DS90C402 Datasheet, PDF (3/8 Pages) National Semiconductor (TI) – Dual Low Voltage Differential Signaling (LVDS) Receiver

Parameter Measurement Information
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FIGURE 1. Receiver Propagation Delay and Transition Time Test Circuit
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FIGURE 2. Receiver Propagation Delay and Transition Time Waveforms
Typical Application
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FIGURE 3. Point-to-Point Application
Applications Information
LVDS drivers and receivers are intended to be primarily used
in an uncomplicated point-to-point configuration as is shown
in Figure 3. This configuration provides a clean signaling en-
vironment for the quick edge rates of the drivers. The re-
ceiver is connected to the driver through a balanced media
which may be a standard twisted pair cable, a parallel pair
cable, or simply PCB traces. Typically the characteristic im-
pedance of the media is in the range of 100Ω. A termination
resistor of 100Ω should be selected to match the media, and
is located as close to the receiver input pins as possible. The
termination resistor converts the current sourced by the
driver into a voltage that is detected by the receiver. Other
configurations are possible such as a multi-receiver configu-
ration, but the effects of a mid-stream connector(s), cable
stub(s), and other impedance discontinuities as well as
ground shifting, noise margin limits, and total termination
loading must be taken into account.
The DS90C402 differential line receiver is capable of detect-
ing signals as low as 100 mV, over a ±1V common-mode
range centered around +1.2V. This is related to the driver off-
set voltage which is typically +1.2V. The driven signal is cen-
tered around this voltage and may shift ±1V around this cen-
ter point. The ±1V shifting may be the result of a ground
potential difference between the driver’s ground reference
and the receiver’s ground reference, the common-mode ef-
fects of coupled noise, or a combination of the two. Both re-
ceiver input pins should honor their specified operating input
voltage range of 0V to +2.4V (measured from each pin to
ground), exceeding these limits may turn on the ESD protec-
tion circuitry which will clamp the bus voltages.
Fail-Safe Feature:
The LVDS receiver is a high gain, high speed device that
amplifies a small differential signal (20mV) to CMOS logic
levels. Due to the high gain and tight threshold of the re-
ceiver, care should be taken to prevent noise from appearing
as a valid signal.
The receiver’s internal fail-safe circuitry is designed to
source/sink a small amount of current, providing fail-safe
protection (a stable known state HIGH output voltage) for
floating, terminated or shorted receiver inputs.
1. Open Input Pins. The DS90C402 is a dual receiver de-
vice, and if an application requires only one receiver, the
unused channel(s) inputs should be left OPEN. Do not
tie unused receiver inputs to ground or any other volt-
ages. The input is biased by internal high value pull up
and pull down resistors to set the output to a HIGH state.
This internal circuitry will guarantee a HIGH, stable out-
put state for open inputs.
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