BQ24765_15 Datasheet, PDF (23/43 Pages) Texas Instruments – SMBus-Controlled Multi-Chemistry Battery Charger With Integrated Power MOSFETs

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bq24765
SLUS999A – NOVEMBER 2009 – REVISED NOVEMBER 2015
tSU:STA tHD:STA tSU:DAT tHD:DAT tHD:DAT tSU:STO tBUF
Figure 15. SMBus Write Timing
A
B
tLOW tHIGH
C
D
EF
G
SMBCLK
SMBDATA
H
I
J
K
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS C LOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW I = ACKNOWLEDGE CLOCK PULSE
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER J = STOP CONDITION
G = MSB OF DATA CLOCKED INTO MASTER K = NEW START CONDITION
H = LSB OF DATA CLOCKED INTO MASTER
Figure 16. SMBus Read Timing
8.5.2 Battery Voltage Regulation
The bq24765 uses a high-accuracy voltage regulator for charging voltage. The battery voltage regulation setting
is programmed by the host microcontroller (µC), through the SMBus interface that sets an 11 bit DAC. The
battery termination voltage is function of the battery chemistry. Consult the battery manufacturer to determine this
voltage.
The VFB pin is used to sense the battery voltage for voltage regulation and should be connected as close to the
battery as possible, or directly on the output capacitor. A 0.1-µF ceramic capacitor from VFB to AGND is
recommended to be as close to the VFB pin as possible to decouple high frequency noise.
To set the output charge voltage regulation limit, use the SMBus to write a 16 bit ChargeVoltage() command
using the data format listed in Table 3. The ChargeVoltage() command uses the Write-Word protocol (see
Figure 14). The command code for ChargeVoltage() is 0x15 (0b00010101). The bq24765 provides a 1.024-V to
19.200-V charge voltage range, with 16 mV resolution. Setting ChargeVoltage() below 1.024 V or above 19.2 V
clears DAC, and terminates charge.
Upon reset, the ChargeVoltage() and ChargeCurrent() values are cleared (0) and the charger remains off until
both the ChargeVoltage() and the ChargeCurrent() command are sent. During reset, both high side and low side
fets remain off until the charger gets started.
8.5.3 Battery Current Regulation
The Charge Current SMBus 6 bit DAC register sets the maximum charging current. Battery current is sensed by
resistor RSR connected between CSOP and CSON. The maximum full-scale differential voltage between CSOP
and CSON is 80.64 mV. Thus, for a 0.010-Ω sense resistor, the maximum charging current is 8.064 A.
The CSOP and CSON pins are used to sense across RSR with default value of 10 mΩ. However, resistors of
other values can also be used. For a larger the sense resistor, you get a larger sense voltage, and a higher
regulation accuracy; but, at the expense of higher conduction loss.
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