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ADM3493ARZ データシート(PDF) 11 Page - Analog Devices |
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ADM3493ARZ データシート(HTML) 11 Page - Analog Devices |
11 / 12 page ADM3493 Rev. 0 | Page 11 of 12 CIRCUIT DESCRIPTION The ADM3493 is a low power transceiver for RS-485 and RS-422 communications. The ADM3493 can transmit and receive at data rates up to 250 kbps in a half duplex configuration. Driver Enable (DE) and Receiver Enable (RE) pins are included when disabled; the driver and receiver outputs are high impedance. Table 5. Transmitting Truth Table Transmitting Inputs Transmitting Outputs RE DE DI B A Mode X1 1 1 0 1 Normal X1 1 0 1 0 Normal 0 0 X1 High-Z2 High-Z2 Normal 1 0 X1 High-Z2 High-Z2 Shutdown 1 X = Don’t care. 2 High-Z = High Impedance. Table 6. Receiving Truth Table Receiving Inputs Receiving Outputs RE DE A - B RO Mode 0 0 ≥+0.2 V 1 Normal 0 0 ≤−0.2 V 0 Normal 0 0 Inputs Open 1 Normal 1 0 X1 High-Z2 Shutdown 1 X = Don’t care. 2 High-Z = High Impedance REDUCED EMI AND REFLECTIONS The ADM3493 is a slew rate limited transceiver, minimizing EMI and reducing reflections caused by improperly terminated cables. LOW POWER SHUTDOWN MODE A low power shutdown mode is initiated by bringing both RE high and DE low. The ADM3493 does not shut down unless both the driver and receiver are disabled (high impedance). In shutdown, the ADM3493 typically draws only 2 nA of supply current. For the ADM3493, the tPSH and tPSL enable times assume the part was in the low power shutdown mode; the tPZH and tPZL enable times assume the receiver or driver was disabled, but the part was not shut down. DRIVER OUTPUT PROTECTION Two methods are implemented to prevent excessive output current and power dissipation caused by faults or by bus contention. Current limit protection on the output stage provides immediate protection against short circuits over the whole common-mode voltage range (see Typical Performance Characteristics). In addition, a thermal shutdown circuit forces the driver outputs into a high impedance state if the die temperature rises excessively. PROPAGATION DELAY 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). The receiver skew time, |tPRLH - tPRHL|, is 20 ns for the ADM3493. The driver skew time is typically under 100 ns. TYPICAL APPLICATIONS The ADM3493 transceiver is designed for bidirectional data communications on multipoint bus transmission lines. Figure 22 shows a typical network application’s circuits. To minimize reflections, the line should be terminated at both ends in its characteristic impedance, and stub lengths off the main line should be kept as short as possible. The slew rate limited ADM3493 is tolerant of imperfect termination. B A R D RO RE DI DE ADM3493 ADM3493 ADM3493 ADM3493 B A R D RO RE DI DE B A R D RO RE DI DE B A R D RO RE DI DE MAXIMUM NUMBER OF TRANSCEIVERS ON BUS = 256 RT RT NOTES 1. RT IS EQUAL TO THE CHARACTERISTIC IMPEDANCE OF THE CABLE. VCC R1 R2 Figure 28. ADM3493 Typical Half Duplex RS-485 Network |
同様の部品番号 - ADM3493ARZ |
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同様の説明 - ADM3493ARZ |
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