BQ24721 Datasheet, PDF (41/48 Pages) Texas Instruments – ADVANCED MULTI-CHEMISTRY AND MULTI-CELL SYNCHRONOUS SWITCH-MODE CHARGER AND SYSTEM POWER SELECTOR

bq24721
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FUNCTIONAL DESCRIPTION
SLUS683 – NOVEMBER 2005
SMBus OVERVIEW
An SMBus communication port provides a simple way for an SMBus compatible host to access system status
information and reset fault modes. Functioning as a SLAVE port enables SMBus compatible hosts to WRITE to
internal registers or READ from internal registers. The bq24721 SMBus port is a 2-wire bidirectional interface
using SCL (clock) and SDA (data) pins; the SDA pin is open drain and requires an external pull-up. The SMBus
is designed to operate at SCL frequencies up to 100 kHz. The standard 8 bit command is supported, the CMD
part of the sequence is the 8 bit register address which is READ from or WRITE to. The bq24721 does not
support packet error correction, PEC, as a mechanism to confirm proper communication between it and the host.
SMBus ADDRESS
The SMBus specification contains several global addresses, to which the slaves on the bus are required to
respond. The bq24721 responds to the SBS charger addresses of 0×12 for writes and 0×13 for reads. The
bq24721 only responds (ACK) to the above listed addresses, and does (NACK) not respond to any other
address.
BYTE
bq24721 SMBus WRITE ADDRESS SBS Charger
bq24721 SMBus READ ADDRESS SBS Charger
COMMAND
I/O DATA BUS
BIT
MSB 6
5
4
3
2
1 LSB
0
0
0
1
0
0
1
0
0
0
0
1
0
0
1
1
0
0
0
1 C3 C2 C1 C0
D7
D6 D5 D4 D3 D2 D1 D0
INTERNAL REGISTER MAP
The status data and control data is referenced by the following Commands.
COMMAND
R/W
0x12
R/W
0x13
R
0x14
R/W
0x15
R/W
0x3F
R/W
REGISTER DESCRIPTION
Charger Mode
Charger Status
Charging Current
Charging Voltage
Input Current
SMBus BUS RELEASE
The bq24721 SMBus engine does not create START or STOP states on the SMBus bus during normal
operation. However, if a 2 second (typical) SDA low timeout is exceeded the bq24721 releases the bus, thus
creating a stop condition.
SMBus COMMUNICATION PROTOCOL
The following conventions is used when describing the communication protocol.
CONDITION
START sent from host
STOP sent from host
bq24721 SMBus slave address sent from host, bus direction set from host to bq24721 (WRITE)
bq24721 register address sent from bq24721, bus direction is from bq24721 to host (READ)
Non-valid SMBus slave address sent from host
Valid bq24721 register address sent from host
Nonvalid bq24721 register address sent from host
I/O data byte (8 bits) sent from host to bq24721
I/O data byte (8 bits) sent from bq24721 to host
Acknowledge (ACK) from host
CODE
S
P
hA0
hA1
hA_N
HCMD
HCMD_N
hDATA
bqDATA
hA
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