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LTC6802-1 Datasheet(PDF) 8 Page - Linear Technology |
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LTC6802-1 Datasheet(HTML) 8 Page - Linear Technology |
8 / 32 page LTC6802-1 8 68021p TIMING DIAGRAM D3 D3 D2 D1 D0 D7 … D4 D3 D3 D4 D2 D1 D0 D7 … D4 t6 t7 t3 t5 t4 t1 t8 t2 PREVIOUS COMMAND CURRENT COMMAND SCKI SDI CSBI SDO 6915 TD OPERATION THEORY OF OPERATION The LTC6802-1 is a data acquisition IC capable of mea- suring the voltage of 12 series connected battery cells. An input multiplexer connects the batteries to a 12-bit delta-sigma analog to digital converter (ADC). An internal 10ppm voltage reference combined with the ADC give the LTC6802-1 its outstanding measurement accuracy. The inherent benefits of the delta-sigma ADC vs other types of ADCs (e.g. successive approximation) are explained in Advantages of Delta-Sigma ADCs in the Applications Information section. Communication between the LTC6802-1 and a host pro- cessor is handled by a SPI compatible serial interface. As shown in Figure 1, the LTC6802-1’s can pass data up and down a stack of devices using simple diodes for isolation. This operation is described in Serial Port in the Applica- tions Information section. The LTC6802-1 also contains circuitry to balance cell volt- ages. Internal MOSFETs can be used to discharge cells. These internal MOSFETs can also be used to control external balancing circuits. Figure 1 illustrates cell balancing by internal discharge. Figure 4 shows the S pin controlling an external balancing circuit. It is important to note that the LTC6802-1 makes no decisions about turning on/off the internal MOSFETs. This is completely controlled by the host processor. The host processor writes values to a configuration register inside the LTC6802-1 to control the switches. The watchdog timer on the LTC6802-1 can be used to turn off the discharge switches if communication with the host processor is interrupted. OPEN CONNECTION DETECTION The open connection detection algorithm assures that an open circuit is not misinterpreted as a valid cell reading. In the absence of external noise filtering, the input resis- tance of the ADC will cause open wires to produce a near zero reading. Internal current sources can be used to determine if the wire is truly open. For example, an open on input C3 will result in a near zero reading for both cells connected to C3. For illustration these cells are labeled B3 and B4 in Figure 2. If a near zero reading is encountered for B3 and B4, the MPU can command the LTC6802-1 to place 100μA current sources from the ADC inputs to V–. If input C3 is open, the new reading will show B3 to be zero and B4 to be full-scale. Some applications may include external noise filtering to improve the quality of the ADC readings. When an RC net- work is used to filter noise, an open wire may not produce Timing Diagram of the Serial Interface |
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