OPA2673: Using this part for driving 50 Ohm Load (One load at LVCOMS3V3 and another at LVCMOS1V8)

Hey Roshan,

The OPA2673 is a high output current feedback device - it requires a feedback R for unity gain, not shorted.

1. you need to provide headroom on the I/O pins to get your ground to +Vin swings, why not +/-6V supplies

2. For unity gain, you will need say a 549ohm feedback R for stability, no Rg to ground as you want unity gain

3. With split +/-6V supplies, your logic control at ground will give full power, not sure you need that much - but you can try powering it back later

Dear Michael

Thanks for the reply.

1.We can't provide +-6V as we have only 12V, 3.3V and 1.8V available on our board, we need to generate +-6V supply which require space and cost. So we are planning to work this on single 12V.

2.Ok We will replace R66,R69 with 549E and Rg (R68,R69) are already NU (Not to be sued).

3.We just need 100mA drive capability at 3.3V, we don't require more than that.

Kindly suggest if anything need to added or removed apart from power supply suggestion which we are planning to operate at single supply of 12V.

 Regards

Roshan

Hello Roshan,

Note that using the part in a single-supply configuration of 12V will give you an input range of 2.4V to 9.6V & an output range of around 1.2V to 10.8V. Unless you planning on adding a DC offset to your input/output you will not be able to reproduce your signal with this device. 

Best,

Hasan Babiker

Dear Hasan

We don't want to add clamping circuit which makes our circuit complicated.

I have simulated the circuit in TINA by using single 12V supply and given input clock pulse from -1.65 to +1.65V with DC offset of 1.65V which makes my clock pulse from 0 to 3.3V and  i did get the o/p clock pulse same replica of input.

We have only 3.3 and 12V supply on our baord.

Is there any Opamp or IC which  will be powered from 3.3V or 12V and can replicate input LVCMOS 3.3V 50Mhz clock at output with 50 ohm driving capability (66mA current driving capability).

Regards

Roshan

Hello Roshan,

Can you share your simulation file? What is the rise/fall time of your signal?

Best,

Hasan Babiker

Dear Hasan

I Have not saved the simulation file and now i am unable to replicate the same results.

Lets leave this OPA2673 discussion and i will start from fresh.

Can you suggest any single needed line driver IC or buffer or any other circuit through which we can drive 50 ohm load through LVCMOS3V3 50MHz clock (50% duty cycle) with minimum jitter on output  less than 2 pico second.

We have 12V, 3.3V and 1.8V on our board and we want to avoid generating any other supply.

so your apparent needs seem like they can be met by 

1. A digital device that simply translates a high impedance input to a line driver output (those exist in the serial digital video world)

2. An amplifier to replicate the digital input - and drive a matched load

one concern in both is the series output 50ohm in the PRL-444, if you need that and terminate in 50ohms you will normally lose 1/2 your swing. and the load looks like 100ohm

Used to be we would recover that matching loss with fixed gain of 2 video line drivers 

Something the OPA2832 might be of interest, that part is not fast enough and cannot support 12V supply, but there are others like it that might in the LMH product line. this was a negative rail in, RRO fixed gain of 2 version. 

Although also not being able to support a 12V supply, the LMH6612 might be another option to consider using with 3.3V. It is also negative rail in and RRO, and has a higher bandwidth than the OPA2832 although it is not a fixed gain device.

For parts that support 12V, the highest bandwidth device I could find that also meets the other requirements (I/O range, output current) is the LMH6639.

Best,

Hasan Babiker

Dear Hasan

LMH6639 will not meet our bandwidth and slew rate requirment.

1. If we will generate 5V0 from 12V0 then are there parts which can fulfill our requirement i.e. meeting bandwidth requirement along with current requirement.

2. I have found One IC SN74BCT25244 which is very old part, it is perfectly supporting 3.3V signal with sufficient current, will it support 50MHz signal as well?

Hello Roshan,

1. In terms of using an amplifier to recreate your signal, you will have more options with a 5V supply. You migh want to look into the OPA356 or LMH6611. 

2. I will move forum over to another expert to give you more info on the SN74BCT25244 or suggest a more suitable digital buffer.

Best,

Hasan Babiker

Dear Sir

Our requirement is as below for SN74BCT25244:

We will provide upto 100MHz LVCMOS 3.3.V clock with 50% duty cycle at input A of the part SN74BCT25244 and we expect O/P Y should be able to drive 50 Ohm load (66mA current ) with same copy of Input.

What will be rise  and fall time and jitter of clock at output Y ?

We need rise time and fall time in range of 1ns, also jitter of the output should be in 1ps range.

which part you suggest best suitable for our application which will satisfy 50Ohm driving capabilities along with rise time fall time and jitter performance ?