Datasheet

A B C D E F G H I J K

tLOW tHIGH

SMBCLK

SMBDATA

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

bq24765

SLUS999 –NOVEMBER 2009

www.ti.com

Figure 30. SMBus Read Timing

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 16bit ChargeVoltage() command

using the data format listed in Table 3. The ChargeVoltage() command uses the Write-Word protocol (see

Figure 28). The command code for ChargeVoltage() is 0x15 (0b00010101). The bq24765 provides a 1.024V to

19.200V charge voltage range, with 16mV resolution. Setting ChargeVoltage() below 1.024V or above 19.2V

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.

Table 3. Charge Voltage Register (0x15)

BIT BIT NAME DESCRIPTION

0 – Not used

1 – Not used

2 – Not used

3 – Not used