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

• Manufacturer Part Number: LTC4088
• Description: High Effi ciency Battery Charger/USB Power Manager
• Manufacturer: LINER [Linear Technology]

LTC4088
OPERATIO
Ideal Diode from BAT to V
The LTC4088 has an internal ideal diode as well as a
controller for an optional 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
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. The on-resistance in
this case is approximately 180mΩ. If this is suffi cient for
the application, then no external components are neces-
sary. However, if more conductance is needed, an external
P-channel MOSFET transistor can be added from BAT to
V
P-channel MOSFET transistor for automatic ideal diode
control. The source of the external P-channel MOSFET
should be connected to V
12
OUT
OUT
OUT
BUS
. The GATE pin of the LTC4088 drives the gate of the
is approximately 15mV (V
from drooping with only the storage capacitance
(USB or wall power) is removed, then all of the
1000
2200
2000
1800
1600
1400
1200
800
600
400
200
Figure 3. Ideal Diode V-I Characteristics
0
0
FORWARD VOLTAGE (mV) (BAT – V
60
U
IDEAL DIODE
VISHAY Si2333
OPTIONAL EXTERNAL
IDEAL DIODE
120
LTC4088
SEMICONDUCTOR
MBRM120LT3
180
OUT
OUT
240 300
ON
FWD
and the drain should be
OUT
360
) below the voltage at
V
drops below BAT.
BUS
OUT
420
= 5V
4088 F03
)
480
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
unavailable, the forward voltage of the ideal diode amplifi er
will be reduced from 15mV to nearly zero.
Suspend LDO
The LTC4088 provides a small amount of power to V
SUSPEND mode by including an LDO from V
This LDO will prevent the battery from 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 specifi cation, the input to the LDO is current
limited so that it will not exceed the low power or high
power suspend specifi cation. If the load on V
the suspend current limit, the additional current will come
from the battery via the ideal diodes. The suspend LDO
sends a scaled copy of the V
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.
3.3V Always-On Supply
The LTC4088 includes an ultralow quiescent current low
dropout regulator that is always powered. This LDO can be
used to provide power to a system pushbutton controller or
standby microcontroller. Designed to deliver up to 25mA,
the always-on LDO requires a 1µF MLCC bypass capacitor
for compensation. The LDO is powered from V
therefore will enter dropout at loads less than 25mA as
V
should be disabled by connecting it to V
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.
OUT
BUS
falls near 3.3V. If the LDO3V3 output is not used, it
Undervoltage Lockout (UVLO)
BUS
BUS
current to the CLPROG
falls below the falling
BUS
OUT
OUT
rises above the
.
will be drawn
OUT
BUS
OUT
exceeds
to V
BUS
BUS
OUT
, and
OUT
and
BUS
4088f
in
is
.