MAX3222/MAX3232/ MAX3237/MAX3241: Transceivers Using Four 0.1μF External Capacitors
The MAX3222/MAX3232/MAX3237/MAX3241 transceivers have a proprietary low-dropout transmitter out- put 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 the normal operating mode and 1Mbps in the MegaBaudTM operating mode, while maintaining RS-232 output levels.
The MAX3222/MAX3232 have 2 receivers and 2 drivers. The MAX3222 features a 1μA shutdown mode that reduces power consumption and extends battery life in portable systems. Its receivers remain active in shutdown mode, allowing external devices such as modems to be monitored using only 1μA supply cur- rent. The MAX3222 and MAX3232 are pin, package, and functionally compatible with the industry-standard MAX242 and MAX232, respectively.
The MAX3241 is a complete serial port (3 drivers/ 5 receivers) designed for notebook and subnotebook computers. The MAX3237 (5 drivers/3 receivers) is ideal for fast modem applications. Both these devices feature a shutdown mode in which all receivers can remain active while using only 1μA supply current. Receivers R1 (MAX3237/MAX3241) and R2 (MAX3241) have extra out- puts in addition to their standard outputs. These extra outputs are always active, allowing external devices such as a modem to be monitored without forward bias- ing the protection diodes in circuitry that may have VCC completely removed.
The MAX3222, MAX3232, and MAX3241 are available in space-saving TSSOP and SSOP packages.
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Features
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Applications • Notebook, Subnotebook, and Palmtop Computers• High-Speed Modems • Battery-Powered Equipment • Hand-Held Equipment • Peripherals Printers |
RS-232 Transmitters
The transmitters are inverting level translators that con- vert CMOS-logic levels to 5.0V EIA/TIA-232 levels.
The MAX3222/MAX3232/MAX3241 transmitters guaran- tee a 120kbps data rate with worst-case loads of 3kΩ in parallel with 1000pF, providing compatibility with PC-to- PC communication software (such as LapLinkTM). Typically, these three devices can operate at data rates of 235kbps. Transmitters can be paralleled to drive multi- ple receivers or mice.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic out- put levels. The MAX3222/MAX3237/MAX3241 receivers have inverting three-state outputs. In shutdown, the receivers can be active or inactive (Table 1).
The complementary outputs on the MAX3237 (R1OUTB) and the MAX3241 (R1OUTB, R2OUTB) are always active, regardless of the state of EN or SHDN. This allows for Ring Indicator applications without forward biasing other devices connected to the receiver outputs. This is ideal for systems where VCC is set to 0V in shutdown to accommodate peripherals, such as UARTs
Interconnection with 3V and 5V Logic
The MAX3222/MAX3232/MAX3237/MAX3241 can directly interface with various 5V logic families, includ- ing ACT and HCT CMOS. See Table 3 for more informa- tion on possible combinations of interconnections.