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M
_______________Detailed Desc ription
The MAX563 consists of three sections: charge-pump
voltage converters, transmitters (drivers), and
receivers. Both the transmitters and the receivers are
inverting.
+3V to ±6V , Dual Charge-Pump V oltage
Converter
Two charge pumps either invert or double the incoming
V
CC
to generate the voltages required by the transmit-
ters. The first charge pump uses capacitor C1 to
double V
CC
; the resulting voltage is stored on the V+
reservoir capacitor. The second charge pump uses
capacitor C2 to invert V+; this negative voltage is
stored on the V- capacitor.
When
SHDN
is low, the charge pumps are turned off,
V+ is pulled down to V
CC
by a 1k
resistor, and V-
rises to GND.
It is possible to draw some power from the V+ and V-
pins for external use. However, doing so diminishes the
charge-pump output voltages and reduces noise mar-
gins, so it is not recommended.
EIA/T IA-562 T ransmitters
The MAX563’s drivers are inverting level translators that
convert +3V logic inputs to EIA/TIA-562 voltage levels.
With a VCC supply of only 3.0V, the driver outputs
deliver the EIA/TIA-562 ±3.7V minimum specification
under worst-case conditions—when both transmitters
are loaded with 3k
receivers (either EIA/TIA-232 or
EIA/TIA-562).
The transmitters are fast: the guaranteed data rate with
standard loads is 116kbps, which is the highest rate
commonly used by PC-to-PC communication software,
such as LapLink. The highest practical data rate may
be reduced if the other communicating device (RS-562
or RS-232) is not as fast, or if the cables present an
excessive capacitive load (>1000pF). Each transmitter
is designed to drive a single receiver; transmitters can
be paralleled to drive multiple receivers.
When
SHDN
is low, the driver outputs are turned off.
Their output leakage currents are less than 10μA when
pulled to GND or when driven to ±15V. This enables
two transmitters to be connected to the same line, pro-
vided that one of them is always disabled by taking
SHDN
low.
+3.3V-Powered, EIA/T IA-562 Dual Transc eiver
with Rec eivers Ac tive in S hutdown
4
_______________________________________________________________________________________
______________________________________________________________Pin Desc ription
10, 13
NAME
FUNCTION
R2
OUT
, R1
OUT
EN
Receiver enable. Connect
EN
to GND to enable receivers, and take
EN
high to disable receivers.
CMOS receiver outputs. These outputs are active regardless of the state of
SHDN
. They
are enabled when
EN
is low, and disabled (Hi-Z) when
EN
is high.
C1+
Positive terminal of positive charge-pump capacitor.
11, 12
V+
+2V
CC
voltage generated by the positive charge pump. The voltage on V+ collapses to
V
CC
when
SHDN
is low.
PIN
1
2
T2
IN
, T1
IN
C1-
Negative terminal of positive charge-pump capacitor.
CMOS driver inputs.
C2+
Positive terminal of inverting charge-pump capacitor.
16
C2-
Negative terminal of inverting charge-pump capacitor.
GND
V-
-2V
CC
voltage generated by the inverting charge pump. The voltage on V- collapses to
GND when
SHDN
is low.
EIA/TIA-562 voltage-level transmitter outputs. These outputs are disabled (Hi-Z) when
SHDN
is low.
3
4
5
Ground.
T2
OUT
, T1
OUT
17
R2
IN
, R1
IN
EIA/TIA-562 and EIA/TIA-232 voltage-level receiver inputs.
6
7
8, 15
9, 14
V
CC
+3.0V to +3.6V supply voltage.
18
SHDN
Shutdown control. Connect to GND to shut down the charge pumps and the transmitters.
Take high to turn on the charge pumps and to enable the transmitters.