BQ24745_14 Datasheet, PDF (20/39 Pages) Texas Instruments – SMBus-Controlled Multi-Chemistry Battery

bq24745
SLUS761D – DECEMBER 2007 – REVISED OCTOBER 2011
A
B
tLOW tHIGH
C
D
EF
G
SMBCLK
SMBDATA
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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
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
Figure 35. SMBus Read Timing
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
BATTERY VOLTAGE REGULATION
The bq24745 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 a 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 GND 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 33). The command code for ChargeVoltage() is 0x15 (0b0001 0101). The bq24745 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 the DAC and terminates charge.
On reset, the ChargeVoltage() and ChargeCurrent() values are cleared (0) and the charger remains off until both
the ChargeVoltage() and the ChargeCurrent() commands are sent. During reset, both high-side and low-side
FETs remain off until the charger is started.
Table 3. Charge Voltage Register (0x15)
BIT
BIT NAME
0
–
1
–
2
–
3
–
4
Charge voltage, DACV 0
5
Charge voltage, DACV 1
6
Charge voltage, DACV 2
7
Charge voltage, DACV 3
8
Charge voltage, DACV 4
9
Charge voltage, DACV 5
10
Charge voltage, DACV 6
DESCRIPTION
Not used
Not used
Not used
Not used
0 = Adds 0 mV of charger voltage
1 = Adds 16 mV of charger voltage⁽¹⁾
0 = Adds 0 mV of charger voltage
1 = Adds 32 mV of charger voltage⁽¹⁾
0 = Adds 0 mV of charger voltage
1 = Adds 64 mV of charger voltage⁽¹⁾
0 = Adds 0 mV of charger voltage
1 = Adds 128 mV of charger voltage⁽¹⁾
0 = Adds 0 mV of charger voltage
1 = Adds 256 mV of charger voltage⁽¹⁾
0 = Adds 0 mV of charger voltage
1 = Adds 512 mV of charger voltage⁽¹⁾
0 = Adds 0 mV of charger voltage
1 = Adds 1,024 mV of charger voltage
(1) Must be used in conjunction with other bits for a minimum output of 1024 mV
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