BQ24735_17 Datasheet, PDF (26/46 Pages) Texas Instruments – 1- to 4-Cell Li+ Battery SMBus Charge Controller for Supporting Turbo Boost Mode With N-Channel Power MOSFET Selector

bq24735
SLUSAK9B – SEPTEMBER 2011 – REVISED APRIL 2015
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To set the input current limit, write a 16-bit InputCurrent() command (0x3FH or 0b0011#1111) using the data
format listed in Table 6. When using a 10-mΩ sense resistor, the bq24735 provides an input current-limit range
of 128 mA to 8.064 A, with 128-mA resolution. The suggested input current limit is set to no less than 512 mA.
Sending InputCurrent() below 128 mA or above 8.064 A clears the register and terminates charging. Upon POR,
the default input current limit is 4096 mA.
The ACP and ACN pins are used to sense R_AC with default value of 10 mΩ. However, resistors of other values
can also be used. For a larger sense resistor, larger sense voltage is given, and a higher regulation accuracy;
but, at the expense of higher conduction loss.
If input current rises above FAST_DPM threshold, the charger will reduce charging current to allow the input
current drop. After a typical 260-µs delay time, if input current is still above FAST_DPM threshold, the charger
will shut down. When the system load current becomes smaller, the charger will soft restart to charge the battery
if the adapter still has power to charge the battery. This prevents a crash if the adapter is overloaded when the
system has a high and fast loading transient. The waiting time between shut down and restart charging is a
natural response time of the input current limit loop.
Table 6. Input Current Register (0x3FH), Using a 10-mΩ Sense Resistor
BIT
BIT NAME
DESCRIPTION
0
–
Not used.
1
–
Not used.
2
–
Not used.
3
–
Not used.
4
–
Not used.
5
–
Not used.
6
–
Not used.
7
Input Current, DACIIN 0 0 = Adds 0 mA of input current.
1 = Adds 128 mA of input current.
8
Input Current, DACIIN 1 0 = Adds 0 mA of input current.
1 = Adds 256 mA of input current.
9
Input Current, DACIIN 2 0 = Adds 0 mA of input current.
1 = Adds 512 mA of input current.
10
Input Current, DACIIN 3 0 = Adds 0 mA of input current.
1 = Adds 1024 mA of input current.
11
Input Current, DACIIN 4 0 = Adds 0 mA of input current.
1 = Adds 2048 mA of input current.
12
Input Current, DACIIN 5 0 = Adds 0 mA of input current.
1 = Adds 4096 mA of input current.
13
–
Not used.
14
–
Not used.
15
–
Not used.
9.6.7 Support Turbo Boost Function
The bq24735 supports Turbo Boost function when the adapter is above 16 V. During Turbo Boost mode, battery
discharge energy is delivered to system when system power demand is temporarily higher than adapter
maximum power level so that adapter will not crash. After POR, the ChargeOption() bit [3] is 0 which disable
Turbo Boost function. To enable it, the ChargeOption() bit [3] must be written to 1 by the host.
When input current is higher than the FAST_DPM comparator threshold, if Turbo Boost function is enabled,
charger IC will allow battery discharge and charger converter will change from buck converter to boost converter.
During Turbo Boost mode the adapter current is regulated at input current limit level so that adapter will not
crash. The battery discharge current depends on system current requirement and adapter current limit. The
SMBus timer can be enabled to prevent converter running at Turbo Boost mode for too long.
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