LTC3566 Datasheet, PDF (13/28 Pages) Linear Technology – High Effi ciency USB Power Manager Plus 1A Buck-Boost Converter

LTC3566
OPERATION
on CLPROG represents the average input current of the
switching regulator. When the input current approaches
the programmed limit, CLPROG reaches V_CLPROG, 1.188V
and power out is held constant.
The input current is programmed by the ILIM0 and ILIM1
pins. It can be configured 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_CLPROG servo voltage and the resistor on CLPROG ac-
cording to the following expression:
I_VBUS
= I_BUSQ
+
V_CLPROG
R_CLPROG
• (h_CLPROG
+
1)
Figure 1 shows the range of possible voltages at V_OUT as
a function of battery voltage.
4.5
4.2
3.9
NO LOAD
3.6
3.3
300mV
3.0
2.7
2.4
2.4 2.7 3.0 3.3 3.6 3.9 4.2
BAT (V)
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Figure 1. V_OUT vs BAT
Ideal Diode from BAT to V_OUT
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_OUT drops below BAT.
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_BUS (USB or wall power) is removed, then all
of the application power will be provided by the battery via
the ideal diode. The transition from input power to battery
power at V_OUT will be quick enough to allow only a 10μF
capacitor to keep V_OUT from drooping. The ideal diode
2200
2000
1800
VISHAY Si2333
OPTIONAL EXTERNAL
IDEAL DIODE
1600
1400
1200
LTC3566
IDEAL DIODE
1000
800
600
ON
400
SEMICONDUCTOR
MBRM120LT3
200
0
0 60 120 180 240 300 360 420 480
FORWARD VOLTAGE (mV) (BAT – V_OUT)
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Figure 2. Ideal Diode Operation
consists of a precision amplifier that enables a large on-
chip P-channel MOSFET transistor whenever the voltage at
V_OUT is approximately 15mV (V_FWD) below the voltage at
BAT. The resistance of the internal ideal diode is approxi-
mately 180mΩ. If this is sufficient 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_OUT.
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_OUT 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 40mΩ or lower.
Suspend LDO
If the LTC3566 is configured for USB suspend mode, the
switching regulator is disabled and the suspend LDO
provides power to the V_OUT pin (presuming there is power
available to V_BUS). 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
(suspended). To remain compliant with the USB specifica-
tion, the input to the LDO is current limited so that it will
not exceed the 500μA low power suspend specification.
If the load on V_OUT exceeds the suspend current limit,
the additional current will come from the battery via the
ideal diode.
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