DS90LV027AQ-Q1: Help with start-up time and device functionality

Alexander Tarasov78

Part Number: DS90LV027AQ-Q1

Hello,

I have a question about a start-up time as well as the mode of operation of this device. In the datasheet, it says that during the power-off event, the outputs will be in a high-z state. I'm planning to use this part (driver) and a receiver for a long(ish) SPI communication off-board (around 1.2 meters) with 4 slave devices daisy-chained on the data line (MISO). There will be only one slave talking to the master MCU on the data at a time. Each slave will talk sequentially 1 through 4 and then the data acquisition cycle will repeat complete and start all over.

I wanted to find out if I could use the high-z state feature of this LVDS driver to bring up the outputs of all slave boards that are not talking at the moment to the high-Z to avoid possible data corruption issues. However, I cannot find the start-up time for this part (start-up to valid output) parameter in the datasheet. Can you please help me with this?

Also, I'd like to know if it's in general a good idea to operate this device in a constant on/off cycle mode for high-z impedance purposes as far as the reliability is concerned.

My data rate is around 220ms per acquisition cycle and each slave device will talk on the line for roughly 50ms. In between the devices talking, the line is unused (floating)

Thank you

Alexander

over 4 years ago

0 Ikechukwu Anyiam over 4 years ago

TI__Mastermind 35130 points

Hi Alexander,

Power-on timing is not specified for this device, but it takes a couple of ms for the outputs to be active after power up. There's no reliability concerns for constant on/off cycling.

Regards,

I.K.

0 Alexander Tarasov78 over 4 years ago in reply to Ikechukwu Anyiam

Prodigy 80 points

Hi I.K,

Thank you for the clarification. I also wanted to ask, what is the output state of this driver when its input is inactive, as in the input is high-z? I could not find the definition in the datasheet. Is the output floating?

This is actually the reason why I want to power up/down the device because I don't know how it behaves with the high-z input.

Thank you

Alexander

0 Ikechukwu Anyiam over 4 years ago in reply to Alexander Tarasov78

TI__Mastermind 35130 points

Hi Alexander,

The outputs will be active when the device is powered on, regardless of whether or not there is an input. For example, assuming the input is inactive at 0V, this means the driver input will be stuck at the input low voltage, so the driver outputs will be stuck at their respective high/low voltages (the non-inverting input will be ~1.1V and the inverting output will be ~1.4V).

Regards,

I.K.

0 Alexander Tarasov78 over 4 years ago in reply to Ikechukwu Anyiam

Prodigy 80 points

Hi I.K.,

Okay, so, I guess then for my application if I want to only have one device talking on the data line, I'd have to in fact power off all the rest inactive drivers so they don't sit at their high/low outputs and become high-z instead, right?

Thank you

Alexander

0 Ikechukwu Anyiam over 4 years ago in reply to Alexander Tarasov78

TI__Mastermind 35130 points

Hi Alexander,

Yep, if you don't want the outputs sitting at their respective high/low with inactive inputs, you should power the devices off.

Regards,

I.K.

0 Alexander Tarasov78 over 4 years ago in reply to Ikechukwu Anyiam

Prodigy 80 points

Thanks!

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DS90LV027AQ-Q1: Help with start-up time and device functionality