Compact, Low-Cost 1S/2S Fuel Gauges

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5

SDA

SCL

SSr

P

S

Figure 1. 2-Wire Bus Timing Diagram

Pin Description

PIN

UCSP

TDFN

NAME

FUNCTION

A1

8

SDA

Serial Data Input/Output. Open-drain 2-wire data line. Connect this pin to the DATA signal of the

2-wire interface. This pin has a 0.2μA typical pulldown to sense disconnection.

A2

7

SCL

Serial Clock Input. Input only 2-wire clock line. Connect this pin to the CLOCK signal of the

2-wire interface. This pin has a 0.2μA typical pulldown to sense disconnection.

A3

1

CTG

Connect to Ground. Connect to VSS during normal operation.

B1

6

EO

External 32kHz Clocking Signal. Input for external clocking signal to be the primary system

clock. Configured to implement interrupt feature with a pulldown set on SEO pin.

B2

—

N.C.

No Connect. Do not connect.

B3

2

CELL

Battery-Voltage Input. The voltage of the cell pack is measured through this pin.

C1

5

SEO

External 32kHz Clocking Signal Enable Input. Input to enable external clocking signal on EO pin

with a pullup state; a pulldown state to configure the interrupt feature. External 32kHz clock

enable. Connects logic-low to enable external interrupt.

C2

3

Power-Supply Input. 2.5V to 4.5V input range. Connect to system power through a decoupling

network. Connect a 10nF typical decoupling capacitor close to pin.

C3

4

GND

Ground. Connect to the negative power rail of the system.

—

—

EP

Exposed Pad (TDFN Only). Connect to ground.

STATE

MACHINE

(SOC, RATE)

2-WIRE

INTERFACE

IC

GROUND

TIME BASE

(32kHz)

ADC (VCELL)

VOLTAGE

REFERENCE

BIAS

GND

CELL

SCL

SDA

CTG

SEO

EO

MAX17040

MAX17041

Figure 2. Block Diagram

Detailed Description

Figure 1 shows the 2-wire bus timing diagram, and

Figure 2 is the MAX17040/MAX17041 block diagram.

ModelGauge Theory of Operation

The MAX17040/MAX17041 use a sophisticated battery

model, which determines the SOC of a nonlinear Li+

battery. The model effectively simulates the internal

dynamics of a Li+ battery and determines the SOC. The

model considers the time effects of a battery caused by

the chemical reactions and impedance in the battery.

The MAX17040/MAX17041 SOC calculation does not

accumulate error with time. This is advantageous