SP3238E Datasheet, PDF (8/20 Pages) Sipex Corporation – Intelligent +3.0V to +5.5V RS-232 Transceivers

DESCRIPTION
The SP3238E device meets the EIA/TIA-232
and ITU-T V.28/V.24 communication protocols
and can be implemented in battery-powered,
portable, or hand-held applications such as
notebook or palmtop computers. The SP3238E
device features Sipex's proprietary and patented
(U.S.-- 5,306,954) on-board charge pump
circuitry that generates ±5.5V RS-232 voltage
levels from a single +3.0V to +5.5V power
supply. The SP3238E device can operate at
a typical data rate of 250kbps fully loaded.
The SP3238E is a 5-driver/3-receiver device,
ideal for portable or hand-held applications.
The SP3238E includes one complementary
always-active receiver that can monitor an
external device (such as a modem) in shutdown.
This aids in protecting the UART or serial
controller IC by preventing forward biasing
of the protection diodes where V may be
CC
disconnected.
VCC
UART
or
Serial µC
+
C5 0.1µF
28 _C1+
+
C1 0.1µF
25 C1-
1 C2+
+
C2 0.1µF
3 C2-
RxD
24 T1IN
CTS
23 T2IN
DSR
22 T3IN
DCD
19 T4IN
RI
17 T5IN
26
VCC
27
V+
+
C3 0.1µF
SP3238E _V- 4
T₁OUT ₅
T₂OUT 6
T₃OUT 7
T₄OUT 10
T₅OUT 12
C4 0.1µF
+
RS-232
OUTPUTS
TxD
RTS
DTR
VCC
16 ^R1^OUT
21 R1OUT
R₁IN ₈
20 R2OUT
5kΩ
R₂IN 9
18 ^R3^OUT
5kΩ
R₃IN 11
5kΩ
14
SHUTDOWN
13 _ONLINE
15 _STATUS
GND
2
RS-232
INPUTS
RESET
µP
Supervisor
VIN
IC
Figure 6. Interface Circuitry Controlled by
Microprocessor Supervisory Circuit
The SP3238E device is an ideal choice for
power sensitive designs. The SP3238E device
features Auto-Online circuitry which reduces
the power supply drain to a 1µA supply current.
In many portable or hand-held applications,
an RS-232 cable can be disconnected or a
connected peripheral can be turned off. Under
these conditions, the internal charge pump and
the drivers will be shut down. Otherwise, the
system automatically comes online. This feature
allows design engineers to address power saving
concerns without major design changes.
THEORY OF OPERATION
The SP3238E device is made up of four basic
circuit blocks: 1. Drivers, 2. Receivers,
3. the Sipex proprietary charge pump, and
4. Auto-Online circuitry.
Drivers
The drivers are inverting level transmitters that
convert TTL or CMOS logic levels to 5.0V EIA/
TIA-232 levels with an inverted sense relative to
the input logic levels. Typically, the RS-232
output voltage swing is +5.4V with no load and
+5V minimum fully loaded. The driver outputs
are protected against infinite short-circuits to
ground without degradation in reliability. These
drivers comply with the EIA-TIA-232F and all
previous RS-232 versions.
The drivers typically can operate at a data rate
of 250kbps. The drivers can guarantee a data
rate of 120kbps fully loaded with 3kΩ in
parallel with 1000pF, ensuring compatibility
with PC-to-PC communication software.
The slew rate of the driver output is internally
limited to a maximum of 30V/µs in order to
meet the EIA standards (EIA RS-232D 2.1.7,
Paragraph 5). The transition of the loaded
output from HIGH to LOW also meets the
monotonicity requirements of the standard.
SP3238EDS/04
SP3238E +3.0V to +5.5V RS-232 Transceivers
8
© Copyright 1999 Sipex Corporation