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BQ2031SN Datasheet(PDF) 7 Page - Texas Instruments |
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BQ2031SN Datasheet(HTML) 7 Page - Texas Instruments |
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7 / 16 page  The resistor values are calculated from the following: Equation 1 RB1 RB2 NV V FLT = ∗ − () . 22 1 Equation 2 RB1 RB2 RB1 RB3 ( N ) BLK += ∗ − V 22 1 . Equation 3 I V R MAX SNS = 0 250 . where: n N = Number of cells n VFLT = Desired float voltage n VBLK = Desired bulk charging voltage n IMAX = Desired maximum charge current These parameters are typically specified by the battery manufacturer. The total resistance presented across the battery pack by RB1 + RB2 should be between 150k Ω and 1M Ω. The minimum value ensures that the divider network does not drain the battery excessively when the power source is disconnected. Exceeding the maximum value increases the noise susceptibility of the BAT pin. An empirical procedure for setting the values in the re- sistor network is as follows: 1. Set RB2 to 49.9 k Ω. (for 3 to 18 series cells) 2. Determine RB1 from equation 1 given VFLT 3. Determine RB3 from equation 2 given VBLK 4. Calculate RSNS from equation 3 given IMAX Battery Insertion and Removal The bq2031 uses VBAT to detect the presence or absence of a battery. The bq2031 determines that a battery is present when VBAT is between the High-Voltage Cutoff (VHCO = 0.6 * VCC) and the Low-Voltage Cutoff (VLCO = 0.8V). When VBAT is outside this range, the bq2031 de- termines that no battery is present and transitions to the Fault state. Transitions into and out of the range between VLCO and VHCO are treated as battery inser- tions and removals, respectively. Besides being used to detect battery insertion, the VHCO limit implicitly serves as an over-voltage charge termination, because exceed- ing this limit causes the bq2031 to believe that the bat- tery has been removed. The user must include a pull-up resistor from the posi- tive terminal of the battery stack to VDC (and a diode to prevent battery discharge through the power supply when the supply is turned off) in order to detect battery removal during periods of voltage regulation. Voltage regulation occurs in pre-charge qualification test 1 prior to all of the fast charge algorithms, and in phase 2 of the Two-Step Voltage fast charge algorithm. Temperature Monitoring The bq2031 monitors temperature by examining the voltage presented between the TS and SNS pins (VTEMP) by a resistor network that includes a Negative Tempera- ture Coefficient (NTC) thermistor. Resistance variations around that value are interpreted as being proportional to the battery temperature (see Figure 7). The temperature thresholds used by the bq2031 and their corresponding TS pin voltage are: n TCO—Temperature cutoff—Higher limit of the tem- perature range in which charging is allowed. VTCO = 0.4 * VCC n HTF—High-temperature fault—Threshold to which temperature must drop after temperature cutoff is exceeded before charging can begin again. VHTF = 0.44 * VCC 7 bq2031 FG203104.eps VCC VLTF = 0.6V VHTF = 0.44V VTCO = 0.4V Hotter VSS TCO HTF LTF Colder Figure 7. Voltage Equivalent of Temperature Thresholds |
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