1.3.1 POWERDOWN OPERATION

Bits F[2] and F[18] provide programmable powerdown modes when the CE pin is HIGH. When CE is LOW, the part is always im-

mediately disabled regardless of powerdown bit status. Refer to

Table 3.

Synchronous and asynchronous powerdown modes are both available by MICROWIRE selection. Synchronous powerdown oc-

curs if the F[18] bit (Powerdown Mode) is HIGH when F[2] bit (Powerdown) becomes HIGH. Asynchronous powerdown occurs

if the F[18] bit is LOW when its F[2] bit becomes HIGH.

In the synchronous powerdown mode (F[18] = HIGH), the powerdown function is gated by the charge pump to prevent unwanted

frequency jumps. Once the powerdown program bit F[2] is loaded, the part will go into powerdown mode after the first successive

charge pump event.

In the asynchronous powerdown mode (F[18] = LOW), the device powers down immediately after latching LOW data into bit F[2].

The device returns to an actively powered up condition in either synchronous or asynchronous mode immediately upon LE latch-

ing LOW data into bit F[2].

Activation of a powerdown condition in either synchronous or asynchronous mode including CE pin activated powerdown has the

following effects:

•

Removes all active DC current paths.

•

Forces the R, N, and timeout counters to their load state

conditions.

•

Will TRI-STATE the charge pump.

•

Resets the digital lock detect circuitry.

•

Debiases the f

•

Disables the oscillator input buffer circuitry.

•

The MICROWIRE control register remains active and ca-

pable of loading the data.

TABLE 3. Power Down Truth Table

CE(Pin 10)

F[2]

F[18]

Mode

LOW

X

X

Asynchronous Power Down

HIGH

0

X

Normal Operation

HIGH

1

0

Asynchronous Power Down

HIGH

1

1

Synchronous Power Down

TABLE 4. The Fo/LD (pin 14) Output Truth Table

F[3]

F[4]

F[5]

Fo/LD Output State

0

0

0

TRI-STATE

0

0

1

R Divider Output (fr)

0

1

0

N Divider Output (fp)

0

1

1

Serial Data Output

1

0

0

Digital Lock Detect (See 1.3.2 LOCK DETECT OUTPUT Section)

1

0

1

n Channel Open Drain Lock Detect (See 1.3.2 LOCK DETECT OUTPUT

Section)

1

1

0

Active HIGH

1

1

1

Active LOW

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