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AN214 Datasheet

74F Extended Octal-Plus Family Applications

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74F extended octal-plus family applications
June 1988
(Revised June 1996)
Page 1

Philips Semiconductors
74F extended octal-plus family applications
Application note
74F Extended Octal-Plus Family Features
8-, 9-, and 10-bit “Light-Load” bus products
With and without latches or registers
With and without 8-bit parity checker/generator
With and without dual registers
With and without 8-bit parity checker/generator
Patented “Light-Load” inputs:
Input Current
= ±20µA per input
Transceiver I/O pins = ±70µA
High performance output drive currents:
IOL = 64mA/48mA @ ±5%/10% VCC
IOH = –15mA/–3mA @ ±5%/10% VCC
“Flow-through” or “broadside” I/O pin configuration
Ideal for MOS CPU, peripherals and semi-custom bus interface
24-pin, 300mil-wide, plastic slim-DIPs
High performance buffers — tP(max) = 7.5ns
High performance latches/registers — fT = 100MHz
The 74F Extended Octal-Plus Family incorporates all of the latest
Philips Semiconductors octal, 9-bit and 10-bit buffer, transceiver,
latch and register functions. all devices in this family utilize the
Philips Semiconductors patented “Light-Load” NPN, ±20µA input
current structure and have “flow-through” or “broadside” input/output
pin configurations where the inputs and outputs are lined-up on
opposite sides of a standard 24-pin Slim-DIP package. The
“light-load” inputs, “broadside” design and high functional
density/performance of the family make this product line ideal for
buffering the limited drive capabilities of standard, custom and
semicustom MOS VLSI devices to the rigorous environments of
today’s leading edge high performance logic designs. The family
also is an excellent choice for all general interface applications.
“Flow-Through” Design
The “flow-through” or “broadside” chip layout/package design is
illustrated in Figure 1 showing the block diagrams and pin
configurations of the 74F828 10-bit Inverting buffer. Note that all of
these “broadside” designs allow logic signals to flow into one side
and out of the other without crossing or folding back on signal paths
such as the 74F240 Octal Buffers (Figure 2). If you compare the
physical layout requirements of the path of PC board bus lines for
the 74F828 to that of the 74F240’s “zig-zag” path, you will see the
significant advantages of the 74F Extended Octal-Plus Family’s
“flow-through” design in simplifying the design and layout of large,
high density, bus-oriented PC boards.
The 24-pin, 300mil-wide, Slip-DIP Solution
With the advent of advanced Schottky TTL technology came the
ability to significantly increase the functional density of standard
logic building blocks. However, not until the development of the
24-pin, 300mil-wide, Slim-DIP package was it possible to take full
advantage of these new chip densities. The entire family provides
significant advantages in package count, pin count and packing
density when compared to older technologies. Further density
enhancements can be achieved by using Philips surface mounted
By combining high functional density into a 24-pin 300mil-wide
Slim-DIP package, the Philips Semiconductors 74F Extended
Octal-Plus Family allows the reduction of PC board parts count and
cost while optimizing layout with “broadside” chip designs, reducing
total system power dissipation and increasing system reliability.
OE0 1
D0 2
D1 3
D2 4
D3 5
D4 6
D5 7
D6 8
D7 9
D8 10
D9 11
GND 12
24 VCC
23 O0
22 O1
21 O2
20 O3
19 O4
18 O5
17 O6
16 O7
15 O8
14 O9
13 OE1
Figure 1. 74F828 Broadside Pin Configuration
OEa 1
Ia0 2
Yb0 3
Ia1 4
Yb1 5
Ia2 6
Yb2 7
Ia3 8
Yb3 9
GND 10
20 VCC
19 OEb
18 Ya0
17 Ib0
16 Ya1
15 Ib1
14 Ya2
13 Ib2
12 Ya3
11 Ib3
Figure 2. 74F240 ’Zig-Zag” Pin Configuration
June 1988
2 Revised: June 1996
Page 2

Philips Semiconductors
74F extended octal-plus family applications
Application note
D5 D6
Q8 Q9
R5 R6
5K 6K
Q4 Q6
D2 Q3
R2 R3
50 10K
1) If IOH/IOL =
R14 =
R11 =
R10 =
R12 =
2) If IOH/IOL =
R14 =
R11 =
R10 =
D12 R12 =
–15/64 mA
–3/24 mA
Figure 3. 74F455 Buffer/Drive Cell Circuit Diagram
The 8-, 9-, and 10-bit Series 24-pin Solution
Whether your system requires an 8–, 9-, or 10-bit bus interface, the
Extended Octal-Plus Family has standardized solutions in
24-pin/Slim-DIP/Broadside input/output packages with corner power
supply pins (12 & 24) and standard designations for common control
functions located at or near the package corners. Octals offer more
mode control inputs than do the 9- or 10-bit products. Virtually all
family devices with 3-State outputs are guaranteed to source/sink
–15/64mA @ VOH/VOL = 2.0/0.55V (except for the 74F841–846
Latched Drivers, which are spec’ed at –15mA/48mA). The AN port
outputs of several of the family’s transceivers are guaranteed to
supply –3mA/48mA).
The Octal Parity Bus Series offers several notable exceptions to the
above standard pinouts. This series has three parts with two
center-package ground pins to minimize ground-bounce noise. All
outputs (except the AN port of the 74F657 Parity Bus Transceiver
spec’ed at –3mA/24mA) are guaranteed to source/sink more than
Current PC board, multi-layer technology make is possible to take
into consideration the physical location of input/output pins,
transmission line characteristics and supply power distribution.
Lining up all inputs and output on opposite sides of the package
allows the address, data and control bus signal to flow in a direct
physical path from the µP CPU through the bus interface chips and
onto the appropriate bus. This “broadside” bus design approach
produces very clean PC board layouts and may, in fact eliminate
and entire PC board interconnection layer. Standardization of power
supply, mode control and input/output pins, whether 8-, 9-, or 10-bit
bus functions, permits simplified, structured PC board layout.
Input Structures
Referring to Figure 3, the 74F455 Inverting Buffer/Driver Cell Circuit
Diagram is an example of the family’s input and output circuitry. The
patented Philips Semiconductors “Light-Load” NPN input structure
(Q1/23/4/5, R1/2/3/4/5/6 and D4) and turn-OFF speed-up circuit (Q2
and D2/3) are used throughout the 74F Extended Octal-Plus Family.
the “Light-Load” NPN input is actually a high speed, differential
amplifier with the reference side, the anode of D4, clamped at two
diode voltage drops above ground (BE junctions of Q8/9/10 and Q
11 of 1.4V at 25°C). When the VIH rises above this clamp voltage,
the BE junction of Q1 is forward based allowing beta amplified, CE
current to flow into the <1.0mA constant current source, Q3 (driven
by Q4/5 and R2/3/4/5/6). The beta of Q1 is guaranteed, by design,
to be >50, thereby guaranteeing that the input base bias current will
be <20µA. The emitter of Q1 rises to 1VBE (300mV) below the
VIH, reverse biasing D4 and permitting C8/9/10 base bias current to
flow through R1.
The patented turn-OFF circuit consisting of Q2 and D2/3 produces a
dynamic speed to help turn Q8/9/10 OFF quickly. During the time
that the Q1 is turned-ON (input = VIH >2.0V), the revers-biased
Schottky diode, D2, acting as a capacitor, will be charged to the
voltage at the emitter of Q1A or 1VBE voltage drop below the input
(>2.0 – 1VBE). When the input is switched to <VIL (or <0.8V), the D2
stored charge discharges through the BE of Q2. Q2 CE current
through D3 rapidly turns Q8/9/10 OFF.
These circuit innovations produce high performance, very low input
bias current (±20µA) gate inputs. This input leakage represents a
30X reduction over the standard 74F family’s 600µA input current
with virtually no loss in speed. The 74F Extended Octal-Plus
June 1988
Page 3

Philips Semiconductors
74F extended octal-plus family applications
Application note
Transceivers have an input loading current of ±70µA, which is the
combination of the “Light-Load” NPN input structure’s ±20µA and the
3-State Hi-Z output’s ±50µA leakage current.
The low “Light-Load” input current and high speed performance
makes this family ideal for interfacing to low drive capability, slower
MOS CPU, peripherals and semi-custom chips used in most of
today’s state-of-the-art logic designs. Besides very low input current
requirements, this “Light-Load” input has another significant
advantage over “traditional” input structures: Very low input
capacitance (smaller stored charge) due to very small device
geometries. Therefore, when Extended Octal-Plus devices are
connected to a bus, they present less AC bus loading and do not
significantly lower the characteristic impedance of the bus to the
extent “traditional” input structures do. Thus, the amount of the AC
current a bus driver has to produce to change the state of the bus is
lowered and in many cases can make a difference between incident
wave switching of the bus versus losing time waiting for a reflected
The Philips Semiconductors 74F “Light-Load” input structure is
discussed in more detail in Application Note AN215.
Output Drive Capabilities
Virtually all devices in the EXtended Octal-Plus Family are
guaranteed to source/sink more than –15mA/64mA @ VOHVOL =
2.0/0.55V. One exception is the 74F841-thru-846 Series of Bus
Interface Latches which are specified at –15/48mA. Several of the
family’s transceiver products have lower AN output drive capabilities
to reduce package power dissipation. Refer to Tables 1 and 3.
For example, the 74F657 Parity Bus Transceiver has two output
ports with different capacities: The AN port is guaranteed to
source/sink –3mA/24mA (IOH/IOL = 2.4/0.50V), and the BN port has
an output drive capability of –15mA/64mA at 2.0V/0.55V. The
74F657’s AN port is designed to interface the chip side of the PC
board to the backplane bus, while the BN port is capable of driving a
transmission line or bus backplane line.
Referring to Figure 3, all of the Family’s 3-State, totem-pole output
structures have a schottky blocking diode, D13, in their pull-up
output structures. These diodes block leakage current from flowing
into the outputs when VCC is either open or shorted to ground.
This gives a very important advantage of being able to power down
a PCB (or several PCBs) without disabling the bus and even without
producing any glitching on the bus due to an undesired change in
the output state of the device being powered down.
The output short-circuit (IOS) limiting resistor (R14), the
anode-to-cathode resistance/voltage drop of D13 and the
collector-to-emitter/base-to-emitter resistance/voltage drop of Q13
limit the amount of current that can be sourced from a HIGH level
output at a specified VOH. For most of the parts in the family, R14 is
equal to 12. the AN port of several of the transceivers utilize an
R14 of 30producing IOH (@ VOH = 20V) of –6mA versus –15mA
from the BN ports 12R14.
The output HIGH level sourcing current, IOH, at a specified output
voltage, VOH, can be calculated by subtracting the voltage drops of
D13, the pull-up darlington transistor, Q12/13, and the desired VOH
level from VCC and dividing by the value of R14 plus the
anode-to-cathode resistance of D13 and the collector-to-emitter/
base-to-emitter resistance.
VD13 ^ 0.5V @ RON = 3@ 25°C),
VQ12/13 ^ 1.2V @ RON = 8@ 25°C)
IOH = 1[VCC–(VD13 + VQ12/Q13 + VOH)]/(R14 + RD13 + RQ13).
IOH(R14 = 12) = –[4.5V–(0.5V + 1.2V + 2.0V)]/23= –35mA
IOH(R14 = 30) = –[4.5V–(0.5V + 1.2V + 2.0V)]/41= –20mA
IOS = IOH @ VOH = 0.0V and VCC = 5.5V
IOS(R14 = 12) = –[5.5V–(0.5V + 1.2V)]/23= –165mA
IOS(R14 = 30) = –[5.5V–(0.5V + 1.2V)]/41= –93mA
Obviously, we have been very conservative in the IOH specification
to guardband against all conditions of temperature and
input/output/supply voltage levels. The RON resistances of the
output pullup transistors and blocking diode are large enough to
prevent IOS from exceeding –225mA for R14 = 12and –150mA for
R14 = 30. (Refer to Table 1.)
Table 1. Family Output Drive Capabilities Using the 74F657 Parity Bus Transceiver
Over recommended operating conditions, VIL = MAX and VIH = MIN)
IOH = –3mA ±10% VCC
All outputs
IOH = –3mA ±5% VCC
2.7 3.4
VOH High-level output voltage
IOH = –15mA ±10% VCC
BN port, PARITY, ERROR IOH = –15mA ±5% VCC
IOL = 24mA ±10% VCC
AN port
IOL = 24mA ±5% VCC
VOL Low-level output voltage
IOL = 48mA ±10% VCC
BN port, PARITY, ERROR IOL = 48mA ±5% VCC
0.35 0.50
0.35 0.50
0.40 0.55
0.40 0.55
AN output High level short circuit current (R14 = 30)
IOS BN output High level short circuit current (R14 = 12)
June 1988
Page 4
Part Number AN214
Manufactur Philips
Description 74F Extended Octal-Plus Family Applications
Total Page 14 Pages
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