6295CV View Datasheet(PDF) - Intersil

Part Name

Description

Manufacturer

6295CV

Low Voltage Fuel Gauge

Intersil 

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

600mΩ sense 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 20mΩ sense resistor is used, the value of the LSB in

units of current is:

5.19µV/20mΩ = 259.5µA

6

FN9074.0

October 25, 2005

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