Low-Power, Adjustable Battery Monitors with

Hysteresis and Integrated µP Reset

10

______________________________________________________________________________________

R3. Because the MAX6848/MAX6849 have very high

Ω.

upper trip point:

lower trip point:

5) LBOL high-trip level:

6) LBOH high-trip level:

Monitoring Multicell Battery Applications

For monitoring multicell Li+ (or a higher number of alka-

R3, see the Resistor-Value Selection section.

DC-DC Converter Application

The MAX6848/MAX6849 dual battery monitors can be

used in conjunction with a DC-DC converter to power

microprocessor systems using a single Li+ cell or two

to three alkaline/NiCd/NiMH cells. The LBOH output

indicates that the battery voltage is weak, and is used

to warn the microprocessor of potential problems.

Armed with this information, the microprocessor can

reduce system power consumption. The LBOL output

indicates the battery is empty and system power should

be disabled. By connecting LBOL to the SHDN pin of the

DC-DC converter, power to the microprocessor is

removed. Microprocessor power does not return until the

(see Figure 7).

RR

R

R

TOTAL

12

3

=

--

R

mV

R

V

R

TOTAL

TRIPLOW

2

582

3

=

×









-

R

mV

R

V

TOTAL

TRIPHIGH

3

582

=

×

PART NO.

SUFFIX

( _ )

RESET

THRESHOLD (V)

T

3.075

S

2.925

R

2.625

Z

2.313

Y

2.188

W

1.665

V

1.575

Threshold Levels

ACTIVE TIMEOUT PERIOD (ms)

TIMEOUT

PERIOD SUFFIX

MIN

MAX

D3

150

300

D7

1200

2400

Guide

DC-DC

SHDN

RESET

MAX6848

MAX6849

LTHIN

HTHIN

NMI

RESET

µP

GND

GND

Li+

3.6V

LBOL

LBOH

OUT

IN

Figure 7. DC-DC Converter Application

MAX6846

MAX6847

MAX6848

MAX6849

LTHIN

HTHIN

GND

* FOR THE MAX6846/MAX6847.

( ) FOR THE MAX6848/MAX6849.

(LBOH)

R1

R2

R3

LBO*

(LBOL)

Figure 6. Monitoring Multicell Li+ Applications