MAX3218CAP

Overview

The MAX3218CAP is a dual-driver, dual-receiver RS-232 transceiver designed for battery-powered EIA/TIA-232E and V.28/V.24 interfaces. It operates from a single supply voltage ranging from 1.8V to 4.25V, enabling direct connection to two alkaline, NiCd, or NiMH cells without external regulators. The device guarantees a data rate of 120kbps while maintaining true RS-232 and EIA/TIA-562 voltage levels. Utilizing an onboard switch-mode power supply with a 15µH inductor, it achieves a typical supply current of 3mA during operation and reduces to 1µA via the AutoShutdown feature when no valid signal is detected. It is housed in a 20-pin SSOP package.

Feature Summary

• AutoShutdown technology automatically disables the onboard power supply and drivers upon detecting invalid receiver input levels, significantly reducing power consumption.
• Integrated switch-mode DC-DC converter generates necessary internal voltages using minimal external components, including a single inductor and capacitors.
• Receiver outputs feature three-state drivers, allowing multiple receivers with different interface standards to be connected on the same bus.
• Logic control inputs (FORCEON/FORCEOFF) allow manual override of automatic shutdown states for system management.

Applications

• Battery-powered subnotebook computers
• Personal Digital Assistants (PDAs)
• Hand-held equipment and cellular phones
• Peripherals requiring low-power serial communication

Procurement Notes

Verify the specific suffix against the manufacturer's ordering information to confirm temperature range and compliance status. The 'CAP' designation indicates a commercial temperature range (0°C to +70°C) and SSOP packaging. Confirm RoHS compliance requirements with the supplier, as lead-free designations may vary by production batch.

Selection Notes

Select this component for applications requiring extended battery life in portable devices where standard bipolar transceivers are too power-intensive. Ensure the design accommodates the external inductor and diode required for the onboard charge pump. Verify that the system logic levels are compatible with the 1.8V to 4.25V operating range.

Part Context

The MAX3218 belongs to Maxim Integrated's family of low-voltage RS-232 transceivers. It shares functional similarities with the MAX218 but offers improved efficiency through its proprietary AutoShutdown circuitry. Unlike traditional charge-pump designs requiring only small capacitors, this device utilizes a switch-mode topology to achieve lower quiescent currents.

Replacement Considerations

Publicly confirmed substitutes include the MAX3218CPP+ (Plastic DIP package) and the MAX3218EAP+ (Extended temperature range). Direct pin-compatible replacements from other manufacturers are not explicitly documented in the provided source material.

FAQ

How does the AutoShutdown feature determine when to enter low-power mode?

The device enters AutoShutdown mode when it senses no valid RS-232 signal level on either receiver input for typically 30µs. This occurs if the cable is disconnected or peripheral transmitters are off.

What external components are required for the onboard power supply?

The circuit requires a 15µH inductor with at least 350mA saturation current, a fast recovery diode (e.g., 1N6050), and four capacitors (C1: 0.47µF, C2/C3/C4: 1µF).

Can the receivers remain active while the transmitters are shut down?

Yes, while shut down, both receivers can remain active to monitor external devices, or they can be disabled under logic control via the FORCEON input.