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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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LTC6802-1 Fiches technique(PDF) 13 Page - Linear Technology |
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LTC6802-1 Fiches technique(HTML) 13 Page - Linear Technology |
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13 / 38 page  LTC6802-1 13 68021fa Figure 2. Open Connection Figure 3 shows an open connection at the same point in the cell stack as Figure 2, but this time there is an external filter network still connected to C3. Depending on the value of the capacitor remaining on C3, a normal measurement of B3 and B4 may not give near-zero readings, since the C3 pin is not truly open. In fact, with a large external ca- pacitance on C3, the C3 voltage will be charged midway between C2 and C4 after several cycles of measuring cells B3 and B4. Thus the measurements for B3 and B4 may indicate a valid cell voltage when in fact the exact state of B3 and B4 is unknown. To reliably detect an open connection, the command STOWAD is provided. With this command, two 100μA current sources are connected to the ADC inputs and turned on during all cell conversions. Referring again to Figure 3, with the STOWAD command, the C3 pin will be pulled down by the 100μA current source during the B3 cell measurement AND during the B4 cell measurement. This will tend to decrease the B3 measurement result and increase the B4 measurement result relative to the normal STCVAD command. The biggest change is observed in the B4 measurement when C3 is open. So, the best method to detect an open wire at input C3 is to look for an increase in the measurement of the cell connected between inputs C3 and C4 (cell B4). Thus the following algorithm can be used to detect an open connection to cell pin CN: (1) Issue a STCVAD command (ADC convert without 100μA current sources). (2) Issue a RDCV command and store all cell measure- ments into array CELLA(N). (3) Issue a STOWAD command (ADC convert with 100μA current sources). (4) Issue a RDCV command and store all cell measure- ments into array CELLB(N). (5) For each value of N from 1 to 11: If CELLB(N+1) – CELLA(N+1) ≥ +200mV, then CN is open, otherwise it is not open. The +200mV threshold is chosen to provide tolerance for errors in the measurement with the 100μA current source connected. Even without an open connection there is al- ways some difference between a cell measured with and without the 100μA current source because of the IR drop across the finite resistance of the MUX switches. On the other hand, with capacitors larger than 0.1μF remaining on an otherwise open C pin, the 100μA current source may not be enough to move the open C pin 200mV with a single STOWAD command. If the STOWAD command is repeated several times, the large external capacitor will discharge enough to create a 200mV change in cell read- ings. To detect an open connection with larger than 0.1μF capacitance still on the pin, one must repeat step (3) above a number of times before proceeding to step (4). The algorithm above determines if the CN pin is open based on measurements of the N+1 Cell. For example, in a 12-cell system, the algorithm finds opens on pins C1 Figure 3. Open Connection with RC Filtering OPERATION MUX C4 C3 C2 B4 B3 C1 V – 100μA 68021 F02 LTC6802-1 MUX C4 C3 CF4 CF3 C2 C1 V – 100μA B4 B3 68021 F03 LTC6802-1 |
Numéro de pièce similaire - LTC6802-1_15 |
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Description similaire - LTC6802-1_15 |
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