LTC3566EUF-2#PBF Linear Technology, LTC3566EUF-2#PBF Datasheet - Page 18

• Manufacturer Part Number: LTC3566EUF-2#PBF
• Description: IC POWER MANAGER USB 24-QFN
• Manufacturer: Linear Technology

Specifications of LTC3566EUF-2#PBF

• Applications: Handheld/Mobile Devices
• Voltage - Supply: 4.35 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -

LTC3566/LTC3566-2
OPERATION
Buck-Boost Regulator Burst Mode Operation
In Burst Mode operation, the buck-boost regulator uses
a hysteretic FB1 voltage algorithm to control the output
voltage. By limiting FET switching and using a hysteretic
control loop, switching losses are greatly reduced. In this
mode output current is limited to 50mA typical. While
operating in Burst Mode operation, the output capacitor
is charged to a voltage slightly higher than the regulation
point. The buck-boost converter then goes into a sleep
state, during which the output capacitor provides the
load current. The output capacitor is charged by charg-
ing the inductor until the input current reaches 275mA
typical and then discharging the inductor until the reverse
current reaches 0mA typical. This process is repeated
until the feedback voltage has charged to 6mV above the
regulation point. In the sleep state, most of the regulator’s
circuitry is powered down, helping to conserve battery
power. When the feedback voltage drops 6mV below the
regulation point, the switching regulator circuitry is pow-
ered on and another burst cycle begins. The duration for
which the regulator sleeps depends on the load current
and output capacitor value. The sleep time decreases as
the load current increases. The maximum load current in
Burst Mode operation is 50mA. The buck-boost regulator
will not go to sleep if the current is greater than 50mA
and if the load current increases beyond this point while
in Burst Mode operation the output will lose regulation.
Burst Mode operation provides a signifi cant improve-
ment in effi ciency at light loads at the expense of higher
output ripple when compared to PWM mode. For many
noise-sensitive systems, Burst Mode operation might
be undesirable at certain times (i.e. during a transmit or
receive cycle of a wireless device), but highly desirable
at others (i.e. when the device is in low power standby
mode). The MODE pin is used to enable or disable Burst
Mode operation at any time, offering both low noise and
low power operation when they are needed.
18
Table 2. USB Current Limit Settings
Table 3. Switching Regulator Modes
Buck-Boost Regulator Soft-Start Operation
Soft-start is accomplished by gradually increasing the
reference voltage input to the error amplifi er over a 0.5ms
(typical) period. This limits transient inrush currents during
start-up because the output voltage is always in regulation.
Ramping the reference voltage input also limits the rate of
increase in the V
overshoot during start-up. A soft-start cycle occurs when-
ever the buck-boost is enabled, or after a fault condition
has occurred (thermal shutdown or UVLO). A soft-start
cycle is not triggered by changing operating modes. This
allows seamless operation when transitioning between
Burst Mode operation and PWM mode.
Low Supply Operation
The LTC3566 family incorporates an undervoltage lockout
circuit on V
buck-boost regulator when V
UVLO prevents unstable operation.
ILIM1
0
0
1
1
OUT
MODE
0
1
(connected to V
C1
voltage which helps minimize output
ILIM0
0
1
0
1
SWITCHING REGULATOR MODE
PWM Mode
Burst Mode Operation
OUT
IN1
USB SETTING
1x Mode (USB 100mA Limit)
10x Mode (Wall 1A Limit)
Suspend
5x Mode (USB 500mA Limit)
) which shuts down the
drops below 2.6V. This
3566fb