Texas Instruments LMH2180 Evaluation Board in Micro SMD LMH2180TMEVAL LMH2180TMEVAL 数据表
产品代码
LMH2180TMEVAL
User's Guide
SNAA053B – January 2008 – Revised May 2013
AN-1776 LMH2180 Evaluation Board in WSON
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General Description
This evaluation board is designed to aid in the characterization of National Semiconductors' LMH2180 75
MHz dual clock buffer. This board simplifies the connection and ease of use of any oscillating input device.
Use this evaluation board as a guide for high frequency layout and as a tool to aid in device testing and
characterization.
MHz dual clock buffer. This board simplifies the connection and ease of use of any oscillating input device.
Use this evaluation board as a guide for high frequency layout and as a tool to aid in device testing and
characterization.
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Basic Operation
The LMH2180 is a device that contains two 75 MHz clock buffer amplifiers. These amplifiers are specially
designed to minimize the effects of spurious signals from the digital chip to other analog or mixed-signal
chips. The LMH2180 also minimizes the influence of varying load resistance and capacitance to the
oscillator and increases the drive capability. The buffers have a 106 V/µs internal slew rate at a supply
current of only 1.3 mA for one enabled channel and 2.3 mA for two enabled channels. Each amplifier in
the LMH2180 is capable of driving loads up to 20 pF. The input of each buffer is internally biased at 1 V.
This allows AC coupling on the input. Each buffer offers an enable pin that can be used to disable the
corresponding channel and to optimize consumption.
designed to minimize the effects of spurious signals from the digital chip to other analog or mixed-signal
chips. The LMH2180 also minimizes the influence of varying load resistance and capacitance to the
oscillator and increases the drive capability. The buffers have a 106 V/µs internal slew rate at a supply
current of only 1.3 mA for one enabled channel and 2.3 mA for two enabled channels. Each amplifier in
the LMH2180 is capable of driving loads up to 20 pF. The input of each buffer is internally biased at 1 V.
This allows AC coupling on the input. Each buffer offers an enable pin that can be used to disable the
corresponding channel and to optimize consumption.
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Channel Activation
Either channel can be independently enabled or shut down. The enable logic can be provided to the
evaluation board by shunting a jumper on JR1 and JR2. For the required control logic, see
evaluation board by shunting a jumper on JR1 and JR2. For the required control logic, see
Table 1. States of LMH2180
Channel On
Enable1
Enable2
IN1 to OUT1
High
Don't Care
IN2 to OUT2
Don't Care
High
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Layout Considerations
Careful consideration for circuitry design and PCB layout eliminates problems and optimizes the
performance of the LMH2180. It is best to have the same ground plane on the PCB for all decoupling and
other ground connections.
performance of the LMH2180. It is best to have the same ground plane on the PCB for all decoupling and
other ground connections.
To ensure a clean supply voltage, it is best to place decoupling capacitors close to the LMH2180, between
V
V
DD
and V
SS
. On the evaluation board, capacitor C1 is placed on the bottom side.
Another important issue is the value of the components, which also determines the sensitivity to
disturbances. Resistor values have to be low enough to prevent noise coupling and large enough to avoid
a significant increase in power consumption while loading inputs or outputs to heavily.
disturbances. Resistor values have to be low enough to prevent noise coupling and large enough to avoid
a significant increase in power consumption while loading inputs or outputs to heavily.
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SNAA053B – January 2008 – Revised May 2013
AN-1776 LMH2180 Evaluation Board in WSON
Copyright © 2008–2013, Texas Instruments Incorporated