ltc3586 Linear Technology Corporation, ltc3586 Datasheet - Page 15

• Manufacturer Part Number: ltc3586
• Description: High Ef? Ciency Usb Power Manager With Boost, Buck-boost And Dual Bucks
• Manufacturer: Linear Technology Corporation

OPERATION
The current at CLPROG is a fraction (h
V
eraging capacitor are connected from CLPROG to GND,
the voltage on CLPROG represents the average input
current of the PowerPath switching regulator. When the
input current approaches the programmed limit, CLPROG
reaches V
The input current limit is programmed by the I
I
possible settings as well as be deactivated (USB Suspend).
The input current limit will be set by the V
voltage and the resistor on CLPROG according to the fol-
lowing expression:
Figure 1 shows the range of possible voltages at V
a function of battery voltage.
Ideal Diode from BAT to V
The LTC3586 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
LIM1
BUS
OUT
I
VBUS
pins to limit average input current to one of several
current. When a programming resistor and an av-
drops below BAT.
=
CLPROG
4.5
4.2
3.9
3.6
3.3
3.0
2.7
2.4
I
VBUSQ
2.4
, 1.188V and power out is held constant.
2.7
NO LOAD
+
Figure 1. V
R
V
3.0
CLPROG
CLPROG
BAT (V)
OUT
3.3
OUT
•
(
3.6
vs BAT
h
300mV
CLPROG
3.9
3586 F01
CLPROG
+
4.2
CLPROG
1
)
–1
LIM0
) of the
OUT
servo
and
as
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
all of the application power will be provided by the bat-
tery via the ideal diode. The transition from input power
to battery power at V
only the10μF capacitor to keep V
ideal diode consists of a precision amplifier that enables
a large on-chip P-channel MOSFET transistor whenever
the voltage at V
the voltage at BAT. The resistance of the internal ideal
diode is approximately 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
When an external P-channel MOSFET transistor is present,
the GATE pin of the LTC3586 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.
OUT
. See Figure 2.
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0
BUS
0
Figure 2. Ideal Diode Operation
OUT
FORWARD VOLTAGE (mV) (BAT – V
60
(USB or wall power) is removed, then
IDEAL DIODE
is approximately 15mV (V
120
VISHAY Si2333
OPTIONAL EXTERNAL
IDEAL DIODE
LTC3586
SEMICONDUCTOR
OUT
180
MBRM120LT3
will be quick enough to allow
240 300
ON
OUT
360
from drooping. The
OUT
420
OUT
LTC3586
3586 F02
)
480
and the drain
FWD
15
) below
3586f