LTC4088-1_12 LINER [Linear Technology], LTC4088-1_12 Datasheet - Page 12

• Manufacturer Part Number: LTC4088-1_12
• Description: High Efficiency Battery Charger/USB Power Manager
• Manufacturer: LINER [Linear Technology]

LTC4088-1/LTC4088-2
operaTion
Ideal Diode from BAT to V
The LTC4088-1/LTC4088-2 has an internal ideal diode as
well as a controller for an external ideal diode. Both the
internal and the external ideal diodes are always on and
will respond quickly whenever V
If the load current increases beyond the power allowed
from the switching regulator, additional power will be
pulled from the battery via the ideal diodes. Furthermore,
if power to V
all of the application power will be provided by the bat-
tery via the ideal diodes. The ideal diodes will be fast
enough to keep V
age capacitance required for the switching regulator. The
internal ideal diode consists of a precision amplifier that
activates a large on-chip MOSFET transistor whenever
the voltage at V
the voltage at BAT. Within the amplifier’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. An external
P-channel MOSFET transistor should be added from BAT
to V
the gate of the external P-channel MOSFET transistor for
automatic ideal diode control. The source of the external
P-channel MOSFET should be connected to V
12
OUT
. The GATE pin of the LTC4088-1/LTC4088-2 drives
1000
2200
2000
1800
1600
1400
1200
800
600
400
200
Figure 3. Ideal Diode V-I Characteristics
0
BUS
0
OUT
FORWARD VOLTAGE (mV) (BAT – V
60
(USB or wall power) is removed, then
OUT
IDEAL DIODE
VISHAY Si2333
EXTERNAL
IDEAL DIODE
LTC4088-1/
is approximately 15mV (V
LTC4088-2
120
SEMICONDUCTOR
from drooping with only the stor-
180
MBRM120LT3
OUT
240 300
ON
OUT
360
V
drops below BAT.
BUS
OUT
420
408812 F03
= 5V
)
480
OUT
FWD
) below
and the
drain should be connected to BAT. Capable of driving a
1nF load, the GATE pin can control an external P-channel
MOSFET transistor having an on-resistance of 30mΩ or
lower. When V
the ideal diode amplifier will be reduced from 15mV to
nearly zero.
Suspend LDO
The LTC4088-1/LTC4088-2 provides a small amount of
power to V
from V
running down when the portable product has access to a
suspended USB port. Regulating at 4.6V, this LDO only
becomes active when the switching converter is disabled.
To remain compliant with the USB specification, the input
to the LDO is current limited so that it will not exceed the
low power or high power suspend specification. If the load
on V
current will come from the battery via the ideal diodes. The
suspend LDO sends a scaled copy of the V
the CLPROG pin, which will servo to approximately 100mV
in this mode. Thus, the high power and low power suspend
settings are related to the levels programmed by the same
resistor for 1x and 5x modes.
V
An internal undervoltage lockout circuit monitors V
keeps the switching regulator off until V
rising UVLO threshold (4.3V). If V
UVLO threshold (4V), system power at V
from the battery via the ideal diodes. The voltage at V
must also be higher than the voltage at BAT by approxi-
mately 170mV for the switching regulator to operate.
Battery Charger
The LTC4088-1/LTC4088-2 includes a constant-current/
constant-voltage battery charger with automatic recharge,
automatic termination by safety timer, low voltage trickle
charging, bad cell detection and thermistor sensor input
for out of temperature charge pausing.
BUS
OUT
Undervoltage Lockout (UVLO)
BUS
exceeds the suspend current limit, the additional
to V
OUT
OUT
BUS
in SUSPEND mode by including an LDO
. This LDO will prevent the battery from
is unavailable, the forward voltage of
BUS
falls below the falling
BUS
OUT
rises above the
BUS
will be drawn
current to
BUS
40881fc
and
BUS