enabled, it is updated every 0.5s by adding the contents of
the assigned result register value to the previous
accumulated value. The accumulators are listed below with
their assigned source registers:
Discharge Current Accumulator Ires (Sign bit = 1)
Charge Current Accumulator Ires (Sign bit = 0)
ITres or ETres
The measurement resolution of the accumulated value is
equal to that selected for the associated conversion, up to a
converter resolution of 15-bits. If a 15-bit A/D value is being
accumulated, then the accumulator resolution in microvolt
Accumulator LSB (µVs) = (VREF/215) µV * 0.5s
When the 170mV reference is selected, this value equates
to 2.59µVs per LSB.
The DCA accumulator is intended to accumulate discharge
current, and the CCA accumulator is intended to accumulate
charge current. Both accumulators use the Ires register as
its source. For this reason, the lres register should be
programmed for current measurement by selecting the SR
pin as the multiplexed ADC input source.
During charging, the voltage at the SR pin will be negative.
This translates to a positive voltage measurement with the
sign bit set to ‘0’. Whenever the sign bit equals ‘0’, the
measured result will be added to the CCA register contents
and the sum is returned to CCA. In this way, total charge
current is accumulated in the CCA.
Similarly, during discharge, a positive voltage will exist at the
SR pin. In this case, the conversion will result in the sign bit
being set to ‘1’ in the Ires register, indicating a negative
value or discharge current condition. Under this condition,
the DCA register will be updated with the discharge current
measured during that conversion.
The value stored in the DCA or CCA register can be
interpreted as illustrated in the following example. Using a
20mΩ sense resistor, the LSB can expressed in units of
current as follows:
Accumulator LSB (µAs) = Voltage LSB/RSENSE
The “Accum” bit in the AccumCtrl register must be enabled for
accumulation to occur in both the CCA and DCA registers.
CHARGE/DISCHARGE TIME COUNTERS
The Charge Time Counter (CTC) will increment at the rate of
2 counts every second as long as a negative voltage is
measured at the SR pin. The CTC can thereby maintain a
time count representing the total time that charge current
has flowed into the battery.
The Discharge Time Counter (DTC) will increment at the rate
of 2 counts every second as long as a positive voltage is
measured at the SR pin. The DTC can thereby maintain a
time count representing the total time that discharge current
has flowed from the battery.
The ISL6295 has five operational power modes: Power-on
Reset, Run, Sample, Sample-Sleep, and Shelf-Sleep. Each
consumes power according to the configuration settings as
When power is first applied to the V input, the ISL6295
automatically executes a Power-on Reset sequence. The
device is held in a RESET state while the voltage is below
the minimum operating threshold, VPOR. When the voltage
on the VP pin rises above the VPOR threshold, the ISL6295
will initialize itself by loading the internal counters, data and
control registers with default values pre-written into the non-
volatile EEPROM memory. Please refer to “Register
Initialization” and “Factory Register Initialization” sections for
a detailed description of the register initialization operation.
When this is complete, the ISL6295 will enter the Run Mode.
During Run mode, the ISL6295 performs continuous A/D
conversion cycles per the programming of the A/D
conversion cycle described in the “A/D Conversion Cycle”
section. During each cycle, one to eight conversions are
performed, and the respective accumulators/time counters
are updated at 0.5s interval using the most recent A/D
Run Mode is entered following a Power-on Reset when the
pack voltage (VPACK) applied to the VP pin rises above the
VPOR threshold. Run Mode can also be entered from the
Sample, Sample-Sleep, and Shelf-Sleep modes as to be
The ISL6295 will remain in RUN mode as long as the pack
voltage is above the VPOR threshold and Sample, Sample-
Sleep, and Shelf-Sleep modes are not active.
In Sample Mode, A/D measurements are not continuously
performed as in Run Mode. Instead, they are performed at a
user selectable rate. The purpose of Sample Mode is to
reduce power consumption during periods of low rate
change (charge or discharge). The power advantage of
Sample Mode comes from the reduction in frequency of A/D
measurements. The accumulation counters and timers will
continue to run at the rate of 0.5s per update.
Sample Mode is entered by programming the "Samp" bit to
‘1’ in the A/D Configuration register. The ISL6295 will remain
October 25, 2005