Rev. 7/21/03
SP502 Multi-Mode Serial Transceiver
8
Copyright 2003 Sipex Corporation
FEATURES…
The
SP502
is a highly integrated serial trans-
ceiver that allows software control of its inter-
face modes. The
SP502
offers hardware inter-
face modes for RS-232 (V.28), RS-422A (V.11),
RS-449, RS-485, V.35, and EIA-530. The inter-
face mode selection is done via an 8–bit switch;
four (4) bits control the drivers and four (4) bits
control the receivers. The
SP502
is fabricated
using low–power BiCMOS process technology,
and incorporates a
Sipex
patented (5,306,954)
charge pump allowing +5V only operation. Each
THEORY OF OPERATION
Charge–Pump
The charge pump is a
Sipex
patented design
(5,306,954) and uses a unique approach com-
pared to older less efficient designs. The charge
pump still requires four external capacitors, but
uses a four–phase voltage shifting technique to
attain symmetrical 10V power supplies.
Figure
3a
shows the waveform found on the positive
side of capcitor C
, and
Figure 3b
shows the
negative side of capcitor C
. There is a free–
running oscillator that controls the four phases
of the voltage shifting. A description of each
phase follows.
Phase 1
— V
charge storage —During this phase of
the clock cycle, the positive side of capacitors
C
and C
are initially charged to +5V. C
then switched to ground and the charge on C
is transferred to C
to +5V, the voltage potential across capacitor
C
2
is now 10V.
+
is
–
–
. Since C
+
is connected
Phase 2
— V
transfer — Phase two of the clock con-
nects the negative terminal of C
to the V
SS
storage capacitor and the positive terminal of C
2
to ground, and transfers the generated –l0V to
C
3
. Simultaneously, the positive side of capaci-
Pin 78 — DSR— Data Set Ready; TTL output;
sourced from DM(a), DM(b) inputs.
Pin 80 — CTS— Clear To Send; TTL output;
sourced from CS(a) and CS(b) inputs.
CONTROL REGISTERS
Pins 2–5 — RDEC0 – RDEC3 — Receiver
decode register; configures receiver modes; TTL
inputs.
Pin 6 — ST/TT — Enables ST or TT drivers,
TTL input.
Pins 12–9 — TDEC0 – TDEC3 — Transmitter
decode register; configures transmitter modes;
TTL inputs.
POWER SUPPLIES
Pins 8, 25, 33, 41, 48, 55, 62, 73, 74 — V
CC
—
+5V input.
Pins 7, 29, 34, 43, 46, 50, 53, 57, 60, 64, 72, 75
— GND — Ground.
Pin 27 — V
+10V Charge Pump Capacitor —
Connects from V
to V
CC
. Suggested capaci-
tor size is 22
μ
F, 16V.
Pin 32 — V
–10V Charge Pump Capacitor —
Connects from ground to V
SS
. Suggested ca-
pacitor size is 22
μ
F, 16V.
Pins 26 and 30 — C
Capacitor — Connects from C
gested capacitor size is 22
μ
F, 16V.
Pins 28 and 31 — C
Capacitor — Connects from C
gested capacitor size is 22
μ
F, 16V.
+
and C
–
— Charge Pump
+
to C
1
–
. Sug-
+
and C
–
— Charge Pump
+
to C
2
–
. Sug-
NOTE: NC pins should be left floating; internal
signals may be present.
device is packaged in an 80–pin Quad FlatPack
package.
The
SP502
is ideally suited for wide area net-
work connectivity based on the interface modes
offered and the driver and receiver configura-
tions. The
SP502
has five (5) independent driv-
ers and six (6) independent receivers and one
half–duplex transceiver channel, which allows
a maximum of six (6) drivers and seven (7)
receivers. The driver and receiver configuration
for the
SP502
is ideal for DTE applications. The
SP502
is made up of four separate circuit blocks
– the charge pump, drivers, receivers, and
decoder. Each of these circuit blocks is de-
scribed in detail below.