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BQ24382 Datasheet(PDF) 9 Page - Texas Instruments |
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BQ24382 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 18 page DETAILED FUNCTIONAL DESCRIPTION POWER DOWN POWER ON RESET DETAILED FUNCTIONAL DESCRIPTION Input Overvoltage Protection Battery Overvoltage Protection Thermal Protection bq24380 bq24381 bq24382 www.ti.com......................................................................................................................................................... SLUS805B – APRIL 2008 – REVISED MARCH 2009 The bq2438x is a highly integrated circuit designed to provide protection to Li-ion batteries from failures of the charging circuit and the input source. The IC continuously monitors the input voltage and the battery voltage. The device operates like a linear regulator, maintaining a 5.5-V (bq24380) or 5-V (bq24381, bq24382) output with input voltages up to the input overvoltage threshold (VOVP). If the input voltage exceeds VOVP, the IC shuts off the pass FET and disconnects the system from input power. Additionally, if the battery voltage rises above 4.35 V, the IC switches off the pass FET, removing the power from the system until the battery voltage falls to safe levels. The IC also monitors its die temperature and switches the pass FET off if it exceeds 140°C. The IC can be controlled by a processor, and also provides status information about fault conditions to the host. The device remains in power-down mode when the input voltage at the IN pin is below the undervoltage threshold (UVLO) of 2.8 V. The FET connected between the IN and OUT pins is off, and the status output, FAULT, is set to HI-Z. The device resets when the input voltage at the IN pin exceeds the UVLO threshold. During power-on reset, the IC waits for duration tDGL(PGOOD) for the input voltage to stabilize. If, after tDGL(PGOOD), the input voltage and battery voltage are within operation limits, the pass FET is turned ON. The IC has a soft-start feature to control the inrush current. The soft-start minimizes the ringing at the input due to the resonant circuit formed by the parasitic inductance of the adapter cable and the input bypass capacitor. During the soft-start time, tSStart, the current limit is stepped up in 8 equal steps every 625 µs. Each step is 1/8 of the I O(SC). After the soft-start sequence is over, the IC samples the load current. If the load current exceeds IO(SC), the IC initiates short circuit protection. See the Startup Short-Circuit Protection section for details. If no overcurrent event is measured, the current monitoring circuitry is disabled for normal operation. In the event a short-circuit is detected at power-on, to prevent the input voltage from spiking up when the pass FET is switched off (due to the inductance of the input cable), The pass FET is turned off by gradually reducing its gate-drive, resulting in a soft-stop (tSStop). The device continuously monitors the input voltage and the battery voltage as described in detail below: The OUT output of the bq2438x operates similar to a linear regulator. While the input voltage is less than VO(REG), and above the UVLO, the output voltage tracks the input voltage (less the drop caused by RDS(on) of the pass FET). When the input voltage is greater than VO(REG) (plus the RDS(on) drop) and less than VOVP, the output voltage is regulated to VO(REG). VO(REG) is 5.5 V for the bq24380, and 5 V for the bq24381 and bq24382. If the input voltage is increased above VOVP, the internal pass FET is turned off, removing power from the charging circuitry connected to OUT. The FAULT output is then asserted low. When the input voltage drops below VOVP – Vhys(OVP) (but is still above UVLO), the pass FET is turned on after a deglitch time of tREC(OVP). The deglitch time ensures that the input supply has stabilized. The condition 5 in Figure 18 illustrates an input overvoltage event. The battery overvoltage threshold BVOVP is internally set to 4.35 V for the bq2438x. Condition 3 in Figure 18 illustrates a battery overvoltage event. If the battery voltage exceeds the BVOVP threshold for longer than tDGL(BVovp), the pass FET is turned off (using soft-stop), and FAULT is asserted low. The pass FET is turned on (using the soft-start sequence) once the battery voltage drops to BVOVP – Vhys(BVovp). If the junction temperature of the device exceeds TJ(OFF), the pass FET is turned off, and the FAULT output is asserted low. The FET is turned on when the junction temperature falls below TJ(OFF) – TJ(OFF-HYS). Copyright © 2008–2009, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Link(s): bq24380 bq24381 bq24382 |
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