BQ24704 Datasheet, PDF (16/31 Pages) Texas Instruments – Low Cost, Host-Controlled Li-Ion and Li-Polymer Battery Charger With Low Iq

bq24704
SLUS838 – MAY 2009........................................................................................................................................................................................................ www.ti.com
I_ADAPTER
=
V_ACSET 0.125
´
V_REF R_AC
(3)
The input voltage range of ACSET is between 0 and VREF, up to 3.3 V.
The ACP and ACN pins are used to sense R_AC with default value of 10mΩ. However, resistors of other values
can also be used. A larger the sense resistor, gives a larger sense voltage, and a higher regulation accuracy;
but, at the expense of higher conduction loss.
ADAPTER DETECT AND POWER UP
An external resistor voltage divider attenuates the adapter voltage before it goes to ACDET. The adapter detect
threshold should typically be programmed to a value greater than the maximum battery voltage, and lower than
the minimum allowed adapter voltage. The ACDET divider should be placed before the ACFET in order to sense
the true adapter input voltage whether the ACFET is on or off.
If PVCC is below 4 V, the device is disabled.
If ACDET is below 0.6 V but PVCC is above 4 V, part of the bias is enabled, including a crude bandgap
reference. IADAPT is disabled and pulled down to GND. The total quiescent current is less than 10 µA.
Once ACDET rises above 0.6 V and PVCC is above 4 V, all the bias circuits are enabled. VREF goes to 3.3 V
and REGN output goes to 6 V. IADAPT becomes valid to proportionally reflect the adapter current.
When ACDET rises and passes 2.4 V, a valid AC adapter is present. Then the following occurs:
• ACGOOD becomes high through external pull-up resistor to the host digital voltage rail;
• Charger turns on if all the conditions are satisfied (see Enable and Disable Charging).
ENABLE AND DISABLE CHARGING
The following conditions must be valid before a charge is enabled:
• CHGEN is LOW;
• PVCC > UVLO;
• Adapter is detected;
• Adapter is higher than PVCC-BAT threshold;
• Adapter is not over voltage;
• 1.2 s delay is complete after adapter detected;
• REGNGOOD and VREFGOOD are valid;
• Thermal Shut (TSHUT) is not valid;
One of the following conditions will stop on-going charging:
• CHGEN is HIGH;
• PVCC < UVLO;
• Adapter is removed;
• Adapter is less than PVCC-BAT threshold;
• Adapter is over voltage;
• Adapter is over current;
• TSHUT IC temperature threshold is reached (155°C on rising-edge with 20°C hysteresis).
AUTOMATIC INTERNAL SOFT-START CHARGER CURRENT
The charger automatically soft-starts the charger regulation current every time the charger is enabled to ensure
there is no overshoot or stress on the output capacitors or the power converter. The soft-start consists of
stepping-up the charge regulation current into 8 evenly divided steps up to the programmed charge current. Each
step lasts around 1.7ms, for a typical rise time of 13.6ms. No external components are needed for this function.
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