LTC4100 datasheet(9/24 Pages) LINER

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LTC4100

sn4100 4100is

OPERATIO

I2C is a trademark of Philips Electronics N.V.

*http://www. SBS-FORUM.org

PWM Watchdog Timer

There is a watchdog timer that observes the activity on the

TGATE pin. If TGATE stops switching for more than 40

µs,

the watchdog activates and turns off the top MOSFET for

about 400ns. The watchdog engages to prevent very low

frequency operation in dropout – a potential source of

audible noise when using ceramic input and output ca-

pacitors.

Charger Start-Up

When the charger is enabled, it will not begin switching

until the ITH voltage exceeds a threshold that assures initial

current will be positive. This threshold is 5% to 15% of the

maximum programmed current. After the charger begins

switching, the various loops will control the current at a

level that is higher or lower than the initial current. The

duration of this transient condition depends upon the loop

compensation, but is typically less than 1ms.

SMBus Interface

All communications over the SMBus are interpreted by the

SMBus interface block. The SMBus interface is an SMBus

slave device. All internal LTC4100 registers may be up-

dated and accessed through the SMBus interface, and

charger controller as required. The SMBus protocol is a

derivative of the I2C

TM bus (Reference “I2C-Bus and How

to Use It, V1.0” by Philips, and "System Management Bus

Specification", Version 1.1, from the SBS Implementers

Forum, for a complete description of the bus protocol

requirements.)

All data is clocked into the shift register on the rising edge

of SCL. All data is clocked out of the shift register on the

falling edge of SCL. Detection of an SMBus Stop condition,

or power-on reset via the VDD power-fail, will reset the

SMBus interface to an initial state at any time.

The LTC4100 command set is interpreted by the SMBus

interface and passed onto the charger controller block as

control signals or updates to internal registers.

Description of Supported Battery Charger Functions

The functions are described as follows (see Table 1 also):

FunctionName() 'hnn (command code)

Description: A brief description of the function.

Purpose: The purpose of the function, and an example

where appropriate.

• SMBus Protocol: Refer to Section 5 of the Smart

Battery Charger specification for more details.

Input, Output or Input/Output: A description of the data

supplied to or returned by the function.

ChargerSpecInfo() ('h11)

Description: The SMBus Host uses this command to read

the LTC4100’s extended status bits.

Purpose: Allows the System Host to determine the speci-

fication revision the charger supports as well as other

extended status information.

• SMBus Protocol: Read Word.

Output: The CHARGER_SPEC indicates that the LTC4100

supports Version 1.1 of the Smart Battery Charger Speci-

fication. The SELECTOR_SUPPORT indicates that the

LTC4100 does not support the optional Smart Battery

Selector Commands.

ChargerMode() ('h12)

Description: The SMBus Host uses this command to set

the various charger modes. The default values are set to

allow a Smart Battery and the LTC4100 to work in concert

without requiring an SMBus Host.

Purpose: Allows the SMBus Host to configure the charger

and change the default modes. This is a write only func-

tion, but the value of the “mode” bit, INHIBIT_CHARGE

may be determined using the ChargerStatus() function.

• SMBus Protocol: Write Word.

Input: The INHIBIT_CHARGE bit allows charging to be

inhibited without changing the ChargingCurrent() and

ChargingVoltage() values. The charging may be resumed

by clearing this bit. This bit is automatically cleared when

power is re-applied or when a battery is re-inserted.

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