LTC1998 LINER [Linear Technology], LTC1998 Datasheet - Page 10

• Manufacturer Part Number: LTC1998
• Description: 2.5uA, 1% Accurate SOT-23 Comparator and Voltage Reference for Battery Monitoring
• Manufacturer: LINER [Linear Technology]

LTC1998
APPLICATIONS INFORMATION
The calculation of the resistor values R1, R2 and R3 is
quite straightforward and similar to the procedure outlined
in the previous paragraph.
Choose a value for the sum of R1 + R2 + R3 as well as the
values for low battery threshold and hysteresis.
Solve for resistor R1:
Solve for the sum of
then solve for R2 and R3.
Example: A system needs to detect a low battery
voltage of 3V (V
(V
(R1 + R2 + R3) = 1M.
R1 = 539k, R1 + R2 = 667k, R2 = 128k, R3 = 333k.
Choose the closest 1% values, that is 536k, 332k, 127k.
Figure 4 graphically shows the function of the LTC1998 as
described above.
10
(
R
TH2
1
R
+
1
R
=
= 3.25V). Set the value of the resistor divider
2
(
) (
R
=
1
+
R
R
1
+
2
R
+
BATT.Th
2
R
+
3
)
R
⎛
⎝ ⎜
3
V
)
= 3V) with 250mV hysteresis
5
TH
⎛
⎝ ⎜
V
V
2
BATT Th
–
5
1
V
⎞
⎠ ⎟
.
–
1
⎞
⎠ ⎟
PROGRAMMED
PROGRAMMED
VERSATILE OUTPUT DRIVER
V
The LTC1998 uses a CMOS push-pull output stage to drive
the low battery output signal. This output pin (BATTLO)
has a separate supply pin, (V
provide an output voltage rail matching the V
microprocessors. The V
age lower than the voltage at the BATT pin. The V
pin may also be tied to a voltage higher than V
series resistor greater than 10k. The output will then act
as an open-drain device.
In a given application, if it is possible for BATTLO to be
shorted to GND or a supply, a series resistor should be
added to limit the short-circuit current to 5mA.
LOGIC
HYSTERESIS
THRESHOLD
THRESHOLD
LOW BATT
BATTLO
V
3.25V
2.50V
LOGIC
, BATTLO (Pins 5,6)
Figure 4. LTC1998 Function Plot
THRESHOLD RANGE
PROGRAMMABLE
BATTERY
VOLTAGE
LOGIC
LOGIC
pin may be tied to a volt-
) that can be used to
HYSTERESIS
BATTERY VOLTAGE
RECOVERS UNDER
REDUCED LOAD
DD
BATT
logic of
LOGIC
via a
1998fa
1998 F04