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LTC4069 Datasheet(PDF) 15 Page - Linear Technology |
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LTC4069 Datasheet(HTML) 15 Page - Linear Technology |
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15 / 18 page  LTC4069 15 4069fc For more information www.linear.com/LTC4069 Thermistors The LTC4069 NTC trip points are designed to work with thermistors whose resistance-temperature character- istics follow Vishay Dale’s “R-T Curve 1.” The Vishay NTHS0603N01N1003Jisanexampleofsuchathermistor. However, Vishay Dale has many thermistor products that follow the “R-T Curve 1” characteristic in a variety of sizes. Furthermore, any thermistor whose ratio of RCOLDtoRHOT is about 6 will also work (Vishay Dale R-T Curve 1 shows a ratio of RCOLD to RHOT of 3.266/0.5325 = 6.13). Designers may want to use thermistors whose room temperature value is different than 100k. Vishay Dale has a number of values of thermistor from 32k to 100k that follow the “R-T Curve 1.” Using different R-T curves, such as Vishay Dale “R-T Curve 2”, is also possible. This curve, combined with LTC4069 internal thresholds, gives temperaturetrippointsofapproximately–3°C(falling)and 42°C (rising), a delta of 45°C. This delta in temperature can be moved in either direction by changing the value of RNOM with respect to RNTC. Increasing RNOM will move both trip points to higher temperatures. To calculate RNOM for a shift to lower temperature for example, use the following equation: RNOM = RCOLD 3.266 • RNTC at 25°C where RCOLD is the resistance ratio of RNTC at the desired coldtemperaturetrippoint.Ifyouwanttoshiftthetrippoints to higher temperatures use the following equation: RNOM = RHOT 0.5325 • RNTC at 25°C where RHOT is the resistance ratio of RNTC at the desired hot temperature trip point. Here is an example using a 10k R-T Curve 2 thermistor from Vishay Dale. The difference between the trip points is 45°C, from before, and we want the cold trip point to be 0°C, which would put the hot trip point at 45°C. The RNOM needed is calculated as follows: RNOM = RCOLD 3.266 • RNTC at 25°C = 2.816 3.266 • 10k = 8.62k The nearest 1% value for RNOM is 8.66k. This is the value used to bias the NTC thermistor to get cold and hot trip points of approximately 0°C and 45°C respectively. To extend the delta between the cold and hot trip points, a resistor, R1, can be added in series with RNTC (see Figure 6). The values of the resistors are calculated as follows: RNOM = RCOLD −RHOT 3.266 − 0.5325 R1 = 0.5325 3.266 − 0.5325 ⎛ ⎝⎜ ⎞ ⎠⎟ • RCOLD −RHOT ( )−RHOT where RNOM is the value of the bias resistor and RHOT and RCOLD are the values of RNTC at the desired temperature trip points. Continuing the example from before with a desired trip point of 50°C: RNOM = RCOLD −RHOT 3.266 −0.5325 = 10k • 2.816 −0.4086 ( ) 3.266 −0.5325 = 8.8k, 8.87k is the nearest 1% value. R1 = 10k • 0.5325 3.266 −0.5325 ⎛ ⎝⎜ ⎞ ⎠⎟ • 2.816 −0.4086 ( )−0.4086 = 604Ω, 604 is the nearest 1% value. applicaTions inForMaTion |
Similar Part No. - LTC4069_15 |
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Similar Description - LTC4069_15 |
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