DS92LV3221_14 Datasheet, PDF (16/30 Pages) Texas Instruments – 20-50 MHz 32-Bit Channel Link II Serializer / Deserializer

DS92LV3221, DS92LV3222
SNLS319C – OCTOBER 2009 – REVISED APRIL 2013
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The Pre-Emphasis circuit increases the drive current to I = 48 / (R_PRE). For example if R_PRE = 15 kOhms, then
the current is increased by an additional 3.2 mA. To calculate the expected increase in V_OD, multiply the increase
in current by 50 ohms. So for the case of R_PRE = 15 kOhms, the boost to V_OD would be 3.2 mA x 50 Ohms = 160
mV. The duration of the current is controlled to one bit by time. If more than one bit value is repeated in the next
cycle(s), the Pre-Emphasis current is turned off (back to the normal output current level) for the next bit(s). To
boost high frequency data and pre-equalize teh data patternreduce ISI (Inter-Symbol Interference) improving the
resulting eye pattern.
V_OD SELECT
The SER Line Driver Differential Output Voltage (V_OD) magnitude is selectable. Two levels are provided and are
selected by the VSEL pin. When this pin is LOW, normal output levels are obtained. For most application set the
VSEL pin LOW. When this pin is HIGH, the output current is increased to double the V_OD level. Use this setting
only for extra long cables or high-loss interconnects.
VSEL Pin Setting
LOW
HIGH
Table 1. V_OD Control
Effect
Small V_OD, typ 440 mV_P-P
Large V_OD, typ 850 mV_P-P
SERIAL INTERFACE
The serial links between the DS92LV3221 and the DS92LV3222 are intended for a balanced 100 Ohm
interconnects. The links must be configured as an AC coupled interface.
The SER and DES support AC-coupled interconnects through an integrated DC balanced encoding/decoding
scheme. An external AC coupling capacitors must be placed, in series, in the LVDS signal path. The DES input
stage is designed for AC-coupling by providing a built-in AC bias network which sets the internal common mode
voltage (VCM) to +1.8V.
For the high-speed LVDS transmission, small footprint packages should be used for the AC coupling capacitors.
This will help minimize degradation of signal quality due to package parasitics. NPO class 1 or X7R class 2 type
capacitors are recommended. 50 WVDC should be the minimum used for best system-level ESD performance.
The most common used capacitor value for the interface is 100 nF (0.1 uF) capacitor. One set of capacitors may
be used for isolation. Two sets (both ends) may also be used for maximum isolation of both the SER and DES
from cable faults.
The DS92LV3221 and the DS92LV3222 differential I/O’s are internally terminated with 100 Ohm resistance
between the inverting and non-inverting pins and do not require external termination. The internal resistance
value will be between 90 ohm and 130 ohm. The integrated terminations improve signal integrity, reduce stub
lengths, and decrease the external component count resulting in space savings.
AT-SPEED BIST FEATURE
The DS92LV3221/ DS92LV3222 serial link is equipped with built-in self-test (BIST) capability to support both
system manufacturing and field diagnostics. BIST mode is intended to check the entire high-speed serial
interface at full link-speed without the use of specialized and expensive test equipment. This feature provides a
simple method for a system host to perform diagnostic testing of both SER and DES. The BIST function is easily
configured through the SER BISTEN pin. When the BIST mode is activated, the SER generates a PRBS
(pseudo-random bit sequence) pattern (2^7-1). This pattern traverses each lane to the DES input. The
DS92LV3222 includes an on-chip PRBS pattern verification circuit that checks the data pattern for bit errors and
reports any errors on the data output pins of the DES.
The AT-Speed BIST feature is enabled by setting the BISTEN to High on SER. The BISTEN input must be High
or Low for 4 or more TxCLKIN clock cycles in order to activate or deactivate the BIST mode. An input clock
signal for the Serializer TxCLKIN must also be applied during the entire BIST operation. Once BIST is enabled,
all the Serializer data inputs (TxIN[31:0]) are ignored and the DES outputs (RxOUT[31:0]) are not available. Next,
the internal test pattern generator for each channel starts transmission of the BIST pattern from SER to DES.
The DES BIST mode will be automatically activated by this sequence. A maximum of 128 consecutives clock
symbols on DS92LV3222 DES is needed to detect BIST enable function. The BIST is implemented with
independent transmit and receive paths for the two serial links. Each channel on the DES will be individually
compared against the expected bit sequence of the BIST pattern.
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