LMH0387SL Datasheet, PDF (10/23 Pages) Texas Instruments – LMH0387 3 Gbps HD/SD SDI Configurable I/O Adaptive Cable Equalizer / Cable Driver

LMH0387
SNLS315G – APRIL 2010 – REVISED APRIL 2013
DEVICE DESCRIPTION
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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
Application Circuit diagram shows the typical configuration. The TERM_RX input must be properly terminated with
a 1.0 µF capacitor followed by a 220Ω 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 100Ω LVDS outputs. These outputs
can be DC coupled to most common differential receivers.
The default output common mode voltage (V_OS) is 1.25V. The output common mode voltage may be adjusted via
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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