lm2326slbx National Semiconductor Corporation, lm2326slbx Datasheet - Page 12

• Manufacturer Part Number: lm2326slbx
• Description: Pllatinum? Low Power Frequency Synthesizer For Rf Personal Communications
• Manufacturer: National Semiconductor Corporation

www.national.com
Note 7: When the GO bit N[19] is set to one, the part is forced into the high gain mode. When the timeout counter is activated, termination of the counter cycle resets
the GO bit to 0. If the timeout counter is not activated, N[19] must be reprogrammed to zero in order to remove the high gain state. See below for descriptions of each
individual FastLock mode.
1.0 Functional Description
There are two techniques of switching in and out of FastLock. To program the device into any of the FastLock modes, the GO bit
N[19] must be set to one to begin FastLock operation. In the first approach, the timeout counter can be used (FastLock 2 and 4)
to stay in FastLock mode for a programmable number of phase detector reference cycles (up to 63) and then reset the GO bit
automatically. In the second approach (FastLock 1 and 3) without the timeout counter, the PLL will remain in FastLock mode until
the user resets the GO bit via the MICROWIRE serial bus. Once the GO bit is set to zero by the timeout counter or by MICROW-
IRE, the PLL will then return to normal operation. This transition does not effect the charge on the loop filter capacitors and is en-
acted synchronous with the charge pump output. This creates a nearly seamless transition between FastLock and standard
mode.
FastLock Mode 1 In this mode, the output level of the FL
FastLock Mode 2 Identical to mode 1, except the switching of the device out of FastLock is controlled by the Timeout counter.
FastLock Mode 3 This mode is similar to mode 1 in that the output level of the FL
FastLock Mode 4 Identical to mode 3, except the switching of the device out of FastLock is controlled by the Timeout counter.
*
FastLock Mode # 1
FastLock Mode # 2
FastLock Mode # 3
FastLock Mode # 4
Normal Operation FastLock Normal Operation is defined as the device being in low current mode and standard divider values.
FastLock Status
device remains in this state until a command is received, resetting the N[19] bit to zero. Programming N[19]
to zero will return the device to normal operation
The device will remain in FastLock until the timeout counter has counted down the appropriate number of
phase detector cycles, at which time the PLL returns to normal operation
Additionally, the R and N divide ratios are reduced by one fourth during the transient, resulting in a 16x im-
proved gain. As in mode 1, the device remains in this state until a MICROWIRE command is received, reset-
ting the N[19] bit to zero and returning the device to normal operation
The device will remain in FastLock until the timeout counter has counted down the appropriate number of
phase detector cycles, at which time the PLL returns to normal operation
F[8]
1
1
1
1
F[9]
0
0
1
1
(Continued)
TABLE 5. FastLock Decoding
F[10]
0
1
0
1
o
is programmed in a low state while the ICP
12
1 (Note 7)
1 (Note 7)
*
(Note 7)
., i.e., ICP
N[19]
1
1
o
o
= 1x and FL
is low and the ICP
No Timeout Counter - 1X Divider
Timeout Counter - 1X Divider
No Timeout Counter - 1/4X Divider
Timeout Counter - 1/4X Divider
*
.
*
*
o
.
.
FastLock State
returned to TRI-STATE.
o
is switched to the 4x state.
o
is in the 4x state. The
DS100127-8