LTC4099 Linear Technology Corporation, LTC4099 Datasheet - Page 17

• Manufacturer Part Number: LTC4099
• Description: I2C Controlled USB Power Manager/Charger
• Manufacturer: Linear Technology Corporation

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OPERATION
application power will be provided by the battery via the
ideal diodes. The ideal diodes will be fast enough to keep
V
required for the switching regulator. The internal ideal
diode consists of a precision amplifi er that activates a
large on-chip MOSFET transistor whenever the voltage at
V
BAT. Within the amplifi er’s linear range, the small-signal
resistance of the ideal diode will be quite low, keeping
the forward drop near 15mV. At higher current levels, the
MOSFET will be in full conduction.
To supplement the internal ideal diode, an external P-
channel MOSFET transistor may be added from BAT to
V
the external P-channel MOSFET transistor for automatic
ideal diode control. The source of the external P-channel
MOSFET should be connected to V
be connected to BAT. Capable of driving a 1nF load, the
IDGATE pin can control an external P-channel MOSFET
transistor having an on-resistance of 30mΩ or lower.
Battery Charger
The LTC4099 includes a battery charger with low voltage
precharge, constant-current/constant-voltage charging,
C/x state-of-charge detection, automatic termination by
safety timer, automatic recharge, bad cell detection and
thermistor sensor input for out-of-temperature charge
pausing.
OUT
OUT
OUT
. The IDGATE pin of the LTC4099 drives the gate of
is approximately 15mV (V
from drooping with only the storage capacitance
Figure 3. Ideal Diode V-I Characteristics
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0
FORWARD VOLTAGE (mV) (BAT – V
60
IDEAL DIODE
VISHAY Si2333
EXTERNAL
IDEAL DIODE
120
LTC4099
SEMICONDUCTOR
MBRM120LT3
180
240 300
FWD
ON
OUT
) below the voltage at
360
and the drain should
OUT
420
)
480
4099
Precharge
When a battery charge cycle begins, the battery charger
fi rst determines if the battery is deeply discharged. If the
battery voltage is below V
trickle charge feature sets the battery charge current to
one-fi fth of the default charge current. If the low voltage
persists for more than one-half hour, the battery charger
automatically terminates and indicates via the I
that the battery was unresponsive.
Constant-Current
Once the battery voltage is above V
charging in full power constant-current mode. The current
delivered to the battery will try to reach V
1030 where V
from 500mV to 1.2V in 100mV steps. The default value
of V
and external load conditions, the battery charger may or
may not be able to charge at the full programmed rate.
The external load will always be prioritized over the battery
charge current. Likewise, the USB current limit program-
ming will always be observed and only additional power
will be available to charge the battery. When system loads
are light, battery charge current will be maximized.
As mentioned above, the upper limit of charge current is
programmed by the combination of a resistor from PROG
to ground and the PROG servo voltage value set in the
I
expression:
Eight values of V
I
In either the constant-current or constant-voltage charging
modes, the voltage at the PROG pin will be proportional to
the actual charge current delivered to the battery. The charge
current can be determined at any time by monitoring the
PROG pin voltage and using the following relationship:
2
CHARGE1
C port. The charge current will be given by the following
I
I
CHG
BAT
PROG
and I
R
is 500mV. Depending on available input power
R
V
V
PROG
PROG
PROG
PROG
PROG
CHARGE0
• 1030
• 1030
PROG
can be set by the I
may be selected by the I
bits in the I
TRKL
, typically 2.85V, an automatic
TRKL
2
C port. See Table 3.
, the charger begins
2
C port and ranges
LTC4099
PROG
/R
CHARGE2
2
17
PROG
C port
4099f
,