M2040 Datasheet Rev 1.0 7 of 12 Revised 28Jan2005
Integrated Circuit Systems, Inc. ● Networking & Communications ● www.icst.com ● tel (508) 852-5400
M2040
F
REQUENCY
T
RANSLATION
PLL
WITH
A
UTO
S
WITCH
Product Data Sheet
Integrated
Circuit
Systems, Inc.
Hitless Switching Option
Hitless Switching is a device option that can be
specified at time of order. (Please contact ICS.) The
M2040-01 remains in wide bandwidth mode if
NBW = 0.
When
NBW = 0, placing the device into wide bandwidth
operation, the optional Hitless Switching (HS) function
will automatically place the device into narrow
bandwidth operation during reference reselection. This
provides a controlled output clock phase change while
the PLL is acquiring phase lock to a new reference
clock phase. The HS function is trigged by a loss of lock
event. Wide bandwidth is resumed once the PLL
relocks to the input reference. (When the NBW pin = 1,
the device operates in narrow bandwidth continually
and hence the HS mode does not apply).
The HS function is armed after the device locks to the
input clock reference (8 successive phase detector
clock cycles with LOL low). Once armed, HS is
triggered by detection at the phase detector of a single
phase error greater than 4 ns (rising edges).
Once triggered, the HS function narrows the loop band-
width until the PLL is locked to the selected reference (8
successive phase detector clock cycles with LOL low).
When pin AUTO = 1 (automatic reference reselection
mode) HS is used in conjunction with input reselection.
When AUTO = 0 (manual mode), HS will still occur upon
an input phase transient, however the clock input is not
reselected (this enables hitless switching when using an
external MUX for clock selection).
Power-Up Initialization Function (INIT Pin)
The initialization function provides a short-term override
of the narrow bandwidth mode when the device is
powered up in order to facilitate phase locking.
When
INIT is set to logic 1, initialization is enabled. With
NBW set to logic 1 (narrow bandwidth mode), the
initialization function puts the PLL into wide bandwidth
mode until eight consecutive phase detector cycles
occur without a single LOL event. Once the eight valid
PLL locked states have occurred, the PLL bandwidth is
automatically reduced to narrow bandwidth mode.
When
INIT is logic 0, the device is forced into wide
bandwidth mode unconditionally.
External Loop Filter
The M2040 requires the use of an external loop filter
components. These are connected to the provided filter
pins (see Figure 5).
Because of the differential signal path design, the
implementation consists of two identical
complementary RC filters as shown in Figure 5, below.
Figure 5: External Loop Filter
PLL bandwidth is affected by the total “M” (feedback
divider) value, loop filter component values, and other
device parameters. See Table 7, External Loop Filter
Component Values, below.
PLL Simulator Tool Available
A free PC software utility is available on the ICS website
(www.icst.com). The M2000 Timing Modules PLL
Simulator is a downloadable application that simulates
PLL jitter and wander transfer characteristics. This
enables the user to set appropriate external loop
component values in a given application.
C
POST
C
POST
V
nVC
R
POST
nOP_OUTOP_OUT
R
POST
R
LOOP
R
LOOP
C
LOOP
C
LOOP
OP_IN nOP_IN
6 7549 8
External Loop Filter Component Values
1
VCSO Parameters: K
VCO
= 800kHz/V, VCO Bandwidth = 700kHz. See AC Characteristics on pg. 9 for PLL Loop Constants.
Device Configuration External Loop Filter Component Values
NBW
Mode
2
Nominal Performance Using These Values
F
VCSO
(MHz)
M
Divider
Value
R loop C loop R post C post
PLL Loop
Bandwidth
Damping
Factor
Passband
Peaking (dB)
533.333 30, 32
30kΩ 1.0µF 33kΩ 100pF
1 110 Hz
2.2 0.35
0 3 kHz
10 0.02
Table 7: External Loop Filter Component Values
Note 1: Recommended values for hitless switching. For PLL Simulator software, go to www.icst.com.
Note 2: NBW mode 1 = Narrow Bandwidth, where R
IN
= 2100 kΩ . NBW mode 0 = Wide Bandwidth, where R
IN
= 100 kΩ.
Note 3: This table does not apply to the 400 MHz VCSO option since the Kvco value is different.
