isl3330 Intersil Corporation, isl3330 Datasheet - Page 14

• Manufacturer Part Number: isl3330
• Description: 3.3v, ?15kv Esd Protected, Dual Protocol Rs-232/rs-485 Transceivers
• Manufacturer: Intersil Corporation

ISL333x Advantages
These dual protocol ICs offer many parametric
improvements vs those offered on competing dual protocol
devices. Some of the major improvements are:
• 3.3V Supply Voltage - Eliminates the 5V supply that
• 15kV Bus Pin ESD - Eases board level requirements
• Full Failsafe RS-485 Rx - Eliminates bus biasing
• Selectable RS-485 Data Rate - Up to 20Mbps, or slew
• High RS-232 Data Rate - >250kbps
• Lower Tx and Rx Skews - Wider, consistent bit widths
• Lower I
• Flow-Thru Pinouts - Tx, Rx bus pins on one side/logic
• Packaging - Smaller (QFN) and Pb-free.
RS-232 Mode
RX FEATURES
RS-232 receivers invert and convert RS-232 input levels
(±3V to ±25V) to the standard TTL/CMOS levels required by
a UART, ASIC, or µcontroller serial port. Receivers are
designed to operate at faster data rates than the drivers, and
they feature very low skews (20ns) so the receivers
contribute negligibly to bit width distortion. Inputs include the
standards required 3kΩ to 7kΩ pull-down resistor, so unused
inputs may be left unconnected. Rx inputs also have built-in
hysteresis to increase noise immunity and to decrease
erroneous triggering due to slowly transitioning input signals.
Rx outputs are short circuit protected, and are tri-statable via
the active high RXEN pin, when the IC is shutdown (SHDN;
see Tables 2 and 3, and the “Low Power Shutdown (SHDN)
Mode” on page 16), or via the active low RXEN pin available
on the QFN package option (see “ISL3331 (QFN Package)
Special Features” on page 17).
TX FEATURES
RS-232 drivers invert and convert the standard TTL/CMOS
levels from a UART, or µcontroller serial port to RS-232
compliant levels (±5V minimum). The Tx delivers these
compliant output levels even at data rates of 400kbps, and
with loads of 1000pF. The drivers are designed for low skew
(typically 12% of the 400kbps bit width), and are compliant to
the RS-232 slew rate specification (4V to 30V/µs) for a wide
range of load capacitances. Tx inputs float if left
unconnected and may cause I
results, connect unused inputs to GND.
Tx outputs are short circuit protected, and incorporate a
thermal SHDN feature to protect the IC in situations of
severe power dissipation. See the “RS-485 Mode” on
page 14 for more details. Drivers disable via the active high
powers just the interface IC
rate limited for low EMI and fewer termination issues
pins on the other, for easy routing to connector/UART
CC
- Max I
CC
is 2x to -4x lower than competition
14
CC
increases. For the best
ISL3330, ISL3331
DEN pin, in SHDN (see Tables 2 and 3, and the “Low Power
Shutdown (SHDN) Mode” on page 16), or when the 3.3V
power supply is off. Because RS-232 is a point-to-point (only
one Tx allowed on the bus) standard, the main use for this
DEN disable function is to reduce power by eliminating the
load current (approximately 1mA per Tx output) through the
5kΩ resistor in the Rx at the cable’s far end.
CHARGE PUMPS
The on-chip charge pumps create the RS-232 transmitter
power supplies (typically +5.7/-5.3V) from a single supply as
low as 3.15V, and are enabled only if the port is configured
for RS-232 operation, and not in SHDN. The efficient design
requires only four small 0.1µF capacitors for the voltage
doubler and inverter functions. By operating discontinuously
(i.e., turning off as soon as V+ and V- pump up to the
nominal values), the charge pump contribution to RS-232
mode I
that require the charge pump in RS-485 mode, disabling the
charge pump saves power, and minimizes noise. If the
application is a dedicated RS-485 port, then the charge
pump capacitors aren’t even required.
DATA RATES AND CABLING
Drivers operate at data rates up to 400kbps, and are
guaranteed for data rates up to 250kbps. The charge pumps
and drivers are designed such that one driver can be
operated at the rated load, and at 250kbps (see Figure 33).
Figure 33 also shows that drivers can easily drive several
thousands of picofarads at data rates up to 250kbps, while
still delivering compliant ±5V output levels.
Receivers operate at data rates up to 2Mbps. They are
designed for a higher data rate to facilitate faster factory
downloading of software into the final product, thereby
improving the user’s manufacturing throughput.
Figures 36 and 37 illustrate driver and receiver waveforms at
250kbps, and 400kbps, respectively. For these graphs, one
driver drives the specified capacitive load, and a receiver.
RS-232 doesn’t require anything special for cabling; just a
single bus wire per transmitter and receiver, and another
wire for GND. So an ISL333x RS-232 port uses a five
conductor cable for interconnection. Bus terminations are
not required, nor allowed, by the RS-232 standard.
RS-485 Mode
RX FEATURES
RS-485 receivers convert differential input signals as small
as 200mV, as required by the RS-485 and RS-422
standards, to TTL/CMOS output levels. The differential Rx
provides maximum sensitivity, noise immunity, and common
mode rejection. Per the RS-485 standard, receiver inputs
function with common mode voltages as great as +12V and
-7V, regardless of supply voltage, making them ideal for long
networks where induced voltages are a realistic concern.
CC
is reduced significantly. Unlike competing devices
May 20, 2008
FN6361.0