DATASHEET
VCXO PLUS AUDIO CLOCK FOR STB
Description
The MK3724 is a low cost, low jitter, high performance
VCXO and PLL clock synthesizer designed to replace
expensive discrete VCXOs and multipliers. The patented
on-chip Voltage Controlled Crystal Oscillator accepts a 0 to
3.3 V input voltage to cause the output clocks to vary by
±115 ppm. Using IDT’s analog/digital Phase-Locked Loop
(PLL) techniques, the device uses an inexpensive 27 MHz
pullable crystal input to produce a reference output and a
selectable audio clock.
IDT manufactures the largest variety of VCXO based timing
devices for all applications. Consult IDT to eliminate
VCXOs, crystals, and oscillators from your board.
The frequency of the on-chip VCXO is adjusted by an
external control voltage connected to VIN. Because VIN is
a high impedance input, it can be driven directly from an
PWM RC integrator circuit.
MK3724
Features
•
•
•
•
•
•
•
•
•
•
•
Packaged in 16-pin TSSOP
Pb free packaging
Replaces a VCXO and oscillator
Operating voltage of 3.3 V
Provides output of 27 MHz plus audio clock
Uses an inexpensive 27 MHz pullable crystal
On-chip patented VCXO with pull range of 230 ppm
(minimum)
VCXO tuning voltage of 0 to 3.3 V
Advanced, low power, sub-micron CMOS process
Industrial temperature range available
For other standard audio frequencies see the MK3722
Block Diagram
VDD
3
S2:S0
VIN
X1
27 MHz
Pullable
Crystal
3
PLL/Clock
Synthesis
Circuitry
ACLK
X2
Voltage
Controlled
Crystal
Oscillator
3
27MHz
GND
PDTS
IDT™
VCXO PLUS AUDIO CLOCK FOR STB
1
MK3724
REV E 051310
MK3724
VCXO PLUS AUDIO CLOCK FOR STB
VCXO AND SYNTHESIZER
Pin Assignment
X2
X1
VDD
VDD
VIN
GND
GND
PDTS
1
2
3
4
5
6
7
8
16-pin TSSOP
16
15
14
13
12
11
10
9
S1
NC
VDD
S0
27M
GND
ACLK
S2
Audio Clock Select Table
S2
0
0
0
0
1
1
1
1
S1
0
0
1
1
0
0
1
1
S0
0
1
0
1
0
1
0
1
ACLK (MHz)
3.072
4.096
6.144
8.192
12.288
24.576
33.8688
73.728
Pin Descriptions
Pin
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Pin
Name
X2
X1
VDD
VDD
VIN
GND
GND
PDTS
S2
ACLK
GND
27M
S0
VDD
NC
S1
Pin
Type
Output
Input
Power
Power
Input
Power
Power
Power
Input
Output
Power
Output
Input
Power
--
Input
Pin Description
Crystal connection. Connect to a 27 MHz fundamental mode pullable
crystal.
Crystal connection. Connect to a 27 MHz fundamental mode pullable
crystal.
Connect to +3.3 V.
Connect to +3.3 V.
Voltage input to VCXO. Changing the voltage between 0 to 3.3 V controls
the VCXO frequency.
Connect to ground.
Connect to ground.
Power Down Tri-state. This pin powers down entire chip and tri-states the
outputs when low. Internal pull-up resistor.
Select input S2. Selects ACLK per table above. Internal pull-up resistor.
Audio clock output per table above.
Connect to ground.
27 MHz reference clock output.
Select input S0. Selects ACLK per table above. Internal pull-up resistor.
Connect to +3.3 V.
No connect. Do not connect anything to this pin.
Select input S1. Selects ACLK per table above. Internal pull-up resistor.
IDT™
VCXO PLUS AUDIO CLOCK FOR STB
2
MK3724
REV E 051310
MK3724
VCXO PLUS AUDIO CLOCK FOR STB
VCXO AND SYNTHESIZER
External Component Selection
The MK3724 requires a minimum number of external
components for proper operation.
Decoupling Capacitors
Decoupling capacitors of 0.01
µF
should be connected
between VDD and GND on pins 3 and 4, pins 6 and 7, and
pins 11 and 14 as close to the MK3724 as possible. For
optimum device performance, the decoupling capacitors
should be mounted on the component side of the PCB.
Avoid the use of vias in the decoupling circuit.
capacitors, one between X1 and ground, and another
between X2 and ground. Stuffing of these capacitors on the
PCB is optional. The need for these capacitors is
determined at system prototype evaluation, and is
influenced by the particular crystal used (manufacture and
frequency) and by PCB layout. The typical required
capacitor value is 1 to 4 pF.
To determine the need for and value of the crystal
adjustment capacitors, you will need a PC board of your final
layout, a frequency counter capable of about 1 ppm
resolution and accuracy, two power supplies, and samples
of the crystals which you plan to use in production. You will
also need measured initial accuracy for each crystal at the
specified crystal load capacitance (C
L
).
To determine the value of the crystal capacitors:
1. Connect VDD to 3.3 V. Connect pin 5 to the second power
supply. Adjust the voltage on pin 5 to 0V. Measure and
record the frequency of the CLK output.
2. Adjust the voltage on pin 5 to 3.3 V. Measure and record
the frequency of the same output.
To calculate the centering error:
Series Termination Resistor
When the PCB traces between the clock outputs and the
loads are over 1 inch, series termination should be used. To
series terminate a 50
Ω
trace (a commonly used trace
impedance), place a 33
Ω
resistor in series with the clock
line, as close to the clock output pin as possible. The
nominal impedance of the clock output is 20
Ω.
Quartz Crystal
The MK3724 VCXO function consists of the external crystal
and the integrated VCXO oscillator circuit. To assure the
best system performance (frequency pull range) and
reliability, a crystal device meeting IDT’ recommended
parameters must be used, and the layout guidelines
discussed in the following section must be followed.
See Application Note MAN05 for a full list of crystal
parameters.
The frequency of oscillation of a quartz crystal is determined
by its “cut” and by the load capacitors connected to it. The
MK3724 incorporates on-chip variable load capacitors that
“pull” (change) the frequency of the crystal. The crystal
specified for use with the MK3724 is designed to have zero
frequency error when the total of on-chip + stray
capacitance is 14 pF.
The external crystal must be connected as close to the chip
as possible and should be on the same side of the PCB as
the MK3724. There should be no via’s between the crystal
pins and the X1 and X2 device pins. There should be no
signal traces underneath or close to the crystal.
6
(
f
3.3
(
3.0
)V
–
f
t arg et
)
+
(
f
0V
–
f
t arg et
)
Error = 10 x ----------------------------------------------------------------------------------------
–
error
xtal
f
t arg et
Where:
f
target
= nominal crystal frequency
error
xtal
=actual initial accuracy (in ppm) of the crystal being
measured
If the centering error is less than ±25 ppm, no adjustment is
needed. If the centering error is more than 25 ppm negative,
the PC board has excessive stray capacitance and a new
PCB layout should be considered to reduce stray
capacitance. (Alternately, the crystal may be re-specified to
a higher load capacitance. Contact IDT for details.) If the
centering error is more than 25 ppm positive, add identical
fixed centering capacitors from each crystal pin to ground.
The value for each of these caps (in pF) is given by:
Crystal Tuning Load Capacitors
The crystal traces should include pads for small fixed
IDT™
VCXO PLUS AUDIO CLOCK FOR STB
3
MK3724
REV E 051310
MK3724
VCXO PLUS AUDIO CLOCK FOR STB
VCXO AND SYNTHESIZER
External Capacitor =
2 x (centering error)/(trim sensitivity)
Trim sensitivity is a parameter which can be supplied by your
crystal vendor. If you do not know the value, assume it is 30
ppm/pF. After any changes, repeat the measurement to
verify that the remaining error is acceptably low (typically
less than ±25 ppm).
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the MK3724. These ratings, which are
standard values for IDT commercially rated parts, are stress ratings only. Functional operation of the device at these
or any other conditions above those indicated in the operational sections of the specifications is not implied.
Exposure to absolute maximum rating conditions for extended periods can affect product reliability. Electrical
parameters are guaranteed only over the recommended operating temperature range.
Item
Supply Voltage, VDD
All Inputs and Outputs
Ambient Operating Temperature, Commercial
Ambient Operating Temperature, Industrial
Storage Temperature
Soldering Temperature
7V
Rating
-0.5 V to VDD+0.5 V
0 to +70° C
-40 to +85° C
-65 to +150° C
260° C
Recommended Operation Conditions
Parameter
Ambient Operating Temperature, Commercial
Ambient Operating Temperature, Industrial
Power Supply Voltage (measured in respect to GND)
Reference crystal parameters
Min.
0
-40
+3.135
Typ.
Max.
+70
+85
+3.465
Units
°
C
°
C
V
Refer to page 3
DC Electrical Characteristics
VDD=3.3 V ±5%
, Ambient temperature -40 to +85° C, unless stated otherwise
Parameter
Operating Voltage
Output High Voltage
Output Low Voltage
Output High Voltage (CMOS
Level)
Output Low Voltage (CMOS
Level)
Input High Voltage (S1:S0)
Symbol
VDD
V
OH
V
OL
V
OH
V
OL
V
IH
Conditions
I
OH
= -12 mA
I
OL
= 12 mA
I
OH
= -4 mA
I
OH
= +4 mA
Min.
3.135
2.4
Typ.
Max.
3.465
0.4
Units
V
V
V
V
VDD-0.4
0.375
2.0
V
V
IDT™
VCXO PLUS AUDIO CLOCK FOR STB
4
MK3724
REV E 051310
MK3724
VCXO PLUS AUDIO CLOCK FOR STB
VCXO AND SYNTHESIZER
Parameter
Input High Voltage (S2)
Input Low Voltage (S1:S0)
Input Low Voltage (S2)
Input High Current
Input Low Current
Operating Supply Current
Short Circuit Current
VIN, VCXO Control Voltage
On Chip Pull-up Resistor,
inputs
Input Capacitance
Nominal Output Impedance
Symbol
V
IH
V
IL
V
IL
I
IH
I
IL
IDD
I
OS
V
IA
R
PU
C
IN
Z
OUT
Conditions
Min.
2.5
Typ.
Max.
0.8
0.5
Units
V
V
V
µA
µA
mA
mA
at 3.3V, Sx, PDTS
at 0V, Sx, PDTS
No load
0
Input selects
Input selects
0.1
-8.5
11
±50
3.3
360
5
20
V
kΩ
pF
Ω
AC Electrical Characteristics
VDD = 3.3 V ±5%,
Ambient Temperature -40 to +85° C, unless stated otherwise
Parameter
Crystal Pullability
VCXO Gain
Output Rise Time
Output Fall Time
Output Clock Duty Cycle
Maximum Output Jitter,
short term
Changing Frequency
Setting Time
Power-up time
Symbol
f
P
t
OR
t
OF
t
D
t
J
Conditions
0V< VIN < 3.3 V, Note 1
VIN = VDD/2 + 1 V, Note 1
20% to 80%, C
L
=15 pF
80% to 20%, C
L
=15 pF
Measured at 1.65 V, C
L
=15
pF
C
L
=15 pF
Min.
+ 100
Typ.
+ 150
150
1.2
1.2
Max. Units
ppm
ppm/V
2.0
2.0
60
ns
ns
%
ps
1
ms
ms
ms
40
50
+150
PLL lock time from power-up
up to ±1% of final frequency
PDTS goes high until stable
CLK output up to 1% of final
frequency
10
2
Note 1: External crystal device must conform with Pullable Crystal Specifications listed on page 3.
IDT™
VCXO PLUS AUDIO CLOCK FOR STB
5
MK3724
REV E 051310
电源技术
