LTM8029 LINER [Linear Technology], LTM8029 Datasheet - Page 9

• Manufacturer Part Number: LTM8029
• Description: 36VIN, 600mA Step-Down ?Module Converter
• Manufacturer: LINER [Linear Technology]

operaTion
The LTM8029 is a standalone non-isolated step-down
switching DC/DC power supply that can deliver up to 600mA
of output current. This device features a very low quiescent
current and provides a precisely regulated output voltage
from 1.2V to 18V. The input voltage range is 4.5V to 36V.
Given that the LTM8029 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 LTM8029 contains a
current mode controller, power switching element, power
inductor, power Schottky diode and a modest amount of
input and output capacitance. The LTM8029 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 circuitry.
The internal regulator normally draws power from the V
pin, but if the BIAS pin is connected to an external volt-
age higher than 2.25V, bias power will be drawn from the
external source (typically the regulated output voltage).
This improves efficiency.
The RUN pin is used to place the LTM8029 in shutdown.
To optimize efficiency, the LTM8029 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
IN
typically 5μA at no load and 12V
mostly shut down between bursts, the effective switching
frequency will be lower than that programmed at the RT
pin. For the same reason, the output ripple will be differ-
ent than when the part is running at the full programmed
frequency.
The LTM8029 contains a power good comparator which
trips when the FB 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 LTM8029 is enabled and V
4.5V. The LTM8029 features the ability to skip the off-time
in switching cycles when the input voltage approaches the
target output. This allows the LTM8029 to operate at input
voltages lower than other step-down regulators.
In an overload or short-circuit condition, the LTM8029
will protect itself by limiting its peak switching current
and decreasing the operating frequency to reduce overall
power consumption. The LTM8029 is also 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
. Since the LTM8029 is
LTM8029
IN
is above
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