ltc3566 Linear Technology Corporation, ltc3566 Datasheet - Page 13

• Manufacturer Part Number: ltc3566
• Description: High Ef?ciency Usb Power Manager Plus 1a Buck-boost Converter
• Manufacturer: Linear Technology Corporation

OPERATION
on CLPROG represents the average input current of the
switching regulator. When the input current approaches
the programmed limit, CLPROG reaches V
and power out is held constant.
The input current is programmed by the ILIM0 and ILIM1
pins. It can be confi gured to limit average input current to
one of several possible settings as well as be deactivated
(USB Suspend). The input current limit will be set by the
V
cording to the following expression:
Figure 1 shows the range of possible voltages at V
a function of battery voltage.
Ideal Diode from BAT to V
The LTC3566 has an internal ideal diode as well as a con-
troller for an optional external ideal diode. The ideal diode
controller is 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 diode. Furthermore,
if power to V
of the application power will be provided by the battery via
the ideal diode. The transition from input power to battery
power at V
capacitor to keep V
OUT
CLPROG
I
VBUS
drops below BAT.
=I
servo voltage and the resistor on CLPROG ac-
OUT
BUSQ
4.5
4.2
3.9
3.6
3.3
3.0
2.7
2.4
BUS
2.4
will be quick enough to allow only a 10μF
(USB or wall power) is removed, then all
+
2.7
R
Figure 1. V
V
NO LOAD
OUT
CLPROG
CLPROG
3.0
from drooping. The ideal diode
OUT
BAT (V)
3.3
OUT
• (h
CLPROG
vs BAT
3.6
300mV
3.9
+ 1)
3566 F01
CLPROG
4.2
, 1.188V
OUT
as
consists of a precision amplifi er that enables a large on-
chip P-channel MOSFET transistor whenever the voltage at
V
BAT. The resistance of the internal ideal diode is approxi-
mately 180mΩ. If this is suffi cient for the application, then
no external components are necessary. However, if more
conductance is needed, an external P-channel MOSFET
transistor can be added from BAT to V
When an external P-channel MOSFET transistor is present,
the GATE pin of the LTC3566 drives its gate for automatic
ideal diode control. The source of the external P-chan-
nel MOSFET should be connected to V
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 40mΩ or lower.
Suspend LDO
If the LTC3566 is confi gured for USB suspend mode, the
switching regulator is disabled and the suspend LDO
provides power to the V
available to 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
(suspended). To remain compliant with the USB specifi ca-
tion, the input to the LDO is current limited so that it will
not exceed the 500μA low power suspend specifi cation.
If the load on V
the additional current will come from the battery via the
ideal diode.
OUT
is approximately 15mV (V
1000
2200
2000
1800
1600
1400
1200
800
600
400
200
0
BUS
0
Figure 2. Ideal Diode Operation
FORWARD VOLTAGE (mV) (BAT – V
OUT
). This LDO will prevent the battery from
60
VISHAY Si2333
OPTIONAL EXTERNAL
IDEAL DIODE
120
exceeds the suspend current limit,
IDEAL DIODE
SEMICONDUCTOR
OUT
180
MBRM120LT3
LTC3566
pin (presuming there is power
240 300
ON
FWD
360
) below the voltage at
OUT
OUT
420
OUT
LTC3566
3566 F02
)
.
480
and the drain
13
3566p