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BQ2003SG4 Datasheet(PDF) 6 Page - Texas Instruments |
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BQ2003SG4 Datasheet(HTML) 6 Page - Texas Instruments |
6 / 18 page taken on the new battery is compared to ones taken be- fore the original battery was removed and any that may have been taken while no battery was present. If the IC is configured for ∆T/∆t termination, this may result in a premature fast-charge termination on the newly in- serted battery. Maximum temperature termination occurs anytime the voltage on the TS pin falls below the temperature cut-off threshold VTCO. Charge is also terminated if VTEMP rises above the minimum temperature fault threshold, VLTF, after fast charge begins. Maximum charge time is configured using the TM pin. Time settings are available for corresponding charge rates of C/4, C/2, 1C, and 2C. Maximum time-out termi- nation 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 the C/2 through 4C rates. This phase may be necessary on NiMH or other battery 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 TM1 and TM2 input pins. (See Table 2.) During top-off, the MOD pin is enabled at a duty cycle of 4s active for every 30s inactive. This modulation results in an average rate 1/8th that of the fast charge rate. Maximum voltage, time, and temperature are the only termination methods enabled during top-off. External Trickle Resistor Maintenance charging is provided by the use of an exter- nal trickle resistor between the high side of the battery pack and VDC, the input charging supply voltage. (See Figure 1.) This resistor is sized to meet two criteria. n With the battery removed, the resistor must pull the voltage at the BAT input above MCV for battery insertion and removal detection. n With the battery at its fully charged voltage, the trickle current should be approximately equal to the self-discharge rate of the battery. Charge Status Indication Charge status is indicated by the CHG output. The state of the CHG output in the various charge cycle phases is shown in Figure 3 and illustrated in Figure 1. Temperature status is indicated by the TEMP output. TEMP is in the high state whenever VTEMP is within the temperature window defined by the VLTF and VHTF tem- perature limits, and is low when the battery tempera- ture is outside these limits. In all cases, if VCELL exceeds the voltage at the MCV pin, both CHG and TEMP outputs are held high regard- less of other conditions. CHG and TEMP may both be used to directly drive an LED. Charge Current Control The bq2003 controls charge current through the MOD output pin. The current control circuitry is designed to support implementation of a constant-current switching regulator or to gate an externally regulated current source. When used in switch-mode configuration, the nominal regulated current is: IREG = 0.235V/RSNS Charge current is monitored at the SNS input by the voltage drop across a sense resistor, RSNS, between the low side of the battery pack and ground. RSNS is sized to provide the desired fast-charge current. If the voltage at the SNS pin is less than VSNSLO, the MOD output is switched high to pass charge current to the battery. When the SNS voltage is greater than VSNSHI, the MOD output is switched low—shutting off charging current to the battery. VSNSLO = 0.044 ∗ VCC ± 25mV VSNSHI = 0.05 ∗ VCC ± 25mV When used to gate an externally regulated current source, the SNS pin is connected to VSS, and no sense re- sisitor is required. 6 bq2003 |
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