概要

The MAX3222/MAX3232/MAX3237/MAX3241 transceivers have a proprietary low-dropout transmitter output stage enabling true RS-232 performance from a 3.0V to 5.5V supply with a dual charge pump. The devices require only four small 0.1µF external charge-pump capacitors. The MAX3222, MAX3232, and MAX3241 are guaranteed to run at data rates of 120kbps while maintaining RS-232 output levels. The MAX3237 is guaranteed to run at data rates of 250kbps in normal operating mode and 1Mbps in the MegaBaud™ operating mode.

The MAX3222/MAX3232 have 2 receivers and 2 drivers. The MAX3222 and MAX3232 are pin, package, and functionally compatible with the industry-standard MAX242 and MAX232, respectively.

The MAX3222, MAX3232, and MAX3241 are available in space-saving TSSOP and SSOP packages with operating temperatures of either -40°C to +85°C or 0°C to 70°C.

 

アプリケーション

Battery-Powered Equipment

Hand-Held Equipment

Peripherals

Datacom Equipment

 

メリットと特徴

Integrated Features Saves Board Space and Simplifies Design

Charge Pump Circuitry Eliminates the Need for a Bipolar ±12V Supply

Wide Single-Supply Operation From +3V to +5.5V Supply

Always-On Extra Outputs Enable Monitoring of External Devices

Power Saving Extends Battery Life

1µA Supply Current in Shutdown Mode While Receiver is Active

 

MORE DESCRIPTION

Dual Charge-Pump Voltage Converter

The MAX3222/MAX3232/MAX3237/MAX3241’s internal power supply consists of a regulated dual charge pump that provides output voltages of +5.5V (doubling charge pump) and -5.5V (inverting charge pump), regardless of the input voltage (VCC) over the 3.0V to 5.5V range. The charge pumps operate in a discontinuous mode; if the output voltages are less than 5.5V, the charge pumps are enabled, and if the output voltages exceed 5.5V, the charge pumps are disabled. Each charge pump requires a flying capacitor (C1, C2) and a reservoir capacitor (C3, C4) to generate the V+ and V- supplies.

RS-232 Transmitters

The transmitters are inverting level translators that convert CMOS-logic levels to 5.0V EIA/TIA-232 levels.The MAX3222/MAX3232/MAX3241 transmitters guarantee a 120kbps data rate with worst-case loads of 3kΩ in parallel with 1000pF, providing compatibility with PC-to-PC communication software (such as LapLink™). Typically, these three devices can operate at data rates of 235kbps. Transmitters can be paralleled to drive multiple receivers or mice.

When the power is off, the MAX3222/MAX3232/MAX3237/ permit the outputs to be driven up to ±12V.

The transmitter inputs do not have pullup resistors. Connect unused inputs to GND or VCC.

Capacitor Selection

The capacitor type used for C1–C4 is not critical for proper operation; polarized or nonpolarized capacitors can be used. The charge pump requires 0.1μF capacitors for 3.3V operation. For other supply voltages, refer to Table 2 for required capacitor values. Do not use values lower than those listed in Table 2. Increasing the capacitor values (e.g., by a factor of 2) reduces ripple on the transmitter outputs and slightly reduces power consumption.

C2, C3, and C4 can be increased without changing C1’s value. However, do not increase C1 without also increasing the values of C2, C3, and C4, to maintain the proper ratios (C1 to the other capacitors).

When using the minimum required capacitor values, make sure the capacitor value does not degrade excessively with temperature. If in doubt, use capacitors with a higher nominal value. The capacitor’s equivalent series resistance (ESR), which usually rises at low temperatures, influences the amount of ripple on V+ and V-.

High Data Rates

The MAX3222/MAX3232/MAX3241 maintain the RS-232 ±5.0V minimum transmitter output voltage even at high data rates.

Interconnection with 3V and 5V Logic

The MAX3222/MAX3232/MAX3237/MAX3241 can directly interface with various 5V logic families, including ACT and HCT CMOS. See Table 3 for more information on possible combinations of interconnections.