MAX6849KAYD7-T Maxim Integrated, MAX6849KAYD7-T Datasheet - Page 9

• Manufacturer Part Number: MAX6849KAYD7-T
• Description: Battery Management
• Manufacturer: Maxim Integrated
• Series: MAX6846, MAX6847, MAX6848, MAX6849r

Specifications of MAX6849KAYD7-T

• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Package / Case: SOT-23

Many microprocessor-based products require manual
reset capability, allowing the operator, a test technician,
or external logic circuitry to initiate a reset while the
monitored supplies remain above their reset thresholds.
These devices have a dedicated active-low MR pin.
When MR is pulled low, RESET asserts a one-shot low
pulse for the MR reset timeout period. The MR input has
an internal 1.5kΩ pullup resistor to V
unconnected if not used. MR can be driven with CMOS-
logic levels, open-drain/open-collector outputs, or a
momentary pushbutton switch to GND (the MR function
is internally debounced for the t
create a manual reset function. If MR is driven from long
cables, or if the device is used in a noisy environment,
connect a 0.1µF capacitor from MR to GND to provide
additional noise immunity (see Figure 4).
Hysteresis increases the comparator’s noise margin by
increasing the upper threshold or decreasing the lower
threshold. The hysteresis prevents the output from
oscillating (chattering) when monitor input is near the
low-battery threshold. This is especially important for
applications where the load on the battery creates sig-
nificant fluctuations in battery voltages (see Figures 2
and 3).
For the MAX6846/MAX6847, hysteresis is set using three
external resistors (see Figure 5). The MAX6848/MAX6849
have dual, low-battery input levels. Each input level has a
5% (typ) hysteresis.
Use the following steps to determine values for R1, R2,
and R3 of Figure 5.
1) Choose a value for R
R3. Because the MAX6846/MAX6847 have very high
input impedance, R
Resistor-Value Selection (Programming
Low-Power, Adjustable Battery Monitors with
V
V
TRIPHIGH
TRIPLOW
V
R
LTH
Applications Information
TOTAL
_______________________________________________________________________________________
=
=
=
the Adjustable Thresholds)
V
V
TOTAL
V
HTH
LTH
=
HTH
TOTAL
R
1
×
×
+
can be up to 500kΩ.
Hysteresis and Integrated µP Reset
=



, the sum of R1, R2, and



R
R
R
615
2
DEB
1
1
R
+
+
MAX6846/MAX6847
+
2
R
mV
R
CC
R
R
+
3
timeout period) to
2
Manual Reset
2
3
R
+
+
and can be left
3
R
R
Hysteresis
3
3






2) Calculate R3 based on R
3) Calculate R2 based on R
4) Calculate R1 based on R
Use the following steps to determine values for R1, R2,
and R3 of Figure 5.
Figure 5. Adjustable Threshold Selection
upper trip point:
lower trip point:
V
LBOL low-trip level:
LBOH low-trip level:
R
V
V
LTH-
TRIPLOW
TRIPHIGH
TOTAL
V
DD
= V
R1
R2
R3
R
2
=
HTH-
R
R
=
=
R
=
1
3
1



V
V
+
= 582mV
=
=
LTH
615
V
LTHIN
HTHIN
HTH
R
DD
R
2
615
-
TOTAL
mV
+
-
V
×
TRIPLOW
R
×
mV
V
MAX6846
MAX6847
MAX6848
MAX6849
3
* FOR THE MAX6846/MAX6847.
( ) FOR THE MAX6848/MAX6849.



TRIPHIGH
×



R
TOTAL
TOTAL
R
1
R
×
-
1
R
+
TOTAL
TOTAL
+
2
R
R
R
2
R
+
R
2
TOTAL
2
, R3, and R2:
, R3, and the desired
3
R
-
MAX6848/MAX6849
(LBOH)
(LBOL)
+
+
3
LBO*
GND
R
R

 -

R
and the desired
3
3
3






R
3
9