DS34LV87T: DS34LV87T

We don't have the char data for this device anymore (it was made in 2006 and I think it was done by National Semi which we bought out). 

I would probably need to order a break out board and perform the measurement manually. This would probably take a week or 2 to get the parts and board and another day to test. Are you able to wait that long for the data?

-Bobby

Hello Bobby, one week is ok fro me, thank you for support to give the Driver High-Level Output Voltage vs High-Level Output Current/ Driver Low-Level Output Voltage vs Low-Level Output Current and Figure of Driver Differential Output Voltage vs Output Current for me; 

by the way, i want to know the Figure which i mentioned above is the worst data? (means i get the Vo from the relevant output current , it will be ok for me to do the worst case calculation?)

?? ? said:

by the way, i want to know the Figure which i mentioned above is the worst data? (means i get the Vo from the relevant output current , it will be ok for me to do the worst case calculation?)

The worst data is when there is more current draw. The higher the current the larger the VoL or lower the VoH is which would lower the total VoD (VoH-VoL). Do you just want me to measure at around 100mA instead of the incremental steps that the figures use? 

In my opinion, data outside of 60mA is probably overkill in a normal RS485 application. Normally you are driving a 60 ohm load (or 100 ohm load for RS422) which would likely have 60 mA or less of current (this device shows 26mA drive for 100 ohms typical). So the electric characteristic of VOD2 is normally enough to know the device's drive in normal conditions. (This device will output a typical VoD of 2.6V under a 100 ohm load which is higher than the minimum RS422 standard of 2V). 

I'll need to work with my Admin to see if we can get a breakout board ordered. Usually takes a week to receive it, sometimes a little longer. I'll update you when I get it.

-Bobby

Hello Bobby，I think I needs to describe my question more clearly，sorry for misunderstanding. Take SN65176B for example, in the Io=30mA, in the Figure 6-3 for example; the Vo is about 2.8V; I want to know whether the min vo is 2.8V in the Io=30mA？

Hello，the  Vo of PIN10 and PIN11 will out put the REA_CLK_L and REA_CLK_H to drive the optocoupler, the guarantee drive current of the optocoupler s 5mA; the circuit of optocoupler LED supply total 178Ω; as you know, if the min output Vo of DS34LV87TM is 2V, LED voltage drop of optocoupler is 1.4voltage,  the current equal to (2V-1.4V)/178Ω=3.26mA＜5mA；so，  maybe you can give me the min Vo when output is 5mA; it can solve my question

I probably wouldn't be able to provide an absolute min voltage since that usually takes 30x units across temperature and also run through design simulations with different silicon doping levels to verify a min with a 6 sigma standard deviation. 

The best I could do is measure a few units at room temp at whatever current load you want. I could set up a resistor that equals 5mA or 10mA and see what the VoD is.

But this would be a DC measurement. I assume your signal is going to be flipping/switching so the AC component of this would also play a part. If the switching is too fast, the VoD may not get high enough to turn on the LED in your circuit because of the RC constant. The LED would probably also create a unsymmetric waveform (When LED is on the load is smaller when LED is off the load is much larger). If you're communicating through cabling then this would create reflections since the impedance is changing. 

1) Are you trying to transmit through a cable or is this onboard communication?

2) Are you planning on keeping those 1000pF caps? They add a large AC load (RC constant) which would affect the switching frequency

3) How fast are you planning to switch this clock signal?

Clemen's suggestion may be a easier solution if you're not married to that optocoupler/design. Using a simple digital signal rather than a differential signal would make this easier. TI likely has a isolation device that could fit the bill if the signal is TTL instead of differential. 

-Bobby

Using two lines per optocoupler (even if one of them is connected to constant 3.3 V at the source) still results in a differential current flow.

Hello, The optocouple is this circuit function is to isolate the signal to delivery the RS-422 signal better. my purpose as above is to know the min voltage when the DS34LV87T output current is 5mA; could you please tell me after test?

By the way, I want to know whether the relevant voltage is the min voltage reflecting on Figure of Driver differential output voltage vs output current.

it maybe more function to guide the circuit design

Hello, I will consider your suggestion and give the feedback to our team; by the bay. As for the reply as follow, could you please give the feedback of -20℃/100℃ Vo， not only the room temperature:

I can provide you with a typical VoD for 5mA at room temperature for a few units.

?? ? said:

Hello, I will consider your suggestion and give the feedback to our team; by the bay. As for the reply as follow, could you please give the feedback of -20℃/100℃ Vo， not only the room temperature:

I can try.... renting a thermal stream may add additional delays (set up on these also can be tricky to minimize air leaks). Some thermal streams don't support cold temperature so we may need to try to locate one that does.... Generally though, higher temperatures increase Vth of FETs and Ron of FETs can double around 100C. So looking at the colder temperature likely wouldn't be necessary when the worst case would be at higher temp for a DC measurement like this. 

Even if the device supports the VoD you are looking for, we're only looking at the DC performance of the part. Not the AC portion of the system which could fail (as I stated in my post on August 9th).

-Bobby

Just an update, I've received the 16 pin SOIC breakout boards from my Admin. I'm waiting on the DS34 devices to arrive, I received an email stating they were shipped yesterday. 

-Bobby

Sorry the delay, I just received the units about an hour ago. I've soldered them but won't be able to test today. I will be out of the office next week but one of my coworkers will take the measurements next week in my place. They should get back to you then.

-Bobby

OK. Thank you for your great support. 

Hi,

I am just writing to give a brief update. Unfortunately - we are limited in our teams bandwidth this week for a few urgent issues that have popped up and since Bobby is out for the week we are short a person. Originally we thought we had the bandwidth to support this testing this week, but it most likely going to be postponed until next week. I am very sorry for the delay and we haven't forgotten about the issue. 

I will note that when we are able to get data next week - it's not guaranteed and shouldn't be read as such.

Once again I am really sorry for the further delay and we really do appreciate your patience  - but we should be able to finish testing next week when we have more resources available for the lab testing. 

Best,

Parker Dodson

It is OK for me，Thank you for your great support