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BQ2002C Datasheet(PDF) 5 Page - Texas Instruments |
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BQ2002C Datasheet(HTML) 5 Page - Texas Instruments |
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 V ∆ BAT 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. Synchronized Voltage Sampling Voltage sampling at the BAT pin for PVD and - V termi ∆ nation may be synchronized to an external stimulus using the INH input. Low-high-low input pulses between 100ns and 3.5ms in width must be applied at the INH pin with a frequency greater than the “maximum synchronized sampling period” set by the state of the TM pin as shown in Table 1. Voltage is sampled on the falling edge of such pulses. If the time between pulses is greater than the synchronizing period, voltage sampling “free-runs” at once every 17 seconds. A sample is taken by averaging together voltage measurements taken 57µs 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 effect of any AC line ripple that may feed through the power supply from either 50 or 60Hz AC sources. If the INH input remains high for more than 12ms, the voltage sample history kept by the IC and used for PVD and - V termination decisions is ∆ erased and a new history is started. Such a reset is required when transitioning from free-running to synchronized voltage sampling. The response of the IC to pulses less than 100ns in width or between 3.5ms and 12ms is indeterminate. The tolerance on all timing is ±12%. 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 maximum cell voltage, VMCV, fast charge is terminated. Maximum temperature termination occurs anytime the voltage on the TS pin falls below the temperature cut-off threshold VTCO, where VTCO = 0.5 x VCC ± 5%. 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 termination is enforced on the fast-charge phase. There is no time limit on the trickle-charge phase. 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 once per second for the period specified in Table 1. This results in a trickle rate of C/32. TM Pin The TM pin is a three-level pin used to select the charge timer, voltage termination mode, trickle rate, and voltage hold-off period options. Table 1 describes the states selected by the TM pin. The mid-level selection input is developed by a resistor divider 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. In the charge pending state, the LED pin is driven low for 500ms, then to high-Z for 500ms. The LED pin is driven to the high-Z state for all other conditions. Figure 2 outlines the state of the LED pin during charge. Charge Inhibit Fast charge may be inhibited by using the INH pin. When high, INH suspends all fast charge activity and the internal charge timer. INH freezes the current state of LED until inhibit is removed. Temperature monitoring is not affected by the INH pin. During charge inhibit, the bq2002C 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 are driven to the high-Z state. The operating current is reduced to less than 1µA in this mode. When VBAT returns to a value below VPD, the IC pulse- trickle charges until the next new charge cycle begins. bq2002C 5 |
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