LMH0387

SNLS315G – APRIL 2010 – REVISED APRIL 2013

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DEVICE DESCRIPTION

The LMH0387 3 Gbps HD/SD SDI Configurable I/O Adaptive Cable Equalizer / Cable Driver is used at the input

or output port of digital video equipment. It is designed to allow the sharing of a single BNC connector for either

input or output.

CONFIGURING THE INPUT (EQUALIZER) OR OUTPUT (CABLE DRIVER) MODE

The LMH0387 must be configured in either the input mode as an equalizer, or the output mode as a cable driver.

Input Mode (Equalizer)

To configure the LMH0387 in the input mode, the equalizer must be enabled and the cable driver must be

disabled as described in the following steps:

1. Disable the cable driver by pulling the TX_EN pin low.

2. Enable the equalizer by setting the sleep mode via the SPI to either auto sleep or disabled (never sleep). To

do this, write either “01” (auto sleep – default) or “00” (never sleep) to bits [4:3] of SPI register 00h.

3. Set the equalizer launch amplitude fine tuning to the nominal setting via the SPI. To do this, write 30h

(“00110000” binary) to SPI register 02h.

Output Mode (Cable Driver)

To configure the LMH0387 in the output mode, the cable driver must be enabled. The equalizer may either be

disabled for power savings or enabled to provide a loopback path for the data being transmitted. For the normal

output mode (equalizer disabled for power savings) follow these steps:

1. Disable the equalizer by forcing it to sleep via the SPI. To do this, write “10” (force sleep) to bits [4:3] of SPI

register 00h.

2. Enable the cable driver by pulling the TX_EN pin high.

To configure the LMH0387 for the output mode with the loopback path, the equalizer can be enabled in output

mode by writing either “01” (auto sleep – default) or “00” (never sleep) to bits [4:3] of SPI register 00h. In this

case, the LMH0387 input/output mode may be configured simply by toggling the TX_EN pin since the equalizer

remains active in either mode (TX_EN set low for input mode and high for output mode).

INPUT MODE (EQUALIZER) DESCRIPTION

SPI register access is required while operating the LMH0387 in the input mode. The equalizer launch amplitude

fine tuning must be set to nominal via the SPI for correct equalizer operation. To do this, write 30h (“00110000

binary”) to SPI register 02h. The SPI registers provide access to many other useful LMH0387 features while in

the input mode. Refer to the Input Mode (Equalizer) SPI Register Access section for details.

INPUT INTERFACING

The LMH0387 accepts single-ended input at the BNC_IO pin. The input must be AC coupled. The Typical

a 1.0 µF capacitor followed by a 220

Ω resistor to ground as shown.

The LMH0387 BNC_IO input can be optimized for different launch amplitudes via the SPI (see LAUNCH

AMPLITUDE OPTIMIZATION (REGISTER 02h) in the Input Mode (Equalizer) SPI Register Access section).

The LMH0387 correctly handles equalizer pathological signals for standard definition and high definition serial

digital video, as described in SMPTE RP 178 and RP 198, respectively.

OUTPUT INTERFACING

The LMH0387 equalizer outputs, SDO and SDO, are internally terminated 100

Ω LVDS outputs. These outputs

can be DC coupled to most common differential receivers.

the SPI in 200 mV increments, from 1.05V to 1.85V (see OUTPUT DRIVER ADJUSTMENTS (REGISTER 01h)

in the Input Mode (Equalizer) SPI Register Access section). This adjustable output common mode voltage offers

flexibility for interfacing to many types of receivers.

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