LTC1998CS6#PBF Linear Technology, LTC1998CS6#PBF Datasheet - Page 7

• Manufacturer Part Number: LTC1998CS6#PBF
• Manufacturer: Linear Technology

Specifications of LTC1998CS6#PBF

• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 6
• Lead Free Status / RoHS Status: Compliant

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
via the voltage threshold adjust pin (V
adjust pin (V
value of the low battery threshold voltage.
Typical Application
Table 1: Design Equations for R1, R2, R3, Figure 1
Choose desired values for:
Solve:
• V
• V
• I
R
R
R
R
1
2
3
TOTAL
R
BATT.Th
HYST
=
: Max Allowable Resistor Current
=
=
R
R
R
TOTAL
: Hysteresis Voltage
TOTAL
TOTAL
H.A
=
: Low Battery Threshold Voltage
) will add hysteresis to the programmed
R
1
•
+
•
–
⎛
⎜
⎝
⎛
⎜
⎝
R
R
V
V
2
1
BATT Th
BATT Th
+
–
5
R
R
V
.
3
2
.
5
=
V
+
–
4 2
V
.
I
1
R
HYST
⎞
⎟
⎠
V
–
R
TH.A
1
–
1
). A 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.
R
R1 = 787k, R2 = 66.5k, R3 = 147k
Figure 1. Low Battery Threshold Detector with Hysteresis
TOTAL
1.5V TO 4.2V
+
= 1MΩ, R1 = 786k, R2 = 66k and R3 = 148k
1%
1%
1%
R1
R2
R3
4
3
0.1μF
V
V
H.A
TH.A
LTC1998
BATT
GND
BATTLO
V
1
2
LOGIC
REGULATOR
6
5
LTC1998
V
LOGIC
μP
1998 F01
1998fb
7