ONET1151M: I/O coupling and drive

xjonathanx xdufourx

Part Number: ONET1151M
Other Parts Discussed in Thread: ONET1130EC

Hi, I have some questions about the ONET1151M:

1.) According to the datasheet, the internal modulation path appears DC-coupled. If this is true, is the tau of the coupling caps what limits the max ON time? Are there other time-out constants internal to the driver that would limit ON time? Is there a minimum input toggle rate; can it do single-shot?

2.) The datasheet block diagram (figure 1) shows an internal active back termination for the modulated output differential pair. The datasheet application schematic (figure 5) shows additional OUT+ and OUT- pull-up inductors tying to Vcc. Why are the external pull-up inductors necessary?

3.) Is the modulation current limit 35mA, long-term? The datasheet mentions the requirement to AC-couple inputs and outputs, is there a thermal / dissipation limit too, or is the coupling-cap requirement to accommodate internal bias voltage offsets with respect to the outside world?

4.) I'm unclear about whether the ONET1151M inverts. If the input goes from logic FALSE to TRUE, what is the polarity of the transition on OUT+ ?

Thanks for your exceptional help, J

over 6 years ago

0 Nasser Mohammadi over 6 years ago

TI__Guru* 93570 points

Greetings,
While I am looking into your questions above, can you please let me know if ONET1130EC would meet your application requirements? You can bypass CDR of ONET1130EC and I thought this would meet your requirement. Please let me know.
Regards,,nasser

0 xjonathanx xdufourx over 6 years ago in reply to Nasser Mohammadi

Prodigy 240 points

Thanks for sending the ONET1130EC reference; will it pass signal to TXOUTwith just Vcc applied, no digital?

I'm looking for a driver that doesn't require me to toggle the digital interface lines to operate. It looks like the ONET1151M will pass signal from the DIN+/DIN- inputs to the MOD+/MOD- outputs with only Vcc, no serial loading required. Another advantage of the ONET1151M is the analog AMP control. -J

0 Nasser Mohammadi over 6 years ago in reply to xjonathanx xdufourx

TI__Guru* 93570 points

For input equalization or pre-emphasis settings in either case - ONET1151M or ONET1130EC we need a small controller to setup the device. You can consider MSP430 controller for this task. ONET1130EC device has evaluation board that you can use to check / verify your design before you do your own board. You can mount your own TOSA and ROSA and do your evaluation.
Regards,,nasser

0 xjonathanx xdufourx over 6 years ago in reply to Nasser Mohammadi

Prodigy 240 points

If input EQ and pre-emphasis isn't needed, will the ONET1151M pass signal from DIN to OUT when powered up without a controller? I'm trying to avoid another controller.
Thanks.

0 Nasser Mohammadi over 6 years ago in reply to xjonathanx xdufourx

TI__Guru* 93570 points

Greetings,
It is possible.
However, I2C interface provides more flexibility and it is recommended to use this interface for performance optimization.
Regards,,nasser

0 xjonathanx xdufourx over 6 years ago in reply to Nasser Mohammadi

Prodigy 240 points

Hi Nasser,

I'm getting close to a design with the ONET1151M and need to double check the following:

1.) If the input DIN+/DIN- pulses logic TRUE, does the OUT+ signal pulse in the negative direction ?

2.) Will the ONET1151M pass signal from DIN+/DIN- to OUT+/OUT- without a controller ?

3.) What is the common-mode DC voltage at the DIN+/DIN- pins ?

Thanks for your help,

0 Nasser Mohammadi over 6 years ago in reply to xjonathanx xdufourx

TI__Guru* 93570 points

Greetings,
We do not recommend to use this part without a controller. A controller would allow us to optimize performance.

Regards,,,,nasser

0 xjonathanx xdufourx over 6 years ago in reply to Nasser Mohammadi

Prodigy 240 points

Hi,
Yes, of course, no EQ/optimization without a controller, that's understood.

The question is: Will signal pass from DIN+/DIN- to OUT+/OUT- when power is applied (and a voltage is impressed on the AMP pin).

Please, I hope you can answer this, I'm trying to design with your part.
Thanks.

0 Nasser Mohammadi over 6 years ago in reply to xjonathanx xdufourx

TI__Guru* 93570 points

Greetings,
The signal will pass through. Just want to make sure for performance optimization then we need to fine tune registers.
Regards,,nasser

0 xjonathanx xdufourx over 6 years ago in reply to Nasser Mohammadi

Prodigy 240 points

Hi, greetings,

Does the ENA bit come up true at power-up?

If not, how can I enable the ONET1151M without a controller?

I connected a sample unit per Figure 5 in the datasheet, without a controller. DIS is tied to ground to enable the chip; SCK and SDA are left floating, pulled up to +3.3Vcc via internal pullups.

The chip toggles, however I'm only seeing inverted, 10mV pk-pk, single-ended output pulses into 50-Ohms; the chip should be capable of 1.5V.

The analog AMP pin doesn't change the output, it stays 10mV pp whether 0V or +2V is applied to the pin.

Whether DIS is tied to ground (chip enable), or left floating, the output remains 10mV pp, making me suspect that the ENA (enable) bit is low.

Thanks,
J

0 Nasser Mohammadi over 6 years ago in reply to xjonathanx xdufourx

TI__Guru* 93570 points

Hi,

1). Could you please send me your schematic.
2). Also, could you please use your voltmeter and measure voltage on pin 10(BGV). What is the voltage at this point?

Regards,,nasser

0 xjonathanx xdufourx over 6 years ago in reply to Nasser Mohammadi

Prodigy 240 points

Hi Nasser,

The voltage at pin 10 (BGV) reads +1.164.

I've attached the schematic:

Here are the input and output waveforms:

Thanks,

0 Nasser Mohammadi over 6 years ago in reply to xjonathanx xdufourx

TI__Guru* 93570 points

Hi JD,

You scope has 100-ohm termination or you have two 50-ohm Resistors on board? I was expecting to see SMA connector and then your scope would have 100-ohm termination?

It is possible that ENA bit has to be set. I am checking on this and will let you know.

Regards,,nasser

0 xjonathanx xdufourx over 6 years ago in reply to Nasser Mohammadi

Prodigy 240 points

Hi Nasser,

Thanks for looking into whether and how the ENA bit is to be set to operate.

The prior-attached waveform shows the differential waveform I'm sending the DIN+/DIN- inputs, probed at the device side of the coupling caps using a FET probe.

OUT+ is terminated with 50-Ohms on-board.

OUT- feeds an SMA cable, into the 50-Ohm scope. I ran out of SMA cables to connect the OUT+ to a scope, hence only the OUT- being displayed in the waveform. The two single-ended 50-Ohms is effectively 100-Ohms, differential loading to the ONET1151M.

Much appreciated,

0 Nasser Mohammadi over 6 years ago in reply to xjonathanx xdufourx

TI__Guru* 93570 points

Hi JD,

I have checked and indeed we need ENA bit through SMBus register (reg 0x00[7] )to be set to operate the device. This was done mainly because of laser safety as well as the availability for an asynchronous disable.

Regards,,nasser

0 xjonathanx xdufourx over 6 years ago in reply to Nasser Mohammadi

Prodigy 240 points

Hi Nasser,
Thank you for confirming that ENA has to be set true in order to operate the device.
JD

Interface

Interface forum

ONET1151M: I/O coupling and drive