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DS481 Schematic ( PDF Datasheet ) - National Semiconductor

Teilenummer DS481
Beschreibung Low Power RS-485/RS-422 Multipoint Transceiver with Sleep Mode
Hersteller National Semiconductor
Logo National Semiconductor Logo 




Gesamt 10 Seiten
DS481 Datasheet, Funktion
July 1998
DS481
Low Power RS-485/RS-422 Multipoint Transceiver with
Sleep Mode
General Description
The DS481 is a low-power transceiver for RS-485 and
RS-422 communication. The device contains one driver and
one receiver. The drivers slew rate allows for operation up to
2.0 Mbps (see Applications Information section).
The transceiver draws 200 µA of supply current when un-
loaded or 0.2 µA when in the automatic sleep mode. Sleep
mode is activated by inactivity on the enables (DE and RE
(Note 1)). Holding DE =L and RE (Note 1)=H for greater than
600 ns will enable the sleep mode. The DS481 operates
from a single +5V supply.
The driver is short-circuit current limited and is protected
against excessive power dissipation by thermal shutdown
circuitry that places the driver outputs into TRI-STATE®
(High Impedance state) under fault conditions. The driver
guarantees a minimum of 1.5V differential output voltage
with maximum loading across the common mode range
(VOD3).
The receiver has a failsafe feature that guarantees a
logic-high output if the input is open circuit.
The DS481 is available in surface mount and DIP packages
and is characterized for Industrial and Commercial tempera-
ture range operation.
Features
n Meets TIA/EIA RS-485 multipoint standard
n Sleep mode reduces ICC to 0.2 µA
n Guaranteed full load output voltage (V OD3)
n Low quiescent current: 200 µA typ
n −7V to +12V common-mode input voltage range
n TRI-STATE outputs on driver and receiver
n AC performance:
— Driver transition time: 25 ns typ
— Driver propagation delay: 40 ns typ
— Driver skew: 1 ns typ
— Receiver propagation delay: 200 ns typ
— Receiver skew: 20 ns typ
n Half-duplex flow through pinout
n Operates from a single 5V supply
n Allows up to 128 transceivers on the bus (DS481N/M)
n Allows up to 64 tranceivers on the bus (DS481TN/M)
n Current-limiting and thermal shutdown for driver
overload protection
n Industrial temperature range operation
n Pin and functional compatible with MAX481C and
MAX481E
Connection and Logic Diagram
*Note: Non Terminated, Open Input only
DS012919-1
Order Number
DS481N
DS481M
DS481TN
DS481TM
Temp. Range
0˚C to +70˚C
0˚C to +70˚C
−40˚C to +85˚C
−40˚C to +85˚C
Package/###
DIP/N08E
SOP/M08A
DIP/N08E
SOP/M08A
Truth Table
DRIVER SECTION
RE DE DI A
(Note 1)
B
X H HH
L
X H LL
H
X L X Z Z (Note 2)
RECEIVER SECTION
RE
(Note 1)
DE
A-B
RO
LL
LL
+0.2V
−0.2V
H
L
HX
X Z (Note 2)
L
L OPEN (Note 1)
H
X = indeterminate
Z = TRI-STATE
Note 1: Non Terminated, Open Input only
Note 2: Device enters sleep mode if enable conditions are held > 600 ns,
DE = L and RE (Note 1) = H.
TRI-STATE® is a registered trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation DS012919
www.national.com






DS481 Datasheet, Funktion
Parameter Measurement Information (Continued)
DS012919-15
*Note: Non Terminated, Open Input only
FIGURE 14. Entering Sleep Mode Conditions (modes and exit parameters shown)
TABLE 1. Device Pin Descriptions
Pin Name
Description
No.
1 RO Receiver Output: When RE (Receiver Enable) is LOW, the receiver is enabled (ON), if DO/RI DO
(Note 1)/RI (Note 1) by 200 mV, RO will be HIGH. If DO/RI DO (Note 1)/RI (Note 1) by 200 mV,
RO will be LOW. Additionally RO will be HIGH for OPEN (Non-terminated) Inputs.
2 RE Receiver Output Enable: When RE (Note 1) is LOW the receiver output is enabled. When RE (Note
(Note 1) 1) is HIGH, the receiver output is in TRI-STATE (OFF). When RE (Note 1) is HIGH and DE is LOW,
the device will enter a low-current sleep mode after 600 ns.
3 DE Driver Output Enable: When DE is HIGH, the driver outputs are enabled. When DE is LOW, the
driver outputs are in TRI-STATE (OFF). When RE (Note 1) is HIGH and DE is LOW, the device will
enter a low-current sleep mode after 600 ns.
4 DI Driver Input: When DE (Driver Enable) is HIGH, the driver is enabled, if DI is LOW, then DO/RI will
be LOW and DO (Note 1)/RI (Note 1) will be HIGH. If DI is HIGH, then DO/RI is HIGH and DO
(Note 1)/RI (Note 1) is LOW.
5 GND Ground Connection.
6 DO/RI Driver Output/Receiver Input, 485 Bus Pin.
7 DO Driver Output/Receiver Input, 485 Bus Pin.
(Note 1)
/RI
(Note 1)
8 VCC Positive Power Supply Connection: Recommended operating range for VCC is +4.75V to +5.25V.
Unit Load
A unit load for an RS-485 receiver is defined by the input cur-
rent versus the input voltage curve. The gray shaded region
is the defined operating range from −7V to +12V. The top
border extending from −3V at 0 mA to +12V at +1 mA is de-
fined as one unit load. Likewise, the bottom border extending
from +5V at 0 mA to −7V at −0.8 mA is also defined as one
unit load (see Figure 15 ). An RS-485 driver is capable of
driving up to 32 unit loads. This allows up to 32 nodes on a
single bus. Although sufficient for many applications, it is
sometimes desirable to have even more nodes.
The DS481 has 12 unit load and 14 unit load (UL) options
available. These devices will allow up to 64 nodes or 128
nodes guaranteed over temperature depending upon which
option is selected. The 12 UL option is available in industrial
temperature and the 14 UL is available in commercial tem-
perature.
First, for a 12 UL device the top and bottom borders shown in
Figure 15 are scaled. Both 0 mA reference points at +5V and
−3V stay the same. The other reference points are +12V at
+0.5 mA for the top border and −7V at −0.4 mA for the bot-
tom border (see Figure 15 ). Second, for a 14 UL device the
top and bottom borders shown in Figure 15 are scaled also.
Again, both 0 mA reference points at +5V and −3V stay the
same. The other reference points are +12V at +0.25 mA for
the top border and −7V at −0.2 mA for the bottom border
(see Figure 15 ).
The advantage of the 12 UL and 14 UL devices is the in-
creased number of nodes on one bus. In a single master
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