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BQ2002FSNTR Datasheet(PDF) 5 Page - Texas Instruments |
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BQ2002FSNTR Datasheet(HTML) 5 Page - Texas Instruments |
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5 / 17 page  PVD and - ∆V Termination There are two modes for voltage termination depending on the state of TM. For - ∆V (TM = high), if VBAT is lower than any previously measured value by 12mV ±3mV, fast charge is terminated. For PVD (TM = low or mid), a decrease of 2.5mV ±2.5mV terminates fast charge. The PVD and - ∆V tests are valid in the range 1V<VBAT <2V. Voltage Sampling Voltage is sampled at the BAT pin for PVD and - ∆V ter- mination once every 17s. The sample is an average of voltage measurements taken 570 µs apart.The IC takes 32 measurements in PVD mode and 16 measurements in - ∆V mode. The resulting sample periods (9.17 and 18.18ms, respectively) filter out harmonics centered around 55 and 109Hz. This technique minimizes the ef- fect of any AC line ripple that may feed through the power supply from either 50 or 60Hz AC sources. Toler- ance on all timing is ±20%. Voltage Termination Hold-off A hold-off period occurs at the start of fast charging. During the hold-off time, the PVD and - ∆V terminations are disabled. This avoids premature termination on the voltage spikes sometimes produced by older batteries when fast-charge current is first applied. Maximum voltage and temperature terminations are not affected by the hold-off period. Maximum Voltage, Temperature, and Time Any time the voltage on the BAT pin exceeds the maxi- mum cell voltage,VMCV, fast charge or optional top-off charge is terminated. Maximum temperature termination occurs anytime the voltage on the TS pin falls below the temperature cut-off threshold VTCO. Maximum charge time is configured using the TM pin. Time settings are available for corresponding charge rates of C/2, 1C, and 2C. Maximum time-out termina- tion is enforced on the fast-charge phase, then reset, and enforced again on the top-off phase, if selected. There is no time limit on the trickle-charge phase. Top-off Charge An optional top-off charge phase may be selected to follow fast charge termination for 1C and C/2 rates. This phase may be necessary on NiMH or other bat- tery chemistries that have a tendency to terminate charge prior to reaching full capacity. With top-off en- abled, charging continues at a reduced rate after fast-charge termination for a period of time selected by the TM pin. (See Table 1.) During top-off, the CC pin is modulated at a duty cycle of 286 µs active for every 4290 µs inactive. This modulation results in an average rate 1/16th that of the fast charge rate. Maxi- mum voltage, time, and temperature are the only ter- mination methods enabled during top-off. Pulse-Trickle Charge Pulse-trickle is used to compensate for self-discharge while the battery is idle in the charger. The battery is pulse-trickle charged by driving the CC pin active for a period of 286 µs for every 18.0ms of inactivity for 1C and 2C selections, and 286 µs for every 8.86ms of inactivity for C/2 selection. This results in a trickle rate of C/64 for the top-off enabled mode and C/32 otherwise. TM Pin The TM pin is a three-level pin used to select the charge timer, top-off, voltage termination mode, trickle rate, and voltage hold-off period options. Table 1 de- scribes the states selected by the TM pin. The mid- level selection input is developed by a resistor di- vider between VCC and ground that fixes the voltage on TM at VCC/2 ± 0.5V. See Figure 4. Charge Status Indication A fast charge in progress is uniquely indicated when the LED pin goes low. The LED pin is driven to the high-Z state for all conditions other than fast charge. Figure 2 outlines the state of the LED pin during charge. Charge Inhibit Fast charge and top-off may be inhibited by using the INH pin. When high, INH suspends all fast charge and top-off activity and the internal charge timer. INH freezes the current state of LED until inhibit is re- moved. Temperature monitoring is not affected by the INH pin. During charge inhibit, the bq2002/F continues to pulse-trickle charge the battery per the TM selection. When INH returns low, charge control and the charge timer resume from the point where INH became active. Low-Power Mode The IC enters a low-power state when VBAT is driven above the power-down threshold (VPD) where VPD = VCC - (1V ±0.5V) Both the CC pin and the LED pin are driven to the high-Z state. The operating current is reduced to less than 1 µA in this mode. When VBAT returns to a value below VPD, the IC pulse-trickle charges until the next new charge cycle begins. 5 bq2002/F |
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