Detailed Description
Figure 2 shows the receiver test circuit. Figure 3 shows
driver propagation delay and Figure 4 shows receiver
propagation delay.
Dual Charge-Pump Voltage Converter
The MAX13223E internal power supply consists of a
dual-mode regulated charge pump that provides output
voltages of +5.5V (doubling charge pump) and -5.5V
(inverting charge pump), regardless of the input volt-
age (V
CC
) 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. If the output voltages exceed 5.5V, the charge
pumps are disabled. Each charge pump requires a fly-
ing 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
logic levels to EIA/TIA-232/V.28 levels. They guarantee a
250kbps data rate with worst-case loads of 3kΩ in parallel
with 1000pF, providing compatibility with PC-to-PC com-
munication software. The MAX13223E can operate at data
rates of 250kbps (max). Transmitters can be paralleled to
drive multiple receivers. When FORCEOFF is driven to
ground, or the AutoShutdown circuitry senses invalid volt-
age levels at all receiver inputs, the transmitters are dis-
abled and the outputs are forced into a high-impedance
state. Figure 5 shows a complete system connection.
RS-232 Receivers
The MAX13223E’s receivers convert RS-232 signals to
logic output levels. Both receiver outputs can be three-
stated using the EN input. In shutdown (FORCEOFF or
AutoShutdown), the MAX13223E’s receiver outputs are
active and asserted low if EN = Low (Table 1). Driving
EN high places the receivers’ outputs in a high-imped-
ance state.
MAX13223E
±70V Fault-Protected, 3.0V to 5.5V,
2Tx/2Rx RS-232 Transceiver
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Pin Description
PIN NAME FUNCTION
1 EN
Receiver Enable Control Input. Drive EN low for normal operation. Drive EN high to force the receiver outputs
(R1OUT, R2OUT) into a high-impedance state.
2 C1+ Positive Terminal of the Voltage Doubler Charge-Pump Capacitor
3 V+ +5.5V Generated by Charge Pump
4 C1- Negative Terminal of the Voltage Doubler Charge-Pump Capacitor
5 C2+ Positive Terminal of Inverting Charge-Pump Capacitor
6 C2- Negative Terminal of Inverting Charge-Pump Capacitor
7 V- -5.5V Generated by Charge Pump
8 T2OUT RS-232 Transmitter 2 Output
9 R2IN RS-232 Receiver 2 Input
10 R2OUT Receiver 2 Logic Output
11 INVALID Valid Signal Detector Output. INVALID is high if a valid RS-232 level is present on any receiver input.
12 T2IN Transmitter 2 Logic Input
13 T1IN Transmitter 1 Logic Input
14 FORCEON
Active-High FORCEON Input. Drive FORCEON high to override AutoShutdown, keeping transmitters and
charge pump on (FORCEOFF must be high).
15 R1OUT Receiver 1 Logic Output
16 R1IN RS-232 Receiver 1 Input
17 T1OUT RS-232 Transmitter 1 Output
18 GND Ground
19 V
CC
+3.0V to +5.5V Supply Voltage. Bypass V
CC
with a 0.1µF ceramic capacitor located as close to the device
as possible.
20 FORCEOFF
Active-Low FORCEOFF Input. Drive FORCEOFF low to shut down transmitters, receivers, and on-board
charge pumps, overriding AutoShutdown and FORCEON.
