BQ24187 Datasheet, PDF(17/44 Page) Texas Instruments

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BQ24187 Datasheet, PDF (17/44 Pages) Texas Instruments – 1A USB-OTG Support

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Not Recommended for New Designs

bq24187

SLUSBM0 â APRIL 2014

Device Functional Modes (continued)

8.4.1.1.3.1 Charge Time Optimizer

The CC to CV transition is enhanced in the bq24187 architecture. The "knee" between CC and CV is very sharp.

This enables the charger to remain in CC mode as long as possible before beginning to taper the charge current

(CV mode). This provides a decrease in charge time as compared to older topologies.

8.4.1.1.4 Battery Detection

When termination conditions are met, a battery detection cycle is started. During battery detection, IDETECT is

pulled from VBAT for tDETECT(SNK) to verify there is a battery. If the battery voltage remains above VDETECT for the

full duration of tDETECT(SNK), a battery is determined to be present and the IC enters âCharge Doneâ. If VBAT falls

below VDETECT, a âBattery Not Presentâ fault is signaled, the charge parameters are reset (VBATREG, ICHARGE and

ITERM) and battery detection continues. The next cycle of battery detection, the bq24187 turns on IBATSHRT for

tDETECT(SRC). If VBAT rises to VDET(SRC1), the current source is turned off and a âNo Batteryâ condition is registered.

In order to keep VBAT high enough to close the battery protector, the current source turns on if VBAT falls to

VDET(SRC2). The source cycle continues for tDETECT(SRC). After tDETECT(SRC), the battery detection continues through

another current sink cycle. Battery detection continues until charge is disabled or a battery is detected. Once a

battery is detected, the fault status clears and a new charge cycle begins. Battery detection is not performed

when termination is disabled.

8.4.1.1.5 Battery Overvoltage Protection (BOVP)

If the battery is ever above the battery OVP threshold (VBOVP), the battery OVP circuit shuts the PWM converter

off to discharge the battery to safe operating levels. A battery OVP most commonly occurs when the bq24187

returns to DEFAULT mode after a watchdog timer expiration or RESET bit written to '1'. In this condition, the

VBATREG is reset and may be below the battery voltage. Other conditions may be when the input is initially

plugged in before I2C communication is established or TS WARM conditions or when writing the VBATREG to

less than the battery voltage. The battery OVP condition is cleared when the battery voltage falls below the

hysteresis of VBOVP either by the battery discharging or writing the VBATREG to a higher value. When a battery

OVP event exists for tDGL(BOVP), the bq24187 sends a single 128Î¼s pulse on the STAT/ INT outputs and the

STATx and FAULT_x bits are updated in the I2C. Once the BOVP fault is removed, the STATx bits are cleared

and the device returns to normal operation. The FAULT_x bits are not cleared until they are read in the I2C after

the BOVP condition no longer exists.

8.4.1.1.6 Default Mode

DEFAULT mode is used when I2C communication is not available. DEFAULT mode is entered in the following

situations:

1. When the charger is enabled before I2C communication is established

2. When the watchdog timer expires without a reset from the I2C interface

3. The RESET bit is written in the I2C register

In DEFAULT mode, the I2C registers are reset to the default values. The 1.25 min safety timer is reset and starts

when DEFAULT mode is entered if a charge cycle is underway. The default value for VBATREG is 3.6V, and the

default value for ICHARGE is 1A. The input current limit in DEFAULT mode is set by PSEL. (See Power Source

Selector Input section) DEFAULT mode is exited by writing to the I2C interface. Note that if termination is

enabled and charging has terminated, a new charge cycle is NOT initiated when entering DEFAULT mode.

8.4.1.1.7 Power Source Selector Input (PSEL)

The bq24187 contains a PSEL input that is used to program the input current limit during DEFAULT mode. Drive

PSEL high to indicate a USB source is connected to the input and program the 100mA current limit for IN. Drive

PSEL low to indicate that an AC Adapter is connected to the input. When PSEL is low, the IC starts up with a

1.5A input current limit. Once an I2C write is done and the device is in HOST mode, the PSEL has no effect on

the input current limit until the watchdog timer expires and returns the bq24187 to DEFAULT mode.

Product Folder Links: bq24187

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