AD9512BCPZ datasheet(25/48 Pages) AD

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AD9512

Rev. A | Page 25 of 48

DIVIDERS

Each of the five clock outputs of the AD9512 has its own

divider. The divider can be bypassed to get an output at the

same frequency as the input (1×). When a divider is bypassed, it

is powered down to save power.

All integer divide ratios from 1 to 32 may be selected. A divide

ratio of 1 is selected by bypassing the divider.

Each divider can be configured for divide ratio, phase, and duty

cycle. The phase and duty cycle values that can be selected

depend on the divide ratio that is chosen.

Setting the Divide Ratio

The divide ratio is determined by the values written via the SCP

to the registers that control each individual output, OUT0 to

OUT4. These are the even numbered registers beginning at 4Ah

and going through 52h. Each of these registers is divided into

bits that control the number of clock cycles the divider output

stays high (high_cycles <3:0>) and the number of clock cycles

the divider output stays low (low_cycles <7:4>). Each value is 4

bits and has the range of 0 to 15.

The divide ratio is set by

Divide Ratio = (high_cycles + 1) + (low_cycles + 1)

Example 1:

Set the Divide Ratio = 2

high_cycles = 0

low_cycles = 0

Divide Ratio = (0 + 1) + (0 + 1) = 2

Example 2:

Set Divide Ratio = 8

high_cycles = 3

low_cycles = 3

Divide Ratio = (3 + 1) + (3 + 1) = 8

Note that a Divide Ratio of 8 may also be obtained by setting:

high_cycles = 2

low_cycles = 4

Divide Ratio = (2 + 1) + (4 + 1) = 8

Although the second set of settings produces the same divide

ratio, the resulting duty cycle is not the same.

Setting the Duty Cycle

The duty cycle and the divide ratio are related. Different divide

ratios have different duty cycle options. For example, if Divide

Ratio = 2, the only duty cycle possible is 50%. If the Divide

Ratio = 4, the duty cycle can be 25%, 50%, or 75%.

The duty cycle is set by

Duty Cycle = (high_cycles + 1)/[(high_cycles + 1) + (low_cycles + 1)]

See Table 12 for the values of the available duty cycles for each

divide ratio.

Table 12. Duty Cycle and Divide Ratio

4Ah to 52h

Divide Ratio

Duty Cycle (%)

LO<7:4>

HI<3:0>

4Ah to 52h

Divide Ratio

Duty Cycle (%)

LO<7:4>

HI<3:0>

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