SP3282 Datasheet, PDF (6/15 Pages) Sipex Corporation – Intelligent +2.35V to +5.5V RS-232 Transceivers

DESCRIPTION
The SP3282EB device meets the EIA/TIA-232
and ITU-T V.28/V.24 communication protocols
and can be implemented in battery-powered, por-
table, or hand-held applications such as notebook
or palmtop computers. The SP3282EB 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 +3.3V to +5.5V power supply. The
SP3282EB will adhere to EIA/TIA-562 voltage
levels with V_CC as low as 2.35V.
The SP3282EB device is an ideal choice for power
sensitive designs. The SP3282EB device features
AUTO ON-LINE^® 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 condi-
tions, the internal charge pump and the drivers will
be shut down. Otherwise, the system automati-
cally comes online. This feature allows design
engineers to address power saving concerns with-
out major design changes.
VCC
UART
or
Serial µC
+
C5 0.1µF
28 _C1+
+
C1 0.1µF
25 C1-
1 C2+
+
C2 0.1µF
3 C2-
RxD
24 ^T1^IN
CTS
23 T2IN
DSR
22 T3IN
DCD
19 T4IN
RI
17 T5IN
26
VCC
27
V+
SP3282EB V- ⁴
T₁OUT ₅
T₂OUT 6
T₃OUT ₇
T₄OUT 10
T₅OUT 12
+
C3 0.1µF
C4 0.1µF
+
RS-232
OUTPUTS
TxD
RTS
DTR
VCC
21 R1OUT
20 R2OUT
18 ^R3^OUT
R₁IN ₈
5kΩ
R₂IN ₉
5kΩ
R₃IN ₁₁
5kΩ
14
SHUTDOWN
13 _ONLINE
15 _STATUS
GND
VL ¹⁶
2
RS-232
INPUTS
RESET
µP
Supervisor
VIN
IC
Figure 5. Interface Circuitry Being Controlled by
Microprocessor Supervisory Circuit
THEORY OF OPERATION
The SP3282EB device is made up of four basic
circuit blocks: 1. Drivers, 2. Receivers,
3. The Sipex proprietary charge pump, and
4. AUTO ON-LINE^® circuitry.
Drivers
The drivers are inverting level transmitters that ,
when V_CC is between +3.3V and +5.5V, 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 driver outputs will adhere to EIA/
TIA-562 when V_CC is as low as 2.35V.
The SP3282EB drivers can guarantee a data rate of
250 kbps fully loaded with 3kΩ in parallel with
1000pF, ensuring compatibility with PC-to-PC
communication software. All unused driver inputs
must be connected to V_L or GND.
Figure 6 shows a loopback test circuit used to test
the SP3282EB RS-232 drivers. Figure 7 shows the
test results of the loopback circuit with all five
drivers active at 120kbps with typical RS-232
loads in parallel with 1000pF capacitors. Figure 8
shows the test results where one driver was active
at 250kbps and all five drivers loaded with an RS-
232 receiver in parallel with a 1000pF capacitor. A
solid RS-232 data transmission rate of 120kbps
provides compatibility with many designs in per-
sonal computer peripherals and LAN applications.
Receivers
The receivers convert ±5.0V EIA/TIA-232
levels to TTL or CMOS logic output levels.
Receivers are not active when in shutdown. If
there is no activity present at the receivers for a
period longer than 100µs during AUTO ON-
LINE^® mode or when SHUTDOWN is enabled,
the device goes into a standby mode where the
circuit draws 1µA. The truth table logic of the
driver and receiver outputs can be found in
Table 3.
Date: 02/24/05
SP3282EB Intelligent +2.35V to +5.5V RS-232 Transceivers
6
© Copyright 2005 Sipex Corporation