Linear Technology LTC6804-1, Руководство пользователя

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LTC6804-1/LTC6804-2
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Table 9. Conversion Times for ADSTAT Command Measuring SOC, ITMP, VA, VD
CONVERSION TIMES (in µs)
MODE t
0
t
1M
t
2M
t
3M
t
4M
t
1C
t
2C
t
3C
t
4C
27kHz 0 57 103 150 197 338 474 610 748
14kHz 0 86 162 237 313 455 591 726 865
7kHz 0 144 278 412 546 804 1,056 1,308 1,563
3kHz 0 260 511 761 1,011 1,269 1,522 1,774 2,028
2kHz 0 493 976 1,459 1,942 2,200 2,452 2,705 2,959
26Hz 0 29,817 59,623 89,430 119,237 122,986 126,729 130,472 134,218
Table 9 shows the conversion time of the ADSTAT com-
mand measuring all 4 internal parameters. t
4C
indicates
the total conversion time for the ADSTAT command.
Sum of Cells Measurement: The sum of all cells measurement
is the voltage between C12 and C0 with a 20:1 attenuation.
The 16-bit ADC value of sum of cells measurement (SOC)
is stored in status register group A. Any potential differ-
ence between the CO and V
–
pins results in an error in the
SOC measurement equal to this difference. From the SOC
value, the sum of all cell voltage measurements is given by:
Sum of all Cells = SOC
• 20 • 100µV
Internal Die Temperature: The ADSTAT command can
measure the internal die temperature. The 16-bit ADC
value of the die temperature measurement (ITMP) is
stored in status register group A. From ITMP the actual
die temperature is calculated using the expression:
Internal Die Temperature (°C) = (ITMP)
• 100µV/
(7.5mV)°C – 273°C
Power Supply Measurements: The ADSTAT command is
also used to measure the analog power supply (V
REG
) and
digital power supply (V
REGD
).
The 16-bit ADC value of the analog power supply measure-
ment (VA) is stored in Status Register Group A. The 16-bit
ADC value of the digital power supply measurement (VD)
is stored in status register group B. From VA and VD, the
power supply measurements are given by:
Analog power supply measurement (V
REG
) = V
A
• 100µV
Digital power supply measurement (V
REGD
) = V
D
• 100µV
The nominal range of V
REG
is 4.5V to 5.5V. The nominal
range of V
REGD
is 2.7V to 3.6V.
Issuing an ADSTAT command with CHST = 100 runs an
ADC measurement of just the digital supply (V
REGD
). This
is not recommended following an ADCV command. With
large cell voltages, running the ADSTAT command with
CST = 100 following an ADCV command with CH = 000
(all cells) can cause the LTC6804 to perform a power on
reset. If using the ADSTAT command with CHST = 100,
it is necessary to run an ADCV command with CH = 001
prior to running the ADSTAT command with CHST = 100.
This charges the high voltage multiplexer to a low poten-
tial before the V
REGD
measurement is executed. To save
time, this sacrificial ADCV command run prior to running
the V
REGD
measurement can be executed in FAST mode
(MD = 01).
Accuracy Check
Measuring an independent voltage reference is the best
means to verify the accuracy of a data acquisition system.
The LTC6804 contains a 2nd reference for this purpose.
The ADAX command will initiate the measurement of the
2nd reference. The results are placed in auxiliary register
group B. The range of the result depends on the ADC
measurement accuracy and the accuracy of the 2nd ref-
erence, including thermal hysteresis and long term drift.
Readings outside the range 2.985 to 3.015 indicate the
system is out of its specified tolerance.
MUX Decoder Check
The diagnostic command DIAGN ensures the proper op-
eration of each multiplexer channel. The command cycles
through all channels and sets the MUXFAIL bit to 1 in
status register group B if any channel decoder fails. The
MUXFAIL bit is set to 0 if the channel decoder passes the