SP505 Datasheet, PDF (18/35 Pages) Sipex Corporation – WAN Multi-Mode Serial Transceiver

FEATURES…
The SP505 is a highly integrated serial
transceiver that allows software control of
its interface modes. Similar to the SP504,
the SP505 offers the same hardware inter-
face modes for RS-232 (V.28), RS-422A
(V.11), RS-449, RS-485, V.35, EIA-530 and
includes V.36 and EIA-530A. The interface
mode selection is done via a 4–bit switch
for the drivers and receivers. The SP505
is fabricated using low–power BiCMOS
process technology, and incorporates a
Exar–patented (5,306,954) charge pump
allowing +5V only operation. Each device
is packaged in an 80–pin JEDEC Quad
FlatPack package.
The SP505 is ideally suited for wide area
network connectivity based on the interface
modes offered and the driver and receiver
configurations. The SP505 has seven (7)
independent drivers and seven (7) indepen-
dent receivers. In V.35 mode, the SP505
includes the necessary components and
termination resistors internal within the de-
vice for compliant V.35 operation.
Theory of Operation
The SP505 is made up of five separate
circuit blocks — the charge pump, drivers,
receivers, decoder and switching array. Each
of these circuit blocks is described in more
detail below.
Charge–Pump
The SP505 charge pump is based on the
SP504 design where Exar's patented charge
pump design (5,306,954) uses a four–phase
voltage shifting technique to attain symmetri-
cal 10V power supplies. The charge pump
still requires external capacitors to store the
charge. In addition the SP504 charge pump
supplies +10V or +5V on V_SS and V_DD de-
pending on the mode of operation. There is
a free–running oscillator that controls the four
phases of the voltage shifting. A description
of each phase follows.
The SP505 charge pump is used for RS-
232 where the output voltage swing is
typically +10V and also used for RS-423.
However, RS-423 requires the voltage
swing on the driver output be between
+4V to +6V during an open-circuit (no
load). The charge pump would need to
be regulated down from +10V to +5V.
A typical +10V charge pump would require
external clamping such as 5V zener diodes
on V_DD and V_SS to ground. The +5V output
has symmetrical levels as in the +10V output.
The +5V is used in the following modes where
RS-423 (V.10) are used: RS-449, EIA-530,
EIA-530A and V.36.
Phase 1 (±10V)
— V_SS charge storage — During this phase of
the clock cycle, the positive side of capacitors
C₁ and C₂ are initially charged to +5V. C_l+ is
then switched to ground and the charge on
C_1– is transferred to C_2–. Since C₂₊ is con-
nected to +5V, the voltage potential across
capacitor C₂ is now 10V.
Phase 1 (±5V)
— V_SS & V_DD charge storage and transfer
— With the C₁ and C₂ capacitors initially
casshtwnoadirtractghhgeeeedcdcthoataop+rag5gcrVeoi,touoCnnr_l.⁺_{CdiSs1a–itmnhisdeutnrl5taasVnwnsceiftheocarhurreseglddyetttooohngethrCCoeu22V+–}n_SiidssS
transferred to the V_DD storage capacitor.
V CC = +5V
+
C_{1 –}
–5 V
+5V
+
C_{2 –}
–5 V
C4
+ – V _DD S torage C apa citor
– + _{VSS S torage C apa citor}
C3
Figure 45. Charge Pump Phase 1 for +10V.
V _CC = +5V
+
C_{1 –}
–5 V
+5V
+
C_{2 –}
C₄
+ – _{V DD S torage C apa citor}
– + _{VSS S torage C apa citor}
C₃
Figure 46. Charge Pump Phase 1 for +5V.
Exar Coporation 48720 Kato Road, Fremont CA, 94538 • [phone] • Fax [phone] • www.exar.com
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