PLL Frequency Synthesizers for Electronic Tuning

Ordering number : EN5815B
LC72121, 72121M,
72121V
http://onsemi.com
CMOS LSI
PLL Frequency Synthesizers
for Electronic Tuning
Overview
The LC72121 and the LC72121M and the LC72121V are high input sensitivity (20 mVrms at 130 MHz) PLL
frequency synthesizers for 3 V systems. These ICs are serial data (CCB) compatible with the LC72131, and
feature the improved input sensitivity and lower spurious radiation (provided by a redesigned ground system)
required in high-performance AM/FM tuners.
Functions
 High-speed programmable divider
— FMIN: 10 to 160 MHz ... Pulse swallower technique
(With built-in divide-by-2 prescaler)
— AMIN: 2 to 40 MHz ... Pulse swallower technique
0.5 to 10 MHz ... Direct division technique
 IF counter
— IFIN: 0.4 to 15 MHz ... For AM and FM IF counting
 Reference frequency
— One of 12 reference frequencies can be selected
(using a 4.5 or 7.2 MHz crystal element)
1, 3, 5, 9, 10, 3.125, 6.25, 12.5, 15, 25, 50, and 100 kHz
 Phase comparator
— Supports dead zone control.
— Built-in unlocked state detection circuit
— Built-in deadlock clear circuit
 An MOS transistor for an active low-pass filter is built in.
 I/O ports
— Output-only ports: 4 pins
— I/O ports: 2 pins
— Supports the output of a clock time base signal.


 Operating ranges
— Supply voltage: 2.7 to 3.6 V
— Operating temperature: – 40 to 85°C
 Package
— DIP22S, MFP24S, SSOP24
 Comparison with the LC72131/M
— Serial data compatible (CCB)
— Identical pin functions
— Two VSS pins were added.
— The DIP version is pin compatible
(VSS pins were inserted as the DIP22S NC pins.)
— The MFP product provides a modified pin
assignment
(The MFP20 package was replaced by an MFP24
package, and extra VSS pins were added.)
— The SSOP24 is a newly developed package
that has the same pin assignment as the MFP24S
product.
CCB is ON Semiconductor® ’s original format. All addresses are managed
by ON Semiconductor® for this format.
CCB is a registered trademark of Semiconductor Components Industries, LLC.
ORDERING INFORMATION
See detailed ordering and shipping information on page 23 of this data sheet.
Semiconductor Components Industries, LLC, 2013
July, 2013
10803AS(OT)/D3098HA(OT)/70398RM(OT) No.5815-1/23
LC72121, 72121M, 72121V
Package Dimensions
unit: mm
unit: mm
DIP22S
MFP24S
[LC72121]
[LC72121M]
12
13
24
6.35
7.6
1
5.4
0.25
7.62
6.4
22
11
0.48
1.78
1.5
0.15
0.625
1.8max
3.9max
12
12.6
1.7
0.35
DIP22S
1.0 0.8
0.1
0.95
1
3.3
0.51min 3.25
21.2
MFP24S
unit: mm
SSOP24
1.0
[LC72121V]
24
0.5
7.6
5.6
13
12
1.6max
1
0.15
0.1
8.0
0.22
0.65
0.43
SSOP24
Pin Assignments
Top view
No. 5815-2/23
LC72121, 72121M, 72121V
Block Diagram
No. 5815-3/23
LC72121, 72121M, 72121V
Specifications
Absolute Maximum Ratings at Ta = 25°C, VSSd = VSSa = VSSX = 0 V
Parameter
Maximum supply voltage
Maximum input voltage
Maximum output voltage
Maximum output current
Allowable power dissipation
Symbol
Conditions
Ratings
Unit
VDD max
VDD
–0.3 to +7.0
VIN1 max
CE, DI, CL, AIN
–0.3 to +7.0
V
VIN2 max
XIN, FMIN, AMIN, IFIN
–0.3 to VDD +0.3
V
V
V
VIN3 max
IO1, IO2
–0.3 to +15
VO1 max
DO
–0.3 to +7.0
V
VO2 max
XOUT, PD
–0.3 to VDD +0.3
V
VO3 max
BO1 to BO4, IO1, IO2, AOUT
IO1 max
DO, AOUT
IO2 max
BO1 to BO4, IO1, IO2
Pd max
–0.3 to +15
V
0 to +6.0
(Ta ≤ 85°C)
mA
0 to +10.0
mA
DIP22S:
350
mW
MFP24S:
200
mW
SSOP24:
150
mW
Operating temperature
Topr
–40 to +85
°C
Storage temperature
Tstg
–55 to +125
°C
Allowable Operating Ranges at Ta = – 40 to +85°C, VSSd = VSSa = VSSX = 0 V
Parameter
Supply voltage
Input high-level voltage
Input low-level voltage
Output voltage
Input frequency
Input amplitude
Guaranteed crystal oscillator frequency
Symbol
Conditions
Ratings
min
typ
Unit
max
VDD
VDD
2.7
3.6
V
VIH1
CE, DI, CL
0.7 VDD
6.5
V
VIH2
IO1, IO2
V
0.7 VDD
13
VIL
CE, DI, CL, IO1, IO2
0
0.3 VDD
V
VO1
DO
0
6.5
V
VO2
BO1 to BO4, IO1, IO2, AOUT
0
13
V
fIN1
XIN: VIN1
1
8
MHz
fIN2
FMIN: VIN2
10
160
MHz
fIN3
AMIN (SNS = 1): VIN3
2
40
MHz
fIN4
AMIN (SNS = 0): VIN4
0.5
10
MHz
fIN5
IFIN: VIN5
0.4
15
MHz
VIN1
XIN: fIN1
200
800
mVrms
mVrms
VIN2-1
FMIN: f = 10 to 130 MHz
20
800
VIN2-2
FMIN: f = 130 to 160 MHz
40
800
mVrms
VIN3
AMIN (SNS = 1): fIN3
40
800
mVrms
VIN4
AMIN (SNS = 0): fIN4
40
800
mVrms
VIN5-1
IFIN: fIN5, IFS = 1
40
800
mVrms
VIN5-2
IFIN: fIN5, IFS = 0
70
800
mVrms
4
8
Xtal
XIN, XOUT: *
MHz
Note: Recommended value for CI for the crystal oscillator element: CI ≤ 120Ω (4.5MHz), CI ≤ 70Ω (7.2MHz)
Electrical Characteristics in the Allowable Operating Ranges
Parameter
Symbol
Conditions
Ratings
min
typ
max
Unit
Rf1
XIN
1
MΩ
Rf2
FMIN
500
kΩ
Rf3
AMIN
500
kΩ
Rf4
IFIN
250
Rpd1
FMIN
100
200
400
kΩ
Rpd2
AMIN
100
200
400
kΩ
Hysteresis
VHIS
CE, DI, CL
Output high-level voltage
VOH1
PD: IO = –1 mA
Internal feedback resistance
Internal pull-down resistance
0.1 VDD
VDD – 1.0
kΩ
V
V
Continued on next page.
No. 5815-4/23
LC72121, 72121M, 72121V
Continued from preceding page.
Parameter
Symbol
VOL1
VOL2
Output low-level voltage
VOL3
Input low-level current
typ
Unit
max
PD: IO = 1 mA
1.0
V
BO1 to BO4, IO1, IO2: IO = 1 mA
0.2
V
BO1 to BO4, IO1, IO2: IO = 8 mA
1.6
V
DO: IO = 1 mA
0.2
V
V
DO: IO = 5 mA
1.0
0.5
V
IIH1
CE, DI, CL: VI = 6.5 V
5.0
µA
IIH2
IO1, IO2: VI = 13 V
5.0
µA
IIH3
XIN: VI = VDD
1.3
8
µA
IIH4
FMIN, AMIN: VI = VDD
2.5
15
µA
IIH5
IFIN: VI = VDD
5.0
30
µA
IIH6
AIN: VI = 6.5 V
200
nA
IIL1
CE, DI, CL: VI = 0 V
5.0
µA
IIL2
IO1, IO2: VI = 0 V
5.0
µA
IIL3
XIN: VI = 0 V
1.3
8
µA
IIL4
FMIN, AMIN: VI = 0 V
2.5
15
µA
IIL5
IFIN: VI = 0 V
5.0
30
µA
IIL6
AIN: VI = 0 V
200
nA
BO1 to BO4, IO1, IO2, AOUT: VO = 13 V
5.0
µA
IOFF1
Output off leakage current
Ratings
min
AOUT: IO = 1 mA, AIN = 1.3 V
VOL4
Input high-level current
Conditions
IOFF2
DO: VO = 6.5 V
5.0
µA
High-level 3-state off leakage current
IOFFH
PD: VO = VDD
0.01
200
nA
Low-level 3-state off leakage current
IOFFL
PD: VO = 0 V
0.01
200
nA
Input capacitance
Supply current
CIN
FMIN
IDD1
VDD: Xtal = 7.2 MHz, fIN2 = 130 MHz,
VIN2 = 20 mVrms
2.5
IDD2
VDD: PLL block stopped (PLL inhibit mode)
Crystal oscillator operating
(crystal frequency: 7.2 MHz)
0.3
IDD3
VDD: PLL block stopped, crystal oscillator
stopped
6
pF
6
mA
mA
10
µA
Pin Descriptions
Pin
name
Pin No.
LC72121
Type
LC72121M
LC72121V
XIN
1
1
XOUT
22
24
Xtal
Function
Equivalent circuit
• Crystal oscillator element connections (4.5 or 7.2 MHz)
• FMIN is selected when DVS in the serial data is set to 1.
• Input frequency: 10 to 160 MHz
FMIN
16
17
Local
oscillator
signal input
• The signal is passed through an internal divide-by-two prescaler and
then input to the swallow counter.
• The divisor can be set to a value in the range 272 to 65535. Since
the internal divide-by-two prescaler is used, the actual divisor will be
twice the set value.
• AMIN is selected when DVS in the serial data is set to 0.
• When SNS in the serial data is set to 1:
• Input frequency: 2 to 40 MHz
• The signal is input to the swallow counter directly.
AMIN
15
16
Local
oscillator
signal input
• The divisor can be set to a value in the range 272 to 65535. The
set value becomes the actual divisor.
• When SNS in the serial data is set to 0:
• Input frequency: 0.5 to 10 MHz
• The signal is input to a 12-bit programmable divider directly.
• The divisor can be set to a value in the range 4 to 4095. The set
value becomes the actual divisor.
Continued on next page.
No. 5815-5/23
LC72121, 72121M, 72121V
Continued from preceding page.
Pin No.
Pin
name
LC72121
LC72121M
LC72121V
CE
3
3
Chip enable
• This pin must be set high to enable serial data input (DI) or serial
data output (DO).
DI
4
4
Input data
• Input for serial data transferred from the controller
CL
5
5
Clock
• Clock used for data synchronization for serial data input (DI) and
serial data output (DO).
DO
6
6
Output data
• Output for serial data transmitted to the controller. The content of the
data transmitted is determined by DOC0 through DOC2.
VDD
17
18
Power supply
• LC72121 power supply (VDD 2.7 to 3.6 V)
• The power on reset circuit operates when power is first applied.
——
Type
Function
Equivalent circuit
VSSX
2
2
Ground
• Ground for the crystal oscillator circuit
——
VSSa
21
22
Ground
——
VSSd
14
15
Ground
• Ground for the low-pass filter MOS transistor
• Ground for the LC72121 digital systems other than those that use
VSSa or VSSX.
IO1
11
11
IO2
13
14
BO1
7
7
BO2
8
8
BO3
9
9
BO4
10
10
I/O port
• Shared function I/O ports
• The pin function is determined by IOC1 and IOC2 in the serial data.
When the data value 0: Input port
When the data value 1: Output port
• When specified to function as an input port:
The input pin state is reported to the controller through the DO pin.
When the input state is low: The data will be 0:
When the input state is high: The data will be 1:
• When specified to function as an output port:
The output state is determined by IO1 and IO2 in the serial data.
When the data value is 0: The output state will be the open circuit
state.
When the data value is 1: The output state will be a low level.
• These pins are set to input mode after a power on reset.
Output port
• Output-only ports
• The output state is determined by BO1 through BO4 in the serial
data.
When the data value is 0: The output state will be the open circuit
state.
When the data value is 1: The output state will be a low level.
• A time base signal (8 Hz) is output from BO1 when TBC in the serial
data is set to 1.
Charge pump
output
• PLL charge pump output
A high level is output when the frequency of the local oscillator signal
divided by N is higher than the reference frequency, and a low level
is output when that frequency is lower. This pin goes to the highimpedance state when the frequencies match.
PD
18
19
AIN
19
20
AOUT
20
21
Low-pass filter
• Connections for the MOS transistor used for the PLL active low-pass
amplifier
filter.
transistor
IFIN
12
13
IF counter
NC
—
12
23
NC pin
——
• The input frequency range is 0.4 to 15 MHz
• The signal is passed directly to the IF counter.
• The result is output, MSB first, through the DO pin.
• Four measurement periods are supported: 4, 8, 32, and 64 ms.
• No connection
——
No. 5815-6/23
LC72121, 72121M, 72121V
Procedures for Input and Output of Serial Data
This product uses the CCB (Computer Control Bus), which is original audio product serial bus format, for data input and
output. This product adopts an 8-bit address CCB format.
I/O mode
1
2
3
IN1 (82)
IN2 (92)
OUT (A2)
Address
Function
B0
B1
B2
B3
A0
A1
A2
A3
0
0
0
1
0
1
0
0
• Control data input (serial data input) mode
• 24 bits of data are input.
• See the “DI Control Data (serial data input)” section for details on the
content of the input data.
0
• Control data input (serial data input) mode
• 24 bits of data are input.
• See the “DI Control Data (serial data input)” section for details on the
content of the input data.
0
• Data output (serial data output) mode
• The number of bits output is equal to the number of clock cycles.
• See the “DO output Data (serial data output)” section for details on the
content of the output data.
1
0
0
1
0
0
1
1
0
0
1
1
0
0
I/O mode determined
Normally high
Normally low
No. 5815-7/23
LC72121, 72121M, 72121V
Structure of the DI Control Data (serial data input)
• IN1 mode
• IN2 mode
No. 5815-8/23
LC72121, 72121M, 72121V
DI Control Data
No.
Control block/data
Function
Related data
• Specifies the divisor for the programmable divider.
This is a binary value in which P15 is the MSB. The LSB changes depending on DVS and SNS.
(* : don’t care)
DVS
Programmable
divider data
1
SNS
LSB
Set divisor (N)
Actual divisor
1
*
P0
272 to 65535
Twice the set value
0
1
P0
272 to 65535
The set value
0
0
P4
4 to 4095
The set value
* LSB: When P4 is the LSB, P0 to P3 are ignored.
P0 to P15
DVS, SNS
• These pins select the signal input to the programmable divider (FMIN or AMIN) and switch the input
frequency range.
(* : don’t care)
DVS
SNS
Input pin
Frequency range accepted by the input pin
10 to 160 MHz
1
*
FMIN
0
1
AMIN
2 to 40 MHz
0
0
AMIN
0.5 to 10 MHz
* See the “Structure of the Programmable Divider” section for details.
• Reference frequency selection
2
Reference divider
data
R0 to R3
XS
R3
R2
R1
R0
0
0
0
0
Reference frequency
100
0
0
0
1
50
0
0
1
0
25
0
0
1
1
25
0
1
0
0
12.5
0
1
0
1
6.25
0
1
1
0
3.125
0
1
1
1
1
0
0
0
10
1
0
0
1
9
1
0
1
0
5
1
0
1
1
1
1
1
0
0
3
1
1
0
1
15
1
1
1
0
PLL INHIBIT + Xtal OSC STOP
1
1
1
1
PLL INHIBIT
kHz
3.125
* PLL INHIBIT mode
In this mode, the programmable divider and the IF counter block are stopped, the FMIN, AMIN, and IFIN
pins are pulled down to ground, and the charge pump output goes to the high-impedance state.
• Crystal oscillator element selection data
XS = 0: 4.5 MHz
XS = 1: 7.2 MHz
Note that 7.2 MHz is selected after a power on reset.
• IF counter measurement start command data
CTE = 1: Starts the counter
CTE = 0: Resets the counter
3
IF counter control
data
• Determines the IF counter measurement time.
GT1
GT0
Measurement time
Wait time
CTE
0
0
4 ms
3 to 4 ms
GT0, GT1
0
1
8
3 to 4
1
0
32
7 to 8
1
1
64
7 to 8
IFS
* See the “Structure of the IF Counter” section for details.
Continued on next page.
No. 5815-9/23
LC72121, 72121M, 72121V
Continued from preceding page.
No.
Control block/data
4
I/O port setup data
IOC1,IOC2
5
Output port data
BO1 to BO4
IO1,IO2
Function
Related data
• Specifies input or output for the shared function I/O pins (IO1 and IO2).
Data = 0: Input port
Data = 1: Output port
• Determines the output state of the BO1 through BO4, IO1, and IO2 output ports.
Data = 0: Open
Data = 1: Low level
• The data is reset to 0, setting the pins to the open state, after a power on reset.
IOC1
IOC2
• Determines the DO pin output.
6
DOC2
DOC1
DOC0
0
0
0
DO pin state
Open
0
0
1
Low when the PLL is unlocked
0
1
0
end-UC *1
0
1
1
Open
1
0
0
Open
1
0
1
The IO1 pin state *2
1
1
0
The IO2 pin state *2
1
1
1
Open
UL0, UL1
The open state is selected after a power on reset.
DO pin control data
*1. end-UC: IF counter measurement end check
DOC0
CTE
DOC1
IOC1
DOC2
IOC2
(1)When end-UC is selected and an IF count is started (by switching CTE from 0 to 1), the DO pin
automatically goes to the open state.
(2)When the IF counter measurement period completes, the DO pin goes to the low level, allowing
applications to test for the completion of the count period.
(3)The DO pin is set to the open state by performing a serial data input or output operation (when the CE
pin is set high).
*2. The DO pin will go to the open state if the corresponding IO pin is set up to be an output port.
Note: During the data input period (the period that CE is high in IN1 or IN2 mode), the DO pin goes to the
open state regardless of the DO pin control data (DOC0 to DOC2). During the data output period (the
period that CE is high in OUT mode) the DO pin state reflects the internal DO serial data in
synchronization with the CL clock, regardless of the DO pin control data (DOC0 to DOC2).
• Selects the width of the phase error (øE) detected for PLL lock state discrimination. The state is taken to
be unlocked if a phase error in excess of the detection width occurs.
7
Unlocked state
detection data
UL0, UL1
UL1
UL0
øE detection width
Detection output
0
0
Stopped
Open
0
1
0
øE is output directly
1
0
±0.55 µs
øE is extended by 1 to 2 ms
1
1
±1.11 µs
øE is extended by 1 to 2 ms
DOC0
DOC1
DOC2
* When the PLL is unlocked, the DO pin goes low and UL in the serial data output is set to 0.
• Controls the phase comparator dead zone
8
DZ1
DZ
Dead zone mode
Phase comparator
control data
0
0
DZA
0
1
DZB
DZ0, DZ1
1
0
DZC
1
1
DZD
Dead zone width: DZA < DZB < DZC < DZD
Continued on next page.
No. 5815-10/23
LC72121, 72121M, 72121V
Continued from preceding page.
No.
9
Control block/data
Clock time base
TBC
Function
• Setting the TBC bit to 1 causes an 8-Hz clock time base signal with a 40% duty to be output from the
BO1 pin. (The BO1 data will be ignored.)
Related data
BO1
• Forcibly controls the charge pump output.
10
Charge pump
control data
DLC
11
IF counter control
data
IFS
12
13
Test data
TEST0 to 2
DNC
DLC
Charge pump output
0
Normal operation
1
Forced to low
* If the circuit deadlocks due to the VCO control voltage (Vtune) being 0 and the VCO being stopped,
applications can get out of the deadlocked state by setting the charge pump output to low and setting
Vtune to VCC. (Deadlock clear circuit)
• This data is normally set to 1. Setting this data to 0 sets the circuit to reduced input sensitivity mode, in
which the sensitivity is reduced by about 10 to 30 mV rms.
* See the “IF Counter Operation” section for details.
• Test data
TEST0
TEST1
All these bits must be set to 0.
TEST2
All these bits are set to 0 after a power on reset.
• This bit must be set to 0.
Structure of the DO Output Data (serial data output)
• OUT mode
DO Output Data
No.
1
Control block/data
I/O port data
12, I1
2
PLL unlocked state
data
3
IF counter binary
data
UL
C19 to C0
Function
Related data
• Data latched from the I/O port IO1 or IO2 pin states.
• These bits reflect the pin states regardless of the I/O port mode (input or output).
The data is latched at the point the circuit enters data output mode (OUT mode).
H:1
I1 ← The IO1 pin state
I2 ← The IO2 pin state
L:0
IOC1
IOC2
• Indicates the state of the unlocked state detection circuit.
UL ← 0: When the PLL is unlocked.
UL ← 1: When the PLL is locked or in the detection disabled mode.
UL0
UL1
• Indicates the value of the IF counter (20-bit binary counter).
C19 ← MSB of the binary counter
C0 ← LSB of the binary counter
CTE
GT0
GT1
No. 5815-11/23
LC72121, 72121M, 72121V
Serial Data Input (IN1/IN2) tSU, tHD, tEL, tES, tEH ≥ 0.75 µs t LC < 0.75 µs
• CL: Normally high
• CL: Normally low
Serial Data Output (Out) tSU, tHD, tEL, tES, tEH ≥ 0.75 µs t DC, tDH < 0.35 µs
• CL: Normally high
• CL: Normally low
Note:
The data conversion times (tDC and tDH) depend on the value of the pull-up resistor and the printed circuit board capacitance since the DO pin is an
n-channel open-drain circuit.
No. 5815-12/23
LC72121, 72121M, 72121V
Serial Data Timing
When CL is Stopped at the Low Level
When CL is Stopped at the High Level
Parameter
Symbol
Conditions
Ratings
min
typ
max
Unit
Data setup time
tSU
DI, CL
0.75
µs
Data hold time
tHD
DI, CL
0.75
µs
Clock low level time
tCL
CL
0.75
µs
Clock high level time
tCH
CL
0.75
µs
CE wait time
tEL
CE, CL
0.75
µs
CE setup time
tES
CE, CL
0.75
µs
CE hold time
tEH
CE, CL
0.75
Data latch change time
tLC
Data output time
µs
0.75
µs
tDC
DO, CL
These values differ depending on the value of the pull-up
0.35
µs
tDH
DO, CE
resistor used and the printed circuit board capacitance.
0.35
µs
No. 5815-13/23
LC72121, 72121M, 72121V
Structure of the Programmable Divider
DVS
SNS
Input pin
Set divisor
Actual divisor
Input frequency range
A
1
*
FMIN
272 to 65535
Twice the set value
10 to 160 MHz
B
0
1
AMIN
272 to 65535
The set value
2 to 40 MHz
C
0
0
AMIN
4 to 4095
The set value
0.5 to 10 MHz
*: Don’t care
Sample Programmable Divider Divisor Calculations
• For FM with a step size of 50 kHz (DVS = 1, SNS = *: FMIN selected)
FM RF = 90.0 MHz (IF +10.7 MHz)
FM VCO = 100.7 MHz
PLL fref = 25 kHz (R0 = 0, R1 = 1, R2 = 0, R3 = 0)
100.7 MHz (FM VCO) ÷ 25 kHz (fref) ÷ 2 (for the FMIN 1/2 prescaler) 2014 → 07DE (hexadecimal)
• For SW with a step size of 5 kHz (DVS = 0, SNS = 1: AMIN high-speed operation selected)
SW RF = 21.75 MHz (IF +450 kHz)
SW VCO = 22.20 MHz
PLL fref = 5 kHz (R0 = 0, R1 = 1, R2 = 0, R3 = 1)
22.2 MHz (SW VCO) ÷ 5 kHz (fref) = 4440 → 1158 (hexadecimal)
• For MW with a step size of 9 kHz (DVS = 0, SNS = 0: AMIN low-speed operation selected)
MW RF = 1008 kHz (IF +450 kHz)
WM VCO = 1458 kHz
PLL fref =9 kHz (R0 = 1, R1 = 0, R2 = 0, R3 = 1)
1458 (MW VCO) ÷ 9 kHz (fref) = 162 → 0A2 (hexadecimal)
No. 5815-14/23
LC72121, 72121M, 72121V
Structure of the IF Counter
The LC72121 IF counter is a 20-bit binary counter, and takes the IF signal from the IFIN pin as its input. The result of
the count can be read out serially, MSB first, from the DO pin.
GT1
GT0
0
Measurement time
Measurement time (GT)
Wait time (tWU)
0
4 ms
3 to 4 ms
0
1
8
3 to 4 ms
1
0
32
7 to 8 ms
1
1
64
7 to 8 ms
The IF frequency (Fc) is measured by determining how many pulses were input to the IF counter in the stipulated
measurement time, GT.
C (C = Fc x GT)
Fc =——
GT
C: Counted value (the number of pulses)
IF Counter Frequency Measurement Examples
• When the measurement time (GT) is 32 ms and the counted value (C) is 53980 (hexadecimal) or 342,400 (decimal).
IF frequency (FC) = 342400 ÷ 32 ms = 10.7 MHz
• When the measurement time (GT) is 8 ms and the counted value (C) is E10 (hexadecimal) or 3600 (decimal).
IF frequency (FC) = 3600 ÷ 8 ms = 450 kHz
No. 5815-15/23
LC72121, 72121M, 72121V
IF Counter Operation
Applications must first, before starting an IF count operation reset the IF counter by setting CTE in the serial data to 0.
The IF counter operation is started setting CTE in the serial data from 0 to 1. Although the serial data is latched by
dropping the CE pin from high to low, the IF signal input to the IFIN pin must be provided within the wait time from the
point CE goes low. Next, the readout of the IF counter after measurement is complete must be performed while CTE is
still 1, since the counter will be reset if CTE is set to 0.
Note: If IF counting is used, applications must determine whether or not the IF IC SD (station detect) signal is present in
the microcontroller software, and perform the IF count only if that signal is asserted. This is because auto-search
techniques that use IF counting only are subject to incorrect stopping at points where there is no station due to IF
buffer leakage.
Note that the LC72121 input sensitivity can be controlled with the IFS bit in the serial data.
Reduced sensitivity mode (IFS = 0) must be selected when this IC is used in conjunction with an IF IC that does
not provide an SD output and auto-search is implemented using only IF counting.
IFIN Minimum Sensitivity Standard
Input frequency : f [MHz]
IFS data
0.4 ≤ f < 0.5
0.5 ≤ f < 8
8 ≤ f ≤ 15
1(Normal mode)
40 mVrms (0.1 to 3 mVrms)
40 mVrms
40 mVrms (1 to 15 mVrms)
0 (Degraded sensitivity mode)
70 mVrms (5 to 10 mVrms)
70 mVrms
70 Vrms (30 to 40 mVrms)
Note: Values in parentheses are actual performance values that are provided for reference purposes.
No. 5815-16/23
LC72121, 72121M, 72121V
Unlocked State Detection Timing
• Unlocked state detection timing
Unlocked state detection is performed during the reference frequency (fref) period (interval). This means that a period
at least as long as the period of the reference frequency is required to recognize the locked/unlocked state. However,
applications must wait at least twice the period of the reference frequency immediately after changing the divisor (N)
before checking the locked/unlocked state.
Figure 1 Unlocked State Detection Timing
For example, if fref is 1 kHz (a period of 1 ms) applications must wait at least 2 ms after the divisor N is changed
before performing a locked/unlocked check.
Figure 2 Circuit Structure
No. 5815-17/23
LC72121, 72121M, 72121V
Figure 3 Combining with Software
• Outputting the unlocked state data in the serial data
At the point of data output 1 in figure 3, the unlocked state data will indicate the unlocked state, since the VCO
frequency is not stable (locked) yet. In cases such as this, the application should wait at least one whole period and then
check again whether or not the frequency has stabilized with the data output 2 operation in the figure. Applications can
implement even more reliable recognition of the locked state by performing several more checks of the state and
requiring that the locked state be detected sequentially.
<Flowchart for Lock Detection>
Divisor N changed (data input)
Wait at least 2 reference frequency periods.
Data output (1)
Valid output data is acquired by using an interval of at
least one reference frequency period.
Data output (2)
Locked state check
*
*: Even more reliable recognition of the locked state
can be achieved by performing several checks of the
state and requiring that the locked state be detected
sequentially.
NO
YES
A10180
• Directly outputting the unlocked state to the DO pin
Since the unlocked state (high level when locked, low when unlocked) is output from the DO pin, applications can
check for the locked state by waiting at least two reference frequency periods after changing the divisor N. However, in
this case also, even more reliable recognition of the locked state can be achieved by performing several checks of the
state and requiring that the locked state be detected sequentially.
No. 5815-18/23
LC72121, 72121M, 72121V
Clock Time Base Usage Notes
When using the clock time base output function, the output pin (BO1) pull-up resistor must have a value of over 100 kΩ.
The use of a Schmitt input in the microcontroller that accepts this signal is recommended to reduce chattering. This is to
prevent degradation of the VCO C/N characteristics when combining with a loop filter that uses the internal transistor
provided to form a low-pass filter. Although the ground for the clock time base output pin (VSSd) and the ground for the
transistor (VSSa) are isolated internally on the chip, applications must take care to avoid ground loops and minimize
current fluctuations in the time base pin to prevent degradation of the low-pass filter characteristics.
Pin States after a Power on Reset
No. 5815-19/23
LC72121, 72121M, 72121V
Sample Application Circuit
(Using the DIP22S package)
Since this is a high-impedance circuit,
it is susceptible to noise. Therefore,
lines in the printed circuit board
pattern should be made as short as
possible and it should be surrounded
by the ground pattern.
No. 5815-20/23
LC72121, 72121M, 72121V
Other Items
• Notes on the phase comparator dead zone
DZ1
DZ0
Dead zone mode
Charge pump
Dead zone
0
0
DZA
ON/ON
– –0s
0
1
DZB
ON/ON
–0s
1
0
DZC
OFF/OFF
+0s
1
1
DZD
OFF/OFF
+ +0s
When the charge pump is used with one of the ON/ON modes, correction pulses are generated from the charge pump
even if the PLL is locked. As a result, it is easy for the loop to become unstable, and special care is required in
application design. The following problems can occur if an ON/ON mode is used.
— Sidebands may be created by reference frequency leakage.
— Sidebands may be created by low-frequency leakage due to the correction pulse envelope.
Although the loop is more stable when a dead zone is present (i.e. when an OFF/OFF mode is used), a dead zone
makes it more difficult to achieve excellent C/N characteristics. On the other hand, while it is easy to achieve good C/N
characteristics when there is no dead zone, achieving good loop stability is difficult. Accordingly, the DZA and DZB
settings, in which there is no dead zone, can be effective in situations where a signal-to-noise ratio of 90 to 100 dB or
higher is required in FM reception, or where it is desirable to increase the pilot margin in AM stereo reception.
However, if such a high signal-to-noise ratio is not required for FM reception, if an adequate pilot margin can be
acquired in AM stereo reception, or if AM stereo is not required, then either DZC or DZD, in which there is a dead
zone, should be chosen.
Dead Zone
As shown in figure 1, the phase comparator compares a reference frequency (fr) with fp. As shown in figure 2, the phase
comparator's characteristics consist of an output voltage (V) that is proportional to the phase difference ø. However, due
to internal circuit delay and other factors, an actual circuit has a region (the dead zone, B) where the circuit cannot
actually compare the phases. To implement a receiver with a high S/N ratio, it is desirable that this region be as small as
possible. However, it is often desirable to have the dead zone be slightly wider in popularly-priced models. This is
because in certain cases, such as when there is a strong RF input, popularly-priced models can suffer from mixer to VCO
RF leakage that modulates the VCO. When the dead zone is small, the circuit outputs signals to correct this modulation
and this output further modulates the VCO. This further modulation may then generate beats and the RF signal.
Figure 1
Figure 2
• Notes on the FMIN, AMIN, and IFIN pins
Coupling capacitors should be placed as close to their pin as possible. A capacitance of about 100 pF is desirable for
these capacitors. In particular, if the IFIN pin coupling capacitor is not held under 1000 pF, the time to reach the bias
level may become excessive and incorrect counts may result due to the relationship with the wait time.
• Notes on IF counting → Use the SD signal in conjunction with IF counting
When counting the IF frequency, the microcontroller must determine the presence or absence of the IF IC SD (station
detect) signal and turn on the IF counter buffer output and execute the IF count only if there is an SD signal. Autosearch techniques that only use the IF counter are subject to incorrect stopping at points where there is no station due to
IF buffer leakage.
No. 5815-21/23
LC72121, 72121M, 72121V
• DO pin usage
The DO pin can be used for IF counter count completion checking and as an unlock detection output in addition to its
use in data output mode. It is also possible to have the DO pin reflect the state of an input pin to input that state to the
microcontroller.
• Power supply pins
Capacitors must be inserted between the power supply VDD and VSS pins for noise exclusion. These capacitors must be
placed as close as possible to the VDD and VSS pins.
• VCO setup
Applications must be designed so that the VCO (local oscillator) does not stop, even if the control voltage (Vtune) goes
to 0 V. If it is possible for the oscillator to stop, the application must use the control data (DLC) to temporarily force
Vtune to VCC to prevent deadlock from occurring. (Deadlock clear circuit)
• Front end connection example
Since this product (and the LC72131 as well) is designed with the relatively high resistance of 200 kΩ for the pulldown (on) resistors built in to the FMIN and AMIN pins, a common AM/FM local oscillator buffer can be used as
shown in the following circuit.
• PD pin
Note that the charge pump output voltage is reduced when this IC, which is a 3-V system, is used to replace the
LC72131, which is a 5-V system. This means that since the loop gain is reduced, the loop filter constants, the lock time
(SD wait time), and other related parameters must be reevaluated in the end product design.
No. 5815-22/23
LC72121, 72121M, 72121V
ORDERING INFORMATION
Device
LC72121-D-E
Package
DIP22S(300mil)
(Pb-Free)
Shipping (Qty / Packing)
LC72121M-TLM-E
MFP24S(300mil)
(Pb-Free)
2000 / Tape and Reel
LC72121V-D-MPB-E
SSOP24(275mil)
(Pb-Free)
60 / Fan-Fold
LC72121V-D-TML-E
SSOP24(275mil)
(Pb-Free)
1000 / Tape and Reel
LC72121V-TLM-E
SSOP24(275mil)
(Pb-Free)
1000 / Tape and Reel
22 / Fan-Fold
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PS No.5815-23/23