Not Intended For New Designs
August 1992
11C90/11C91
650 MHz Prescalers
General Description
The 11C90 and 11C91 are high-speed prescalers designed
specifically for communication and instrumentation applica-
tions. All discussions and examples in this data sheet are
applicable to the 11C91 as well as the 11C90.
also allows power consumption to be reduced by leaving
the separate V pin open if the TTL output is not used.
EE
To facilitate capacitive coupling of the clock signal, a 400X
resistor (V
) is connected internally to the V reference.
REF BB
The 11C90 will divide by 10 or 11 and the 11C91 by 5 or 6,
both over a frequency range from DC to typically 650 MHz.
The division ratio is controlled by the Mode Control. The
divide-by-10 or -11 capability allows the use of pulse swal-
lowing techniques to control high-speed counting modulos
by lower-speed circuits. The 11C90 may be used with either
ECL or TTL power supplies.
Connecting this resistor to the Clock Pulse input (CP) auto-
matically centers the input about the switching threshold.
Maximum frequency operation is achieved with a 50% duty
cycle.
Each of the Mode Control inputs is connected to an internal
2 kX resistor with the other end uncommitted (RM and
1
RM ). An M input can be driven from a TTL circuit operating
2
In addition to the ECL outputs Q and Q, the 11C90 contains
an ECL-to-TTL converter and a TTL output. The TTL output
from the same V by connecting the free end of the asso-
CC
ciated 2 kX resistor to V
. When an M input is driven
CCA
operates from the same V and V levels as the counter,
CC EE
from the ECL circuit, the 2 kX resistor can be left open or, if
but a separate pin is used for the TTL circuit V . This mini-
EE
mizes noise coupling when the TTL output switches and
required, can be connected to V
resistor.
to act as a pull-down
EE
Logic Symbol
Connection Diagram
16-Pin DIP
TL/F/9892–2
TL/F/9892–1
Pin Names
Description
CE
CP
Count Enable Input (Active LOW)
Clock Pulse Input
M
Count Modulus Control Input
Asynchronous Master Set Input
ECL Outputs
n
MS
Q, Q
QTTL
TTL Output
RM
2 kX Resistor to M
n
n
V
REF
400X Resistor to V
BB
C
1995 National Semiconductor Corporation
TL/F/9892
RRD-B30M115/Printed in U. S. A.
NSC [ National Semiconductor ]
