aduc7030 Analog Devices, Inc., aduc7030 Datasheet - Page 77

• Manufacturer Part Number: aduc7030
• Description: Integrated Precision Battery Sensor For Automotive
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
ADUC7030/ ADUC7033 LOW POWER CLOCK
CALIBRATION
The low power 131 kHz oscillator may be calibrated using
either the precision 131kHz oscillator, or an external 32.768
kHz watch crystal. Two dedicated calibration counters and an
oscillator trim register are used to implement this feature.
One counter, 9-bits wide, is clocked by the accurate clock
oscillator, either the Precision oscillator or external watch
crystal. The second counter, 10-bits wide, is clocked by the low
power oscillator, either directly at 131kHz or via a divide by 4
block generating 32.768kHz. The source for each calibration
counter should be of the same frequency. The trim register
(OSC0TRM) is an 8-bit wide register, the lower 4-bits of which
are user accessible trim bits. Increasing the value in OSC0TRM
will decrease the frequency of the low power oscillator,
decreasing the value will increase the frequency. Based on a
nominal frequency of 131kHz, the typical trim range is between
127kHz to 135kHz.
The clock calibration mode is configured and controlled by the
following MMRs:
OSC0CON:
OSC0STA:
OSC0VAL0:
OSC0VAL1:
OSC0TRM:
An example calibration routine is shown in Figure 28. User
code configures and enables the calibration sequence via
OSC0CON. When the precision oscillator calibration counter,
OSC0VAL0, reaches 0x1FF, both counters are disabled.
User code then reads back the value of the low power oscillator
calibration counter. There are three possible scenarios:
OSC0VAL0 = OSC0VAL1. No Further Action is required.
OSC0VAL0 > OSC0VAL1. The Low Power Oscillator is running
slow. OSC0TRM must be decreased.
OSC0VAL0 < OSC0VAL1. The Low Power Oscillator is running
fast. OSC0TRM must be increased.
Control bits for calibration.
Calibration Status Register
9-Bit counter. Counter 0.
10-Bit counter. Counter 1.
Oscillator Trim Register.
Rev. PrE | Page 77 of 150
When the OSC0TRM has been changed the routine should be
re-run and the new frequency checked.
Using the internal precision 131kHz oscillator, it will take
approximately 4milliseconds to execute the calibration routine.
If the external 32.768kHz crystal is used, this time increases to
16milliseconds.
NOTE: Prior to the clock calibration routine been started, it is
required that the user switch to either the precision 131kHz
oscillator or the external 32.768KHz watch crystal as the PLL
Clock Source. If this is not done, it is possible that the PLL will
lose lock each time OSC0TRM is modified. This will increase
the length of time it takes to calibrate the Low Power, Oscillator.
OSC0VAL0 < OSC0VAL1
Figure 28. Example OSC0TRM Calibration Routine
INCREASE
OSC0TRM
NO
OSC0VAL0 = OSC0VAL1
IS ERROR WITHIN
DESIRED LEVEL?
OSCSTA[0] = 1
CALIBRATION
CALIBRATION
ROUTINE
ROUTINE
BEGIN
WHILE
ADuC7030/ADuC7033
END
YES
OSC0VAL0 > OSC0VAL1
DECREASE
OSC0TRM