ltc3586 Linear Technology Corporation, ltc3586 Datasheet - Page 24

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

OPERATION
LTC3586
Zero Current Comparator
The zero current comparator monitors the inductor current
to the output and shuts off the synchronous rectifi er once
the current drops to approximately 65mA. This prevents
the inductor current from reversing in polarity thereby
improving effi ciency at light loads.
Antiringing Control
The antiringing control circuitry prevents high frequency
ringing of the SW pin as the inductor current goes to zero
in discontinuous mode. The damping of the resonant
circuit formed by L and C
pin) is achieved internally by switching a 150Ω resistor
across the inductor.
PMOS Synchronous Rectifi er
To prevent the inductor current from running away,
the PMOS synchronous rectifi er is only enabled when
V
Output Disconnect and Inrush Limiting
The LTC3586 boost converter is designed to allow true
output disconnect by eliminating body diode conduction
of the internal PMOS rectifi er. This allows V
zero volts during shutdown, drawing zero current from
the input source. It also allows for inrush current limit-
ing at start-up, minimizing surge currents seen by the
input supply. Note that to obtain the advantage of output
disconnect, there must not be an external Schottky diode
connected between the SW4 and V
Short Circuit Protection
Unlike most boost converters, the LTC3586 boost converter
allows its output to be short-circuited due to the output
24
OUT
> (V
IN
+ 130mV).
SW
(capacitance of the SW4
OUT4
pin.
OUT
to go to
disconnect feature. It incorporates internal features such as
current limit foldback and thermal shutdown for protection
from an excessive overload or short-circuit.
V
The LTC3586 boost converter will maintain voltage regula-
tion even if the input voltage is above the output voltage. This
is achieved by terminating the switching of the synchronous
PMOS and applying V
that the slope of the inductor current will reverse during
the time when current is fl owing to the output. Since the
PMOS no longer acts as a low impedance switch in this
mode, there will be more power dissipation within the IC.
This will cause a sharp drop in the effi ciency (see Typical
Performance Characteristics, Boost Effi ciency vs V
The maximum output current should be limited in order
to maintain an acceptable junction temperature.
Boost Soft-Start
The LTC3586 boost converter provides soft-start by
slowly ramping the peak inductor current from zero to
a maximum of 2.4A in about 500μs. Ramping the peak
inductor current limits transient inrush currents during
start-up. A soft-start cycle occurs whenever the boost is
enabled, or after a fault condition has occurred (thermal
shutdown or UVLO).
Boost Overvoltage Protection
If the FB4 node were inadvertently shorted to ground, then
the boost converter output would increase indefi nitely with
the maximum current that could be sourced from V
The LTC3586 protects against this by shutting off the main
switch if the output voltage exceeds 5.3V.
IN
> V
OUT
Operation
IN4
statically on its gate. This ensures
IN4
IN4
3586f
).
.