LTC3586_15 Datasheet, PDF (24/36 Pages) Linear Technology – High Efficiency USB Power Manager with Boost, Buck-Boost and Dual Bucks

LTC3586/LTC3586-1
OPERATION
Zero Current Comparator
The zero current comparator monitors the inductor current
to the output and shuts off the synchronous rectifier once
the current drops to approximately 65mA. This prevents
the inductor current from reversing in polarity thereby
improving efficiency 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_SW (capacitance of the SW4
pin) is achieved internally by switching a 150Ω resistor
across the inductor.
PMOS Synchronous Rectifier
To prevent the inductor current from running away,
the PMOS synchronous rectifier is only enabled when
V_OUT > (V_IN + 130mV).
Output Disconnect and Inrush Limiting
The LTC3586/LTC3586-1 boost converter is designed to
allow true output disconnect by eliminating body diode
conduction of the internal PMOS rectifier. This allows V_OUT
to go to zero volts during shutdown, drawing zero current
from the input source. It also allows for inrush current
limiting 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_OUT4 pin.
Short Circuit Protection
Unlike most boost converters, the LTC3586/LTC3586-1
boost converter allows its output to be short-circuited
due to the output disconnect feature. It incorporates
internal features such as current limit foldback and thermal
shutdown for protection from an excessive overload or
short circuit.
V_IN > V_OUT Operation
The LTC3586/LTC3586-1 boost converter will maintain
voltage regulation even if the input voltage is above
the output voltage. This is achieved by terminating the
switching of the synchronous PMOS and applying V_IN4
statically on its gate. This ensures that the slope of the
inductor current will reverse during the time when cur-
rent is flowing 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 efficiency (see Typical Performance
Characteristics, Boost Efficiency vs V_IN4). The maximum
output current should be limited in order to maintain an
acceptable junction temperature.
Boost Soft-Start
The LTC3586/LTC3586-1 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 indefinitely with
the maximum current that could be sourced from V_IN4. The
LTC3586/LTC3586-1 protects against this by shutting off
the main switch if the output voltage exceeds 5.3V.
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