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ADM206EAR Datasheet(PDF) 9 Page - Analog Devices |
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ADM206EAR Datasheet(HTML) 9 Page - Analog Devices |
9 / 16 page ADM206E/ADM207E/ADM208E/ADM211E/ADM213E REV. B –9– GENERAL DESCRIPTION The ADM206E/ADM207E/ADM208E/ADM211E/ADM213E are ruggedized RS-232 line drivers/receivers which 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 compatibility with the EU directive on electromag- netic compatibility. EM compatibility includes protection against radiated and conducted interference 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 IE1000-4-2 and IEC1000-4-4 requirements. The devices are ideally suited for operation in electrically harsh environments or where RS-232 cables are frequently being plugged/unplugged. They are also immune to high RF field strengths without special shielding precautions. Emissions are also controlled to within very strict limits. CMOS technology is used to keep the power dissipation to an absolute minimum allowing maximum battery life in portable applications. The ADMxxE is a modification, enhancement and improvement to the AD230–AD241 family and derivatives thereof. It is essentially plug-in compatible and does not have materially different applications. CIRCUIT DESCRIPTION The internal circuitry consists of four main sections. These are: 1. A charge pump voltage converter. 2. 5 V logic to EIA-232 transmitters. 3. EIA-232 to 5 V logic receivers. 4. Transient protection circuit on all I-O lines. Charge Pump DC-DC Voltage Converter The charge pump voltage converter consists of an 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 below. 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 in- verted to generate –10 V using C2 as the storage element. Capacitors C3 and C4 are used to reduce the output ripple. If desired, larger capacitors (up to 47 µF) can be used for capaci- tors C1–C4. This facilitates direct substitution with older gen- eration charge pump RS-232 transceivers. The V+ and V– supplies may also be used to power external circuitry if the current requirements are small. Please refer to Figure 19 in the Typical Performance section. S1 S2 C1 S4 S3 C3 V+ = 2VCC VCC VCC INTERNAL OSCILLATOR GND Figure 20. Charge Pump Voltage Doubler S1 S2 C2 S4 S3 C4 V– = –(V+) V+ GND INTERNAL OSCILLATOR GND FROM VOLTAGE DOUBLER 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 out- put voltage swing is typically ±9 V. Unused inputs may be left unconnected, as an internal 400 k Ω 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 which accept EIA-232 input levels and translate them into 5 V logic output levels. The inputs have internal 5 k Ω pull-down resistors to ground and are also 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 k Ω 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 input with a hysteresis level of 0.5 V. This ensures error-free reception for both noisy inputs and for inputs with slow transition times. ENABLE AND SHUTDOWN Table II and Table III show the truth tables for the enable and shutdown control signals. The enable function is intended to facilitate data bus connections where it is desirable to three state the receiver outputs. In the disabled mode, all receiver outputs are placed in a high impedance state. The shutdown function is intended to shut the device down, thereby minimizing the quies- cent current. In shutdown, all transmitters are disabled and all receivers on the ADM211E are three-stated. On the ADM213E, receivers R4 and R5 remain enabled in shutdown. Note that the transmitters are disabled but are not three-stated in shutdown, so it is not permitted to connect multiple (RS-232) driver out- puts together. The shutdown feature is very useful in battery operated systems since it reduces the power consumption to 1 µW. During shut- down the charge pump is also disabled. The shutdown control input is active high on the ADM211E, and it is active low on the ADM213E. When exiting shutdown, the charge pump is restarted and it takes approximately 100 µs for it to reach its steady state operating conditions. High Baud Rate The ADM2xxE feature high slew rates permitting data transmis- sion at rates well in excess of the EIA-232-E specifications. RS-232 levels are maintained at data rates up to 230 kb/s even under worst case loading conditions. This allows for high speed data links between two terminals or indeed it is suitable for the |
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