ZL30409/DDA ZARLINK [Zarlink Semiconductor Inc], ZL30409/DDA Datasheet - Page 18

• Manufacturer Part Number: ZL30409/DDA
• Description: T1/E1 System Synchronizer with Stratum 3 Holdover
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

Lock Indicator
The LOCK pin toggles at a random rate when the PLL is frequency locked to the input reference. In Figure 11 the
RC-time-constant circuit can be used to hold the high state of the LOCK pin.
Once the PLL is frequency locked to the input reference, the minimum duration of LOCK pin’s high state would be
32ms and the maximum duration of LOCK pin’s low state would not exceed 1 second. The following equations can
be used to calculate the charge and discharge times of the capacitor.
t
t
A digital alternative to the RC-time-constant circuit is presented in Figure 12. The circuit in Figure 12 can be used to
generate a steady lock signal. The circuit monitors the ZL30409’s LOCK pin, as long as it detects a positive pulse
every 1.024 seconds or less, the Advanced Lock output will remain high. If no positive pulse is detected on the
LOCK output within 1.024 seconds, the Advanced LOCK output will go low.
C
D
= - R
= - R C ln(V
D
t
R
C = Capacitor value (1µF)
V
Schmidt Trigger (3.0 V)
V
t
R = Resistor value (3.3 MΩ)
C = Capacitor value (1µF)
V
Schmidt Trigger (2.0 V)
V
C
D
C ln(1 – V
T+
DD
T-
DD
D
= Capacitor’s charge time
= Capacitor’s discharge time
= Dynamic resistance of the diode (100 Ω)
= Negative going threshold voltage of the
= Positive going threshold voltage of the
= 3.3 V
= 3.3 V
T-
/V
DD
T+
ZL30409
) = 1.65 seconds
/V
DD
) = 240 µs
LOCK
Figure 11 - Time-constant Circuit
IN4148
R=3.3M
Zarlink Semiconductor Inc.
ZL30409
+
C=1µf
18
74HC14
74HC14
LOCK
Data Sheet