isl88731 Intersil Corporation, isl88731 Datasheet - Page 10

• Manufacturer Part Number: isl88731
• Description: Smbus Level 2 Battery Charger
• Manufacturer: Intersil Corporation

Undervoltage Detect and Battery Trickle Charging
If the voltage at CSON falls below 2.5V ISL88731 reduces
the charge current limit to 128mA to trickle charge the
battery. When the voltage rises above 2.7V the charge
current reverts to the programmed value in the
ChargeCurrent register.
Over Temperature Protection
If the die temp exceeds +150°C, it stops charging. Once the
die temp drops below +125°C, charging will start up again.
The System Management Bus
The System Management Bus (SMBus) is a 2 wire bus that
supports bidirectional communications. The protocol is
described briefly here. More detail is available from
www.smbus.org.
General SMBus Architecture
Data Validity
The data on the SDA line must be stable during the HIGH
period of the SCL, unless generating a START or STOP
condition. The HIGH or LOW state of the data line can only
change when the clock signal on the SCL line is LOW. Refer
to Figure 15.
START and STOP Conditions
As shown in Figure 16, START condition is a HIGH to LOW
transition of the SDA line while SCL is HIGH.
SDA
SCL
CPU
SMBus master
control
control
SCL
SDA
DATA VALID
DATA LINE
input
input
output
output
STABLE
FIGURE 15. DATA VALIDITY
VDDSMB
ALLOWED
slave devices
CHANGE
OF DATA
to other
10
output
output
output
output
input
input
input
input
SMBus Slave
SMBus Slave
control
control
control
control
SDA
SDA
SCL
SCL
machine ,
registers ,
machine ,
registers ,
memory ,
memory ,
state
etc.
state
etc.
ISL88731
START
SDA
SCL
The STOP condition is a LOW to HIGH transition on the SDA
line while SCL is HIGH. A STOP condition must be sent before
each START condition.
Acknowledge
Each address and data transmission uses 9 clock pulses. The
ninth pulse is the acknowledge bit (ACK). After the start
condition, the master sends 7 slave address bits and a R/W bit
during the next 8 clock pulses. During the ninth clock pulse, the
device that recognizes its own address holds the data line low
to acknowledge. The acknowledge bit is also used by both the
master and the slave to acknowledge receipt of register
addresses and data as described below.
SMBus Transactions
All transactions start with a control byte sent from the SMBus
master device. The control byte begins with a Start condition,
followed by 7-bits of slave address (0001001 for the ISL88731)
followed by the R/W bit. The R/W bit is 0 for a write or 1 for a
read. If any slave devices on the SMBus bus recognize their
address, they will Acknowledge by pulling the serial data (SDA)
line low for the last clock cycle in the control byte. If no slaves
exist at that address or are not ready to communicate, the data
line will be 1, indicating a Not Acknowledge condition.
Once the control byte is sent, and the ISL88731
acknowledges it, the 2nd byte sent by the master must be a
register address byte such as 0x14 for the ChargeCurrent
register. The register address byte tells the ISL88731 which
register the master will write or read. See Table 1 for details
of the registers. Once the ISL88731 receives a register
address byte it responds with an acknowledge.
SDA
SCL
CONDITION
START
FIGURE 17. ACKNOWLEDGE ON THE I
S
FIGURE 16. START AND STOP WAVEFORMS
MSB
1
2
8
2
C BUS
ACKNOWLEDGE
November 20, 2006
FROM SLAVE
CONDITION
STOP
P
9
FN9258.0