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SP230A Datasheet(PDF) 10 Page - Sipex Corporation

Part No. SP230A
Description  5V Powered Multi-Channel RS-232 Drivers/Receivers
Download  17 Pages
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Maker  SIPEX [Sipex Corporation]
Homepage  http://www.sipex.com
Logo SIPEX - Sipex Corporation

SP230A Datasheet(HTML) 10 Page - Sipex Corporation

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Date: 8/3/04
+ 5V Powered Multi-Channel RS-232 Drivers/Receivers
© Copyright 2004 Sipex Corporation
10
of the charge pump. If the SP2XXB is powered
up with SD low, then only the 2ms delay time
will apply (refer to Figure 6). Under normal
operation, both the wait time and delay time
should be transparent to the user.
With only the receivers activated, the device
typically draws less than 5
µA (10µA max) sup-
ply current. In the case of a modem interfaced to
a computer in power-down mode, the RI (ring
indicator) signal from the modem would be used
to “wake up” the computer, allowing it to accept
the data transmission.
After the ring indicator signal has propagated
through the SP2XXB receiver, it can be used to
trigger the power management circuitry of the
computer to power up the microprocessor and
bring the SD pin to the SP2XXB low, taking it
out of shutdown. The receiver propagation de-
lay is typically 1
µs. The enable time for V+ and
V- is typically 2ms. After V+ and V- have
settled to their final values, a signal can be sent
back to the modem on the DTR (Data Terminal
Ready) pin signifying that the computer is ready
to accept and transmit data.
All receivers that are active during shutdown
maintain 500mV (typ.) of hysteresis.
Varying Capacitor Values
As stated earlier, the capacitor values are some-
what non-critical. Since they are an actual compo-
nent of the charge pump circuitry, their value will
affect its performance, which in turn affects the
V
OH and VOL levels. There is no upper limit for the
value of any of the four capacitors; lower values
will impact performance. C
1 and C2 are respon-
sible for the charge accumulation and can be
reduced to 1
µF; this will increase the output im-
pedance of V+ and V. Reducing these capacitor
values will limit the ability of the SP2XXA/B to
maintain the dc voltages needed to generate the
RS-232 output levels. Capacitors C
3 and C4 can
also be reduced to 1
µF; doing so will increase the
ripple on V+ and V–.
Typically each driver will require 1
µF of capaci-
tance as a minimum to operate within all specified
parameters; if five drivers are active in the circuit,
then C
3 and C4 should be 5µF. In order to operate
at these minimum values, the supply voltage must
be maintained at +5.0V
±5%. Also, the ambient
operating temperature must be less than 60
°C.
The capacitor values must be chosen to suit the
particular application. The designer must bal-
ance board space, cost and performance to maxi-
mize the design. The capacitors can be polarized
or non–polarized, axial-leaded or surface-mount.
As the size and value decrease, so does the cost;
however, the value should be chosen to accom-
modate worst-case load conditions.
IBM Modem Port Interconnections
Computer
D
R
D
R
R
D
R
D
Transmitted Data
(To Be Printed)
Ready To Send
Clear To Send
Data Set Ready
Signal Ground
4
2
5
6
7
Received Data
(To Be Printed)
Ready To Send
Clear To Send
Data Set Ready
Signal Ground
Modem
R
D
Received Data
3
Received Data
R
D
Data Carrier Detect
8
Data Carrier Detect
D
R
Data Terminal Ready
20
Data Terminal Ready
R
D
Ring Indicator
22
Ring Indicator
SP239A
SP237A
INTERFACE EXAMPLE – A MODEM
ON THE IBM PC SERIAL PORT
The RS-232 standard defines 22 serial interface
signals. These signals consist of ground lines,
timing, data, control and test signals, plus a set
of signals rarely used for a second data channel.
Many of these signal lines are not used in typical
RS-232 applications; in fact, the IBM® PC serial
port is implemented using only nine pins.
For example, consider the case of a PC using this
nine pin port to communicate with a peripheral
device such as a modem. We see the following
activity on each of the RS-232 lines as the
computer and modem are activated and commu-
nicate with each other as well as the remote
modem at the other end of the phone line.
Signal Ground (GND)
The Signal Ground pin acts as a reference for all
the other signals. This pin is simply maintained
at a 0V level to serve as a level to which all other
signals are referenced. Both the PC and the
modem will have this line connected to their
respective internal ground lines.


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