LTC1998 Просмотр технического описания (PDF) - Linear Technology

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LTC1998

2.5µA, 1% Accurate SOT-23 Comparator and Voltage Reference for Battery Monitoring

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LTC1998

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 (VTH.A). A hysteresis

adjust pin (VH.A) will add hysteresis to the programmed

value of the low battery threshold voltage.

Typical Application

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

Choose desired values for:

• VBATT.Th: Low Battery Threshold Voltage

• VHYST: Hysteresis Voltage

• IR: Max Allowable Resistor Current

Solve:

RTOTAL

=

R1+

R2

+

R3

=

4.2V

IR

R1= RTOTAL

•

⎛

⎝⎜

5V

VBATT.Th +

VHYST

– 1⎞⎠⎟

R2

=

RTOTAL

•

⎛

⎝⎜

5V

VBATT.Th

– 1⎞⎠⎟

– R1

R3 = RTOTAL – R1– R2

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.

RTOTAL = 1MΩ, R1 = 786k, R2 = 66k and R3 = 148k

Choose standard 1% values.

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

1.5V TO 4.2V

+

R1

1%

R2

1%

R3

1%

REGULATOR

0.1μF 1

4

BATT

5

VH.A VLOGIC

LTC1998

3 VTH.A BATTLO 6

GND

2

VLOGIC

μP

1998 F01

Figure 1. Low Battery Threshold Detector with Hysteresis

1998fa

7

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