
ISL12022M
19
FN6668.9
June 20, 2012
TEMP SENSOR CONVERSION IN BATTERY MODE BIT
(BTSE)
This bit enables the Temperature Sensing and Correction in battery
mode. BTSE = 0 (default) no conversion, Temp Sensing or
Compensation in battery mode. BTSE = 1 indicates Temp Sensing
and Compensation enabled in battery mode. The BTSE is disabled
when the battery voltage is lower than 2.7V. No temperature
compensation will take place with VBAT <2.7V.
FREQUENCY OF TEMPERATURE SENSING AND
CORRECTION BIT (BTSR)
This bit controls the frequency of Temp Sensing and Correction.
BTSR = 0 default mode is every 10 minutes, BTSR = 1 is every
1.0 minute. Note that BTSE has to be enabled in both cases. See
The temperature measurement conversion time is the same for
battery mode as for VDD mode, approximately 22ms. The battery
mode current will increase during this conversion time to typically
68A. The average increase in battery current is much lower than
this due to the small duty cycle of the ON-time versus OFF-time for
the conversion.
To figure the average increase in battery current, we take the
change in current times the duty cycle. For the 1 minute
temperature period, the average current is expressed in Equation
1:For the 10 minute temperature period the average current is
If the application has a stable temperature environment that
doesn’t change quickly, the 10 minute option will work well and
the backup battery lifetime impact is minimized. If quick
temperature variations are expected (multiple cycles of more
than 10° within an hour), then the 1 minute option should be
considered and the slightly higher battery current figured into
overall battery life.
GAIN FACTOR OF AT BIT (BETA<4:0>)
Beta is specified to take care of the Cm variations of the crystal.
Most crystals specify Cm around 2.2fF. For example, if Cm > 2.2fF,
the actual AT steps may reduce from 1ppm/step to approximately
0.80ppm/step. Beta is then used to adjust for this variation and
restore the step size to 1ppm/step.
BETA values are limited in the range from 01000 to 11111, as
shown in Table 16. To use Table 16, the device is tested at two AT settings as follows:
BETA VALUES = (AT(max) - AT (min))/63, where:
AT(max) = FOUT in ppm (at AT = 00H) and
AT(min) = FOUT in ppm (at AT = 3FH).
The BETA VALUES result is indexed in the right hand column and
the resulting Beta factor (for the register) is in the same row in
the left column.
The ISL12022M has a preset BETA value corresponding to the
crystal in the module. This value is recalled on initial power-up
and is preset in device production. It is READ ONLY and cannot
be overwritten by the user.
TABLE 15. FREQUENCY OF TEMPERATURE SENSING AND
CORRECTION BIT
BTSE
BTSR
TC PERIOD IN
BATTERY MODE
00
OFF
01
OFF
10
10 Minutes
11
1 Minute
ΔI
BAT
0.022s
60s
------------------
=
68
μA 250nA
=
×
(EQ. 1)
ΔI
BAT
0.022s
600s
------------------
=
68
μA 25nA
=
×
(EQ. 2)
TABLE 16. BETA VALUES
BETA<4:0>
AT STEP ADJUSTMENT
01000
0.5000
00111
0.5625
00110
0.6250
00101
0.6875
00100
0.7500
00011
0.8125
00010
0.8750
00001
0.9375
00000
1.0000
10000
1.0625
10001
1.1250
10010
1.1875
10011
1.2500
10100
1.3125
10101
1.3750
10110
1.4375
10111
1.5000
11000
1.5625
11001
1.6250
11010
1.6875
11011
1.7500
11100
1.8125
11101
1.8750
11110
1.9375
11111
2.0000