ltc3528-2 Linear Technology Corporation, ltc3528-2 Datasheet - Page 9

• Manufacturer Part Number: ltc3528-2
• Description: Ltc3528-2 - 1a, 2mhz Synchronous Step-up Dc/dc Converter In 2mm ? 3mm Dfn
• Manufacturer: Linear Technology Corporation

OPERATION
The LTC3528-2 is a 2MHz synchronous boost converter
housed in an 8-lead 3mm × 2mm DFN package. With the
ability to start up and operate from inputs less than 0.88V,
the device features fixed frequency, current mode PWM
control for exceptional line and load regulation. The cur-
rent mode architecture with adaptive slope compensation
provides excellent transient load response and requires
minimal output filtering. Internal soft-start and internal
loop compensation simplifies the design process while
minimizing the number of external components.
With its low R
MOSFET switch and P-channel MOSFET synchronous recti-
fier, the LTC3528-2 achieves high efficiency over a wide
range of load current. The LTC3528-2 features continuous
2MHz PWM operation over a wide range of load current.
At very light loads, the LTC3528-2 will enter Burst Mode
operation to maintain high efficiency. Operation can be
best understood by referring to the Block Diagram.
LOW VOLTAGE START-UP
The LTC3528-2 includes an independent start-up oscillator
designed to operate at an input voltage of 0.70V (typical).
Soft-start and inrush current limiting are provided during
start-up, as well as normal operating mode.
When either V
normal operating mode. Once the output voltage exceeds
the input by 0.24V, the IC powers itself from V
V
on the V
a large input capacitor. The input voltage can drop as low
as 0.5V. The limiting factor for the application becomes
the availability of the power source to supply sufficient
power to the output at the low voltages, and the maximum
duty cycle, which is clamped at 92% typical. Note that
at low input voltages, small voltage drops due to series
resistance become critical, and greatly limit the power
delivery capability of the converter.
IN
. At this point the internal circuitry has no dependency
IN
input voltage, eliminating the requirement for
DS(ON)
IN
or V
and low gate charge internal N-channel
OUT
(Refer to Block Diagram)
exceeds 1.6V typical, the IC enters
OUT
instead of
LOW NOISE FIXED FREQUENCY OPERATION
Soft-Start
The LTC3528-2 contains internal circuitry to provide soft-
start operation. The internal soft-start circuitry slowly
ramps the peak inductor current from zero to its peak
value of 1.5A (typical), allowing start-up into heavy loads.
The soft-start time is approximately 0.5ms. The soft-start
circuitry is reset in the event of a commanded shutdown
or a thermal shutdown.
Oscillator
An internal oscillator sets the frequency of operation to
2MHz.
Shutdown
The converter is shut down by pulling the SHDN pin below
0.25V, and activated by pulling SHDN above 0.88V. Although
SHDN can be driven above V
maximum rating) without damage, the LTC3528-2 has a
proprietary test mode that may be engaged if SHDN is held
in the range of 0.5V to 1V higher than the greater of V
V
action is interrupted, which can cause undesirable opera-
tion in some applications. Therefore, in applications where
SHDN may be driven above V
means must be employed to keep the SHDN voltage below
(V
being engaged. Please refer to Figure 1 for two possible
implementations
OUT
IN
V
R > (V
CNTRL
. If the test mode is engaged, normal PWM switching
+ 0.4V) to prevent the possibility of the test mode
CNTRL
4M
±30%
Figure 1. Recommended Shutdown Circuits
when Driving SHDN Above V
LTC3528-2
R
/(V
IN
SHDN
+ 0.4) – 1) M
1M
V
IN
IN
IN
or V
, a resistor divider or other
V
ZETEX ZC2811E
CNTRL
IN
OUT
LTC3528-2
4M
±30%
(up to the absolute
1M
LTC3528-2
SHDN
3528 F01
35282fa
IN
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