LTC3567 Datasheet, PDF (20/28 Pages) Linear Technology – High Effi ciency USB Power Manager Plus 1A Buck-Boost Converter with I2C Control

LTC3567
OPERATION
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 significant improvement
in efficiency 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 unde-
sirable 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
B6 bit of the I²C port is used to enable or disable Burst
Mode operation at any time, offering both low noise and
low power operation when they are needed.
Buck-Boost Regulator Soft-Start Operation
Soft-start is accomplished by gradually increasing the
reference voltage input to the error amplifier over a 0.5ms
(typical) period. This limits transient inrush currents during
start-up because the output voltage is always “in regula-
tion.” Ramping the reference voltage input also limits the
rate of increase in the V_C1 voltage which helps minimize
output overshoot during start-up. A soft-start cycle oc-
curs whenever 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 LTC3567 incorporates an undervoltage lockout cir-
cuit on V_OUT (connected to V_IN1) which shuts down the
buck-boost regulator when V_OUT drops below 2.6V. This
UVLO prevents unstable operation.
APPLICATIONS INFORMATION
CLPROG Resistor and Capacitor
As described in the High Efficiency Switching PowerPath
Controller section, the resistor on the CLPROG pin deter-
mines the average input current limit when the switching
regulator is set to either the 1x mode (USB 100mA), the
5x mode (USB 500mA) or the 10x mode. The input cur-
rent will be comprised of two components, the current
that is used to drive V_OUT and the quiescent current of the
switching regulator. To ensure that the USB specification
is strictly met, both components of input current should
be considered. The Electrical Characteristics table gives
values for quiescent currents in either setting as well as
current limit programming accuracy. To get as close to
the 500mA or 100mA specifications as possible, a 1%
resistor should be used. Recall that I_VBUS = I_VBUSQ +
V_CLPROG/R_CLPROG • (h_CLPROG + 1).
An averaging capacitor or an R-C combination is required
in parallel with the CLPROG resistor so that the switching
regulator can determine the average input current. This
network also provides the dominant pole for the feedback
loop when current limit is reached. To ensure stability, the
capacitor on CLPROG should be 0.1μF or larger.
Choosing the PowerPath Inductor
Because the input voltage range and output voltage range
of the PowerPath switching regulator are both fairly nar-
row, the LTC3567 was designed for a specific inductance
value of 3.3μH. Some inductors which may be suitable
for this application are listed in Table 6.
Table 6. Recommended Inductors for PowerPath Controller
MAX MAX
INDUCTOR L I_DC DCR
TYPE (μH) (A) (Ω)
SIZE IN mm
(L × W × H) MANUFACTURER
LPS4018 3.3 2.2 0.08 3.9 × 3.9 × 1.7 Coilcraft
www.coilcraft.com
D53LC 3.3 2.26 0.034 5.0 × 5.0 × 3.0 Toko
DB318C 3.3 1.55 0.070 3.8 × 3.8 × 1.8 www.toko.com
WE-TPC 3.3 1.95 0.065 4.8 × 4.8 × 1.8 Würth Elektronik
Type M1
www.we-online.com
CDRH6D12 3.3 2.2 0.0625 6.7 × 6.7 × 1.5 Sumida
CDRH6D38 3.3 3.5 0.020 7.0 × 7.0 × 4.0 www.sumida.com
3567f
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