SLLS348O June 1999 – June 2015 MAX3221
The MAX3221 device is a one-driver and one-receiver RS-232 interface device. All RS-232 inputs and outputs are protected to ±15 kV using the Human Body Model. The charge pump requires only four small 0.1-μF capacitors for operation from a 3.3-V supply. The MAX3221 is capable of running at data rates up to 250 kbps, while maintaining RS-232-compliant output levels.
Automatic power-down can be disabled when FORCEON and FORCEOFF are high. With automatic power-down plus enabled, the device activates automatically when a valid signal is applied to any receiver input. The device can automatically power down the driver to save power when the RIN input is unpowered.
INVALID is high (valid data) if receiver input voltage is greater than 2.7 V or less than –2.7 V, or has been between –0.3 V and 0.3 V for less than 30 μs. INVALID is low (invalid data) if receiver input voltages are between –0.3 V and 0.3 V for more than 30 μs. Refer to Figure 7 for receiver input levels.
The power block increases, inverts, and regulates voltage at V+ and V- pins using a charge pump that requires four external capacitors. Auto-power-down feature for driver is controlled by FORCEON and FORCEOFF inputs. Receiver is controlled by EN input. See Table 1 and Table 2
When MAX3221 is unpowered, it can be safely connected to an active remote RS232 device.
One driver interfaces standard logic level to RS232 levels. DIN input must be valid high or low.
One receiver interfaces RS232 levels to standard logic levels. An open input will result in a high output on ROUT. RIN input includes an internal standard RS232 load. A logic high input on the EN pin will shutdown the receiver output.
The INVALID output goes low when RIN input is unpowered for more than 30 μs. The INVALID output goes high when receiver has a valid input. The INVALID output is active when Vcc is powered irregardless of FORCEON and FORCEOFF inputs (see Table 3).
|DIN||FORCEON||FORCEOFF||VALID RIN RS-232
|L||H||H||X||H||Normal operation with
automatic power down disabled
|L||L||H||Yes||H||Normal operation with
automatic power down enabled
|L||L||H||No||Z||Powered off by
automatic power down feature
|RIN||EN||VALID RIN RS-232