LTC4100 Linear Technology, LTC4100 Datasheet - Page 9

• Manufacturer Part Number: LTC4100
• Description: Smart Battery Charger Controller
• Manufacturer: Linear Technology

OPERATIO
PWM Watchdog Timer
There is a watchdog timer that observes the activity on the
TGATE pin. If TGATE stops switching for more than 40 s,
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 I
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 I
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 V
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.
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*http://www. SBS-FORUM.org
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voltage exceeds a threshold that assures initial
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Description of Supported Battery Charger Functions
The functions are described as follows (see Table 1 also):
Description: A brief description of the function.
Purpose: The purpose of the function, and an example
where appropriate.
Input, Output or Input/Output: A description of the data
supplied to or returned by the function.
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.
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.
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.
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.
FunctionName() 'hnn (command code)
ChargerSpecInfo() ('h11)
ChargerMode() ('h12)
• SMBus Protocol: Refer to Section 5 of the Smart
Battery Charger specification for more details.
• SMBus Protocol: Read Word.
• SMBus Protocol: Write Word.
LTC4100
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