MB15E05 Fujitsu Media Devices, MB15E05 Datasheet - Page 10

• Manufacturer Part Number: MB15E05
• Description: ASSP Single Serial Input PLL Frequency Synthesizer On-Chip 2.0GHz Prescaler
• Manufacturer: Fujitsu Media Devices

10
MB15E05
When designing a synthesizer, the FC pin setting depends on the VCO and LPF characteristics.
Power Saving Mode (Intermittent Mode Control Circuit)
Setting a PS pin to Low, the IC enters into power saving mode resultatly current sonsumption can be limited to
10 A (max.). Setting PS pin to High, power saving mode is released so that the IC works normally.
In addition, the intermittent operation control circuit is included which helps smooth start up from the power saving
mode. In general, the power consumption can be saved by the intermittent operation that powering down or waking
up the synthesizer. Such case, if the PLL is powered up uncontrolled, the resulting phase comparator output signal
is unpredictable due to an undefined phase relation between reference frequency (f
(f
To prevent this, the intermittent operation control circuit enforces a limited error signal output of the phase detector
during power up, thus keeping the loop locked.
During the power saving mode, the corresponding section except for indispensable circuit for the power saving
function stops working, then current consumption is reduced to 10 A per one PLL section.
At that time, the Do and LD become the same state as when a loop is locking. That is, the Do becomes high
impedance.
A VCO control voltage is naturally kept at the locking voltage which defined by a LPF”s time constant. As a result
of this, VCO’s frequency is kept at the locking frequency.
Table.8 PS Pin Setting
Table.9 ZC Pin Setting
p
) and may in the worst case take longer time for lock up of the loop.
Note:
PS pin
ZC pin
H
H
L
L
: When the LPF and VCO characteristics are
: When the VCO characteristics are similar to
similar to
While the power saving mode is executed, ZC pin should be set at ”H” or open. If ZC is set at ”L”
during power saving mode, approximately 10 A current flows.
PS pin must be set ”L” at Power-ON.
The power saving mode can be released (PS : L
During the power saving mode, it is possible to input the serial data.
, set FC bit low.
PLL
Normal mode
Power saving mode
Normal output
High impedance
, set FC bit high.
LPF
Do output
Status
VCO
Frequency
Output
VCO
H) 1 s later after power supply remains stable.
LPF Input Voltage
r
) and comparison frequency