Datasheet LTC1998 (Analog Devices) - 7
| Manufacturer | Analog Devices |
| Description | 2.5µA, 1% Accurate SOT-23 Comparator and Voltage Reference for Battery Monitoring |
| Pages / Page | 12 / 7 — QUICK DESIGN GUIDE. How to Calculate the External Resistor Values. … |
| File Format / Size | PDF / 139 Kb |
| Document Language | English |
QUICK DESIGN GUIDE. How to Calculate the External Resistor Values. Typical Application
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LTC1998
QUICK DESIGN GUIDE How to Calculate the External Resistor Values
Example 1: A system using a 4.2V (fully charged) Lithium- Ion battery requires a low battery threshold of 2.7V, 100mV The LTC1998 is a low battery warning indicator and is es- hysteresis and can allow up to 4.2μA maximum resistor pecially designed for monitoring the voltage of single-cell current. Lithium-Ion batteries. The LTC1998 compares its supply pin (BATT) to an accurate internal reference; if the battery RTOTAL = 1MΩ, R1 = 786k, R2 = 66k and R3 = 148k voltage falls below the programmed low battery threshold Choose standard 1% values. voltage of the LTC1998, the battery low pin (BATTLO) will change state, from high to low, to indicate a low battery R1 = 787k, R2 = 66.5k, R3 = 147k condition. The low battery threshold voltage is programmed 1.5V TO 4.2V V via the voltage threshold adjust pin (V LOGIC TH.A). A hysteresis REGULATOR adjust pin (V 0.1μF H.A) will add hysteresis to the programmed R1 1 + 1% BATT value of the low battery threshold voltage. 4 5 VH.A VLOGIC R2 LTC1998 μP
Typical Application
1% Li-Ion 3 6 V BATTLO TH.A
Table 1: Design Equations for R1, R2, R3, Figure 1
R3 GND 1% 2 Choose desired values for: 1998 F01 • V
Figure 1. Low Battery Threshold Detector with Hysteresis
BATT.Th: Low Battery Threshold Voltage • VHYST: Hysteresis Voltage • IR: Max Allowable Resistor Current Solve: 4. V 2 R = R1+ R2 + R TOTAL 3 = IR ⎛ V 5 ⎞ R1= RTOTAL • – 1 ⎝⎜ V . + V BATT Th HYST ⎠⎟ V 5 ⎞ R2 = ⎛ R • – 1 – R TOTAL 1 ⎝⎜ VBATT.Th ⎠⎟ R3 = R – R1– R TOTAL 2 1998fb 7
QUICK DESIGN GUIDE How to Calculate the External Resistor Values
Example 1: A system using a 4.2V (fully charged) Lithium- Ion battery requires a low battery threshold of 2.7V, 100mV The LTC1998 is a low battery warning indicator and is es- hysteresis and can allow up to 4.2μA maximum resistor pecially designed for monitoring the voltage of single-cell current. Lithium-Ion batteries. The LTC1998 compares its supply pin (BATT) to an accurate internal reference; if the battery RTOTAL = 1MΩ, R1 = 786k, R2 = 66k and R3 = 148k voltage falls below the programmed low battery threshold Choose standard 1% values. voltage of the LTC1998, the battery low pin (BATTLO) will change state, from high to low, to indicate a low battery R1 = 787k, R2 = 66.5k, R3 = 147k condition. The low battery threshold voltage is programmed 1.5V TO 4.2V V via the voltage threshold adjust pin (V LOGIC TH.A). A hysteresis REGULATOR adjust pin (V 0.1μF H.A) will add hysteresis to the programmed R1 1 + 1% BATT value of the low battery threshold voltage. 4 5 VH.A VLOGIC R2 LTC1998 μP
Typical Application
1% Li-Ion 3 6 V BATTLO TH.A
Table 1: Design Equations for R1, R2, R3, Figure 1
R3 GND 1% 2 Choose desired values for: 1998 F01 • V
Figure 1. Low Battery Threshold Detector with Hysteresis
BATT.Th: Low Battery Threshold Voltage • VHYST: Hysteresis Voltage • IR: Max Allowable Resistor Current Solve: 4. V 2 R = R1+ R2 + R TOTAL 3 = IR ⎛ V 5 ⎞ R1= RTOTAL • – 1 ⎝⎜ V . + V BATT Th HYST ⎠⎟ V 5 ⎞ R2 = ⎛ R • – 1 – R TOTAL 1 ⎝⎜ VBATT.Th ⎠⎟ R3 = R – R1– R TOTAL 2 1998fb 7
