3.3V Spread-Spectrum EconOscillator

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13

The expected output frequency is not exactly equal to the

desired frequency of 11.0592MHz. The difference is

450Hz. In terms of percentage, Equation 6 shows that the

expected error is 0.004%. The expected error assumes

typical values and does not include deviations from the

typical as specified in the electrical tables.

Example #2: Calculate the register values needed to

generate a desired output frequency of 50MHz.

Since the desired frequency is already within the valid

master oscillator frequency range, the prescaler is set

to divide by 1, and hence, PRESCALER = 0000h

(currently ignoring the other setting).

frequencies centered around the desired frequency. To

determine what value to write to the OFFSET register,

the RANGE register must first be read. Assuming 12h

was read in this example, 13h (OS + 1) is written to the

OFFSET register.

Finally, the DAC value is calculated as shown in

Equation 8.

The result is then converted to hex (0118h) and then

left-shifted, resulting in 4600h to be programmed into

the DAC register.

In summary, the DS1086L is programmed as follows:

PRESCALER = 0000h

OFFSET = OS + 1 or 13h (if RANGE was read as 12h)

DAC = 4600h

Since the expected output frequency is equal to the

desired frequency, the calculated error is 0%.

f

MHz

kHz

MHz

MHz

OUTPUT

(.

)

(

)

.

.

=

+×

=

=

48 6

280

5

2

50 0

1

50 0

0

DAC VALUE

MHz

MHz

kHz STEP SIZE

decimal

(.

.

)

.

(

)

=

−

=

50 0

48 6

5

280 00

%

%

.

.

.

.

.%

ERROR

ff

f

ERROR

MHz

MHz

MHz

Hz

MHz

EXPECTED

DESIRED

EXPECTED

DESIRED

EXPECTED

=

−

×

=

−

×

=×

=

100

11 0592

11 05875

11 0592

100

450

11 0592

100

0 004

STOP

CONDITION

OR REPEATED

START

CONDITION

REPEATED IF MORE BYTES

ARE TRANSFERRED

ACK

START

CONDITION

ACK

ACKNOWLEDGEMENT

SIGNAL FROM RECEIVER

ACKNOWLEDGEMENT

SIGNAL FROM RECEIVER

SLAVE ADDRESS

MSB

SCL

SDA

R/W

DIRECTION

BIT

12

6

7

8

9

12

8

9

3–7

Figure 4. 2-Wire Data Transfer Protocol

(6)

(7)

(8)

(9)