ltm8022 Linear Technology Corporation, ltm8022 Datasheet - Page 7

• Manufacturer Part Number: ltm8022
• Description: 1a, 36v Dc/dc ?module
• Manufacturer: Linear Technology Corporation

OPERATION
The LTM8022 is a standalone non-isolated step-down
switching DC/DC power supply. It can deliver up to 1A of
DC output current with only bulk external input and output
capacitors. This module provides a precisely regulated
output voltage programmable via one external resistor
from 0.8V
to 36V. Given that the LTM8022 is a step-down converter,
make sure that the input voltage is high enough to support
the desired output voltage and load current. A simplifi ed
Block Diagram is shown above.
The LTM8022 contains a current mode controller, power
switching element, power inductor, power Schottky diode
and a modest amount of input and output capacitance.
The LTM8022 is a fi xed frequency PWM regulator. The
switching frequency is set by simply connecting the ap-
propriate value resistor from the R
An internal regulator provides power to the control cir-
cuitry. The bias regulator normally draws power from the
V
BLOCK DIAGRAM
IN
pin, but if the BIAS pin is connected to an external
DC
to 10V
V
SHARE
RUN/SS
SYNC
IN
DC
. The input voltage range is 3.6V
0.1μF
CURRENT MODE
CONTROLLER
T
pin to GND.
GND
voltage higher than 2.4V, bias power will be drawn from
the external source (typically the regulated output voltage).
This improves effi ciency. The RUN/SS pin is used to place
the LTM8022 in shutdown, disconnecting the output and
reducing the input current to less than 1μA.
To further optimize effi ciency, the LTM8022 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 cur-
rent to 50μA in a typical application. The oscillator reduces
the LTM8022’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 LTM8022 contains a power good comparator which
trips when the ADJ pin is at 92% of its regulated value.
The PG output is an open-collector transistor that is off
when the output is in regulation, allowing an external
resistor to pull the PG pin high. Power good is valid when
the LTM8022 is enabled and V
R
T
4.7μH
4.7pF
ADJ
499k
10μF
IN
is above 3.6V.
V
BIAS
AUX
OUT
8022 BD
LTM8022
PG
7
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