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MAX3228E-MAX3229E Datasheet(PDF) 6 Page - Maxim Integrated Products

Part No. MAX3228E-MAX3229E
Description  ±15kV ESD-Protected 2.5V to 5.5V RS-232 Transceivers in UCSP
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Maker  MAXIM [Maxim Integrated Products]
Homepage  http://www.maxim-ic.com
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MAX3228E-MAX3229E Datasheet(HTML) 6 Page - Maxim Integrated Products

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±15kV ESD-Protected +2.5V to +5.5V
RS-232 Transceivers in UCSP
6
_______________________________________________________________________________________
Detailed Description
Dual-Mode Regulated Charge-Pump
Voltage Converter
The MAX3228E/MAX3229E internal power supply con-
sists of a dual-mode regulated charge pump. For sup-
ply voltages above +3.7V, the charge pump will
generate +5.5V at V+ and -5.5V at V-. 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.
For supply voltages below +2.85V, the charge pump
will generate +4.0V at V+ and -4.0V at V-. The charge
pumps operate in a discontinuous mode. If the output
voltages are less than ±4.0V, the charge pumps are
enabled, if the output voltages exceed ±4.0V, 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- supply voltages.
Voltage Generation in the
Switchover Region
The MAX3228E/MAX3229E include a switchover circuit
between these two modes that have approximately
400mV of hysteresis around the switchover point. The
hysteresis is shown in Figure 1. This large hysteresis
eliminates mode changes due to power-supply
bounce.
For example, a three-cell NiMh battery system starts at
VCC = +3.6V, and the charge pump will generate an
output voltage of ±5.5V. As the battery discharges, the
PIN
MAX3228E
MAX3229E
NAME
FUNCTION
C5
C5
FORCEOFF
FORCEOFF Input, Active-Low. Drive FORCEOFF low to shut down transmitters,
receivers, and on-board charge pump. This overrides all automatic circuitry and
FORCEON. Pulls itself high internally if not connected.
C6, D6
C6
R_OUT
Receiver Output(s)
D1
D1
C1-
Negative Terminal of Positive Regulated Charge-Pump Capacitor
E1
E1
GND
Ground
E2
E2
INVALID
Output of Valid Signal Detector. INVALID is enabled low if no valid RS-232 level is
present on any receiver input.
E3, E4
E3
T_OUT
RS-232 Transmitter Output(s)
E5, E6
E5
R_IN
RS-232 Receiver Input(s)
Pin Description (continued)
SYSTEM SUPPLY (V)
VCC (V)
VL (V)
RS-232 MODE
1 Li+ Cell
+2.4 to +4.2
Regulated System Voltage
Compliant/Compatible
3 NiCad/NiMh Cells
+2.4 to +3.8
Regulated System Voltage
Compliant/Compatible
Regulated Voltage Only
(VCC falling)
+3.0 to +5.5
+3.0 to +5.5
Compliant
Regulated Voltage Only
(VCC falling)
+2.5 to +3.0
+2.5 to +3.0
Compatible
Table 1. Operating Supply Options
Figure 1. V+ Switchover for Changing VCC
0
6V
4V
0
20ms/div
VCC
V+


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