MAX8731EVSYS Maxim Integrated, MAX8731EVSYS Datasheet - Page 20

• Manufacturer Part Number: MAX8731EVSYS
• Description: Battery Management SMBus Level 2 Battery Charger with Remote Sense
• Manufacturer: Maxim Integrated
• Series: MAX8731Ar

Specifications of MAX8731EVSYS

• Battery Type: Li-Ion, Li-Polymer, NiCd, NiMH, Lead Acid, Universal
• Output Voltage: 5.4 V
• Operating Supply Voltage: 8 V to 26 V
• Charge Safety Timers: Yes
• Operating Supply Current: 2 uA
• Product Type: Charge Management
• Temperature Monitoring: No
• Uvlo Start Threshold: 2.5 V
• Uvlo Stop Threshold: 100 mV

SMBus Level 2 Battery Charger with
Remote Sense
The MAX8731 receives control inputs from the SMBus
interface. The MAX8731 uses a simplified subset of the
commands documented in System Management Bus
Specification V1.1, which can be downloaded from
www.smbus.org. The MAX8731 uses the SMBus Read-
Word and Write-Word protocols (Figure 3) to communi-
cate with the smart battery. The MAX8731 performs
only as an SMBus slave device with address
0b0001001_ (0x12) and does not initiate communica-
tion on the bus. In addition, the MAX8731 has two iden-
tification (ID) registers (0xFE): a 16-bit device ID
register and a 16-bit manufacturer ID register (0xFF).
The data (SDA) and clock (SCL) pins have Schmitt-trig-
ger inputs that can accommodate slow edges. Choose
pullup resistors (10kΩ) for SDA and SCL to achieve rise
times according to the SMBus specifications.
Figure 3. SMBus Write-Word and Read-Word Protocols
20
______________________________________________________________________________________
S
S
a) Write-Word Format
b) Read-Word Format
LEGEND:
S = START CONDITION OR REPEATED START CONDITION
ACK = ACKNOWLEDGE (LOGIC-LOW)
W = WRITE BIT (LOGIC-LOW)
MSB
MSB
ADDRESS
PRESET TO
0b0001001
ADDRESS
0b0001001
Preset to
SLAVE
SLAVE
7 BITS
7 BITS
MASTER TO SLAVE
SLAVE TO MASTER
LSB
LSB
W
W
1b
1b
0
0
ACK
ACK
1b
1b
0
0
ChargerMode() = 0x12
ChargeCurrent() = 0x14
ChargeVoltage() = 0x15
AlarmWarning() = 0x16
InputCurrent() = 0x3F
ChargerSpecInfo() = 0x11
ChargerStatus() = 0x13
SMBus Interface
MSB
MSB
COMMAND
COMMAND
8 BITS
8 BITS
BYTE
BYTE
LSB
LSB
ACK
ACK
1b
1b
0
0
P = STOP CONDITION
NACK = NOT ACKNOWLEDGE (LOGIC-HIGH)
R = READ BIT (LOGIC-HIGH)
D7
S
MSB
LOW DATA
MSB
BYTE
8 BITS
ADDRESS
PRESET TO
0b0001001
SLAVE
7 BITS
LSB
D0
Communication starts when the master signals a
START condition, which is a high-to-low transition on
SDA, while SCL is high. When the master has finished
communicating, the master issues a STOP condition,
which is a low-to-high transition on SDA, while SCL is
high. The bus is then free for another transmission.
Figures 4 and 5 show the timing diagram for signals on
the SMBus interface. The address byte, command
byte, and data bytes are transmitted between the
START and STOP conditions. The SDA state changes
only while SCL is low, except for the START and STOP
conditions. Data is transmitted in 8-bit bytes and is
sampled on the rising edge of SCL. Nine clock cycles
are required to transfer each byte in or out of the
MAX8731 because either the master or the slave
acknowledges the receipt of the correct byte during the
ninth clock cycle. The MAX8731 supports the charger
commands as described in Table 4.
LSB
ACK
1b
0
1b
R
1
D15
ACK
MSB
HIGH DATA
1b
0
BYTE
8 BITS
D7
MSB
LOW DATA
LSB
BYTE
D8
8 BITS
LSB
ACK P
1b
0
D0
ACK
1b
0
D15
MSB
HIGH DATA
BYTE
8 BITS
LSB
D8
NACK P
1b
1