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LTC4088EDE-2-PBF 数据表(PDF) 18 Page - Linear Technology |
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LTC4088EDE-2-PBF 数据表(HTML) 18 Page - Linear Technology |
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18 / 24 page  LTC4088-1/LTC4088-2 18 40881fb charger for more current than is available will not cause the average input current limit to be violated. It will merely allow the battery charger to make use of all available power to charge the battery as quickly as possible, and with minimal power dissipation within the charger. Alternate NTC Thermistors and Biasing The LTC4088-1/LTC4088-2 provides temperature qualified charging if a grounded thermistor and a bias resistor are connected to NTC. By using a bias resistor whose value is equal to the room temperature resistance of the thermis- tor (R25) the upper and lower temperatures are pre-pro- grammed to approximately 40°C and 0°C, respectively (assuming a Vishay “Curve 1” thermistor). The upper and lower temperature thresholds can be ad- justed by either a modification of the bias resistor value or by adding a second adjustment resistor to the circuit. If only the bias resistor is adjusted, then either the upper or the lower threshold can be modified but not both. The other trip point will be determined by the characteristics of the thermistor. Using the bias resistor in addition to an adjustment resistor, both the upper and the lower tempera- ture trip points can be independently programmed with the constraint that the difference between the upper and lower temperature thresholds cannot decrease. Examples of each technique are given below. NTC thermistors have temperature characteristics which are indicated on resistance-temperature conversion tables. The Vishay-Dale thermistor NTHS0603N011-N1003F, used in the following examples, has a nominal value of 100k and follows the Vishay “Curve 1” resistance-temperature characteristic. In the explanation below, the following notation is used. R25 = Value of the Thermistor at 25°C RNTC|COLD = Value of thermistor at the cold trip point RNTC|HOT = Value of the thermistor at the hot trip point rCOLD = Ratio of RNTC|COLD to R25 rHOT = Ratio of RNTC|COLD to R25 RNOM = Primary thermistor bias resistor (see Figure 4a) R1 = Optional temperature range adjustment resistor (see Figure 4b) The trip points for the LTC4088-1/LTC4088-2’s tempera- ture qualification are internally programmed at 0.349 • VBUS for the hot threshold and 0.765 • VBUS for the cold threshold. Therefore, the hot trip point is set when: R RR VV NTCHOT NOM NTCHOT BUS BUS | | •. • + = 0 349 and the cold trip point is set when: R RR VV NTC COLD NOM NTC COLD BUS BUS | | •. • + = 0 765 Solving these equations for RNTC|COLD and RNTC|HOT results in the following: RNTC|HOT = 0.536 • RNOM and RNTC|COLD = 3.25 • RNOM By setting RNOM equal to R25, the above equations result in rHOT = 0.536 and rCOLD = 3.25. Referencing these ratios to the Vishay Resistance-Temperature Curve 1 chart gives a hot trip point of about 40°C and a cold trip point of about 0°C. The difference between the hot and cold trip points is approximately 40°C. By using a bias resistor, RNOM, different in value from R25, the hot and cold trip points can be moved in either direc- tion. The temperature span will change somewhat due to the non-linear behavior of the thermistor. The following equations can be used to easily calculate a new value for the bias resistor: R r R R r R NOM HOT NOM COLD = = 0 536 25 325 25 . • . • where rHOT and rCOLD are the resistance ratios at the desired hot and cold trip points. Note that these equations are linked. Therefore, only one of the two trip points can APPLICATIO S I FOR ATIO |
类似零件编号 - LTC4088EDE-2-PBF |
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类似说明 - LTC4088EDE-2-PBF |
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