DS90LV028AH_13 Datasheet, PDF (5/16 Pages) Texas Instruments – High Temperature 3V LVDS Dual Differential Line Receiver

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DS90LV028AH
www.ti.com
SNLS201A – SEPTEMBER 2005 – REVISED APRIL 2013
The DS90LV028AH differential line receiver is capable of detecting signals as low as 100 mV, over a ±1V
common-mode range centered around +1.2V. This is related to the driver offset voltage which is typically +1.2V.
The driven signal is centered around this voltage and may shift ±1V around this center 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 effects of coupled noise, or a combination of the two. The AC parameters
of both receiver input pins are optimized for a recommended operating input voltage range of 0V to +2.4V
(measured from each pin to ground). The device will operate for receiver input voltages up to V_CC, but exceeding
V_CC will turn on the ESD protection circuitry which will clamp the bus voltages.
POWER DECOUPLING RECOMMENDATIONS
Bypass capacitors must be used on power pins. Use high frequency ceramic (surface mount is recommended)
0.1μF and 0.01μF capacitors in parallel at the power supply pin with the smallest value capacitor closest to the
device supply pin. Additional scattered capacitors over the printed circuit board will improve decoupling. Multiple
vias should be used to connect the decoupling capacitors to the power planes. A 10μF (35V) or greater solid
tantalum capacitor should be connected at the power entry point on the printed circuit board between the supply
and ground.
PC BOARD CONSIDERATIONS
Use at least 4 PCB board layers (top to bottom): LVDS signals, ground, power, TTL signals.
Isolate TTL signals from LVDS signals, otherwise the TTL signals may couple onto the LVDS lines. It is best to
put TTL and LVDS signals on different layers which are isolated by a power/ground plane(s).
Keep drivers and receivers as close to the (LVDS port side) connectors as possible.
DIFFERENTIAL TRACES
Use controlled impedance traces which match the differential impedance of your transmission medium (ie. cable)
and termination resistor. Run the differential pair trace lines as close together as possible as soon as they leave
the IC (stubs should be < 10mm long). This will help eliminate reflections and ensure noise is coupled as
common-mode. In fact, we have seen that differential signals which are 1mm apart radiate far less noise than
traces 3mm apart since magnetic field cancellation is much better with the closer traces. In addition, noise
induced on the differential lines is much more likely to appear as common-mode which is rejected by the
receiver.
Match electrical lengths between traces to reduce skew. Skew between the signals of a pair means a phase
difference between signals which destroys the magnetic field cancellation benefits of differential signals and EMI
will result! (Note that the velocity of propagation, v = c/E _r where c (the speed of light) = 0.2997mm/ps or 0.0118
in/ps). Do not rely solely on the autoroute function for differential traces. Carefully review dimensions to match
differential impedance and provide isolation for the differential lines. Minimize the number of vias and other
discontinuities on the line.
Avoid 90° turns (these cause impedance discontinuities). Use arcs or 45° bevels.
Within a pair of traces, the distance between the two traces should be minimized to maintain common-mode
rejection of the receivers. On the printed circuit board, this distance should remain constant to avoid
discontinuities in differential impedance. Minor violations at connection points are allowable.
TERMINATION
Use a termination resistor which best matches the differential impedance or your transmission line. The resistor
should be between 90Ω and 130Ω. Remember that the current mode outputs need the termination resistor to
generate the differential voltage. LVDS will not work correctly without resistor termination. Typically, connecting a
single resistor across the pair at the receiver end will suffice.
Surface mount 1% - 2% resistors are the best. PCB stubs, component lead, and the distance from the
termination to the receiver inputs should be minimized. The distance between the termination resistor and the
receiver should be < 10mm (12mm MAX).
Copyright © 2005–2013, Texas Instruments Incorporated
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