MAX6848 데이터 시트보기 (PDF) - Maxim Integrated

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MAX6848

Low-Power, Adjustable Battery Monitors with Hysteresis and Integrated µP Reset

Maxim Integrated 

Low-Power, Adjustable Battery Monitors with

Hysteresis and Integrated µP Reset

1) Choose a value for RTOTAL, the sum of R1, R2, and

R3. Because the MAX6848/MAX6849 have very high

input impedance, RTOTAL can be up to 500kΩ.

2) Calculate R3 based on RTOTAL and the desired

upper trip point:

R3 = 582mV × RTOTAL

VTRIPHIGH

3) Calculate R2 based on RTOTAL, R3, and the desired

lower trip point:

R2

=





582mV × RTOTAL

VTRIPLOW





-

R3

4) Calculate R1 based on RTOTAL, R3, and R2:

R1 = RTOTAL - R2 - R3

5) LBOL high-trip level:

VTRIPLOW ✕ 1.05

6) LBOH high-trip level:

VTRIPHIGH ✕ 1.05

Monitoring Multicell Battery Applications

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

line/NiCd/NiMH cells), connect VDD to a supply voltage

between 1.6V to 5.5V. Figure 6 shows VDD connected

directly to VCC. To calculate the values of R1, R2, and

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

battery has recharged to a voltage greater than VLTH+

(see Figure 7).

Table 1. Factory-Trimmed VCC Reset

Threshold Levels

PART NO.

SUFFIX

(_)

T

S

R

Z

Y

W

V

VCC NOMINAL

RESET

THRESHOLD (V)

3.075

2.925

2.625

2.313

2.188

1.665

1.575

Table 2. VCC Reset Timeout Period Suffix

Guide

TIMEOUT

PERIOD SUFFIX

D3

D7

ACTIVE TIMEOUT PERIOD (ms)

MIN

MAX

150

300

1200

2400

VMONITORED

R1

R2

R3

VDD

VCC

VCC

LBO*

LTHIN

MAX6846

MAX6847

MAX6848

MAX6849

(LBOL)

(LBOH)

HTHIN

GND

* FOR THE MAX6846/MAX6847.

( ) FOR THE MAX6848/MAX6849.

Figure 6. Monitoring Multicell Li+ Applications

IN DC-DC OUT

SHDN

Li+

3.6V

VDD LBOL VCC

VCC

LBOH

NMI

LTHIN

MAX6848

MAX6849

HTHIN

RESET

µP

RESET

GND

GND

Figure 7. DC-DC Converter Application

10 ______________________________________________________________________________________

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