The SP5610 is programmed from an I C Bus. Data and
the reference divider. The reference divider division ratio is
switchable from 512 to 1024, and is controlled by bit 7 of byte
4 (TS0); a logic 1 for 512; a logic 0 for 1024. The SP5610 differs
Clock are fed in on the SDA and SCL lines respectively as
defined by the I C Bus format. The synthesiser can either
accept new data (write mode) or send data (read mode). The
LSB of the address byte (R/W) sets the device into write mode
if it is low and read mode if it is high. The Tables in Fig. 3
illustrate the format of the data. The device can be
programmed to respond to several addresses, which enables
from the SP5510 in this respect, only 512 being available on
the SP5510. Note, the comparison frequency is 7.8125kHz
when a 4MHz reference is used, and divide by 512 is selected.
Bit 2 of byte 4 of the programming data (CP) controls the
current in the charge pump circuit, a logic 1 for "170mA and
a logic 0 for "50mA allowing compensation for the variable
tuning slope of the tuner and also to enable fast channel
changes over the full band. When the device is ‘frequency
locked’ the charge pump current is internally set to "50mA
the use of more than one synthesiser in an I C Bus system.
Table 4 shows how the address is selected by applying a
voltage to P3. When the device receives a correct address
byte, it pulls the SDA line low during the acknowledge period,
and during following acknowledge periods after further data
bytes are programmed. When the device is programmed into
the read mode, the controller accepting the data must pull the
SDA line low during all status byte acknowledge periods to
read another status byte. If the controller fails to pull the SDA
line low during this period, the device generates an internal
STOP condition, which inhibits further reading.
regardless of CP
Bit 4 of byte 4 (T0) disables the charge pump when it is set
to a logic 1.
Bit 8 of byte 4 (OS) switches the charge pump drive
amplifier’s output off when it is set to a logic 1.
Bit 3 of byte 4 (T1) enables various test modes when set
high. These modes are selected by bits 5, 6, 7 of byte 4 (TS2,
TS1, TS0) as detailed in Table 5. When T1 is set low, TS2 and
TS1 are assigned a ‘don’t care’ condition, and TS0 selects the
reference divider ratio as previously described.
Byte 5 programs the output ports P3 to P7; a logic 0 for a
high impedance output and a logic 1 for low impedance (on).
WRITE MODE (Frequency Synthesis)
When the device is in write mode bytes 2+3 select the
synthesised frequency, while bytes 4+5 control the output port
states, charge pump, reference divider ratio and various test
Once the correct address is received and acknowledged,
the first bit of the next byte determines whether that byte is
interpreted as byte 2 or 4; a logic 0 for frequency information
and a logic 1 for control and output port information. When byte
When the device is in read mode the status byte read from
the device on the SDA line takes the form shown in Table 2.
Bit 1 (POR) is the power–on reset indicator and is set to
logic 1 if the VCC supply to the device has dropped below 3V
(at 25 C), e.g. when the device is initially turned on. The POR
is received the device always expects byte 3 next. Similarly,
when byte 4 is received the device expects byte 5 next.
Additional data bytes can be entered without the need to
is reset to 0 when the read sequence is terminated by a stop
command. When POR is set high (at low VCC), the
programmed information is lost and the output ports are all set
to high impedance.
re–address the device until an I C stop condition is
recognised. This allows a smooth frequency sweep for fine
tuning or AFC purposes.
If the transmission of data is stopped mid–byte (e.g. by
another device on the bus) then the previously programmed
byte is maintained.
Frequency data from bytes 2 and 3 is stored in a 15–bit
register and is used to control the division ratio of the 15–bit
programmable divider. This is preceded by a divide–by–8
prescaler and amplifier to give excellent sensitivity at the local
oscillator input, see Fig. 5. The input impedance is shown in
Bit 2 (FL) indicates whether the device is phase locked, a
logic 1 is present if the device is locked, and a logic 0 if the
device is unlocked.
Bits 3, 4 and 5 (I2, I1, I0) show the status of the I/O Ports P7,
P5 and P4 respectively. A logic 0 indicates a low level and a
logic 1 a high level. If the ports are to be used as inputs they
should be programmed to a high impedance state (logic 1).
These inputs will then respond to data complying with TTL
type voltage levels.
The programmed frequency can be calculated by
multiplying the programmed division ratio by 8 times the
Bits 6, 7 and 8 (A2, A1, A0) combine to give the output of
the 5 level ADC. The ADC can be used to feed AFC
information to the microprocessor from the IF section of the
receiver, as illustrated in the typical application circuit.
comparison frequency FCOMP
When frequency data is entered, the phase comparator, via
a charge pump and varicap drive amplifier, adjusts the local
oscillator control voltage until the output of the programmable
divider is frequency and phased locked to the comparison
The reference frequency may be generated by an external
source capacitively coupled into pin 2, or provided by an
on–board crystal controlled oscillator. The comparison
frequency FCOMP is derived from the reference frequency via
A typical application is shown in Fig. 4. All input/output
interface circuits are shown in Fig. 6. The SP5610 is function
and pin equivalent to the SP5510 device apart from the
switchable reference divider, and has much lower power
dissipation, improved RF sensitivity and better ESD