BQ24735_17 Datasheet, PDF (24/46 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
Table 3. Charge Options Field Descriptions (continued)
Bit Field
[0]
Charge Inhibit
Type
Reset Description
R/W 0: Enable Charge <default at POR>
1: Inhibit Charge
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9.6.4 Setting the Charge Current
To set the charge current, write a 16-bit ChargeCurrent() command (0x14H or 0b00010100) using the data
format listed in Table 4. With 10-mΩ sense resistor, the bq24735 provides a charge current range of 128 mA to
8.128 A, with 64-mA step resolution. Sending ChargeCurrent() below 128 mA or above 8.128 A clears the
register and terminates charging. Upon POR, charge current is 0 A. TI recommends a 0.1-µF capacitor between
SRP and SRN for differential mode filtering, a 0.1-µF capacitor between SRN and ground for common mode
filtering, and an optional 0.1-µF capacitor between SRP and ground for common mode filtering. Meanwhile, the
capacitance on SRP should not be higher than 0.1 µF to properly sense the voltage across SRP and SRN for
cycle-by-cycle undercurrent and overcurrent detection.
The SRP and SRN pins are used to sense R_SR with default value of 10 mΩ. 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
overcurrent 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 20 mΩ is suggested.
To provide secondary protection, the bq24735 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 1.6 V, which is
the maximum charge current regulation limit. Equation 2 shows the voltage set on the ILIM pin with respect to the
preferred charge current limit:
( ) V_ILIM = 20 × V_SRP - V_SRN = 20 ´ I_CHG ´ R_SR
(2)
Table 4. Charge Current Register (0x14H), 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
Charge Current, DACICHG 0 0 = Adds 0 mA of charger current.
1 = Adds 64 mA of charger current.
7
Charge Current, DACICHG 1 0 = Adds 0 mA of charger current.
1 = Adds 128 mA of charger current.
8
Charge Current, DACICHG 2 0 = Adds 0 mA of charger current.
1 = Adds 256 mA of charger current.
9
Charge Current, DACICHG 3 0 = Adds 0 mA of charger current.
1 = Adds 512 mA of charger current.
10
Charge Current, DACICHG 4 0 = Adds 0 mA of charger current.
1 = Adds 1024 mA of charger current.
11
Charge Current, DACICHG 5 0 = Adds 0 mA of charger current.
1 = Adds 2048 mA of charger current.
12
Charge Current, DACICHG 6 0 = Adds 0 mA of charger current.
1 = Adds 4096 mA of charger current.
13
–
Not used.
14
–
Not used.
15
–
Not used.
24
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