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BQ2012SN Datasheet(PDF) 8 Page - Texas Instruments |
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BQ2012SN Datasheet(HTML) 8 Page - Texas Instruments |
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8 / 26 page  Self-Discharge Estimation The bq2012 continuously decrements NAC and increments DCR for self-discharge based on time and temperature. The self-discharge count rate is programmed to be a nomi- nal 1 64 * NAC or 1 47 * NAC per day or disabled as selected by PROG5. This is the rate for a battery whose tempera- ture is between 20°–30°C. The NAC register cannot be decremented below 0. Count Compensations The bq2012 determines fast charge when the NAC up- dates at a rate of ≥2 counts/sec. Charge and discharge are compensated for temperature and charge/discharge rate before updating the NAC and/or DCR. Self-dis- charge estimation is compensated for temperature be- fore updating the NAC or DCR. Charge Compensation Two charge efficiency compensation factors are used for trickle charge and fast charge. Fast charge is defined as a rate of charge resulting in ≥ 2 NAC counts/sec (≥ 0.15C to 0.32C depending on PFC selections; see Table 2). The compensation defaults to the fast charge factor until the actual charge rate is determined. Temperature adapts the charge rate compensation factors over three ranges between nominal, warm, and hot tem- peratures. The compensation factors are shown below. Discharge Compensation Corrections for the rate of discharge are made by adjusting an internal discharge compensation factor. The discharge factor is based on the dynamically measured VSR. The compensation factors during discharge are: Temperature compensation during discharge also takes place. At lower temperatures, the compensation factor increases by 0.05 for each 10°C temperature range below 10°C. Compensation factor = 1.0 + (0.05 * N) Where N = Number of 10°C steps below 10°C and -150mV < VSR <0. For example: T > 10°C : Nominal compensation, N = 0 0°C<T< 10°C: N = 1 (i.e., 1.0 becomes 1.05) -10°C<T<0°C: N=2 (i.e., 1.0 becomes 1.10) -20°C<T< -10°C: N = 3 (i.e., 1.0 becomes 1.15) -20°C<T< -30°C: N = 4 (i.e., 1.0 becomes 1.20) Self-Discharge Compensation The self-discharge compensation is programmed for a nominal rate of 1 64 * NAC or 1 47 * NAC per day. This is the rate for a battery within the 20–30°C temperature range (TMPGG = 6x). This rate varies across 8 ranges from <10°C to >70°C, doubling with each higher tem- perature step (10°C). See Table 3. Digital Magnitude Filter The bq2012 has a programmable digital filter to eliminate charge and discharge counting below a set threshold. The de- fault setting is -0.30mV for VSRD and +0.38mV for VSRQ. The proper digital filter setting can be calculated using the following equation. Table 4 shows typical digital filter settings. VSRD (mV) = -45 / DMF VSRQ (mV) = -1.25 * VSRD 8 bq2012 Temperature Step Typical Rate PROG5 = Z PROG5 = L < 10°C NAC 256 NAC 188 10–20°C NAC 128 NAC 94 20–30°C NAC 64 NAC 47 30–40°C NAC 32 NAC 23 5 . 40–50°C NAC 16 NAC 11 8 . 50–60°C NAC 8 NAC 588 . Table 3. Self-Discharge Compensation Charge Temperature Trickle Charge Compensation Fast Charge Compensation <30°C 0.80 0.95 30–40°C 0.75 0.90 > 40°C 0.65 0.80 Approximate VSR Threshold Discharge Compensation Factor Efficiency VSR > -150 mV 1.00 100% VSR < -150 mV 1.05 95% DMF DMF Hex. VSRD (mV) VSRQ (mV) 75 4B -0.60 0.75 100 64 -0.45 0.56 150 (default) 96 -0.30 0.38 175 AF -0.26 0.32 200 C8 -0.23 0.28 Table 4. Typical Digital Filter Settings Not Recommended For New Designs |
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