lc72136 Sanyo Semiconductor Corporation, lc72136 Datasheet - Page 20

• Manufacturer Part Number: lc72136
• Description: Frequency Synthesizer Electronic Tuning
• Manufacturer: Sanyo Semiconductor Corporation

When directly outputting data from the DO pin (set up by the DO pin control data)
Since the DO pin outputs the unlocked state (locked: high, unlocked: low) the timing considerations in the technique
described in the previous section are not necessary. After changing the value of N, the locked state can be determined
after waiting at least two periods of the reference frequency.
Notes on Clock Time Base Usage
When the clock time base output is used, the value of the pull-up resistor for the output pin (BO1) must be at least 100 kΩ.
This is to avoid degradation of the VCO C/N characteristics when using the built-in low-pass filter transistor to form the
loop filter. Since the clock time base output pin and the low-pass filter transistor ground are the same node in the IC, the
time base output pin current fluctuations must be suppressed to limit the influence on the low-pass filter. We recommend
the use of a Schmitt input on the receiving controller (microprocessor) to prevent chattering.
Other Items
1. Notes on the Phase Comparator Dead Zone
Since correction pulses are output from the charge pump even if the PLL is locked when the charge pump is in the
ON/ON state, the loop can easily become unstable. This point requires special care when designing application
circuits.
The following problems may occur in the ON/ON state.
• Side band generation due to reference frequency leakage
• Side band generation due to both the correction pulse envelope and low frequency leakage
DZ1
0
0
1
1
DZ0
0
1
0
1
Dead-zone mode
DZA
DZB
DZC
DZD
Charge pump
OFF/OFF
OFF/OFF
ON/ON
ON/ON
LC72136, 72136M
Dead zone
+ +0 sec
– –0 sec
–0 sec
+0 sec
No. 5038-20/23