LMH0303_13 Datasheet, PDF (6/19 Pages) Texas Instruments – 3 Gbps HD/SD SDI Cable Driver with Cable Detect

LMH0303
SNLS285G – APRIL 2008 – REVISED APRIL 2013
DEVICE OPERATION
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INPUT INTERFACING
The LMH0303 accepts either differential or single-ended input. For single-ended operation, the unused input
must be properly terminated.
OUTPUT INTERFACING
The LMH0303 uses current mode outputs. Single-ended output levels are 800 mV_P-P into 75Ω AC-coupled
coaxial cable with an R_REF resistor of 750Ω. The R_REF resistor is connected between the R_REF pin and V_CC. The
only resistor value that should be used for R_REF is 750Ω.
The R_REF resistor should be placed as close as possible to the R_REF pin. In addition, the copper in the plane
layers below the R_REF network should be removed to minimize parasitic capacitance.
OUTPUT SLEW RATE CONTROL
The LMH0303 output rise and fall times are selectable for either SMPTE 259M or SMPTE 424M / 292M
compliance via the SD/HD pin. For slower rise and fall times, or SMPTE 259M compliance, SD/HD is set high.
For faster rise and fall times, or SMPTE 424M and SMPTE 292M compliance, SD/HD is set low. SD/HD may
also be controlled using the SMBus, provided the SD/HD pin is held low. SD/HD has an internal pulldown.
OUTPUT ENABLE
The SDO/SDO output driver can be enabled or disabled with the ENABLE pin. When set low, the output driver is
powered off and the LMH0303 enters a deep power save mode. ENABLE has an internal pullup.
INPUT LOS OF SIGNAL DETECTION (LOS)
The LMH0303 detects when the input signal does not have a video-like pattern. Self oscillation and low levels of
noise are rejected. This loss of signal detect allows a very sensitive input stage that is robust against coupled
noise without any degradation of jitter performance.
Via the SMBus, the loss of signal detect can either add an input offset or mute the outputs. An offset is added by
default. Additionally, the loss of signal detect can be linked to the ENABLE functionality so that when the LOS
goes low, ENABLE will also go low.
OUTPUT CABLE DETECTION
The LMH0303 detects when an output is locally terminated. When a video signal (or AC test signal) is present on
SDI, the device senses the SDO and SDO amplitudes. If the output is not properly terminated (via a terminated
cable or local termination), the amplitude will be higher than expected, and the Termination Fault signal is
asserted. The Termination Fault signal is de-asserted when the proper termination is applied. This feature allows
the system designer the flexibility to react to cable attachment and removal. Note that a long length of cable will
look like a proper termination at the device output.
The cable driver must be enabled for the termination detection to operate. If the Termination Fault will be used to
power down the LMH0303, then periodic polling (enabling) is recommended to monitor the output termination.
For example, when a Fault condition is triggered, ENABLE can be driven low to power down the device. The
LMH0303 should be re-enabled periodically to check the status of the output termination. The LMH0303 needs to
be powered on for roughly 4 ms for Termination Fault detection to work.
SMBus Interface
The System Management Bus (SMBus) is a two-wire interface designed for the communication between various
system component chips. By accessing the control functions of the circuit via the SMBus, pincount is kept to a
minimum while allowing a maximum amount of versatility. The LMH0303 has several internal configuration
registers which may be accessed via the SMBus.
The 7-bit default address for the LMH0303 is 17h. The LSB is set to 0b for a WRITE and 1b for a READ, so the
8-bit default address for a WRITE is 2Eh and the 8-bit default address for a READ is 2Fh. The SMBus address
may be dynamically changed.
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