LMH2180 75 MHz Dual Clock Buffer
January 24, 2008
LMH2180
75 MHz Dual Clock Buffer
General Description
The LMH2180 is a high speed dual clock buffer designed for
portable communications and applications requiring multiple
accurate multi-clock systems. The LMH2180 integrates two
75 MHz low noise buffers with independent shutdown pins
into a small package. The LMH2180 ensures superb system
operation between the baseband and the oscillator signal
path by eliminating crosstalk between the multiple clock sig-
nals.
Unique technology and design provides the LMH2180 with
the ability to accurately drive both large capacitive and resis-
tive loads. Low supply current combined with shutdown pins
for each channel means the LMH2180 is ideal for battery
powered applications. The LMH2180's rapid recovery after
disable optimizes performance and current consumption.
This part does not use an internal ground reference, thus pro-
viding additional system flexibility. The LMH2180 operates
both with single and split supplies.
The flexible buffers provide system designers the capacity to
manage complex clock signals in the latest wireless applica-
tions. Each buffer delivers 106 V/μs internal slew rate with
independent shutdown and duty cycle precision. The patent-
ed analog circuit of each buffer drives capacitive loads greater
than 20 pF. Each input is internally biased to 1V, removing
the need for external resistors. Both channels have rail-to-rail
inputs and outputs, a gain of one, and are AC coupled with
the use of one capacitor.
Replacing a discrete buffer solution with the LMH2180 pro-
vides many benefits: simplified board layout, minimized par-
asitic components, simplified BOM, design durability across
multiple applications, simplification of clock paths, and the
ability to reduce the number of clock signal generators in the
system. The LMH2180 is produced in the tiny 8-pin LLP solder
bump and no pullback packages minimizing the required PCB
space. National’s advanced packaging offers direct PCB-IC
evaluation via pin access.
Features
(Typical values are: V
SUPPLY
= 2.7V and C
L
= 10 pF, unless
otherwise specified.)
78 MHz
■
Small signal bandwidth
Supply voltage range
2.4V to 5V
■
-123dBc/Hz
■
Phase noise (V
IN
= 1 V
PP
,
f
C
= 38.4 MHz,
Δf
= 1kHz)
106 V/μs
■
Slew rate
2.3 mA
■
Total supply current
30 µA
■
Shutdown current
Rail-to-rail input and output
■
■
Individual buffer enable pins
■
Rapid T
on
technology
■
Crosstalk rejection circuitry
■
8-pin LLP, pin access packaging
−40°C to 85°C
■
Temperature range
Applications
■
■
■
■
■
3G mobile applications
WLAN–WiMAX modules
TD_SCDMA multi-mode MP3 and camera
GSM modules
Oscillator modules
Typical Application
30024602
© 2008 National Semiconductor Corporation
300246
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
