SN74ALS990
8-BIT D-TYPE TRANSPARENT READ-BACK LATCH
SDAS027B – APRIL 1984 – REVISED JANUARY 1995
•
•
•
•
DW OR N PACKAGE
(TOP VIEW)
3-State I/O-Type Read-Back Inputs
Bus-Structured Pinout
True Logic Outputs
Package Options Include Plastic
Small-Outline (DW) Packages and Standard
Plastic (N) 300-mil DIPs
OERB
1D
2D
3D
4D
5D
6D
7D
8D
GND
description
This 8-bit latch is designed specifically for storing
the contents of the input data bus and providing
the capability of reading back the stored data onto
the input data bus.
1
20
2
19
3
18
4
17
5
16
6
15
7
14
8
13
9
12
10
11
VCC
1Q
2Q
3Q
4Q
5Q
6Q
7Q
8Q
LE
The eight latches are transparent D-type latches.
While the latch-enable (LE) input is high, the
Q outputs follow the data (D) inputs.
Read back is provided through the output-enable (OERB) input. When OERB is taken low, the data present at
the output of the data latches is allowed to pass back onto the input data bus. When OERB is taken high, the
output of the data latches is isolated from the D inputs. OERB does not affect the internal operation of the latches;
however, precautions should be taken not to create a bus conflict.
The SN74ALS990 is characterized for operation from 0°C to 70°C.
logic symbol†
1
OERB
LE
1D
11
2
EN2
C1
1D
19
2
2D
3D
4D
5D
6D
7D
8D
3
18
4
17
5
16
6
15
7
14
8
13
9
12
1Q
2Q
3Q
4Q
5Q
6Q
7Q
8Q
† This symbol is in accordance with ANSI/IEEE Std 91-1984 and IEC Publication 617-12.
Copyright 1995, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
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1
SN74ALS990
8-BIT D-TYPE TRANSPARENT READ-BACK LATCH
SDAS027B – APRIL 1984 – REVISED JANUARY 1995
logic diagram (positive logic)
OERB
LE
1D
1
11
2
1D
19
1Q
C1
To Seven Other Channels
timing diagram
Data Bus
Input Data
tsu
Read Back
Input Data
th
LE
tsu†
ten
tdis
OERB
tpd
tpd
Q
† This setup time ensures that the read-back circuit will not create a conflict on the input data bus.
absolute maximum ratings over operating free-air temperature range (unless otherwise noted)‡
Supply voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 V
Input voltage, VI (OERB and LE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 V
Voltage applied to D inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 V
Operating free-air temperature range, TA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0°C to 70°C
Storage temperature range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . – 65°C to 150°C
‡ Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
2
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SN74ALS990
8-BIT D-TYPE TRANSPARENT READ-BACK LATCH
SDAS027B – APRIL 1984 – REVISED JANUARY 1995
recommended operating conditions
VCC
VIH
Supply voltage
VIL
Low-level input voltage
IOH
High level output current
High-level
IOL
Low level output current
Low-level
tw
Pulse duration, LE high
High-level input voltage
MIN
NOM
MAX
4.5
5
5.5
2
Q
– 2.6
D
– 0.4
Q
24
D
8
10
10
Data before OERB↓
10
tsu
Setup time
th
TA
Hold time, data after LE↓
5
Operating free-air temperature
0
V
V
0.8
Data before LE↓
UNIT
V
mA
mA
ns
ns
ns
70
°C
electrical characteristics over recommended operating free-air temperature range (unless
otherwise noted)
PARAMETER
VIK
VOH
TEST CONDITIONS
All outputs
VCC = 4.5 V,
VCC = 4.5 V to 5.5 V,
II = – 18 mA
IOH = – 0.4 mA
Q
VCC = 4.5 V,
D
VCC = 4
4.5
5V
IOH = – 2.6 mA
IOL = 4 mA
VOL
Q
II
OERB, LE
D inputs
VCC = 4
4.5
5V
VCC = 5
5.5
5V
UNIT
– 1.2
V
VCC – 2
2.4
V
3.2
IOL = 8 mA
IOL = 12 mA
0.35
0.5
0.25
0.4
IOL = 24 mA
VI = 5.5 V
0.35
0.5
0.1
VI = 7 V
VCC = 5
5.5
5V
V,
VI = 2
2.7
7V
IIL
OERB, LE
D inputs‡
5V
VCC = 5
5.5
V,
4V
VI = 0
0.4
VCC = 5.5 V,
VO = 2.25 V
Outputs high
VCC = 5.5 V,
OERB high
MAX
0.4
OERB, LE
D inputs‡
ICC
TYP†
0.25
IIH
IO§
MIN
Outputs low
0.1
20
20
– 0.1
– 0.1
– 30
–112
27
50
40
70
V
mA
µA
mA
mA
mA
† All typical values are at VCC = 5 V, TA = 25°C.
‡ For I/O ports (QA thru QH), the parameters IIH and IIL include the off-state output current.
§ The output conditions have been chosen to produce a current that closely approximates one half of the true short-circuit output current, IOS.
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3
SN74ALS990
8-BIT D-TYPE TRANSPARENT READ-BACK LATCH
SDAS027B – APRIL 1984 – REVISED JANUARY 1995
switching characteristics (see Figure 1)
PARAMETER
FROM
((INPUT))
TO
(OUTPUT)
(
)
tPLH
tPHL
D
Q
tPLH
tPHL
LE
Q
OERB
D
ten‡
tdis§
VCC = 4.5 V to 5.5 V,
CL = 50 pF,
TA = MIN to MAX†
MIN
MAX
4
17
5
24
6
26
8
26
4
21
ns
19
ns
4
OERB
D
† For conditions shown as MIN or MAX, use the appropriate value specified under recommended operating conditions.
‡ ten = tPZH or tPZL
§ tdis = tPHZ or tPLZ
4
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UNIT
ns
ns
SN74ALS990
8-BIT D-TYPE TRANSPARENT READ-BACK LATCH
SDAS027B – APRIL 1984 – REVISED JANUARY 1995
PARAMETER MEASUREMENT INFORMATION
7V
S1
1 kΩ
Test
Point
From Output
Under Test
CL
(see Note A)
CL
(see Note A)
500 Ω
LOAD CIRCUIT FOR Q OUTPUTS
1 kΩ
LOAD CIRCUIT FOR D OUTPUTS
3.5 V
Timing
Input
Test
Point
From Output
Under Test
1.3 V
3.5 V
High-Level
Pulse
1.3 V
1.3 V
0.3 V
0.3 V
tw
th
tsu
3.5 V
Data
Input
1.3 V
1.3 V
0.3 V
VOLTAGE WAVEFORMS
SETUP AND HOLD TIMES
1.3 V
0.3 V
3.5 V
Output
Control
(low-level
enabling)
1.3 V
tPHL
tPLH
VOH
1.3 V
1.3 V
tPHL
Out-of-Phase
Output
(see Note B)
Waveform 1
S1 Closed
(see Note C)
VOL
tPLH
VOH
1.3 V
1.3 V
VOL
VOLTAGE WAVEFORMS
PROPAGATION DELAY TIMES
1.3 V
0.3 V
tPZL
1.3 V
tPLZ
0.3 V
In-Phase
Output
1.3 V
VOLTAGE WAVEFORMS
PULSE DURATIONS
3.5 V
1.3 V
Input
3.5 V
Low-Level
Pulse
[3.5 V
1.3 V
tPHZ
tPZH
Waveform 2
S1 Open
(see Note C)
VOL
0.3 V
VOH
1.3 V
0.3 V
[0 V
VOLTAGE WAVEFORMS
ENABLE AND DISABLE TIMES, 3-STATE OUTPUTS
NOTES: A. CL includes probe and jig capacitance.
B. When measuring propagation delay times of 3-state outputs, switch S1 is open.
C. Waveform 1 is for an output with internal conditions such that the output is low except when disabled by the output control.
Waveform 2 is for an output with internal conditions such that the output is high except when disabled by the output control.
D. All input pulses have the following characteristics: PRR ≤ 1 MHz, tr = tf = 2 ns, duty cycle = 50%.
Figure 1. Load Circuits and Voltage Waveforms
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PACKAGE OPTION ADDENDUM
www.ti.com
14-Oct-2022
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
SN74ALS990DW
ACTIVE
SOIC
DW
20
25
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
ALS990
Samples
SN74ALS990DWR
ACTIVE
SOIC
DW
20
2000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
ALS990
Samples
SN74ALS990N
ACTIVE
PDIP
N
20
20
RoHS &
Non-Green
NIPDAU
N / A for Pkg Type
0 to 70
SN74ALS990N
Samples
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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