LMH2180SDEVAL

User's Guide SNAA053B – January 2008 – Revised May 2013 AN-1776 LMH2180 Evaluation Board in WSON 1 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. 2 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. 3 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 Table 1. Table 1. States of LMH2180 4 Channel On Enable1 Enable2 IN1 to OUT1 High Don't Care IN2 to OUT2 Don't Care High 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. To ensure a clean supply voltage, it is best to place decoupling capacitors close to the LMH2180, between VDD and VSS. 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. All trademarks are the property of their respective owners. SNAA053B – January 2008 – Revised May 2013 Submit Documentation Feedback AN-1776 LMH2180 Evaluation Board in WSON Copyright © 2008–2013, Texas Instruments Incorporated 1 Layout Considerations www.ti.com JR1 R4 510 kÖ JP1 GND C5 100 nF VDD IN1 tp1 J1 U1A C3 2 R3 OPT 10 nF 8 1 7 5 GND R1 C1 10 PF + JP2 VDD C2 100 nF tp2 OUT1 J2 C4 OPT R2 30 kÖ VDD IN2 tp3 J3 U1B C6 3 R6 OPT 10 nF 4 1 6 5 GND VDD C8 JR2 R5 tp4 OUT2 J4 R7 30 kÖ 100 nF C7 OPT R8 510 kÖ Figure 1. Schematic of the Evaluation Board Figure 2. Layout of the Evaluation Board The Bill of Material (BOM) of the evaluation board is given in Table 2. 2 AN-1776 LMH2180 Evaluation Board in WSON SNAA053B – January 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Measurement Procedure www.ti.com Table 2. Bill of Material 5 Designator Description Comment R1, R5 0603 Resistor 0Ω R2, R7 0603 Resistor 30 kΩ R3, R6 0603 Resistor Optional R4, R8 0603 Resistor 510 kΩ C1 Case B, Tantalum Capacitor 10 µF 16V C2, C5, C8 0603 Capacitor 100 nF C3, C6 0603 Capacitor 10 nF C4, C7 0603 Capacitor Optional JR1, JR2 Jumper Header 1x3 J1, J2, J3, J4 Connector SMA JP1 Power Connector pin 1.5 mm, Black JP2 Power Connector pin 1.5 mm, Red U1 WSON-8 LMH2180 Measurement Procedure The performance of the LMH2180 can be measured with the setup given in Figure 3. VDD Power Supply GND VDD 4395A Network Analyzer Source 41800A Active Probe JR1 J1 LMH2180 Eval Board 4395A Network Analyzer Input tp2 GND Figure 3. Measurement Setup A supply voltage between 2.5 V to 5.0 V can be set by an external power supply connected to the JP2 (Red) VDD pin and JP1 (Black) GND pin. In order to test its functionality, the buffer is tested by looking at the frequency response. Make sure to enable the buffer that has to be evaluated. The frequency response is tested by using a network analyzer (4395A). For small signal bandwidth evaluation, the source input should be set at −16 dBm. Be aware to measure the output of the buffer with the probe directly connected to TP2 or TP4 to measure the highest available bandwidth. SNAA053B – January 2008 – Revised May 2013 Submit Documentation Feedback AN-1776 LMH2180 Evaluation Board in WSON Copyright © 2008–2013, Texas Instruments Incorporated 3 Measurement Results 6 www.ti.com Measurement Results Figure 4 shows the frequency response of the LMH2180 at 2.7 V and 5.0 V power supply and a source input of VIN = 0.1VPP (−16 dBm @ 50 Ω). 6 2.7V 3 GAIN (dB) 0 -3 5V -6 -9 -12 VIN = 0.1VPP -15 100k 1M 10M 100M FREQUENCY (Hz) Figure 4. Frequency Response 4 AN-1776 LMH2180 Evaluation Board in WSON SNAA053B – January 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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