MB15E07SR Fujitsu Media Devices, MB15E07SR Datasheet - Page 11

• Manufacturer Part Number: MB15E07SR
• Description: Single Serial Input PLL Frequency Synthesizer On-chip 2.5 GHz Prescaler
• Manufacturer: Fujitsu Media Devices

3. Power Saving Mode (Intermittent Mode Control Circuit)
Table 9. PS Pin Setting
When designing a synthesizer, the FC pin setting depends on the VCO and LPF characteristics.
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 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.
Note : Give attention to the polarity for using active type LPF.
PS pin
H
L
PLL
Normal mode
Power saving mode
LPF
VCO
Status
Frequency
Output
VCO
LPF Output Voltage
MB15E07SR
(1)
(2)
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