BQ24745_14 Datasheet, PDF (23/39 Pages) Texas Instruments – SMBus-Controlled Multi-Chemistry Battery

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bq24745
SLUS761D – DECEMBER 2007 – REVISED OCTOBER 2011
Table 5. Input Current Register (0x3F), Using 10-mΩ Sense Resistor. (continued)
BIT
BIT NAME
12
Charge current, DACS 5
13
–
14
–
15
–
DESCRIPTION
0 = Adds 0 mA of charger current
1 = Adds 8,192 mA of charger current; 11,008 mA max
Not used
Not used
Not used
ADAPTER DETECT AND POWER UP
An external resistor voltage divider attenuates the adapter voltage before it goes to ACIN. 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 ACIN divider should be placed before the input power path selector in
order to sense the true adapter input voltage.
If DCIN is below 4 V, the charger is disabled.
If ACIN is below 0.6 V but DCIN is above 4.5 V, AC and VICM are disabled and pulled down to GND. The total
quiescent current is less than 10 µA.
Once ACIN rises above 0.6 V and DCIN is above 4.5 V, VREF goes to 3.3 V and all the bias circuits are
enabled. ACOK low indicates ACIN still below 2.4 V, and the valid adaptor is not available. VICM becomes valid
to reflect the adapter current.
When ACIN keeps rising and passes 2.4 V, a valid ac adapter is present. 100 µs later, the following occurs:
• ACOK becomes high through an external pullup resistor to the host digital voltage rail.
• The 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 charging is enabled:
• Not in UVLO (DCIN > 4.5 V, and VDDSMB >2.5 V)
• Adapter is detected (ACIN > 2.4 V).
• Adapter – Battery voltage is higher than the V_DCIN-VFB comparator threshold.
• 200-μs delay is complete after adapter detection.
• SMBus ChargeVoltage(),ChargeCurrent() and InputCurrent() DAC registers are inside the valid range.
• CE is HIGH.
• 2-ms delay is complete after adapter is detected and CE goes HIGH.
• VDDP and VREF are valid.
• Not in thermal shutdown (TSHUT)
Any of the following conditions stops ongoing charging:
• SMBus ChargeVoltage(), ChargeCurrent(), or InputCurrent() DAC register is outside the valid range.
• CE is LOW.
• Adapter is removed (DCIN <4 V).
• VDDSMB supply is removed. (VDDSMB <2.35 V)
• Adapter – Battery voltage is less than V_DCIN-VFB comparator threshold.
• Battery is over voltage.
• In thermal shutdown: TSHUT IC temperature threshold is above 155°C.
AUTOMATIC INTERNAL SOFT-START CHARGER CURRENT
The charger automatically soft-starts the output 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 in eight evenly divided steps up to the programmed charge current.
Each step lasts around 1.6 ms, for a typical rise time of 12.8 ms. No external components are needed for this
function. The regulation limits can be changed in the middle of charging without soft start.
Copyright © 2007–2011, Texas Instruments Incorporated
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