LTC1998

7

1998fa

QUICK DESIGN GUIDE

How to Calculate the External Resistor Values

The LTC1998 is a low battery warning indicator and is es-

pecially designed for monitoring the voltage of single-cell

Lithium-Ion batteries. The LTC1998 compares its supply

pin (BATT) to an accurate internal reference; if the battery

voltage falls below the programmed low battery threshold

voltage of the LTC1998, the battery low pin (BATTLO) will

change state, from high to low, to indicate a low battery

condition. The low battery threshold voltage is programmed

value of the low battery threshold voltage.

Typical Application

Table 1: Design Equations for R1, R2, R3, Figure 1

Choose desired values for:

Solve:

RR

R

R

V

I

RR

V

VV

RR

V

V

R

RR

R

R

TOTAL

R

TOTAL

BATT Th

HYST

TOTAL

BATT Th

TOTAL

=+

+

=

=

+

⎛

⎝⎜

⎞

⎠⎟

=

⎛

⎝⎜

⎞

⎠⎟

=

12

3

42

1

5

1

2

5

11

31

2

.

•–

•–

–

––

.

.

Figure 1. Low Battery Threshold Detector with Hysteresis

Example 1: A system using a 4.2V (fully charged) Lithium-

Ion battery requires a low battery threshold of 2.7V, 100mV

hysteresis and can allow up to 4.2μA maximum resistor

current.

Choose standard 1% values.

R1 = 787k, R2 = 66.5k, R3 = 147k

1998 F01

LTC1998

R1

1%

R2

1%

R3

1%

BATT

BATTLO

4

3

2

1

5

6

REGULATOR

μP

GND

0.1μF

1.5V TO 4.2V

+