AZT71 Datasheet, PDF (6/14 Pages) Arizona Microtek, Inc – Programmable Capacitive Tuning IC

Arizona Microtek, Inc.
AZT71
Programmable Capacitive Tuning IC
PROGRAMMING FROM THE SHIFT REGISTER
To initially determine the capacitance value for the desired center frequency of the oscillator one should set the
capacitance of the AZT71 directly from the active shift register bits. To accomplish this, the CLK pin is left high after the
last control word bit has been shifted in. Figure 7 shows the control word 11001100100 has been serially entered into the
register. Note that bit0 is the 1^st bit to enter and bit10 is the last. In the AZT71, bit0 does not affect the capacitance value
but still must be included in the serial bit stream. For the shift register, capacitors are selected when bits are active HIGH.
bit 0
bit 1
bit 2
bit 3
bit 4
bit 5
bit 6
bit 7
bit 8
bit 9 bit 10
DA
bit 0
loaded 1^st
Register data
active when
CLK is high
CLK
t
Figure 7 - Shift register programming
WRITING DATA TO THE EEPROM
Once the desired capacitance value has been determined, the digital control word can be written or re-written into the
EEPROM. By storing the control word in the EEPROM, the customer is prevented from making adjustments from the
factory set programming data. This is accomplished within the AZT71 with internal pull-downs on the DA, PV, and CLK
pins. The detailed sequence for writing data to the EEPROM within the AZT71 is described in Table 6. Note that with
EEPROM, capacitors are selected when bits are active LOW.
Table 6 – Data writing sequence for EEPROM
Step
Action
1
Determine the desired capacitor control word with the operational power supply voltage and
desired oscillator conditions
2
Set the V_DD supply voltage to +5.0V
3
If EEPROM is not already erased, erase EEPROM (see
ERASING THE EEPROM)
4
Read the current state of the EEPROM bits (see READING BACK FROM THE EEPROM)
5
Compare the desired control word to the stored EEPROM control word. Count the number of
differences so as to prevent double/redundant writing
6
One bit at a time, load the first desired control word bit (bit selection for EEPROM is active LOW)
7
Set the PV pin to +6V (≥5.6V, ≤6.1V) with the pulse and idle shown in timing diagram (Figure 10)
8
Progress through all necessary control word bits by repeating steps 5 & 6 until all bits are set to the
desired control word.
9
Verify the correct EEPROM contents by reading back the individual bits
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6
Request a Sample
May 2012, Rev 1.2