Linear Technology LTC6804-1 - Page 25

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Table 7. Conversion Times for ADAX Command Measuring All GPIOs and 2nd Reference in Different Modes
CONVERSION TIMES (in µs)
MODE t
0
t
1M
t
2M
t
5M
t
6M
t
1C
t
2C
t
5C
t
6C
27kHz 0 57 103 243 290 432 568 975 1,113
14kHz 0 86 162 389 465 606 742 1,149 1,288
7kHz 0 144 278 680 814 1,072 1,324 2,080 2,335
3kHz 0 260 511 1,262 1,512 1,770 2,022 2,778 3,033
2kHz 0 493 976 2,425 2,908 3,166 3,418 4,175 4,430
26Hz 0 29,817 59,623 149,043 178,850 182,599 186,342 197,571 201,317
Figure 5. Timing for ADAX Command Measuring All GPIOs and 2nd Reference
ADC2
SERIAL
INTERFACE
t
CYCLE
t
SKEW
ADAX + PEC
CALIBRATE
GPIO2
CALIBRATE
2ND REF
CALIBRATE
GPIO1
MEASURE
2ND REF
MEASURE
GPIO2
MEASURE
GPIO1
ADC1
t
0
t
1M
t
2M
t
6M
t
5M
t
1C
t
2C
t
5C
t
6C
680412 F05
t
REFUP
Under/Overvoltage Monitoring
Whenever the C inputs are measured, the results are com-
pared to undervoltage and overvoltage thresholds stored
in
memor
y. If the reading of a cell is above the overvoltage
limit, a bit in memory is set as a flag. Similarly, measure
-
ment results below the undervoltage limit cause a flag to
be set. The overvoltage and undervoltage thresholds are
stored in the configuration register group. The flags are
stored in the status register group B.
Auxiliary (GPIO) Measurements (ADAX Command)
The ADAX command initiates the measurement of the
GPIO inputs. This command has options to select which
GPIO input to measure (GPIO1-5) and which ADC mode.
The ADAX command also measures the 2nd reference.
There are options in the ADAX command to measure each
GPIO and the 2nd reference separately or to measure all 5
GPIOs and the 2nd reference in a single command. See the
section on commands for the ADAX command format. All
auxiliary measurements are relative to the V
–
pin voltage.
This command can be used to read external temperature
by connecting the temperature sensors to the GPIOs.
These sensors can be powered from the 2nd reference
which is also measured by the ADAX command, resulting
in precise ratiometric measurements.
Figure 5 illustrates the timing of the ADAX command
measuring all GPIOs and the 2nd reference. Since all
the 6 measurements are carried out on ADC1 alone, the
conversion time for the ADAX command is similar to the
ADCV command.
Measuring Cell Voltages and GPIOs (ADCVAX
Command)
The ADCVAX command combines twelve cell measure
-
ments with two GPIO measurements (GPIO1 and GPIO2).
This command simplifies the synchronization of battery
cell voltage and current measurements when current sen
-
sors
are connected to GPIO1 or GPIO2 inputs. Figure6
illustrates the timing of the ADCVAX command. See the
section on commands for the ADCVAX command format.
The synchronization of the current and voltage measure
-
ments, t
SKEW1
, in FAST MODE is within 208µs.