bq24735
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SLUSAK9 –SEPTEMBER 2011
To set the input current limit, write a 16-bit InputCurrent() command (0x3FH or 0b00111111) using the data
format listed in Table 6. When using a 10mΩ sense resistor, the bq24735 provides an input-current limit range of
128mA to 8.064A, with 128mA resolution. The suggested input current limit is set to no less than 512mA.
Sending InputCurrent() below 128mA or above 8.064A clears the register and terminates charging. Upon POR,
the default input current limit is 4096mA.
The ACP and ACN pins are used to sense RAC with default value of 10mΩ. 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. 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 10mΩ Sense Resistor
BIT
0
BIT NAME
DESCRIPTION
Not used.
Not used.
Not used.
Not used.
Not used.
Not used.
Not used.
–
1
–
2
–
3
–
4
–
5
–
6
–
7
Input Current, DACIIN 0
0 = Adds 0mA of input current.
1 = Adds 128mA of input current.
8
Input Current, DACIIN 1
Input Current, DACIIN 2
Input Current, DACIIN 3
Input Current, DACIIN 4
Input Current, DACIIN 5
0 = Adds 0mA of input current.
1 = Adds 256mA of input current.
9
0 = Adds 0mA of input current.
1 = Adds 512mA of input current.
10
11
12
0 = Adds 0mA of input current.
1 = Adds 1024mA of input current.
0 = Adds 0mA of input current.
1 = Adds 2048mA of input current.
0 = Adds 0mA of input current.
1 = Adds 4096mA of input current.
13
14
15
–
–
–
Not used.
Not used.
Not used.
Support Turbo Boost Function
The bq24735 supports Turbo Boost function by allowing battery discharge energy 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 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.
Copyright © 2011, Texas Instruments Incorporated
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