ltm8033 Linear Technology Corporation, ltm8033 Datasheet - Page 10

• Manufacturer Part Number: ltm8033
• Description: Ultralow Noise Emc 36vin, 3a Dc/dc
• Manufacturer: Linear Technology Corporation

LTM8033
OPERATION
The LTM8033 is a standalone nonisolated step-down
switching DC/DC power supply that can deliver up to 3A of
output current. It is an EMC product; its radiated emissions
are so quiet that it can pass the stringent requirements of
EN55022 class B as a stand alone product. This μModule
provides a precisely regulated output voltage program-
mable via one external resistor from 0.8V to 25V. The input
voltage range is 3.6V to 36V. Given that the LTM8033 is
a step-down converter, make sure that the input voltage
is high enough to support the desired output voltage and
load current.
As shown in the Block Diagram, the LTM8033 contains an
EMI filter, current mode controller, power switching ele-
ment, power inductor, power Schottky diode and a modest
amount of input and output capacitance. The LTM8033 is
a fixed frequency PWM regulator. The switching frequency
is set by simply connecting the appropriate resistor value
from the RT pin to GND.
An internal regulator provides power to the control cir-
cuitry. The bias regulator normally draws power from the
V
voltage higher than 2.8V, bias power will be drawn from
the external source (typically the regulated output voltage).
This improves efficiency. The RUN/SS pin is used to place
the LTM8033 in shutdown, disconnecting the output and
reducing the input current to less than 1μA.
10
IN
pin, but if the BIAS pin is connected to an external
To further optimize efficiency, the LTM8033 automatically
switches to Burst Mode operation in light load situations.
Between bursts, all circuitry associated with controlling
the output switch is shut down reducing the input supply
current to 50μA in a typical application.
The oscillator reduces the LTM8033’s operating frequency
when the voltage at the ADJ pin is low. This frequency
foldback helps to control the output current during start-
up and overload.
The LTM8033 contains a power good comparator which
trips when the ADJ pin is at roughly 90% of its regulated
value. The PGOOD output is an open-collector transistor
that is off when the output is in regulation, allowing an
external resistor to pull the PGOOD pin high. Power good
is valid when the LTM8033 is enabled and V
3.6V.
The LTM8033 is equipped with a thermal shutdown that
will inhibit power switching at high junction temperatures.
The activation threshold of this function, however, is above
125°C to avoid interfering with normal operation. Thus,
prolonged or repetitive operation under a condition in
which the thermal shutdown activates may damage or
impair the reliability of the device.
IN
is above
8033f