LSF0204: VIL of I/O pin

Antony Lin

Part Number: LSF0204

Hi,

LSF0204 is now used for two cases as listed below with 25MHz data running on it. How can we get the Vil for these signals?

3V3 to 3V3 : Vref_B to Vref_A
3V3 to 1V8 : Vref_B to Vref_A

Thanks!

Antony

over 7 years ago

0 Dylan Hubbard over 7 years ago

TI__Mastermind 46555 points

Hi Antony,

I will advise you again to watch our Logic Minute videos following the link below. It will answer this question for you.

training.ti.com/TLM-LSF-Down

0 Antony Lin over 7 years ago in reply to Dylan Hubbard

TI__Genius 13480 points

Hi Dylan

I read the video. It looks to me, the VIL is related to the criteria when the FET will change from "turned off" to "turned on". If I understood correctly, the criteria is about Vgs>Vth or Vgs<Vth. So, some questinos as below,

Where is the S of the FET? At A-side or B-side?
What is the value of Vth?

Antony

0 Emrys Maier over 7 years ago in reply to Antony Lin

TI__Guru* 97066 points

Hi Antony,
This is a 4-port FET, S and D are defined by the voltages applied (ie V_DS must be positive to cause a current flow in the channel).

The threshold voltage is ~0.8V, however it is not required to know this to operate the device, nor is it related to the Vil spec of the device. The bias circuit forces exactly 1 threshold level drop across the bias channel, and will provide your operating threshold _if_ you configure the circuit correctly.

The LSF family of devices does not have a Vil spec (for the data channels) because it does not have a CMOS input. Once the FET turns ON, the input and output are shorted through a small resistance. The output voltage requirement will determine the Vil requirement as per this equation:

V_ol = V_il + r_on*I_ol

Note that the input low voltage, V_il, is a function of the amount of current sinking into the driver (I_ol).

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LSF0204: VIL of I/O pin