Rainbow Electronics MAX6781 - Manual (Page 8)

MAX6775–MAX6781
Low-Power, 1%-Accurate Battery
Monitor in µDFN and SC70 Packages
8 _______________________________________________________________________________________
Selector Guide
PART
LBO OUTPUT
OUTPUT TYPE HYSTERESIS PIN-PACKAGE
MAX6775XK_+T Single Push-Pull Fixed 5 SC70-5
MAX6775LT_+T Single Push-Pull Fixed 6 µDFN-6
MAX6776XK_+T Single Open-Drain Fixed 5 SC70-5
MAX6776LT_+T Single Open-Drain Fixed 6 µDFN-6
MAX6777XK+T Single Push-Pull Adjustable 5 SC70-5
MAX6777LT+T Single Push-Pull Adjustable 6 µDFN-6
MAX6778XK+T Single Open-Drain Adjustable 5 SC70-5
MAX6778LT+T Single Open-Drain Adjustable 6 µDFN-6
MAX6779LT_+T Dual Push-Pull Fixed 6 µDFN-6
MAX6780LT_+T Dual Open-Drain Fixed 6 µDFN-6
MAX6781LT_+T Dual Mixed Fixed 6 µDFN-6
Calculating an External
Hysteresis Resistive Divider
Setting the hysteresis externally requires calculating
three resistor values, as indicated in Figure 3. First cal-
culate R
H using:
and R L0 using:
(as in the above example). Where R L0 equals R L +
R HYST , determine the total resistor-divider current,
I TOTAL , at the trip voltage using:
Then, determine R HYST using:
where V HYST is the required hysteresis voltage.
Finally, determine R
L
using:
R L = R L0 - R HYST
Monitoring a Battery Voltage Higher
Than the Allowable V
BATT
For monitoring higher voltages, supply power to BATT
that is within the specified supply range, and power the
input resistive divider from the high voltage to be moni-
tored. Do not exceed the Absolute Maximum Ratings.
Adding External Capacitance to
Reduce Noise and Transients
If monitoring voltages in a noisy environment, add a
bypass capacitor of 0.1µF from BATT to GND as close
as possible to the device. For systems with large tran-
sients, additional capacitance may be required. A small
capacitor (<1nF) from LBI_ to GND may provide addi-
tional noise immunity.
R
V
I
HYST
HYST
TOTAL
=
I
V
R R
TOTAL
BATT
H L
=
+
0
R
V x R
V V
L
LBIR H
LBIR BATT
0
=
−
−
R
e x V
I
H
A BATT
L
=