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ADM3311EARS-REEL7 Datasheet(PDF) 13 Page - Analog Devices |
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ADM3311EARS-REEL7 Datasheet(HTML) 13 Page - Analog Devices |
13 / 16 page REV. G ADM3307E/ADM3310E/ADM3311E/ADM3312E/ADM3315E –13– RECEIVER OUTPUT EN INPUT tDR VOH – 0.1V VOL + 0.1V VOH VOL 0V 3V Figure 5. Receiver Disable Timing RECEIVER OUTPUT EN INPUT tER 3V 0.4V VOH VOL 0V 3V Figure 6. Receiver Enable Timing High Baud Rate The ADM33xxE features high slew rates, permitting data trans- mission at rates well in excess of the EIA/RS-232E specifications. RS-232 voltage levels are maintained at data rates up to 230 kbps (460 kbps for ADM3307E) under worst-case loading conditions. This allows for high speed data links between two terminals. LAYOUT AND SUPPLY DECOUPLING Because of the high frequencies at which the ADM33xxE oscillator operates, particular care should be taken with printed circuit board layout, with all traces being as short as possible and C1 to C3 being connected as close to the device as possible. The use of a ground plane under and around the device is also highly recommended. When the oscillator starts up during Green Idle operation, large current pulses are taken from VCC. For this reason, VCC should be decoupled with a parallel combination of 10 mF tantalum and 0.1 mF ceramic capacitors, mounted as close to the VCC pin as possible. Capacitors C1 to C3 can have values between 0.1 mF and 1 mF. Larger values give lower ripple. These capacitors can be either electrolytic capacitors chosen for low equivalent series resistance (ESR) or nonpolarized types, but the use of ceramic types is highly recommended. If polarized electrolytic capacitors are used, polarity must be observed (as shown by C1+). ESD/EFT TRANSIENT PROTECTION SCHEME The ADM33xxE uses protective clamping structures on all inputs and outputs that clamp the voltage to a safe level and dissipate the energy present in ESD (electrostatic) and EFT (electrical fast transients) discharges. A simplified schematic of the protection structure is shown below in Figures 7a and 7b (see Figures 8a and 8b for ADM3307E protection structure). Each input and output contains two back-to-back high speed clamping diodes. During nor- mal operation with maximum RS-232 signal levels, the diodes have no effect as one or the other is reverse biased depending on the polarity of the signal. If however the voltage exceeds about ±50 V, reverse breakdown occurs and the voltage is clamped at this level. The diodes are large p-n junctions designed to handle the instantaneous current surge that can exceed several amperes. The transmitter outputs and receiver inputs have a similar protec- tion structure. The receiver inputs can also dissipate some of the energy through the internal 5 k W (or 22 kW for the ADM3310E) resistor to GND as well as through the protection diodes. RIN Rx D1 D2 RECEIVER INPUT Figure 7a. Receiver Input Protection Scheme Tx D1 D2 TRANSMITTER OUTPUT Figure 7b. Transmitter Output Protection Scheme The ADM3307E protection scheme is slightly different (see Figures 8a and 8b). The receiver inputs, transmitter inputs, and transmitter outputs contain two back-to-back high speed clamping diodes. The receiver outputs (CMOS outputs), SD and EN pins contain a single reverse biased high speed clamping diode. Under normal operation with maximum CMOS signal levels, the receiver output, SD, and EN protection diodes have no effect because they are reversed biased. If, however, the voltage exceeds about 15 V, reverse breakdown occurs and the voltage is clamped at this level. If the voltage reaches –0.7 V, the diode is forward biased and the voltage is clamped at this level. The receiver inputs can also dissipate some of the energy through the internal 5 k W resistor to GND as well as through the protection diodes. D3 RIN D1 D2 RECEIVER INPUT RECEIVER OUTPUT Rx Figure 8a. ADM3307E Receiver Input Protection Scheme Tx D1 D2 TRANSMITTER INPUT TRANSMITTER OUTPUT D3 D4 Figure 8b. ADM3307E Transmitter Output Protection Scheme The protection structures achieve ESD protection up to ±15 kV on all RS-232 I/O lines (and all CMOS lines, including SD and EN for the ADM3307E). The methods used to test the protection scheme are discussed later. |
Similar Part No. - ADM3311EARS-REEL7 |
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Similar Description - ADM3311EARS-REEL7 |
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