Datasheet

0 50 100 150 200 250 300 350 400

100

125

150

175

200

225

250

CLI (decimal value)

BELDEN 1694A CABLE LENGTH (m)

3G/HD

LMH0394

www.ti.com

SNLS312L –AUGUST 2010–REVISED APRIL 2013

The offset voltage is adjustable via bits [5:4] of SPI register 01h. The default value for these register bits is “10”

for an output offset of 1.2V. The output common mode voltage may be adjusted in 200 mV increments, from 0.8V

to 1.2V. It can be set to “11” for the maximum offset voltage. At this maximum offset voltage setting, the outputs

are referenced to the positive supply and the offset voltage is around 1.35V.

The output de-emphasis is turned on or off by bit 3 of SPI register 01h, and the de-emphasis level is set by bits

[2:1] of SPI register 01h. The output de-emphasis level may be set for 0 dB (for driving up to 10” FR4), 3 dB (for

driving 10-20” FR4), 5 dB (for driving 20-30” FR4), or 7 dB (for driving 30-40” FR4).

LAUNCH AMPLITUDE OPTIMIZATION

The LMH0394 can compensate for attenuation of the input signal prior to the equalizer. This compensation is

useful for applications with a passive splitter at the equalizer input or a non-ideal input termination network, and

is controlled by SPI register 02h.

Bit 7 of SPI register 02h is used for the launch amplitude setting. At the default setting of “0”, the LMH0394

operates normally and expects a launch amplitude of 800 mV

P-P

. Bit 7 may be set to “1” to optimize the LMH0394

for input signals with 6 dB of attenuation (400 mV

P-P

CABLE LENGTH INDICATOR (CLI)

The cable length indicator (CLI) provides an indication of the length of the cable attached to input. CLI is

accessible via bits [7:0] of SPI register 06h. The 8-bit setting ranges in decimal value from 0 to 247 (“00000000”

to “11110111” binary), corresponding to 0 to 400m of Belden 1694A cable. For 3G and HD input, CLI is 1.25m

per step. For SD input, CLI is 1.25m per step, less 20m, from 0 to 191 decimal, and 3.5m per step from 192 to

247 decimal.

To calculate the Belden 1694A cable length (in meters) from the CLI decimal value for 3G or HD input:

(1)

To calculate the Belden 1694A cable length (in meters) from the CLI decimal value for SD input:

(2)

Figure 12 shows typical CLI values vs. Belden 1694A cable length. CLI is valid for Belden 1694A cable lengths of

0-200m at 2.97 Gbps, 0-220m at 1.485 Gbps, and 0-400m at 270 Mbps. Note: Given the continuous adaptive

nature of the equalizer, this setting changes by some steps constantly.

Figure 12. CLI vs. Belden 1694A Cable Length

Product Folder Links: LMH0394