MAX6427–MAX6438
Low-Power, Single/Dual-Level Battery Monitors
with Hysteresis
12 ______________________________________________________________________________________
Applications Information
Resistor-Value Selection (Programming
the Adjustable Thresholds)
MAX6433/MAX6434/MAX6435
(See Figure 5)
Use the following steps to determine values for R1, R2,
and R3 of Figure 8.
1) Choose a value for R
TOTAL
, the sum of R1, R2, and
R3. Because the MAX6433/MAX6434/MAX6435
have very high input impedances, R
TOTAL
can be
up to 5MΩ.
2) Calculate R3 based on R
TOTAL
and the desired
upper trip point:
3) Calculate R2 based on R
TOTAL
, R3, and the
desired lower trip point:
4) Calculate R1 based on R
TOTAL
, R3, and R2:
MAX6436/MAX6437/MAX6438
(See Figure 6)
Use the following steps to determine values for R1, R2,
and R3 of Figure 8.
1) Choose a value for R
TOTAL
, the sum of R1, R2, and
R3. Because the MAX6436/MAX6437/MAX6438
have very high input impedances, R
TOTAL
can be
up to 5MΩ.
2) Calculate R3 based on R
TOTAL
and the desired
upper trip point:
3) Calculate R2 based on R
TOTAL
, R3, and the
desired lower trip point:
4) Calculate R1 based on R
TOTAL
, R3, and R2:
V
HTH+
= V
HTH-
✕ 1.05, V
LTH+
= V
LTH-
✕ 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.
