SN65LBC180-Q1: Output Voltage Range

Sakai-san,

Thanks for reaching out. Not all of the pins out listed are output pins. I hope this drawing I made helps visualize the data/logic flow across this device:

Ravi is absolutely correct. Figure 8 and Figure 14 provide overviews of the change in high-level output voltage for the driver and receiver respectively across different output current loads. Here is some additional information using only the “typical” values listed on the datasheet’s electrical characteristics sections:

Output differential voltage V_OD = V_Y – V_Z

When D (“Driver”) is high at 3.3V, you can expect an output of High at Y and Low at Z. This would give a positive V_OD. According to the datasheet, you can expect a typical V_OD of 2 V with 60 Ω termination R_L (and a typical V_OD of 2.5 V with 54 Ω termination R_L). Since this device has a typical common-mode voltage of 2.5 V, you can expect V_Y around 3.5 V and V_Z around 1.5 V. Keep in mind, however, that the figure of merit is differential voltage V_OD.

According to my estimations:

Input differential voltage V_ID = V_A – V_B

The output at R (“Receiver”) is determined only by the input differential voltage V_ID. The voltages at A or B are not independently relevant to the output at R – just the difference between the two (provided the absolute maximum conditions of the device are satisfied). Thus, you can use the logic table on the datasheet along with the receiver electrical characteristics to determine its behavior:

I hope this helps. Let me know if you have any further questions.

Best,

Danny

Sakai-san,

Great to hear from you. I believe I see what your customer is asking. Let me know if I misunderstand.

“The customer considers that when power is applied, a constant voltage is generated even at the input terminal.”

Even though A and B are input terminals, they may present a resting voltage when the device is powered and nothing is connected to the bus. Page 3 of the datasheet shows some schematics of the inputs and outputs. My [very quick and rough] estimation is that the customer may be seeing at least 30% of V_CC on A and B when the device is powered but these pins are left floating. Note that, in normal operation, these pins would not be left unconnected/floating.

“He wants to know the voltage range from min to max. (What is the voltage range of A and B, which are the input terminals?)”

If your customer is asking what the absolute maximum and minimum permissible values are for A and B, along with the other pins, the answer is that the pins can sustain between -10 V and +15 V with respect to GND before the device is expected to sustain damage. For proper operation, however, these are the recommended conditions:

• Voltage at any individual terminal A, B, Y, Z should remain between -7 V and 12 V with respect to GND.
• Differential input voltage between A and B (V_ID) should remain between -6 V and 6 V.
• Voltage at D, R, DE, RE should range from GND to V_CC. “Low” inputs should range from GND to 0.8 V, while “high” inputs should range from 2 V to V_CC.

Please let me know if I can help in any other way regarding this device’s operation.

Best,

Danny

Sakai-san,

You're correct. This is no issue. Just keep in mind that these pins are intended to be used as inputs, so the voltage generated when these pins are left open is irrelevant to their normal operation. Here is a typical application of this device:

Note that these transmission line pins are not left floating in application.

Regarding your 30% question, this is entirely expected. My brain neglected to account for the threshold voltages of the diodes in the equivalent schematics, so an open-circuit voltage of greater than 30% is completely expected and totally fine. I have updated my prior post to reflect this correctly.

Best,

Danny