LTC4012 datasheet(8/18 Pages) AD

8 / 18 page

LTC2959

Rev. 0

For more information www.analog.com

OPERATION

Overview

The LTC2959 is an ultra-low power battery fuel gauge

designed for a wide range of batteries. Its high-precision

coulomb counter keeps track of charge and discharge by

measuring the voltage across an external current sensing

resistor. The resistor can be inserted at any point in the

battery’s current path, accommodating both low-side and

high-side sensing configurations.

The LTC2959’s supply voltage can range between 1.8V

and 60V and can be set independently of the terminal

voltages at the sense resistor. Its extremely low operating

current allows the LTC2959 to keep track of charge over

extended periods of time.

The LTC2959 also measures battery voltage, instanta-

neous current, its own temperature and an auxiliary input

using an internal ADC.

Coulomb Counter

Charge is the time integral of current. The LTC2959

measures charge by monitoring the voltage developed

across an external sense resistor. The differential volt-

age between SENSEP and SENSEN is first low-pass fil-

tered and then applied to a precision coulomb counter.

The coulomb counter integrates and then digitizes the

differential voltage, incrementing and decrementing the

Accumulated Charge Register (ACR) as needed. The ACR

and its programmable thresholds can be read out via the

I2C interface.

The coulomb counter modulates its operating current as

a function of the signal at its differential input. For small

input signals, its typical current reduces to below 1µA.

Even at those reduced current levels, its high precision and

low offset are maintained. The operating current is inde-

pendent of the common mode voltage at the SENSE pins.

The coulomb counter can be set to do not count mode

using register bit C[3]. This stops coulomb counting and

prevents the ACR from incrementing/decrementing. In

this mode, the operating current is statically low and no

longer input dependent.

Coulomb Counter Charge Gain

The coulomb counter’s accumulated charge register

(ACR) has a fixed LSB of 533nAh and a width of 32 bits.

This accommodates a wide variety of batteries; its full

scale of 2289Ah should accommodate most large batter-

ies, while even a 10mAh full-scale charge can be resolved

to well below 0.01%.

The choice of the external sense resistor value influences

the gain of the coulomb counter. The full-scale value of

the ACR is based on an RSENSE with a value of 50mΩ. If

sense resistors with a different value are used, the value

should be scaled as follows:

QBAT,EFF =

50m

RSENSE

QBAT,DEFAULT

Deadbanding

In battery gas gauges, an important parameter is the dif-

ferential offset (VOS) of the circuitry monitoring the bat-

tery charge. This is because coulomb counters essentially

integrate forever, and so the charge error correspond-

ing to a small offset grows linearly over time. Moreover,

for small input voltages (VSENSE), VOS may significantly

contribute to the relative charge error. The LTC2959 was

designed to have a very low offset (typically 1µV and no

more than ±10µV max).

Additionally, the LTC2959 has a programmable dead-

band: if the absolute value of the average VSENSE over a

0.5s period is smaller than a programmable threshold,

the charge measured during that period is not added to

the ACR.

Using register bits C [7:6], the programmable threshold

can be set to 20, 40 or 80µV, or to 0 (no deadbanding).

Voltage, Current, Temperature and GPIO ADC

The LTC2959 includes a fast, precision, No-Latency Σ∆

analog-to-digital converter, with internal clock and ref-

erence circuits. The ADC can be used to monitor the

battery voltage via the SENSEN pin or via the VDD pin

(in low-side sensing applications); it can also measure

LTC4012 Datasheet(PDF) 8 Page - Analog Devices

LTC4012 Datasheet(HTML) 8 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Datasheet Download

Link URL