Datasheet MAX6846, MAX6847, MAX6848, MAX6849 (Maxim) - 10
| Fabricante | Maxim |
| Descripción | Low-Power, Adjustable Battery Monitors with Hysteresis and Integrated μP Reset |
| Páginas / Página | 12 / 10 — Low-Power, Adjustable Battery Monitors with Hysteresis and Integrated µP … |
| Formato / tamaño de archivo | PDF / 222 Kb |
| Idioma del documento | Inglés |
Low-Power, Adjustable Battery Monitors with Hysteresis and Integrated µP Reset. Table 1. Factory-Trimmed V. CC Reset
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Low-Power, Adjustable Battery Monitors with Hysteresis and Integrated µP Reset
1) Choose a value for RTOTAL, the sum of R1, R2, and to three alkaline/NiCd/NiMH cells. The LBOH output R3. Because the MAX6848/MAX6849 have very high indicates that the battery voltage is weak, and is used input impedance, RTOTAL can be up to 500kΩ. to warn the microprocessor of potential problems. 2) Calculate R3 based on R Armed with this information, the microprocessor can TOTAL and the desired upper trip point: reduce system power consumption. The LBOL output indicates the battery is empty and system power should mV 582 RTOTAL be disabled. By connecting LBOL to the SHDN pin of the R3 = × VTRIPHIGH DC-DC converter, power to the microprocessor is removed. Microprocessor power does not return until the 3) Calculate R2 based on RTOTAL, R3, and the desired battery has recharged to a voltage greater than VLTH+ lower trip point: (see Figure 7).
Table 1. Factory-Trimmed V
CC Reset
mV 582 R R TOTAL 2 = × R3
Threshold Levels
VTRIPLOW -
PART NO. VCC NOMINAL
4) Calculate R1 based on R
SUFFIX RESET
TOTAL, R3, and R2:
( _ ) THRESHOLD (V) MAX6846–MAX6849
R1 = R - R2 - R TOTAL 3 T 3.075 5) LBOL high-trip level: S 2.925 VTRIPLOW ✕ 1.05 R 2.625 6) LBOH high-trip level: Z 2.313 V Y 2.188 TRIPHIGH ✕ 1.05 W 1.665
Monitoring Multicell Battery Applications
V 1.575 For monitoring multicell Li+ (or a higher number of alka- line/NiCd/NiMH cells), connect VDD to a supply voltage
Table 2. VCC Reset Timeout Period Suffix
between 1.6V to 5.5V. Figure 6 shows VDD connected directly to V
Guide
CC. To calculate the values of R1, R2, and R3, see the Resistor-Value Selection section.
TIMEOUT ACTIVE TIMEOUT PERIOD (ms) DC-DC Converter Application PERIOD SUFFIX MIN MAX
The MAX6848/MAX6849 dual battery monitors can be D3 150 300 used in conjunction with a DC-DC converter to power D7 1200 2400 microprocessor systems using a single Li+ cell or two VCC IN DC-DC OUT VDD VCC SHDN VMONITORED Li+ LBO* 3.6V VDD LBOL V V CC CC R1 MAX6846 MAX6847 LBOH NMI LTHIN MAX6848 (LBOL) LTHIN MAX6849 R2 (LBOH) µP MAX6848 HTHIN GND MAX6849 HTHIN RESET RESET R3 GND GND * FOR THE MAX6846/MAX6847. ( ) FOR THE MAX6848/MAX6849. Figure 6. Monitoring Multicell Li+ Applications Figure 7. DC-DC Converter Application
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1) Choose a value for RTOTAL, the sum of R1, R2, and to three alkaline/NiCd/NiMH cells. The LBOH output R3. Because the MAX6848/MAX6849 have very high indicates that the battery voltage is weak, and is used input impedance, RTOTAL can be up to 500kΩ. to warn the microprocessor of potential problems. 2) Calculate R3 based on R Armed with this information, the microprocessor can TOTAL and the desired upper trip point: reduce system power consumption. The LBOL output indicates the battery is empty and system power should mV 582 RTOTAL be disabled. By connecting LBOL to the SHDN pin of the R3 = × VTRIPHIGH DC-DC converter, power to the microprocessor is removed. Microprocessor power does not return until the 3) Calculate R2 based on RTOTAL, R3, and the desired battery has recharged to a voltage greater than VLTH+ lower trip point: (see Figure 7).
Table 1. Factory-Trimmed V
CC Reset
mV 582 R R TOTAL 2 = × R3
Threshold Levels
VTRIPLOW -
PART NO. VCC NOMINAL
4) Calculate R1 based on R
SUFFIX RESET
TOTAL, R3, and R2:
( _ ) THRESHOLD (V) MAX6846–MAX6849
R1 = R - R2 - R TOTAL 3 T 3.075 5) LBOL high-trip level: S 2.925 VTRIPLOW ✕ 1.05 R 2.625 6) LBOH high-trip level: Z 2.313 V Y 2.188 TRIPHIGH ✕ 1.05 W 1.665
Monitoring Multicell Battery Applications
V 1.575 For monitoring multicell Li+ (or a higher number of alka- line/NiCd/NiMH cells), connect VDD to a supply voltage
Table 2. VCC Reset Timeout Period Suffix
between 1.6V to 5.5V. Figure 6 shows VDD connected directly to V
Guide
CC. To calculate the values of R1, R2, and R3, see the Resistor-Value Selection section.
TIMEOUT ACTIVE TIMEOUT PERIOD (ms) DC-DC Converter Application PERIOD SUFFIX MIN MAX
The MAX6848/MAX6849 dual battery monitors can be D3 150 300 used in conjunction with a DC-DC converter to power D7 1200 2400 microprocessor systems using a single Li+ cell or two VCC IN DC-DC OUT VDD VCC SHDN VMONITORED Li+ LBO* 3.6V VDD LBOL V V CC CC R1 MAX6846 MAX6847 LBOH NMI LTHIN MAX6848 (LBOL) LTHIN MAX6849 R2 (LBOH) µP MAX6848 HTHIN GND MAX6849 HTHIN RESET RESET R3 GND GND * FOR THE MAX6846/MAX6847. ( ) FOR THE MAX6848/MAX6849. Figure 6. Monitoring Multicell Li+ Applications Figure 7. DC-DC Converter Application
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