ADM3251EARWZ

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1. DESCRIPTION

The ADM3251EARWZ is a high speed, 2.5 kV fully isolated, singlechannel RS-232/V.28 transceiver device that operates from a single 5 V power supply. Due to the high ESD protection on the RIN and TOUT pins, the device is ideally suited for operation in electrically harsh environments or where RS-232 cables are frequently being plugged and unplugged. The ADM3251E incorporates dual-channel digital isolators with isoPower™ integrated, isolated power. There is no requirement to use a separate isolated dc-to-dc converter. Chip-scale transformer iCoupler® technology from Analog Devices, Inc., is used both for the isolation of the logic signals as well as for the integrated dc-to-dc converter. The result is a total isolation solution. The ADM3251E contains isoPower technology that uses hig frequency switching elements to transfer power through the transformer. Special care must be taken during printed circuit board (PCB) layout to meet emissions standards. Refer to Application Note AN-0971, Control of Radiated Emissions with isoPower Devices, for details on board layout considerations. The ADM3251E conforms to the EIA/TIA-232E and ITU-T V. 28 specifications and operates at data rates up to 460 kbps. Four external 0.1 μF charge pump capacitors are used for the voltage doubler/inverter, permitting operation from a single 5 V supply. The ADM3251E is available in a 20-lead, wide body SOIC package and is specified over the −40°C to +85°C temperature range.

2. FEATURES

    1. 2.5 kV fully isolated (power and data) RS-232 transceiver

    2. isoPower integrated, isolated dc-to-dc converter

    3. 460 kbps data rate

    4. 1 Tx and 1 Rx

    5. Meets EIA/TIA-232E specifications

    6. ESD protection on RIN and TOUT pins

        - ±8 kV: contact discharge

        - ±15 kV: air gap discharge

    7. 0.1 μF charge pump capacitors

    8. High common-mode transient immunity: >25 kV/μs

    9. Safety and regulatory approvals

  10. UL recognition

  11. 2500 V rms for 1 minute per UL 1577

  12. VDE Certificate of Conformity

  13. DIN EN 60747-5-2 (VDE 0884 Teil 2): 2003-01

  14. CSA Component Acceptance Notice #5A

  15. Operating temperature range: −40°C to +85°C Wide body, 20-lead SOIC package

3. APPLICATIONS

    1. High noise data communications

    2. Industrial communications

    3. General-purpose RS232 data links

    4. Industrial/telecommunications diagnostic ports

    5. Medical equipment

4. Pin configuration

5. Pin description

6. ISOLATION OF POWER AND DATA

The ADM3251E incorporates a dc-to-dc converter section, which works on principles that are common to most modern power supply designs. VCC power is supplied to an oscillating circuit that switches current into a chip-scale air core transformer. Power is transferred to the secondary side, where it is rectified to a high dc voltage. The power is then linearly regulated to about 5.0 V and supplied to the secondary side data section and to the VISO pin. The VISO pin should not be used to power external circuitry. Because the oscillator runs at a constant high frequency independent of the load, excess power is internally dissipated in the output voltage regulation process. Limited space for transformer coils and components also adds to internal power dissipation. This results in low power conversion efficiency. The ADM3251E can be operated with the dc-to-dc converter enabled or disabled. The internal dc-to-dc converter state of the ADM3251E is controlled by the input VCC voltage. In normal operating mode, VCC is set between 4.5 V and 5.5 V and the internal dc-to-dc converter is enabled. To disable the dc-to-dc converter, lower VCC to a value between 3.0 V and 3.7 V. In this mode, the user must externally supply isolated power to the VISO pin. An isolated secondary side voltage of between 3.0 V and 5.5 V and a secondary side input current, IISO, of 12 mA (maximum) is required on the VISO pin. The signal channels of the ADM3251E then continue to operate normally The TIN pin accepts CMOS input levels (and TTL levels at VCC = 3.3 V). The driver input signal that is applied to the TIN pin is referenced to logic ground (GND). It is coupled across the isolation barrier, inverted, and then appears at the transceiver section, referenced to isolated ground (GNDISO). Similarly, the receiver input (RIN) accepts RS-232 signal levels that are referenced to isolated ground. The RIN input is inverted and coupled across the isolation barrier to appear at the ROUT pin, referenced to logic ground. The digital signals are transmitted across the isolation barrier using iCoupler technology. Chip-scale transformer windings couple the digital signals magnetically from one side of the barrier to the other. Digital inputs are encoded into waveforms that are capable of exciting the primary transformer of the winding. At the secondary winding, the induced waveforms are decoded into the binary value that was originally transmitted. There is hysteresis in the VCC input voltage detect circuit. Once the dc-to-dc converter is active, the input voltage must be decreased below the turn-on threshold to disable the converter. This feature ensures that the converter does not go into oscillation due to noisy input power

7. Package overview