Linear DC101 User Manual download pdf (Page 5)

DEMO MANUAL DC101

SMART BATTERY CHARGER

OPERATIO

Battery Removal, Thermistor Measurements: The

charger periodically checks the thermistor in the battery

through the T-terminal. When the thermistor is out of

normal operating temperature range, the charger switches

to trickle charge mode and increases the flashing fre-

quency of the green LED to indicate an abnormal charg-

ing condition. When the resistance of the thermistor is in

the 500Ω < R

< 1.5k range, the charger assumes a Li-

Ion battery is at the output. Instead of trickle charging the

battery it shuts down the charger until a valid voltage and

current request arrives from the battery. An open ther-

mistor forces the charger into trickle charge mode and

the charger disregards data on the SMBus.

System Management Bus (SMBus)

When charge in the Smart Battery (SB) drops below 85%

of the nominal capacity, it initiates communication over

the SMBus every 64 seconds. After sending a START

sequence, the battery addresses the Smart Battery charger

and waits for an acknowledgment (ACK) from it. If the

charger fails to acknowledge the word, the battery termi-

nates further communication by placing a STOP sequence

onto the SMBus. If the charger acknowledges (ACK) the

reception of the first word, the battery continues the

communication sequence and sends six more words to

the charger. The complete current and voltage request

communication sequence is as follows:

START

address (12 hex)

Charging Current() command code (14 hex),

current_LSB

current_MSB,

address (12 hex)

Charging Voltage() command code (15 hex)

voltage_LSB

voltage_MSB

STOP

The idealized SMBus waveforms shown in Figure 1 illus-

trate SMBus communication between the battery and the

charger. The first seven bits after the START sequence are

the battery address. The R/W bit tells the charger that the

battery is attempting to write to the charger. During the

acknowledge period (ACK), the charger becomes active

and pulls the data line (SDA) low, indicating reception of

a data word. When reception of the data word is not

acknowledged by the charger, the battery terminates the

communication by sending a STOP sequence to the bus.

The clock pulses for the communication are always gen-

erated by the battery (BUS MASTER).

“C” Source Code

The latest version of “C” language source code, header

file, code file and hex dump file is provided on a 3.5" disk.

SCLK

SDA

START

1 2 0 = WRITE

1 = 1ST NIBBLE

2 = 2ND NIBBLE (TRUNCATED)

THIS EXAMPLE = 12(H)

DC101 F01

0001001R/WACK

Figure 1. SMBus Waveforms Indicating Battery Address

1 2 3 4 5 6 7 8

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