DS4026
10MHz to 51.84MHz TCXO
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The output driver is a CMOS square-wave output with
symmetrical rise and fall time.
The temperature sensor provides a 12-bit temperature
reading with a resolution of 0.0625°C. The sensor is in
continuous conversion mode. If DCOMP is set, conver-
sions continue but temperature updates are inhibited.
The controller coordinates the conversion of tempera-
ture into digital codes. When the temperature reading is
different from the previous one or the frequency tuning
register is changed, the controller looks up the two cor-
responding capacitance trim codes from the lookup
table at a 0.5°C increment. The trim codes are interpo-
lated to 0.0625°C resolution.
The result is added with the tuning value from the fre-
quency tuning register and loaded into the DAC regis-
ters to adjust voltage output. The monotonic DAC
provides an analog voltage based on temperature
compensation to drive the variable capacitor.
The DS4026 operates as a slave device on the serial
bus. Access is obtained by implementing a START
condition and providing a device identification code fol-
lowed by data. Subsequent registers can be accessed
sequentially until a STOP condition is executed.
Address Map
Disable Compensation Update (DCOMP)
DCOMP is bit 7 of the frequency tuning register (see
the
Frequency Tuning Register (00h–01h), POR = 00h
table). When set to logic 1, this bit’s temperature-com-
pensation function is disabled. This disabling prevents
the variable capacitor in the oscillator block from
changing. However, the temperature register still per-
forms temperature conversions. The temperature trim
code from the last temperature conversion before
DCOMP is enabled is used for temperature compensa-
tion. The FTUNE registers are still functional when
DCOMP is disabled.
The frequency tuning registers adjust the base frequen-
cy. The frequency tuning value is represented in two’s
complement data. Bit 6 of FTUNEH is the sign, bit 5 is
the MSB, and bit 0 of FTUNEL is the LSB (see Table 1).
When the tuning register low (01h) is programmed with
a value, the next temperature update cycle sums the
programmed value with the factory compensated
value. This allows the user to digitally control the base
frequency using the I
2
C protocol.
These frequency tuning register bits allow the tuning of
the base frequency. Each bit typically represents
about 1ppb (typ). For FTUNEH = 3Fh and FTUNEL =
FFh, the device pushes the base frequency by approx-
imately +15ppm.
Frequency Tuning Register (00h–01h), POR = 00h
