DS8921,DS8921A,DS8921AT
DS8921/DS8921A/DS8921AT Differential Line Driver and Receiver Pair
Literature Number: SNLS374B
DS8921/DS8921A/DS8921AT
Differential Line Driver and Receiver Pair
General Description
The DS8921, DS8921A are Differential Line Driver and Re-
ceiver pairs designed specifically for applications meeting
the ST506, ST412 and ESDI Disk Drive Standards. In addi-
tion, these devices meet the requirements of the EIA Stan-
dard RS-422.
The DS8921, DS8921A receivers offer an input sensitivity of
200 mV over a ±7V common mode operating range. Hys-
teresis is incorporated (typically 70 mV) to improve noise
margin for slowly changing input waveforms.
The DS8921, DS8921A drivers are designed to provide uni-
polar differential drive to twisted pair or parallel wire trans-
mission lines. Complementary outputs are logically ANDed
and provide an output skew of 0.5 ns (typ.) with propagation
delays of 12 ns.
The DS8921, DS8921A are designed to be compatible with
TTL and CMOS.
Features
n12 ns typical propagation delay
nOutput skew - 0.5 ns typical
nMeet the requirements of EIA Standard RS-422
nComplementary Driver Outputs
nHigh differential or common-mode input voltage ranges
of ±7V
n±0.2V receiver sensitivity over the input voltage range
nReceiver input hysteresis-70 mV typical
nDS8921AT industrial temperature
operation: (−40˚C to +85˚C)
Connection Diagram
00851201
Order Number DS8921M, DS8921N, DS8921AM, DS8921AN,
DS8921ATM, or DS8921ATN
See NS Package Number M08A or N08E
Truth Table
Receiver Driver
Input V
OUT
Input V
OUT
V
OUT
V
ID
≥V
TH
(MAX) 1 1 1 0
V
ID
≤V
TH
(MIN) 0 0 0 1
Open 1
May 1998
DS8921/DS8921A/DS8921AT Differential Line Driver and Receiver Pair
© 2004 National Semiconductor Corporation DS008512 www.national.com
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage 7V
Driver Input Voltage −0.5V to +7V
Output Voltage 5.5V
Receiver Output Sink
Current 50 mA
Receiver Input Voltage ±10V
Differential Input Voltage ±12V
Maximum Package Power Dissipation @+25˚C
M Package 730 mW
N Package 1160 mW
Derate M Package 9.3 mW/˚C above
+25˚C
Derate N Package 5.8 mW/˚C above
+25˚C
Storage Temperature
Range −65˚C to +165˚C
Lead Temperature +260˚C
(Soldering, 4 sec.) +260˚C
Maximum Junction
Temperature +150˚C
Recommended Operating
Conditions
Min Max Units
Supply Voltage 4.5 5.5 V
Temperature (T
A
)
DS8921/DS8921A 0 70 ˚C
DS8921AT −40 +85 ˚C
DS8921/DS8921A Electrical Characteristics (Notes 2, 3, 4)
Symbol Conditions Min Typ Max Units
RECEIVER
V
TH
−7V ≤V
CM
≤+7V −200 ±35 +200 mV
V
HYST
−7V ≤V
CM
≤+7V 15 70 mV
R
IN
V
IN
= −7V, +7V 4.0 6.0 kΩ
(Other Input = GND)
I
IN
V
IN
= 10V 3.25 mA
V
IN
= −10V −3.25 mA
V
OH
I
OH
= −400 µA 2.5 V
V
OL
I
OL
= 8 mA 0.5 V
I
SC
V
CC
= MAX, V
OUT
= 0V −15 −100 mA
DRIVER
V
IH
2.0 V
V
IL
0.8 V
I
IL
V
CC
= MAX, V
IN
= 0.4V −40 −200 µA
I
IH
V
CC
= MAX, V
IN
= 2.7V 20 µA
I
I
V
CC
= MAX, V
IN
= 7.0V 100 µA
V
CL
V
CC
= MIN, I
IN
= −18 mA −1.5 V
V
OH
V
CC
= MIN, I
OH
= −20 mA 2.5 V
V
OL
V
CC
= MIN, I
OL
= +20 mA 0.5 V
I
OFF
V
CC
= 0V, V
OUT
= 5.5V 100 µA
|V
T
| – |VT | 0.4 V
V
T
2.0 V
|V
OS
–V
OS
| 0.4 V
I
SC
V
CC
= MAX, V
OUT
= 0V −30 −150 mA
DRIVER and RECEIVER
I
CC
V
CC
= MAX, V
OUT
= Logic 0 35 mA
DS8921/DS8921A/DS8921AT
www.national.com 2
Receiver Switching Characteristics
Figure 1(Figure 2)
Symbol Conditions Min Typ Max Units
8921 8921A 8921AT
T
pLH
C
L
= 30 pF 14 22.5 20 20 ns
(Figures 1, 2 )
T
pHL
C
L
= 30 pF 14 22.5 20 20 ns
(Figures 1, 2)
|T
pLH
–T
pHL
|C
L
= 30 pF 0.5 5 3.5 5 ns
(Figures 1, 2 )
Driver Switching Characteristics
SINGLE ENDED CHARACTERISTICS (Figures 3, 4)
Symbol Conditions Min Typ Max Units
8921 8921A 8921AT
T
pLH
C
L
=30pF 10 15 15 15 ns
(Figures 3, 4)
T
pHL
C
L
=30pF 10 15 15 15 ns
(Figures 3, 4)
T
TLH
C
L
= 30 pF 5 8 8 9.5 ns
(Figures 7, 8)
T
THL
C
L
= 30 pF 5 8 8 9.5 ns
(Figures 7, 8)
Skew CL = 30 pF 1 5 3.5 3.5 ns
(Figures 3, 4)
Driver Switching Characteristics(Note 6)
DIFFERENTIAL CHARACTERISTICS (Figures 3, 5)
Symbol Conditions Min Typ Max Units
8921 8921A 8921AT
T
pLH
C
L
=30pF 10 15 15 15 ns
(Figures 3, 5, 6)
T
pHL
C
L
=30pF 10 15 15 15 ns
(Figures 3, 5, 6)
|T
pLH
–T
pHL
|C
L
= 30 pF 0.5 6 2.75 2.75 ns
(Figures 3, 5, 6)
Note 1: “Absolute Maximum Ratings” are those values beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the device
should be operated at these limits. The Table of “Electrical Characteristics” provides conditions for actual device operation.
Note 2: All currents into device pins are shown as positive values; all currents out of the device are shown as negative; all voltages are referenced to ground unless
otherwise specified. All values shown as max or min are classified on absolute value basis.
Note 3: All typical values are VCC =5V,T
A= 25˚C.
Note 4: Only one output at a time should be shorted.
Note 5: Difference between complementary outputs at the 50% point.
Note 6: Differential Delays are defined as calculated results from single ended rise and fall time measurements. This approach in establishing AC performance
specifications has been taken due to limitations of available Automatic Test Equipment (ATE).
The calculated ATE results assume a linear transition between measurement points and are a result of the following equations:
Where: Tcr = Crossing Point
Tra,T
rb,T
fa and T fb are time measurements with respect to the input. See Figure 6 .
DS8921/DS8921A/DS8921AT
www.national.com3
AC Test Circuits and Switching Diagrams
00851203
FIGURE 1.
00851204
FIGURE 2.
00851205
FIGURE 3.
00851206
FIGURE 4.
00851207
FIGURE 5.
00851202
FIGURE 6.
00851210
FIGURE 7.
00851211
FIGURE 8.
DS8921/DS8921A/DS8921AT
www.national.com 4
Typical Applications
ST506 and ST412 Application
00851208
ESDI Application
00851209
DS8921/DS8921A/DS8921AT
www.national.com5
Physical Dimensions inches (millimeters)
unless otherwise noted
SO Package (M)
Order Number DS8921M, DS8921AM or DS8921ATM
NS Package Number M08A
Molded Dual-In-Line Package (N)
Order Number DS8921N, DS8921AN or DS8921ATN
NS Package Number N08E
DS8921/DS8921A/DS8921AT
www.national.com 6
Notes
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body, or
(b) support or sustain life, and whose failure to perform when
properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
in a significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
system, or to affect its safety or effectiveness.
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National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship
Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned
Substances’’ as defined in CSP-9-111S2.
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Email: new.feedback@nsc.com
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DS8921/DS8921A/DS8921AT Differential Line Driver and Receiver Pair
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