August 1996
ML65541/ML65L541
*
High Speed Octal Buffer/Line Drivers
BLOCK DIAGRAM
1
GENERAL DESCRIPTION
The ML65541 and ML65L541 are non-inverting octal
buffer/line drivers. The high operating frequency (50MHz
driving a 50pF load) and low propagation delay
(ML65541 1.7 ns, ML65L541 2 ns) make them ideal
for very high speed applications such as processor bus
buffering and cache and main memory control.
These buffers use a unique analog implementation to
eliminate the delays inherent in traditional digital designs.
Schottky clamps reduce under and overshoot, and special
output driver circuits limit ground bounce. The ML65541
and ML65L541 conform to the pinout and functionality of
the industry standard FCT541 and are intended for
applications where propagation delay is critical to the
system design.
Note: This part was previously numbered ML6581.
FEATURES
s Low propagation delay -- 1.7ns ML65541
2.0ns ML65L541
s Fast 8-bit TTL level buffer/line driver with three-state
capability on the output
s TTL compatible input and output levels
s Schottky diode clamps on all inputs to handle
undershoot and overshoot
s Onboard schottky diodes minimize noise
s Reduced output swing of 0 4.1 volts
s Ground bounce controlled outputs, typically less
than 400mV
s Industry standard FCT541 type pinout
s Applications include high speed cache memory, main
memory, processor bus buffering, and graphics cards
*This Part Is Obsolete
OE2
2
A0
18
B0
3
A1
17
B1
4
A2
16
B2
5
A3
15
B3
6
A4
14
B4
7
A5
13
B5
8
A6
12
B6
9
A7
11
B7
1
19
OE1
GND
10
VCC
20
VCC
2
ML65541/ML65L541
PIN CONFIGURATION
TOP VIEW
20-Pin SOIC, QSOP
PIN DESCRIPTION
NAME
I/O
DESCRIPTION
Ai
I
Data Bus A
Bi
O
Data Bus B
OE1 & OE2
I
Output Enable
GND
I
Signal Ground
V
CC
I
+ 5V supply
FUNCTION TABLE
OE1/OE2
A
B
H
X
Z
L
L
L
L
H
H
OE1
A0
A1
A2
A3
A4
A5
A6
A7
GND
V
CC
OE2
B0
B1
B2
B3
B4
B5
B6
B7
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
ABSOLUTE MAXIMUM RATINGS
V
CC ................................................................................
0.3V to 7V
DC Input voltage ............................. 0.3V to V
CC
+ 0.3V
AC Input voltage (< 20ns) ....................................... 3.0V
DC Output voltage .......................... 0.3V to V
CC
+ 0.3V
Output sink current (per pin) ................................ 120mA
Storage temperature ................................ 65C to 150C
Junction temperature ............................................. 150C
Thermal Impedance (
q
JA
)
SOIC ............................................................... 96C/W
QSOP ............................................................ 100C/W
L = Logic Low
H = Logic High
X = Don't Care
Z = High Impedance
3
ML65541/ML65L541
ELECTRICAL CHARACTERISTICS
Unless otherwise stated, these specifications apply for: V
CC
= 5.0 5%V, T
A
= 0C to 70C (Note 1).
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
AC ELECTRICAL CHARACTERISTICS (C
LOAD
= 50pF, R
LOAD
= 500)
t
PLH
, t
PHL
Propagation delay
Ai to Bi (Note 2)
ML65541
1.4
1.7
ns
ML65L541
1.6
2.0
ns
t
OE
Output enable time
10
15
ns
OE1, OE2 to Bi
t
OD
Output disable time
10
ns
OE1, OE2 to Bi
C
IN
Input capacitance
8
pF
DC ELECTRICAL CHARACTERISTICS (C
LOAD
= 50pF, R
LOAD
=
)
V
IH
Input high voltage
Logic HIGH
2.0
V
V
IL
Input low voltage
Logic LOW
0.8
V
I
IH
Input high current
Per pin, V
IN
= 3V
ML65541
0.5
1.5
mA
ML65L541
0.3
0.5
mA
I
IL
Input low current
Per pin, V
IN
= 0
ML65541
2.4
3.5
mA
ML65L541
0.8
1.0
mA
I
HI-Z
Three-state output current
V
CC
= 5.25V, 0 < V
IN
< V
CC
5
A
I
OS
Short circuit current
V
CC
= 5.25V, V
O
= GND
60
225
mA
(Note 3)
V
IC
Input clamp voltage
V
CC
= 4.75V, I
IN
= 18mA
0.7
1.2
V
V
OH
Output high voltage
V
CC
= 4.75V, I
OH
= 100A
2.4
V
(Notes 4 & 5)
V
OL
Output low voltage
V
CC
= 4.75V, I
OL
= 25mA
0.6
V
(Notes 4 & 5)
V
OFF
V
IN
V
OUT
per buffer
V
CC
= 4.75V (Note 4) ML65541
0
100
200
mV
ML65L541
0
200
300
mV
I
CC
Quiescent Power
V
CC
= 5.25V, f = 0Hz,
55
80
mA
Supply Current
Inputs/outputs open
Note 1: Limits are guaranteed by 100% testing, sampling or correlation with worst case test conditions
Note 2: One line switching, see Figure 3, t
PLH
, t
PHL
versus C
L
.
Note 3: Not more than one output should be shorted for more than a second.
Note 4: This is a true analog buffer. In the linear region, the output tracks the input with an offset (V
OFF
). For V
OH
, V
IN
= 2.7V.
V
OH MIN
includes V
OFF
. For V
OL
, V
IN
= 0V, V
OL MAX
includes V
OFF
Note 5: See Figure 2 for I
OH
versus V
OH
and I
OL
versus V
OL
data.
1.5V
1.5V
1.5V
1.5V
t
PHL
t
PLH
t
R
, t
F
4ns
3V
0V
3V
0V
INPUT
OUTPUT
4
ML65541/ML65L541
CH1 1.00V CH2 1.00V 10.0ns
CH1 1.00V CH2 1.00V 10.0ns
ML65541
74FCT541
Figure 1. Ground Bounce Comparison, Four Outputs Switching into 50pF Loads.
Figure 3. Propagation Delay (t
PLH
, t
PHL
) Versus Load
Capacitance, One Output Switching.
+20
0
20
40
60
80
100
120
140
160
180
200
2.5
I
OH
(mA)
V
OH
(V)
3.0
3.5
4.0
Figure 2b. Typical V
OH
Versus I
OH
for One Buffer Output.
Figure 2a. Typical V
OL
Versus I
OL
for One Buffer Output.
220
200
180
160
140
120
100
80
60
40
20
0
2.5
0.0
I
OL
(mA)
V
OL
(V)
0.5
1.0
1.5
2.0
3.0
2.5
2.0
1.5
1.0
0.5
0.0
100
30
t
pd
(ns)
LOAD CAPACITANCE (pF)
50
75
150
ML65L541
ML65541
210
190
170
150
130
110
90
70
50
10
I
CC
(mA)
FREQUENCY (MHz)
20
30
40
50
60
70
80
90
150pF
100pF
75pF
50pF
30pF
Figure 4. I
CC
Versus Frequency for Various Load
Capacitances, Four Outputs Switching.
5
ML65541/ML65L541
FUNCTIONAL DESCRIPTION
The ML65541 and ML65L541 are very high speed non-
inverting buffer/line drivers with three-state outputs which
are ideally suited for bus-oriented applications. They
provide a low propagation delay by using an analog
design approach (a high speed unity gain buffer), as
compared to conventional digital approaches. The
ML65541 and ML65L541 follow the pinout and
functionality of the industry standard FCT541 series of
buffer/line drivers and are intended to replace them in
designs where the propagation delay is a critical part of
the system design considerations. The ML65541 and
ML65L541 are capable of driving load capacitances
several times larger than their input capacitance. They are
configured so that the Ai inputs go to the Bi outputs when
enabled by OE1/OE2.
These unity gain analog buffers achieve low propagation
delays by having the output follow the input with a small
offset. The output rise and fall times will closely match
those of the input waveform. All inputs and outputs have
Schottky clamp diodes to handle undershoot or overshoot
noise suppression in unterminated applications. All
outputs have ground bounce suppression (typically
< 400mV), high drive output capability with almost
immediate response to the input signal, and low
output skew.
The I
OL
current drive capability of a buffer/line driver is
often interpreted as a measure of its ability to sink current
in a dynamic sense. This may be true for CMOS buffer/
line drivers, but it is not true for the ML65541 and
ML65L541. This is because their sink and source current
capability depends on the voltage difference between the
output and the input. The ML65541 can sink or source
more than 100mA to a load when the load is switching
due to the fact that during the transition, the difference
between the input and output is large. I
OL
is only
significant as a DC specification, and is 25mA.
ARCHITECTURAL DESCRIPTION
Until now, buffer/line drivers have been implemented in
CMOS logic and made to be TTL compatible by sizing the
input devices appropriately. In order to buffer large
capacitances with CMOS logic, it is necessary to cascade
an even number of inverters, each successive inverter
larger than the preceding, eventually leading to an inverter
that will drive the required load capacitance at the
required frequency. Each inverter stage represents an
additional delay in the gating process because in order for
a single gate to switch, the input must slew more than half
of the supply voltage. The best of these CMOS buffers has
managed to drive a 50pF load capacitance with a delay of
3.2ns. Micro Linear has produced an octal buffer/line
driver with a delay less than 1.7ns by using a unique
circuit architecture that does not require cascaded logic
gates. The ML65541 uses a feedback technique to
produce an output that follows the input. If the output
voltage is not close to the input, then the feedback
circuitry will source or sink enough current to the load
capacitance to correct the discrepancy.
Figure 5. One buffer cell of the ML65541
Q1
IN
OUT
Q2
Q7
R2
R6
R5
GND
R4
Q4
Q3
R1
R8
R3
Q5
Q6
R7
VCC
6
ML65541/ML65L541
The basic architecture of the ML65541 is shown in Figure
5. It is implemented on a 1.5m BiCMOS process.
However, in this particular circuit, all of the active devices
are NPNs -- the fastest devices available in the process.
In this circuit, there are two paths to the output. One path
sources current to the load capacitance when the signal is
asserted, and the other path sinks current from the output
when the signal is negated.
The assertion path is the emitter follower path consisting
of the level shift transistor Q1, the output transistor Q2,
and the bias resistor R8. It sources current to the output
through the 75 resistor R7 which is bypassed by another
NPN (not shown) during fast input transients. The
negation path is a current differencing op amp connected
in a follower configuration. The active components in this
amplifier are transistors Q3-Q7. R3-R6 are bias resistors,
and R1 and R2 are the feedback resistors. The key to
understanding the operation of the current differencing op
amp is to know that the currents in transistors Q3 and Q5
are the same at all times and that the voltages at the bases
of Q4 and Q6 are roughly the same. If the output is higher
than the input, then an error current will flow through R2.
This error current will flow into the base of Q6 and be
multiplied by
b squared to the collector of Q7, closing the
loop. The larger the discrepancy between the output and
input, the larger the feedback current, and the harder Q7
sinks current from the load capacitor.
A number of MOSFETs are not shown in Figure 5. These
MOSFETs are used to three-state dormant buffers. For
instance, the feedback resistors R1 and R2 were
implemented as resistive transmission gates to ensure that
disabled buffers do not load the lines they are connected
to. Similarly, there is a PMOS in series with R8 that is
normally on but shuts off for disable. Other MOSFETs
have been included to ensure that disabled buffers
consume no power.
TERMINATION
R7 in Figure 5 also acts as a termination resistor. This 75
resistor is in series with the output and therefore helps
suppress noise caused by transmission line effects such as
reflections from mismatched impedances. System
designers using CMOS transceivers commonly have to use
external resistors in series with each transceiver output to
suppress this noise. Systems using the ML65541 or
ML65L541 may not have to use these external resistors.
APPLICATIONS
There are a wide variety of needs for extremely fast buffers
in high speed processor system designs like Pentium,
PowerPC, Mips, Sparc, Alpha and other RISC processors.
These applications are either in the cache memory area or
the main memory (DRAM) area. In addition, fast buffers
find applications in high speed graphics and multimedia
applications. The high capacitive loading due to
multiplexed address lines on the system bus demand
external buffers to take up the excess drive current. The
needed current to skew the transitions between rise and
fall times must be done without adding excessive
propagation delay. The ML65541 and ML65L541 are
equipped with Schottky diodes to clean up ringing from
overshoot and undershoot caused by reflections in
unterminated board traces.
7
ML65541/ML65L541
PHYSICAL DIMENSIONS
inches (millimeters)
SEATING PLANE
0.291 - 0.301
(7.39 - 7.65)
PIN 1 ID
0.398 - 0.412
(10.11 - 10.47)
0.498 - 0.512
(12.65 - 13.00)
0.012 - 0.020
(0.30 - 0.51)
0.050 BSC
(1.27 BSC)
0.022 - 0.042
(0.56 - 1.07)
0.095 - 0.107
(2.41 - 2.72)
0.005 - 0.013
(0.13 - 0.33)
0.090 - 0.094
(2.28 - 2.39)
20
0.007 - 0.015
(0.18 - 0.38)
0 - 8
1
0.024 - 0.034
(0.61 - 0.86)
(4 PLACES)
Package: S20
20-Pin SOIC
Package: S20W
20-Pin SOIC
PIN 1 ID
SEATING PLANE
0.150 - 0.160
(3.81 - 4.06)
0.228 - 0.244
(5.79 - 6.20)
0.338 - 0.348
(8.58 - 8.84)
0.008 - 0.012
(0.20 - 0.31)
0.025 BSC
(0.63 BSC)
0.015 - 0.035
(0.38 - 0.89)
0.060 - 0.068
(1.52 - 1.73)
0.004 - 0.010
(0.10 - 0.26)
0.055 - 0.061
(1.40 - 1.55)
0.006 - 0.010
(0.15 - 0.26)
0 - 8
20
0.050 - 0.055
(1.27 - 1.40)
(4 PLACES)
1
Package: K20
20-Pin QSOP
Package: K20
20-Pin QSOP
8
ML65541/ML65L541
DS65541-01
2092 Concourse Drive
San Jose, CA 95131
Tel: 408/433-5200
Fax: 408/432-0295
Micro Linear reserves the right to make changes to any product herein to improve reliability, function or design.
Micro Linear does not assume any liability arising out of the application or use of any product described herein,
neither does it convey any license under its patent right nor the rights of others. The circuits contained in this
data sheet are offered as possible applications only. Micro Linear makes no warranties or representations as to
whether the illustrated circuits infringe any intellectual property rights of others, and will accept no responsibility
or liability for use of any application herein. The customer is urged to consult with appropriate legal counsel
before deciding on a particular application.
Micro Linear 1996
is a registered trademark of Micro Linear Corporation
Products described in this document may be covered by one or more of the following patents: 4,897,611; 4,964,026; 5,027,116;
5,281,862; 5,283,483; 5,418,502; 5,508,570; 5,510,727; 5,523,940; 5,546,017. Other patents are pending.
Intel, Pentium, PCI are registered trademarks of Intel Corporation. Mips, Alpha and Sparc are registered trademarks of Silicon Graphics, DEC and
Sun Microsystems respectively.
ORDERING INFORMATION
PART NUMBER
SPEED
TEMPERATURE RANGE
PACKAGE
ML65541CK
1.7ns
0C to 70C
20-Pin QSOP (K20)
ML65541CS
1.7ns
0C to 70C
20-Pin SOIC (S20)
ML65L541CK (Obsolete)
2.0ns
0C to 70C
20-Pin QSOP (K20)
ML65L541CS (Obsolete)
2.0ns
0C to 70C
20-Pin SOIC (S20)
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