Datasheet

( )
ILIM SRP SRN CHG SR
V = 20 × V V = 20 I R- ´ ´
bq24725A
www.ti.com SLUSAL0 –SEPTEMBER 2011
Setting the Charge Current
To set the charge current, write a 16bit ChargeCurrent() command (0x14H or 0b00010100) using the data format
listed in Table 4. With 10mΩ sense resistor, the bq24725A provides a charge current range of 128mA to 8.128A,
with 64mA step resolution. Sending ChargeCurrent() below 128mA or above 8.128A clears the register and
terminates charging. Upon POR, charge current is 0A. A 0.1µF capacitor between SRP and SRN for differential
mode filtering is recommended, 0.1µF capacitor between SRN and ground for common mode filtering, and an
optional 0.1µF capacitor between SRP and ground for common mode filtering. Meanwhile, the capacitance on
SRP should not be higher than 0.1µF in order to properly sense the voltage across SRP and SRN for
cycle-by-cycle under-current and over current detection.
The SRP and SRN pins are used to sense R
SR
with default value of 10mΩ. However, resistors of other values
can also be used. For a larger sense resistor, a larger sense voltage is given, and a higher regulation accuracy;
but, at the expense of higher conduction loss. If the current sensing resistor value is too high, it may trigger an
over current protection threshold because the current ripple voltage is too high. In such a case, either a higher
inductance value or a lower current sensing resistor value should be used to limit the current ripple voltage level.
A current sensing resistor value no more than 20mΩ is suggested.
To provide secondary protection, the bq24725A has an ILIM pin with which the user can program the maximum
allowed charge current. Internal charge current limit is the lower one between the voltage set by
ChargeCurrent(), and voltage on ILIM pin. To disable this function, the user can pull ILIM above 1.6V, which is
the maximum charge current regulation limit. Equation 1 shows the voltage set on ILIM pin with respect to the
preferred charge current limit:
(1)
Table 4. Charge Current Register (0x14H), Using 10mΩ 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 Charge Current, DACICHG 0 0 = Adds 0mA of charger current.
1 = Adds 64mA of charger current.
7 Charge Current, DACICHG 1 0 = Adds 0mA of charger current.
1 = Adds 128mA of charger current.
8 Charge Current, DACICHG 2 0 = Adds 0mA of charger current.
1 = Adds 256mA of charger current.
9 Charge Current, DACICHG 3 0 = Adds 0mA of charger current.
1 = Adds 512mA of charger current.
10 Charge Current, DACICHG 4 0 = Adds 0mA of charger current.
1 = Adds 1024mA of charger current.
11 Charge Current, DACICHG 5 0 = Adds 0mA of charger current.
1 = Adds 2048mA of charger current.
12 Charge Current, DACICHG 6 0 = Adds 0mA of charger current.
1 = Adds 4096mA of charger current.
13 – Not used.
14 – Not used.
15 – Not used.
Setting the Charge Voltage
To set the output charge regulation voltage, write a 16bit ChargeVoltage() command (0x15H or 0b00010101)
using the data format listed in Table 5. The bq24725A provides charge voltage range from 1.024V to 19.200V,
with 16mV step resolution. Sending ChargeVoltage() below 1.024V or above 19.2V clears the register and
terminates charging. Upon POR, charge voltage limit is 0V.
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