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6295CV Просмотр технического описания (PDF) - Intersil

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6295CV Low Voltage Fuel Gauge Intersil
Intersil Intersil
6295CV Datasheet PDF : 25 Pages
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ISL6295
the user through 8 A/D control registers. These registers
determine the input source, conversion resolution, reference
voltage, and sequence of conversions during an A/D
conversion cycle. During the cycle, the A/D logic accesses
each register in sequence and performs the conversion
specified by the bits within the registers. Each register
contains an enable bit, a resolution field, a select bit for
single-ended (340mV reference) or differential (170mV
reference) conversion, and a select field for the analog input
multiplexer. The result from each conversion is stored in one
of eight corresponding 16-bit result registers.
If the “Enable” bit is set within a control register, a conversion
will be performed. If it is disabled, that conversion will be
skipped and the logic will move on to the next register. In this
manner, the user can specify a sequence of conversions that
will be performed during each A/D cycle.
As stated above, the input source for each of the registers is
programmable. The 3-bit MUX field within each control
register selects one of seven possible input sources for the
A/D conversion. The list of input sources is as follows:
• Charge/discharge Current (Voltage from SR pin to GND)
• Internal temperature sensor
• External thermistor (Constant current source on NTC pin)
• Battery pack voltage
• Reserved
• General purpose A/D voltage
• ADC offset (Conversion performed with ADC input
internally shorted to ground) to determine offset error
associated with the converter
However, the accumulator/timer functions are “hard-wired” to
specific A/D result registers. For this reason, the control/
result registers are given names which indicate their primary
intended usage:
A/D CONTROL RESULT
REGISTER REGISTER REGISTER
INTENDED
INPUT SOURCE
0
Ictrl
Ires Battery Pack Current
(via sense resistor)
1
ITctrl
ITres Internal Temperature Sensor
2
ETctrl
ETres External Temperature
Sensor
3
VPctrl
VPres Battery Pack Voltage
4
Reserved
5
GPADctrl GPADres General Purpose A/D Input
6
OFFSctrl OFFSres Internal ADC offset voltage
(with input grounded)
7
AUXctrl AUXres Any
The 3-bit “resolution” field in each A/D control register
determines the magnitude resolution of the conversion, from
a minimum of 8-bits to a maximum of 15-bits. The time
required to complete the conversion is a function of the
number of bits of resolution selected. The conversion time
can be calculated as follows:
TADC = 30.52µs * 2(N+1)
where “N” is the number of bits of magnitude resolution
selected
The “Ref” bit selects either a differential or single-ended
conversion. For differential conversions, the 170mV
reference is used. For single-ended conversion the 340mV
reference is selected. Single-ended conversions would be
used for measurements of pack voltage while a differential
conversion is required for current measurement.
The value of the LSB in the result register is as follows:
For single-ended conversion,
A/D LSB = 340 mV/215 = 10.38µV
For differential conversion,
A/D LSB = 170 mV/215 = 5.19µV
For both differential and single-ended conversions, the result
value is given in sign-magnitude format (i.e. a sign bit and 15
magnitude bits). When N less than 15 is selected, the
conversion result is padded with trailing zeroes. Note that
15 14
0
S
Magnitude
the single-ended reference should not be used for a
negative measurement. Though the sign-magnitude value
presented may still look valid, the accumulator will not be
able to interpret the result for proper accumulation.
CURRENT MEASUREMENT
Charge and discharge currents are measured using a 5 to
600msense resistor that is connected between the SR and
GND pins. The sense resistor value chosen must
accommodate the system’s lowest and highest expected
charge and discharge currents, including suspend and
standby currents, while maintaining a voltage of no more
than +152mV presented at the SR pin.
In order to perform charge and discharge current
measurements, the Ictrl register must be programmed with
the SR pin as the analog input source. If charge and
discharge accumulation is desired, the Ictrl and
corresponding Ires registers should be used to select current
measurement since the DCA, DTC, CCA, and CTC registers
are updated by the measurement results from the Ires
register.
When a 20msense resistor is used, the value of the LSB in
units of current is:
5.19µV/20m= 259.5µA
6
FN9074.0
October 25, 2005
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