all functions either side of the isolation boundary.
A low-power shutdown mode and high impedance
state for receiver outputs is effected via two pins,
SHUTDOWN and ENABLE. The device is supplied
in a low profile 24 pin DIL package.
4.5
53
.0
9.6
5.5
0
.0
.0
87
µA
µA
µA
kHrs
TEMPERATURE CHARACTERISTICS
Parameter
Operating free-air temperature range
Storage temperature range
MIN.
0
-55
TYP.
MAX.
70
25
Units
ºC
ºC
ABSOLUTE MAXIMUM RATINGS
Supply voltage V
CC
with respect to pin 0
Input voltage to logic pins 3, 7, 8, & with respect to
pin 0
Voltages with respect to ISO GND pin 22
Short circuit on pins 9 & 20
Power dissipation
NM232DDC maximum data rate
Lead case temperature .5mm from case for 0 seconds
EIA-232-D input voltage, pins 7 & 8
EIA-232-D input voltage, pins 9 & 20
Positive input voltage, pins 6 & 2
Negative input voltage, pin 23
-0.3V to +6V
-0.3V to
V
CC
+0.3V
-30V to +30V
-5V to +5V
+4V
-4V
Indefinite
700mW
9.6kbps
300ºC
ISOLATION CHARACTERISTICS
Parameter
Isolation test voltage
. Calulated using MIL-HDBK-27F.
All data taken at T
A
=25°C, V
CC
=5V.
Conditions
Flash tested for second
MIN.
500
TYP.
MAX.
Units
Vrms
www.cd4power.com
KII_NM232DDC.1
Page of 5
NM232DDC
Isolated Dual EIA-232-D Transmitter and Receiver
APPLICATION NOTES
The NM232DDC is an isolated interface device providing EIA-232-D compatibility.
A single supply from the logic side provides all necessary power for the device.
The isolation feature allows the protective or frame ground of DTEs or DCEs to
be isolated from each other, eliminating ground loop currents and inherently long
noise paths. The voltage level between different ground points can be up to ±5V
or ±6V and this level flucuates as the power taken varies. This voltage appears, in
non-isolated equipment, as normal mode noise on the signals. With such high noise
levels present it is clearly very difficult with single ended signals to have reliable
communication. Isolating the input from output so that one side floats relative to
the other allows reliable communication in environments with considerable degrees
of noise between equipments.
Figure shows a typical pcb track layout with a clear separation between the logic
pin connections (pins -2) and the EIA-232-D connections (pins 3-24). Between
the two sides of the layout is a track which can be connected to frame or equip-
ment ground, this can be seen as the boundary between the logic and EIA-232-D
side of the device. No other rules or speed conditions need to be applied other than
to keep the two halves’ separation to a maximum.
An example of a DTE application circuit is shown in figure 2. The schematic is
illustrative of the way the NM232DDC may be connected to implement an isolated
EIA-232-D interface with a typical UART and processor bus. Precise circuitry will
depend on the application and in particular the use of the control lines shown will
need to be altered to suit the situation.
The ENABLE control line (pin ), puts the receiver output pins and 2 into a high
impedance state when set to a high level. The shutdown control line (pin 3) sets the
device into a shutdown power mode when it is at high logic level. The maximum
power drawn in shutdown mode is 50µW, a low enough level for consideration in
battery powered equipment.
Where to use the NM232DDC
The function of the NM232DDC is to provide an isolated signal path between a
UART or similar device and the EIA-232-D interface ‘D’ connector, providing two
receivers and two transmitters which can be used in a number of handshake
modes. One receiver and transmitter will normally be used for the signal lines and
the remaining pair will act as handshake lines. Figure 3 shows simply where the
device will be connected.
More complicated schemes for controlled signal interchange will require two or
more such devices. As the devices are self contained no external DC/DC converter
is required. The enable line provides a means for creating a communications bus
where each NM232DDC can have a different logical address via a decoder. This
would allow one UART to talk with many EIA-232-D connected interfaces (see
figure 4).
Figure
Figure 2
Figure 3
Figure 4
www.cd4power.com
KII_NM232DDC.1
Page 2 of 5
NM232DDC
Isolated Dual EIA-232-D Transmitter and Receiver
TECHNICAL NOTES
ISOLATION VOLTAGE
‘Hi Pot Test’, ‘Flash Tested’, ‘Withstand Voltage’, ‘Proof Voltage’, ‘Dielectric Withstand Voltage’ & ‘Isolation Test Voltage’ are all terms that relate to the same thing, a test voltage,
applied for a specified time, across a component designed to provide electrical isolation, to verify the integrity of that isolation.
C&D Technologies NM232DDC series of DC/DC converters are all 00% production tested at their stated isolation voltage. This is .5kVrms for second.
A question commonly asked is, “What is the continuous voltage that can be applied across the part in normal operation?”
For a part holding no specific agency approvals, such as the NM232DDC series, both input and output should normally be maintained within SELV limits i.e. less than 42.4V peak,
or 60VDC. The isolation test voltage represents a measure of immunity to transient voltages and the part should never be used as an element of a safety isolation system. The part
could be expected to function correctly with several hundred volts offset applied continuously across the isolation barrier; but then the circuitry on both sides of the barrier must
be regarded as operating at an unsafe voltage and further isolation/insulation systems must form a barrier between these circuits and any user-accessible circuitry according to
safety standard requirements.
REPEATED HIGH-VOLTAGE ISOLATION TESTING
It is well known that repeated high-voltage isolation testing of a barrier component can actually degrade isolation capability, to a lesser or greater degree depending on materials,
construction and environment. The NM232DDC series has toroidal isolation transformers, with no additional insulation between primary and secondary windings of enameled wire.
While parts can be expected to withstand several times the stated test voltage, the isolation capability does depend on the wire insulation. Any material, including this enamel
(typically polyurethane) is susceptible to eventual chemical degradation when subject to very high applied voltages thus implying that the number of tests should be strictly limited.
We therefore strongly advise against repeated high voltage isolation testing, but if it is absolutely required, that the voltage be reduced by 20% from specified test voltage.
RoHS COMPLIANCE INFORMATION
This series is compatible with RoHS soldering
systems with a peak wave solder temperature of
300ºC for 0 seconds. The pin termination finish
on this product series is Matte Tin over Nickel
Preplate. The series is backward compatible
with Sn/Pb soldering systems.
For further information, please visit www.cd4power.com/rohs
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