MAX6427ORUR+T Datasheet MAX6437UT+T, MAX6427DHUR+T, MAX6427ORUR+T | P7-P9

MAX6427–MAX6438

Low-Power, Single/Dual-Level Battery Monitors

with Hysteresis

_______________________________________________________________________________________ 7

Detailed Description

The MAX6427–MAX6438 family is available with several

monitoring options. The MAX6427/MAX6428/MAX6429

offer factory-trimmed battery-monitor thresholds, with a

single low-battery output (see Figure 1). The

MAX6430/MAX6431/MAX6432 also feature factory-

trimmed thresholds, but have two low-battery outputs

(see Figure 2). The factory-trimmed thresholds of the

MAX6427–MAX6432 eliminate the requirement for

external components.

The user sets the threshold voltages for the

MAX6433–MAX6438, which permit the user to select

the hysteresis range, and consequently the sensitivity

of the system to noise. A wide hysteresis range pre-

vents chattering that can result during battery recovery

or load removal. The MAX6433/MAX6434/ MAX6435

have single low-battery outputs and the MAX6436/

MAX6437/MAX6438 have dual low-battery outputs (see

Figures 3 and 4).

The MAX6427–MAX6438 combine a 615mV reference

with two comparators, logic, and timing circuitry to pro-

vide the user with information about the charge state of

the power-supply batteries. The MAX6427–MAX6438

monitor separate high-voltage and low-voltage thresh-

olds to determine battery status. The output(s) can be

used to signal when the battery is charged, when the

battery is low, and when the battery is empty. Factory-

trimmed thresholds are ideal for monitoring single-cell

Li+ or multicell alkaline/NiCd/NiMH power supplies.

User-programmable versions are also available with

thresholds determined using an external resistor-

divider (see Resistor-Value Selection).The adjustable

versions can monitor down to 0.62V, making them suit-

able for monitoring single-cell alkaline, NiMH, and NiCd

applications (V

≥ 1.6V).

When the power-supply voltage drops below the speci-

fied low threshold, the low-battery output asserts (see

Low-Battery Output). When the voltage rises above the

specified high threshold following a 140ms (min) time-

out period, the low-battery output is deasserted (see

Threshold Monitoring). This ensures the supply voltage

has stabilized before power-converter or microproces-

sor activity is enabled.

Low-Battery Output

The low-battery outputs are available in active-low

(LBO, LBOH, LBOL, push-pull and open-drain) and

active-high (LBO, LBOL, LBOH, open-drain) configura-

tions. Push-pull outputs are referenced to BATT (for

factory-trimmed versions) or V

(for adjustable thresh-

old versions).

The open-drain devices can be pulled to a voltage inde-

pendent of V

or BATT, up to 5.5V. This allows the

LBO TIMEOUT

PERIOD

BATT

( ) ARE FOR THE MAX6429

615

LBO

(LBO)

Figure 1. MAX6427/MAX6428/MAX6429 Functional Diagram

MAX6427–MAX6438

Low-Power, Single/Dual-Level Battery Monitors

with Hysteresis

8 _______________________________________________________________________________________

device to monitor and operate from direct battery voltage

while interfacing to higher voltage microprocessors.

The MAX6427/MAX6428/MAX6429/MAX6433/MAX6434/

MAX6435 single-output voltage monitors provide a sin-

gle low-battery output, LBO/LBO. The MAX6427/

MAX6428/MAX6429 fixed-threshold parts assert

LBO/LBO when BATT drops below V

LTH

. The

MAX6433/MAX6434/MAX6435 adjustable-threshold

parts assert LBO/LBO when the LTHIN input drops

below the V

LTHIN

threshold (615mV) (see Figure 5).

The MAX6430/MAX6431/MAX6432/MAX6436/MAX6437/

MAX6438 dual-output voltage monitors provide two low-

battery outputs, LBOH/LBOH and LBOL/LBOL. The

MAX6430/MAX6431/MAX6432 fixed-threshold parts

assert LBOH/LBOH when BATT drops below V

HTH-

and assert LBOL/LBOL when BATT drops below V

LTH-

The MAX6436/MAX6437/MAX6438 adjustable-thresh-

old parts assert LBOH/LBOH when HTHIN drops below

HTHIN-

, and assert LBOL/LBOL when LTHIN drops

below V

LTHIN-

(see Figure 6).

Threshold Monitoring

The MAX6433–MAX6438 HTHIN and LTHIN inputs are

high-impedance inputs to comparators. An external resis-

tor-divider network is required between the monitored

voltage, HTHIN, LTHIN, and GND to select the desired

thresholds (see Resistor-Value Selection). The

MAX6433/MAX6434/MAX6435 single-output voltage

monitors assert LBO/LBO when LTHIN drops below the

internal LTHIN reference (615mV). LBO/LBO is deassert-

ed when HTHIN rises above the internal HTHIN reference

level (615mV) for at least 140ms (see Figure 6).

The MAX6436/MAX6437/MAX6438 dual-output voltage

monitors assert LBOL/LBOL when LTHIN drops below

the LTHIN- threshold and deassert LBOL/LBOL when

LTHIN rises above the LTHIN+ threshold for at least

140ms. LBOH/LBOH is asserted when HTHIN drops

below the HTHIN- threshold and is deasserted when

HTHIN rises above the HTHIN+ threshold for at least

140ms (see Figure 7).

(LBOL)

LBO

TIMEOUT

PERIOD

( ) ARE FOR THE MAX6432

HYSTERESIS SWITCH

BATT

615

LBOL

LBOH

(LBOH)

Figure 2. MAX6430/MAX6431/MAX6432 Functional Diagram

MAX6427–MAX6438

Low-Power, Single/Dual-Level Battery Monitors

with Hysteresis

_______________________________________________________________________________________ 9

Hysteresis

Hysteresis increases the comparator’s noise margin by

increasing the upper threshold or decreasing the lower

threshold (see Figure 8). The hysteresis prevents the

output from oscillating (chattering) when BATT or V

is near the low-battery threshold. This is especially

important for applications where the load on the battery

creates significant fluctuations in battery voltages.

Fixed Hysteresis (MAX6427–MAX6432)

The MAX6427/MAX6428/MAX6429 total hysteresis is the

difference between the factory-trimmed V

LTH

and V

HTH.

For the MAX6430/MAX6431/MAX6432, the total hysteresis

is the difference between the factory-trimmed V

HTH-

and

HTH+

or V

LTH-

and V

LTH+

values, approximately 5%.

Adjustable Hysteresis (MAX6433–MAX6438)

Figure 7 shows the correct connections for the external

resistor-dividers. To adjust the low-battery threshold

and hysteresis connect resistor R1 between V

and

LTHIN, resistor R2 between LTHIN and HTHIN, and R3

between HTHIN and GND. The hysteresis for the

MAX6433–MAX6438 is determined by an external resis-

tor-divider network (see Resistor-Value Selection sec-

tion of Applications Information). The hysteresis for the

MAX6436/MAX6437/MAX6438 is the differences

between V

HTHIN-

and V

HTHIN+

(~5%) or V

LTHIN-

and

LTHIN+

(~5%).

LBO TIMEOUT

PERIOD

BATT

LTHIN

HTHIN

( ) ARE FOR THE MAX6435

EXTERNAL

RESISTOR-

DIVIDER

615

LBO

(LBO)

Figure 3. MAX6433/MAX6434/MAX6435 Functional Diagram

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P20

MAX6427ORUR+T

Mfr. #:

Buy MAX6427ORUR+T

Manufacturer:

Maxim Integrated

Description:

Battery Management Single Battery Monitor

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