SP504 Datasheet, PDF (16/32 Pages) Sipex Corporation – WAN Multi-Mode Serial Transceiver

Since both V_DD and V_SS are separately gen-
erated from V_CC in a no–load condition, V_DD
and V_SS will be symmetrical. Older charge
pump approaches that generate V^– from
V⁺ will show a decrease in the magnitude
of V^– compared to V⁺ due to the inherent
inefficiencies in the design.
The clock rate for the charge pump typically
operates at 15kHz. The external capacitors
must be a minimum of 22µF with a 16V
breakdown rating.
External Power Supplies
For applications that do not require +5V only,
external supplies can be applied at the V+ and
V^– pins. The value of the external supply volt-
ages must be no greater than ±l0.5V. The tol-
erance should be ±5% from ±10V. The current
drain for the supplies is used for RS-232 and
RS-423 drivers. For the RS-232 driver,
the current requirement will be 3.5mA per
driver. The RS-423 driver worst case cur-
rent drain will be 11mA per driver. Power
sequencing is required for the SP504. The
supplies must be sequenced accordingly:
+10V, +5V and –10V. An external circuit
would be needed for proper power supply
sequencing. Consult factory for application
circuitry.
Drivers
The SP504 has seven (7) enhanced in-
dependent drivers. Control for the mode
selection is done via a four–bit control word.
The drivers are pre-arranged such that for
each mode of operation, the relative posi-
tion and functionality of the drivers are set
up to accommodate the selected interface
mode. As the mode of the drivers is changed,
the electrical characteristics will change to
support the requirements of clock, data, and
control line signal levels. Table 1 shows the
mode of each driver in the different interface
modes that can be selected.
There are four basic types of driver circuits
— RS-232, RS-423, RS-485 and V.35.
The RS-232 drivers output single–ended
signals with a minimum of ±5V (with 3kΩ
and 2500pF loading), and can operate up
to 120kbps.
The RS-232 drivers are used in RS-
232 mode for all signals, and also in
V.35 mode where they are used as
the control line signals such as DTR
and RTS.
The RS-423 drivers are also single–ended
signals with a minimum voltage output of
±3.6V (with 450Ω loading) and can operate
up to 120kbps. Open circuit V_OL and V_OH
measurements are ±4.0V to ±6.0V. The RS-
423 drivers are used in RS-449, EIA-530,
EIA-530A and V.36 modes as Category II
signals from each of their corresponding
specifications.
The third type of driver produces a differential
signal that can maintain RS-485, ±1.5V dif-
ferential output levels with a worst case load
of 54Ω. The signal levels and drive capability
of the RS-485 drivers allow the drivers to
also support RS-422 (V.11) requirements
of ±2V differential output levels with 100Ω
loads. The RS-422 drivers are used in RS-
449, EIA-530, EIA-530A and V.36 modes as
Category I signals which are used for clock
and data.
The fourth type of driver is the V.35 driver.
V.35 levels require ±0.55V driver output sig-
nals with a load of 100Ω. The SP504 drivers
simplify existing V.35 implementations that
use external termination schemes. The
drivers were specifically designed to comply
with the requirements of V.35 as well as the
driver output impedance values of V.35. The
drivers achieve the 50Ω to 150Ω source
impedance. However, an external 150Ω
resistor to ground must be connected to
the non-inverting outputs; SD(b), ST(b), and
TT(b), in order to comply with the 135Ω to
165Ω short-circuit impedance for V.35. The
V.35 driver itself is disabled and transparent
when the decoder is in all other modes. All
of the differential drivers; RS-485, RS-422,
and V.35, can operate up to 10Mbps.
The driver inputs are both TTL or CMOS
compatible. Since there are no pull-up or
pull-down resistors on the driver inputs, they
should be tied to a known logic state in order
to define the driver output.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
16
SP504_102_121708