LTC3127EDD LINER [Linear Technology], LTC3127EDD Datasheet - Page 11

• Manufacturer Part Number: LTC3127EDD
• Description: 1A Buck-Boost DC/DC Converter with Programmable Input Current Limit
• Manufacturer: LINER [Linear Technology]

operaTion
The input current limit is set by the R
on the PROG pin to SGND. The resistor value can be
calculated using the following formula:
Where I
A secondary 2.5A (typical) current limit forces switches
B and D on and A and C off if tripped. This current limit
is not affected by the value of R
Reverse Current Limit
The reverse current comparator on switch D monitors
the inductor current supplied from the output. When this
current exceeds 300mA (typical) switch D will be turned
off for the remainder of the switching cycle.
Burst Mode Operation
When the MODE pin is held high the LTC3127 will func-
tion in Burst Mode operation as long as the load current
is typically less than 35mA. In Burst Mode operation, the
LTC3127 still switches at a fixed frequency of 1.35MHz,
using the same error amplifiers and loop compensation for
average input current mode control. This control method
eliminates any output transient when switching between
modes. In Burst Mode operation, energy is delivered to
the output until the output voltage reaches the nominal
regulation value. At this point, the LTC3127 transitions to
sleep mode where the output switches are shut off and the
LTC3127 consumes only 35μA of quiescent current from
V
resumes. This maximizes efficiency at very light loads by
minimizing switching and quiescent losses.
Zero Current Comparator
The zero current comparator monitors the inductor cur-
rent to the output and shuts off the synchronous rectifier
when this current reduces to approximately 30mA. This
prevents the inductor current from reversing in polarity,
improving efficiency at light loads. This comparator is
only active in Burst Mode operation.
IN
R
. When the output voltage droops slightly, switching
PROG
LIMIT
= 54.92 • I
is the average input current limit in amps.
LIMIT
(A) + 4.94 (kΩ)
PROG
PROG
.
resistor placed
Anti-Ringing Control
The anti-ringing control connects a resistor from SW1 and
SW2 to PGND to prevent high frequency ringing during
discontinuous current mode operation in Burst Mode.
Although the ringing of the resonant circuit formed by L
and CSW (capacitance on SW pin) is low energy, it can
cause EMI radiation.
Shutdown
Shutdown of the converter is accomplished by pulling
SHDN below 0.3V and enabled by pulling SHDN above
1.2V. Note that SHDN can be driven above V
as long as it is limited to less than the absolute maximum
rating.
Thermal Shutdown
If the die temperature exceeds 150°C (typical) the LTC3127
will be disabled. All power devices will be turned off and
both switch nodes will be high impedance. The LTC3127
will restart (if enabled) when the die temperature drops
to approximately 140°C.
Thermal Regulator
To help prevent the part from going into thermal shutdown
when charging very large capacitive loads, the LTC3127 is
equipped with a thermal regulator. If the die temperature
exceeds 130°C (typical) the average current limit is lowered
to help reduce the amount of power being dissipated in the
package. The current limit will be approximately 0A just before
thermal shutdown. The current limit will return to its full value
when the die temperature drops back below 130°C.
Undervoltage Lockout
If the input supply voltage drops below 1.7V (typical),
the LTC3127 will be disabled and all power devices will
be turned off.
LTC3127
IN
or V

OUT
3127f
,