Texas Instruments M-LVDS, User Manual

Page: 10 / 32

Overview
1-2 The M-LVDS Evaluation Module
1.1 Overview
The EVM comes with all the production devices in Table 1−1. The
SN65MLVD201 and SN65MLVD207 are installed on the circuit board, and can
easily be replaced with the other devices supplied. The M-LVDS devices
evaluated with this EVM are in the SN75ALS180 and SN75176 footprint. Use
of these industry standard footprints allows the designer to easily configure the
parts into a simplex or half-duplex data bus. These are all TIA/EIA−899
M-LVDS standard compliant devices. While initially intended for half-duplex or
multipoint applications, M-LVDS devices are not precluded from being used
in a point-to-point or multidrop configuration. In these configurations there can
be a distinct advantage to the additional current drive provided by an M-LVDS
driver.
The M-LVDS devices shown in Table 1−1 all include output slew-rate limited
drivers, thus the need for different nominal signaling rates. The M-LVDS
standard recommends the transition time not exceed 0.5 of the unit interval
(UI). The definition of transition time (t
r
and t
f
) in M-LVDS is the 10% to 90%
levels shown in Figure 1−1. Using the maximum transition time for each of the
drivers and the 0.5(t
UI
) rule results in the signaling rates shown in Table 1−1.
This slew-rate control differentiates M-LVDS devices from LVDS
(TIA/EIA−644A) compliant devices. The slower transition times available with
M-LVDS help to reduce higher frequency components in the transmitted
signal. This reduces EMI and allows longer stubs on the main transmission
line. For this reason it is generally better to select a driver with a specified
signaling rate no greater than is required in the system.
Figure 1−1. M-LVDS Unit Interval Definition
10%
50%
90%
UI
tf tr
Table 1−1. M-LVDS Devices Supported by the EVM
Nominal
Signaling Rate
(Mbps)
Footprints
Receiver
Type
Part
Number
Status
100 SN75176 Type-1 SN65MLVD200AD Production
200 SN75176 Type-1 SN65MLVD201D Production
100 SN75ALS180 Type-1 SN65MLVD202AD Production
200 SN75ALS180 Type-1 SN65MLVD203D Production
100 SN75176 Type-2 SN65MLVD204AD Production
100 SN75ALS180 Type-2 SN65MLVD205AD Production
200 SN75176 Type-2 SN65MLVD206D Production
200 SN75ALS180 Type-2 SN65MLVD207D Production