SP3238EEY-L-TR Datasheet, PDF (7/21 Pages) Exar Corporation – Intelligent +3.0V to +5.5V RS-232 Transceiver

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
devices feature Exar's proprietary and patented
(U.S.‑‑ 5,306,954) on-board charge pump cir-
cuitry that generates ±5.5V RS-232 voltage levels
from a single +3.0V to +5.5V power supply. The
SP3238E devices can guarantee a 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_CC may be
disconnected.
The SP3238E device is an ideal choice for power
sensitive designs. The SP3238E 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
without major design changes.
THEORY OF OPERATION
The SP3238E device is made up of four basic
circuit blocks:
1. Drivers
2. Receivers
3. The Exar proprietary charge pump, and
4. AUTO ON-LINE^® 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-232-F and all previous
RS-232 versions.
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
V+ ²⁷
+
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
20 R2OUT
18 ^R3^OUT
R₁IN ₈
5kΩ
R₂IN ₉
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 drivers can guarantee a data rate of 250kbps
fully loaded with 3kΩ in parallel with 1000pF,
ensuring compatibility with PC-to-PC communi-
cation software. All unused drivers inputs should
be connected to GND or V_CC.
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.
Figure 7 shows a loopback test circuit used to
test the RS-232 drivers. Figure 8 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 9 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 ca-
pacitor. A solid RS-232 data transmission rate
of 120kbps provides compatibility with many
designs in personal computer peripherals and
LAN applications.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
SP3238E_100_020111