Linear DC101 manual System Management Bus SMBus

DEMO MANUAL DC101

SMART BATTERY CHARGER

OPERATIOU

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 < RTH < 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:

SDA

SCLK

0 0 0 1

START

1

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.

0	0	1	R/W	ACK
				DC101 F01
	2	0	= WRITE
		1	= 1ST NIBBLE
		2	= 2ND NIBBLE (TRUNCATED)
			THIS EXAMPLE = 12(H)

Figure 1. SMBus Waveforms Indicating Battery Address

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