GS3590 datasheet(57/118 Pages) SEMTECH

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GS3590

Final Data Sheet Rev.4



PDS-061414 September 2017

57 of 118

Semtech

Proprietary & Confidential

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4.8.6 Trace Driver DC-Coupling Requirements

Table 4-10 lists the required Vcco (driver supply voltage) and DS (driver swing) required

to achieve three common nominal VDDOppd (peak-to-peak differential output voltages)

and their associated nominal Vcmout (output common mode voltage).

In the DC-coupled case, where Vcco is connected to the same supply as the input buffer

supply voltage of the downstream device, Vcmount in Table 4-10 is the common mode

voltage at the output of the GS3590 driver. For short low-loss transmission lines, this will

also be the common mode voltage created at the input termination of the downstream

input buffer. However, for long and lossy transmission lines, the amplitude will be

attenuated at the downstream receiver and therefore the common mode voltage

created at the input termination will be higher and must be measured or simulated for

accuracy. For proper link operation, the common mode voltage created at the input

termination of the downstream input buffer must be within the Vcmin range specified by

that device.

In the AC-coupled case, Vcmout is the common mode voltage at the driver side of the

AC-coupling capacitor placed near the driver. In the AC-coupled case, Vcmout does not

need to be within the Vcmin range specified by the downstream device. However, the

capacitor should have a voltage rating that exceeds |Vcmout-Vcmin|. In addition to the

voltage rating, the recommended value of the AC-coupling capacitor should be at least

4.7μF to meet the low cut-off frequency requirement of low transition density signals

such as the check-field pattern defined in SMPTE RP-198. The capacitor should have a

temperature rating that maintains the capacitance over the required operating range.

Table 4-10: ΔVDDO (mVppd) and VCMOUT(V) vs. DS Setting and VCCO

ΔVDDO (mVppd) vs. DS Setting

DC-Coupled

VCMOUT (V) vs. DS Setting

AC-Coupled

VCMOUT (V) vs. DS Setting

Vcco (V)

1.2

200

400

—

1.15

1.1

—

1.1

—

1.8

200

400

800

1.75

1.7

1.6

1.7

1.6

1.4

2.5

200

400

800

2.45

2.4

2.3

2.4

2.3

2.1

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