MAX6427 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX6427

Low-Power, Single/Dual-Level Battery Monitors with Hysteresis

Maxim Integrated 

Low-Power, Single/Dual-Level Battery Monitors

with Hysteresis

Applications Information

Resistor-Value Selection (Programming

the Adjustable Thresholds)

MAX6433/MAX6434/MAX6435

(See Figure 5)

VREF = VLTHIN = VHTHIN = 615mV

VTRIPLOW = VLTH

=

VREF





R1

+

R2

R2

+

+ R3

R3





VTRIPHIGH = VHTL

=

VREF





R1

+

R2 +

R3

R3 



RTOTAL = R1 + R2 + R3

Use the following steps to determine values for R1, R2,

and R3 of Figure 8.

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

R3. Because the MAX6433/MAX6434/MAX6435

have very high input impedances, RTOTAL can be

up to 5MΩ.

2) Calculate R3 based on RTOTAL and the desired

upper trip point:

R3 = VREF × RTOTAL = 585mV × RTOTAL

VTRIPHIGH

VTRIPHIGH

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

desired lower trip point:

R2 = 615mV × RTOTAL − R3

VTRIPLOW

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

R1 = RTOTAL − R2 − R3

VBATT

IN

OUT

DC/DC

VCC

BATT

MAX6431 LBOL

SHDN

µP

LBOH

GND

NMI

GND

Figure 9. DC-to-DC Converter Application

MAX6436/MAX6437/MAX6438

(See Figure 6)

VREF = VLTHIN- = VHTHIN- = 585mV

LBOL / LBOL OUTPUT :

VTRIPLOW = VLTH-

=



VREF 



R1

+ R2

R2 +

+ R3

R3





LBOH / LBOH OUTPUT :

VTRIPHIGH = VHTL-

=



VREF 

R1

+



R2 +

R3

R3





RTOTAL = R1 + R2 + R3

Use the following steps to determine values for R1, R2,

and R3 of Figure 8.

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

R3. Because the MAX6436/MAX6437/MAX6438

have very high input impedances, RTOTAL can be

up to 5MΩ.

2) Calculate R3 based on RTOTAL and the desired

upper trip point:

R3 = VREF × RTOTAL = 585mV × RTOTAL

VTRIPHIGH

VTRIPHIGH

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

desired lower trip point:

585mV × RTOTAL − R3

VTRIPLOW

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

R1 = RTOTAL − R2 − R3

VHTH+ = VHTH- ✕ 1.05, VLTH+ = VLTH- ✕ 1.05

DC-to-DC Converter Application

The MAX6430/MAX6431/MAX6432 and MAX6436/

MAX6437/MAX6438 dual-output battery monitors can

be used in conjunction with a step-up DC-to-DC con-

verter to power 5V microprocessor systems using a sin-

gle Li+ cell or two to three alkaline/NiCd/NiMH cells

(Figure 9). The LBOH output indicates that the battery

voltage is weak, and is used to warn the microproces-

sor of potential problems. Armed with this information

the microprocessor can reduce system power con-

sumption. The LBOL output indicates the battery is

empty, and system power should be disabled. By con-

necting LBOL to the SHDN pin of the DC-to-DC con-

verter, power to the microprocessor is removed.

12 ______________________________________________________________________________________

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