LMKDB1108FS datasheet(38/126 Pages) TI2

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a. For example, if you wanted the fastest, second fastest, and the slowest slew rate, assign 0x0, 0x1,

and 0xF to registers SLEWRATE_OPT#. SLEWRATE_OPT1 = 0x0 (fastest), SLEWRATE_OPT2 = 0x1

(second fastest), and SLEWRATE_OPT3 = 0xF (slowest). SLEWRATE_OPT4 does not have to be

assigned, but if you want more than one register set to a slew rate, then SLEWRATE_OPT4 can be

assigned to any of the three previous settings.

2. Set a slew rate option for each output by using the SLEWRATE_SEL_CLKX_LSB and

SLEWRATE_SEL_CLKX_MSB as shown in Table 8-3 or drop-down menus under the Output Slew

Rate Control Section in TICSPro. The default SLEWRATE_OPT# register assignment for all outputs is

SLEWRATE_OPT2, which has a default slew rate of 0x6.

The corresponding ranges for the four default slew rates can be found in Section 6 under CLOCK OUTPUT

CHARACTERISTICS - 100MHz 85Ω PCIe or CLOCK OUTPUT CHARACTERISTICS - 100MHz 100Ω PCIe for

the specification Output slew rate.

Table 8-3. LMKDB11xx Default SLEWRATE_OPT_# Values

Default Value

Default Slew Rate

SLEWRATE_OPT_1

0x0

Highest

SLEWRATE_OPT_2

0x6

High (default for all outputs)

SLEWRATE_OPT_3

0xA

Low

SLEWRATE_OPT_4

0xF

Lowest

Table 8-4. LMKDB11xxFS Default SLEWRATE_OPT_# Values

Default Value

Default Slew Rate

SLEWRATE_OPT_1

0x0

Highest

SLEWRATE_OPT_2

0x2

High (default for all outputs)

SLEWRATE_OPT_3

0x6

Low

SLEWRATE_OPT_4

0xF

Lowest

Table 8-5. SLEWRATE_SEL_CLKX_LSB & SLEWRATE_SEL_CLKX_MSB Slew Rate Selection

SLEWRATE_SEL_CLKX_LSB

SLEWRATE_SEL_CLKX_MSB

Slew Rate Option Selection

SLEWRATE_OPT_4

SLEWRATE_OPT_3

SLEWRATE_OPT_2

SLEWRATE_OPT_1

To program the slew rate to the desired slew rate, the following sequence needs to be followed:

1. [Optional]: if the default assignments shown in Table 8-3 for each slew rate speed is not as desired, one of

the slew rate options value can be changed to another slew rate.

2. [LMKDB1108 and 1104 only]: Program SLEWRATE_CTRL_MODE register to 1 to select SMBus

programming mode for slew rate control. Refer to Section 9 section for LMKDB1108 and LMKDB1104

3. Program SLEWRATE_SEL_CLKX_MSB and SLEWRATE_SEL_CLKX_LSB to assign clock output X to

desired slew rate speed option, as shown in Table 8-5. The default assignments for each option can be

found in Table 8-3.

8.3.4.3 Programmable Output Swing

The LMKDB family supports programmable LP-HCSL swings between a range of 600mV to 975mV. All outputs

are programmed to the same output swing via register AMP and AMP_BANKX for both buffer and mux

respectively. To program the outputs to the desired swing refer to the Register Maps.

LMKDB1102, LMKDB1104, LMKDB1104FS

LMKDB1108, LMKDB1108FS, LMKDB1112, LMKDB1120, LMKDB1120FS

SNAS855F – NOVEMBER 2023 – REVISED NOVEMBER 2025

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