DS90LV048A_16 Datasheet, PDF (11/22 Pages) Texas Instruments – 3-V LVDS Quad CMOS Differential Line Receiver

www.ti.com
DS90LV048A
SNLS045C – JULY 1999 – REVISED JULY 2016
8.3 Feature Description
8.3.1 Fail-Safe Feature
The LVDS receiver is a high-gain, high-speed device that amplifies a small differential signal (20 mV) to CMOS
logic levels. Due to the high gain and tight threshold of the receiver, take care to prevent noise from appearing as
a valid signal.
The internal fail-safe circuitry of the receiver is designed to source or sink a small amount of current, providing
fail-safe protection (a stable known state of HIGH output voltage) for floating, terminated or shorted receiver
inputs.
1. Open Input Pins. The DS90LV048A is a quad receiver device, and if an application requires only 1, 2, or 3
receivers, the unused channel(s) inputs must be left OPEN. Do not tie unused receiver inputs to ground or
any other voltages. The input is biased by internal high value pullup and pulldown resistors to set the output
to a HIGH state. This internal circuitry ensures a HIGH, stable output state for open inputs.
2. Terminated Input. If the driver is disconnected (cable unplugged), or if the driver is in a TRI-STATE or
power-off condition, the receiver output is again in a HIGH state, even with the end of cable 100-Ω
termination resistor across the input pins. The unplugged cable can become a floating antenna which can
pick up noise. If the cable picks up more than 10 mV of differential noise, the receiver may see the noise as
a valid signal and switch. To ensure that any noise is seen as common-mode and not differential, a balanced
interconnect should be used. Twisted pair cable offers better balance than flat ribbon cable.
3. Shorted Inputs. If a fault condition occurs that shorts the receiver inputs together, thus resulting in a 0-V
differential input voltage, the receiver output remains in a HIGH state. Shorted input fail-safe is not supported
across the common-mode range of the device (GND to 2.4 V). It is only supported with inputs shorted and no
external common-mode voltage applied.
External lower value pullup and pulldown resistors (for a stronger bias) may be used to boost fail-safe in the
presence of higher noise levels. The pullup and pulldown resistors must be in the 5-kΩ to 15-kΩ range to
minimize loading and waveform distortion to the driver. The common-mode bias point must be set to
approximately 1.2 V (less than 1.75 V) to be compatible with the internal circuitry.
Additional information on fail-safe biasing of LVDS devices may be found in AN-1194 Failsafe Biasing of LVDS
Interfaces (SNLA051).
8.4 Device Functional Modes
Table 1 lists the functional modes of the DS90LV048A.
Table 1. Truth Table
ENABLES
EN
EN*
H
L or Open
All other combinations of ENABLE inputs
INPUT
R_IN+ − R_IN−
V_ID ≥ 0 V
V_ID ≤ −0.1 V
Full Fail-safe
OPEN/SHORT or
Terminated
X
OUTPUT
R_OUT
H
L
H
Z
Copyright © 1999–2016, Texas Instruments Incorporated
Product Folder Links: DS90LV048A
Submit Documentation Feedback
11