test device through a 1.5kΩ resistor.IEC 1000-4-2The IEC 1000-4-2 standard covers ESD testing and performance of finished equipment; it does not specifi-cally refer to integrated circuits. The MAX3483E family of devices helps you design equipment that meets Level 4 (the highest level) of IEC 1000-4-2, without the need for additional ESD-protection components.The major difference between tests done using the Human Body Model and IEC 1000-4-2 is higher peak cur-rent in IEC 1000-4-2, becau ries resistance is lower in the IEC 1000-4-2 model. Hence, the ESD withstand voltage measured to IEC 1000-4-2 is generally lower than that measured using the Human Body Model. Figure 23a shows the IEC 1000-4-2 model, and Figure 23b shows the current waveform for the ±8kV IEC 1000-4-2, Level 4
ESD contact-discharge test. test.
Figure 21. Line Repeater for MAX3488E/MAX3490E/MAX3491E
MAX3483E/MAX3485E/
MAX3486E/MAX3488E/
MAX3490E/MAX3491E
3.3V-Powered, ±15kV ESD-Protected, 12Mbps and Slew-Rate-Limited True RS-485/RS-422 Transceivers
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