MAX96708 datasheet(65/68 Pages) MAXIM

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Compatibility with Other GMSL Devices

The MAX96708 is designed to pair with the MAX96705−

MAX96711 family of SerDes devices, but interoperates

with any GMSL device. See Table 10 for operating limita-

tions.

Device Configuration and Component Selection

Internal Input Pulldowns

The control and configuration inputs include a pulldown

resistor to GND. External pulldown resistors are not needed.

Multifunction Inputs

The device has several inputs/outputs that function both

as a parallel input/output and as a configuration pin. On

power-up, or when reverting from a power-down state,

the pins act as configuration inputs. After latching the

input state, the configuration inputs become parallel

digital input/outputs. Connect a configuration input through

a 30kΩ resistor to IOVDD to set a high level. Leave the

configuration input open to set a low level.

I2C/UART Pullup Resistors

The I2C and UART open-drain lines require a pullup

resistor to provide a logic-high level. There are tradeoffs

between power dissipation and speed, and a compromise

may be required when choosing pullup resistor values.

Every device connected to the bus introduces some

capacitance even when the device is not in operation. I2C

specifies 300ns rise times (30% to 70%) for fast mode,

which is defined for data rates up to 400kbps. See the

I2C specifications in the I2C/UART Port Timing section in

the AC Electrical Characteristics table for details. To meet

the fast-mode rise-time requirement, choose the pullup

resistors so that rise time tR = 0.85 x RPULLUP x CBUS <

300ns. The waveforms are not recognized if the transition

time becomes too slow. GMSL supports I2C/UART rates

up to 1Mbps (UART-to-I2C mode) and 400kbps (I2C-to-

I2C mode).

AC-Coupling Capacitors

Voltage droop and the digital sum variation (DSV) of

transmitted symbols cause signal transitions to start from

different voltage levels. Because the transition time is fixed,

starting the signal transition from different voltage levels

causes timing jitter. The time constant for an AC-coupled

link needs to be chosen to reduce droop and jitter to an

acceptable level. The RC network for an AC-coupled link

consists of the CML/coax receiver termination resistor

(RTR), the CML/coax driver termination resistor (RTD),

and the series AC-coupling capacitors (C). The RC time

constant for four equal-value series capacitors is (C x

(RTD + RTR))/4. RTD and RTR are required to match the

transmission line impedance (usually 100Ω differential,

50Ω single-ended). This leaves the capacitor selection

to change the system time constant. Use 0.2μF or larger

high-frequency surface-mount ceramic capacitors, with

sufficient voltage rating to withstand a short to battery, to

pass the lower-speed reverse control-channel signal. Use

capacitors with a case size less than 3.2mm x 1.6mm to

have lower parasitic effects to the high-speed signal.

Cables and Connectors

Interconnect for CML typically has a differential imped-

ance of 100Ω. Use cables and connectors that have

matched differential impedance to minimize impedance

discontinuities. Coax cables typically have a characteristic

impedance of 50Ω (contact the factory for 75Ω operation).

Table 11 lists the suggested cables and connectors used

in the GMSL link.

DESERIALIZER FEATURE

GMSL SERIALIZER

HSYNC/VSYNC encoding

If feature not supported in the serializer, turn off in the deserializer.

I2C-to-I2C

If feature not supported in the serializer, use UART-to-I2C or UART-to-UART.

CRC error detection

If feature not supported in the serializer, turn off in the deserializer.

Double input

If feature not supported in the serializer, data is output as a single word at half the input

frequency. Use Crossbar switch to correct input mapping.

Coax

If feature not supported in the serializer, connect unused serial input through 200nF

and 50Ω in series to AVDD, and set the reverse control-channel amplitude to 100mV.

I2S encoding

If supported in the serializer, disable I2S in the serializer

High-immunity mode

If feature not supported in the serializer, turn off in the deserializer.

Table 10. Feature Compatibility

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Maxim Integrated │ 65

MAX96708

14-Bit GMSL Deserializer

with Coax or STP Cable Input

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