GS3490 Datasheet, PDF (17/22 Pages) Semtech Corporation – Configurable Adaptive Cable Equalizer/Cable Driver

4.2.4 Slew Rate Selection (CD_SD_EN)
The GS3490 supports two output slew rates on SDO/SDO.
Control of the slew rate is determined by the setting of the CD_SD_EN input pin.
Table 4-4: Slew Rate Selection
CD_SD_EN
0
1
Floating
Rise/Fall Time
SMPTE ST 424 & SMPTE ST 292 compliant
SMPTE ST 259 compliant
SMPTE ST 259 compliant
4.2.5 Output Amplitude (R_SET)
The output amplitude of the GS3490 can be adjusted by changing the value of the R_SET
resistor as shown in Table 4-5. For an 800mV_pp output with a nominal ±7% tolerance, a
value of 750Ω is required. A ±1% SMT resistor should be used.
The R_SET resistor is part of an internal DC feedback loop in the GS3490. The resistor
should be placed as close as possible to the RSET pin, and connected directly to the VCC
plane with more than one via to minimize inductance (traces/wires may cause
instability).
Note: Care should be taken when considering layout of the R_SET resistor. Please refer to
Section 5.2 for more details.
Table 4-5: Typical R_SET Values
Output Swing (mV_pp)
1040
800
500
R_SET (Ω)
576
750
1210
R_TERM (Ω)
75
75
75
V_TERM (V)
3.3
3.3
3.3
Note 1: Actual swing values may vary based on layout.
Note 2: R_SET is the resistor connected from pin 27 to VCC (refer to Figure 5-1).
Note 3: R_TERM is the SDO/SDO pull up resistor.
GS3490
Final Data Sheet
GENDOC-058568
Rev. 1
April 2014
www.semtech.com
17 of 22
Proprietary & Confidential