LMH6554: DC Coupled driver for ADS42LB69

Morning Sandeep, 

You are cross coupling the feedback paths, here is what you want to do, 

Hi Michael Steffes,

You have posted same circuit of mine, not clear on what to do.

I have designed this circuit by taking one of the post as reference, Can you please provide me a circuit with single supply for VCM of 1.9V?

input : 0 to 2V peak to peak

Freq : 3 MHz

ADC VCM : 1.9V

Regards,

B Sandeep.  

This is what your file showed, this is incorrect, attach the feedback R's to adjacent pins, not crosscoupled like you sent. 

1488.tidr604.pdf

LMH6554 datasheet pin configuration and functions page no. 3 and attached reference design for the same also showing cross coupled connection.

Please correct me i am wrong and let me know the correct method.

Attached is the reference design schematic.

Regards,

B Sandeep.

Hello Sandeep,

   It does look like for this device the pin configuration is as you have shown:

  However, this device will not be able to accept a VCM of 1.9V. The datasheet for the LMH6554 recommends a typical of +/-1.25V at +5V single supply. We can help choose another device that will be able to output the required 1.9V.

   What is your input voltage range, input frequency/signal characteristics, and gain requirements?

Thank you,

Sima 

Hi Sima,

The thread below using LMH6554 amplifier for driving ADS42LB69 with VCM of 1.9V using split supply.

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/360972/lmh6554-fully-dc-coupled-configuration-with-shifted-dual-supplies?tisearch=e2e-sitesearc

Input Voltage : 0 to 2 V peak to peak

Frequency : 3MHz

Unity Gain

Please suggest me alternate part or LMH6554 with split supply for driving ADS42LB69.

Regards,

B Sandeep.

Hello Sandeep,

   Thank you for pointing out the e2e thread! 

   I apologize for the mistake earlier, the output common-mode requirement in the datasheet table was listed for split supply of +/-2.5V. Therefore for a single supply of 5V, the output common mode range is a typical high of +3.75 and a typical low of 1.25V. The thread is showing the optimal supply configuration for best distortion performance which would be mid-supply. From the thread, Rohit sets the VS+ to 4.4 and VS- to -0.6V. Therefore, the mid-supply would be 1.9V. If distortion is a significant factor for your design; I would suggest following this supply configuration.

   It looks like the provided Tina-Ti file the output voltage is clipping due to the set gain in relation to input signal. Is your design's input signal a square wave from 0 to 2Vpp? 

Best Regards,

Sima  

Hi Sima,

It is square wave with 0 to 2V peak to peak input.

Can you provide me gain relation to input signal?

Regards,

B Sandeep.

Hello Sandeep,

  Will this design work? The gain is 1V/V and the input signal is 2Vpp square wave while Vocm is set to 1.9V for ADC interface. Gain can be reconfigured for a change in differential output voltage: 

Sandeep LMH6554_schematic.TSC

Thank you,
Sima 

Hi Sima,

I am designing amplifier circuit for ADC 1st time.

Please suggest me a circuit for 0 to 2V peak to peak input, frequency 3 MHz and VCM of 1.9V.

Regards,

B Sandeep.

Hello Sandeep,

   The above design fits your input and VCM requirements; however, are the supplies, voltage bias capabilities, and output range within your design requirements as shown in the screenshot in the previous reply.

Thank you,
Sima