LTC4100EG#TRPBF Linear Technology, LTC4100EG#TRPBF Datasheet - Page 11

• Manufacturer Part Number: LTC4100EG#TRPBF
• Description: IC SMART BATTERY CHARGER 24-SSOP
• Manufacturer: Linear Technology

Specifications of LTC4100EG#TRPBF

• Function: Charge Management
• Battery Type: Smart Batteries
• Voltage - Supply: 6 V ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SSOP (0.200", 5.30mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

OPERATION
While the top MOSFET is off, the bottom MOSFET is
turned on until either the inductor current trips the current
comparator I
oscillator uses the equation,
to set the bottom MOSFET on-time. The result is quasi-
constant frequency operation: the converter frequency
remains nearly constant over a wide range of output
voltages. This activity is diagrammed in Figure 3.
The peak inductor current, at which I
latch, is controlled by the voltage on I
controlled by several loops, depending upon the situation
at hand. The average current control loop converts the
voltage between CSP and BAT to a representative current.
Error amp CA2 compares this current against the desired
current programmed by the I
I
The voltage at BAT is divided down by an internal resis-
tor divider set by the V
to decrease I
reference.
The amplifi er CL1 monitors and limits the input current,
normally from the AC adapter, to a preset level (100mV/R
At input current limit, CL1 will decrease the I
reduce charging current.
An overvoltage comparator, OV, guards against transient
overshoots (>7%). In this case, the top MOSFET is turned
off until the overvoltage condition is cleared. This feature
is useful for batteries that “load dump” themselves by
opening their protection switch to perform functions such
as calibration or pulse mode charging.
TGATE
TH
BGATE
INDUCTOR
CURRENT
t
for the desired voltage across R
OFF
OFF
OFF
ON
ON
=
(
V
(
V
DCIN
DCIN
REV
TH
if the divider voltage is above the 1.19V
, or the beginning of the next cycle. The
–
•
V
f
OSC
BAT
DAC
)
)
Figure 3
and is used by error amp EA
t
OFF
DAC
at the I
SENSE
CMP
TRIP POINT SET
BY I
DC
TH
TH
.
pin and adjusts
. I
resets the SR
VOLTAGE
TH
TH
voltage to
is in turn
CL
4100 F03
).
PWM Watchdog Timer
There is a watchdog timer that observes the activity on
the TGATE pin. If TGATE stops switching for more than
40μs, 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
capacitors.
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 a SMBus
slave device at address 0x12. All internal LTC4100 registers
may be updated 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
Specifi cation , 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 condi-
tion, or power-on reset via the V
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.
*http://www. SBS-FORUM.org
TH
voltage exceeds a threshold that assures initial
2
C bus (Reference I
DD
power-fail, will reset
LTC4100
2
C-Bus and How
11
4100fb