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ADM208EARUZ-REEL1 Fiches technique(PDF) 10 Page - Analog Devices |
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ADM208EARUZ-REEL1 Fiches technique(HTML) 10 Page - Analog Devices |
10 / 20 page ADM206E/ADM207E/ADM208E/ADM211E/ADM213E Rev. E | Page 10 of 20 THEORY OF OPERATION The ADM206E/ADM207E/ADM208E/ADM211E/ADM213E are ruggedized RS-232 line drivers/receivers that operate from a single 5 V supply. Step-up voltage converters coupled with level shifting transmitters and receivers allow RS-232 levels to be developed while operating from a single 5 V supply. Features include low power consumption, high transmission rates, and compliance with the EU directive on EMC, which includes protection against radiated and conducted interfere- ence, including high levels of electrostatic discharge. All RS-232 inputs and outputs contain protection against electrostatic discharges up to ±15 kV and electrical fast tran- sients up to ±2 kV. This ensures compliance to IEC 100042 and IEC 100044 requirements. The devices are ideally suited for operation in electrically harsh environments or where RS-232 cables are plugged/unplugged frequently. They are also immune to high RF field strengths without special shielding precautions. Emissions are also controlled to within very strict limits. TTL/CMOS technology is used to keep the power dissipation to an absolute minimum, allowing maximum battery life in portable applications. The ADM2xxE is a modification, enhancement, and improvement to the ADM2xx family and its derivatives. It is essentially plug-in compatible and does not have materially different applications. CIRCUIT DESCRIPTION The internal circuitry consists of four main sections: • A charge pump voltage converter. • 5 V logic to EIA-232 transmitters. • EIA-232 to 5 V logic receivers. • Transient protection circuit on all I/O lines. Charge Pump DC-to-DC Voltage Converter The charge pump voltage converter consists of a 200 kHz oscillator and a switching matrix. The converter generates a ±10 V supply from the input 5 V level. This is done in two stages using a switched capacitor technique as illustrated in Figure 20 and Figure 21. First, the 5 V input supply is doubled to 10 V using Capacitor C1 as the charge storage element. The 10 V level is then inverted to generate −10 V using C2 as the storage element. Capacitor C3 and Capacitor C4 are used to reduce the output ripple. If desired, larger capacitors (up to 47 μF) can be used for Capacitor C1 to Capacitor C4. This facilitates direct substitution with older generation charge pump RS-232 transceivers. The V+ and V– supplies can also be used to power external circuitry, if the current requirements are small (see the Typical Performance Characteristics section). + + VCC GND S1 S2 C1 S3 S4 C3 V+ = 2VCC VCC INTERNAL OSCILLATOR Figure 20. Charge Pump Voltage Doubler FROM VOLTAGE DOUBLER + + V+ GND S1 S2 C2 S3 S4 C4 GND V– = –(V+) INTERNAL OSCILLATOR Figure 21. Charge Pump Voltage Inverter Transmitter (Driver) Section The drivers convert 5 V logic input levels into EIA-232 output levels. With VCC = 5 V and driving an EIA-232 load, the output voltage swing is typically ±9 V. Unused inputs can be left unconnected, as an internal 400 kΩ pull-up resistor pulls them high, forcing the outputs into a low state. The input pull-up resistors typically source 8 μA when grounded, so unused inputs should either be connected to VCC or left unconnected in order to minimize power consumption. Receiver Section The receivers are inverting level shifters that accept EIA-232 input levels and translate them into 5 V logic output levels. The inputs have internal 5 kΩ pull-down resistors to ground and are protected against overvoltages of up to ±25 V. The guaranteed switching thresholds are 0.4 V minimum and 2.4 V maximum. Unconnected inputs are pulled to 0 V by the internal 5 kΩ pull- down resistor. This, therefore, results in a Logic 1 output level for unconnected inputs or for inputs connected to GND. The receivers have Schmitt trigger inputs with a hysteresis level of 0.65 V. This ensures error-free reception for both noisy inputs and for inputs with slow transition times. ENABLE AND SHUTDOWN Table 3 and Table 4 are truth tables for the enable and shutdown control signals. The enable function is intended to facilitate data bus connections where it is desirable to tristate the receiver outputs. In the disabled mode, all receiver outputs are placed in a high impedance state. The shutdown function is intended to shut down the device, thereby minimizing the quiescent current. In shutdown, all transmitters are disabled and all receivers on the ADM211E are tristated. |
Numéro de pièce similaire - ADM208EARUZ-REEL1 |
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Description similaire - ADM208EARUZ-REEL1 |
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