FUJITSU MB15E07SL - Manual (Page 11)

MB15E07SL
11
When designing a synthesizer, the FC pin setting depends on the VCO and LPF characteristics.
3. Do Output Control
Table 9. ZC Pin Setting
4. Power Saving Mode (Intermittent Mode Control Circuit)
Table 10. PS Pin Setting
The intermittent mode control circuit reduces the PLL power consumption.
By setting the PS pin low, the device enters into the power saving mode, reducing the current consumption. See
the Electrical Characteristics chart for the specific value.
The phase detector output, Do, becomes high impedance.
For the signal PLL, the lock detector, LD, remains high, indicating a locked condition.
Setting the PS pin high, releases the power saving mode, and the device works normally.
The intermittent mode control circuit also ensures a smooth startup when the device returns to normal operation.
When the PLL is returned to normal operation, the phase comparator output signal is unpredictable. This is
because
of the unknown relationship between the comparison frequency (fp) and the reference frequency (fr) which can
cause a major change in the comparator output, resulting in a VCO frequency jump and an increase in lockup
time.
To prevent a major VCO frequency jump, the intermittent mode control circuit limits the magnitude of the error
signal from the phase detector when it returns to normal operation.
When power (V
CC
) is first applied, the device must be in standby mode, PS = Low, for at least 1
µ
s.
ZC pin Do output
H Normal output
L High impedance
PS pin Status
H Normal mode
L Power saving mode
(1)
(2)
* : When the LPF and VCO characteristics are similar
to (1), set FC bit high.
* : When the VCO characteristics are similar to (2), set
FC bit low.
VCO
Output
Frequency
LPF Output Voltage
PLL LPF VCO