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LTM8046IY

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LTM8046
7
8046fb
For more information www.linear.com/LTM8046
Typical perForMance characTerisTics
Temperature Rise vs Output
Current 8V
OUT
Temperature Rise vs Output
Current 12V
OUT
Output Ripple Step Input Start-Up Waveform
Temperature Rise vs Output
Current 5V
OUT
OUTPUT CURRENT (mA)
TEMPERATURE RISE (°C)
20
15
0
10
5
8046 G27
0 700500 600100 200 300 400
3.3V
IN
5V
IN
12V
IN
24V
IN
OUTPUT CURRENT (mA)
TEMPERATURE RISE (°C)
20
0
15
5
10
8046 G29
0 300100 200
3.3V
IN
5V
IN
12V
IN
OUTPUT CURRENT (mA)
TEMPERATURE RISE (°C)
15
0
10
5
8046 G28
0 100 200 300 400
3.3V
IN
5V
IN
12V
IN
24V
IN
, 5V
OUT
570mA LOAD
DC1559A DEMO BOARD
UNMODIFIED
150MHz BW
50mV/
DIV
8046 G30
2µs/DIV
24V
IN
, 5V
OUT
20Ω RESISTIVE LOAD
1V/
DIV
8046 G31
200µs/DIV
C
SS
= 0.1µF
C
SS
= 0.033µF
NO C
SS
LTM8046
8
8046fb
For more information www.linear.com/LTM8046
pin FuncTions
V
IN
(Bank 1): V
IN
supplies current to the LTM8046’s
internal regulator and to the integrated power switch.
These pins must be locally bypassed with an external,
low ESR capacitor.
GND (Bank 2): This is the primary side local ground of
the LTM8046 primary. In most applications, the bulk of
the heat flow out of the LTM8046 is through the GND and
V
OUT
–
pads, so the printed circuit design has a large impact
on the thermal performance of the part. See the PCB Layout
and Thermal Considerations sections for more details.
V
OUT
–
(Bank 3): V
OUT
–
is the return for V
OUT
. V
OUT
and
V
OUT
–
comprise the isolated output of the LTM8046. In
most applications, the bulk of the heat flow out of the
LTM8046 is through the GND and V
OUT
–
pads, so the
printed circuit design has a large impact on the thermal
performance of the part. See the PCB Layout and Thermal
Considerations sections for more details. Apply an external
capacitor between V
OUT
and V
OUT
–
.
V
OUT
(Bank 4): V
OUT
and V
OUT
–
comprise the isolated
output of the LTM8046 flyback stage. Apply an external
capacitor between V
OUT
and V
OUT
–
. Do not allow V
OUT
–
to
exceed V
OUT
.
RUN (Pin L3): A resistive divider connected to V
IN
and this
pin programs the minimum voltage at which the LTM8046
will operate. Below 1.24V, the LTM8046 does not deliver
power to the secondary. Above 1.24V, power will be de
-
livered to the secondary and 8µA will be fed into the SS
pin. When RUN is less than 1.24V, the pin draws 2.5µA,
allowing for a programmable hysteresis. Do not allow a
negative voltage (relative to GND) on this pin.
BIAS (Pin L4): This pin supplies the power necessary to
operate the LTM8046. It must be locally bypassed with
a low ESR capacitor of at least 1μF. Do not allow this pin
voltage to rise above V
IN
.
SS (Pin L5): Place a soft-start capacitor here to limit inrush
current and the output voltage ramp rate. Do not allow a
negative voltage (relative to GND) on this pin.
FB (Pin L6): Apply a resistor from this pin to GND to set
the output voltage, using the recommended value given
in Table 1. If Table 1 does not list the desired V
OUT
value,
the equation
R
FB
= 31.6 V
OUT
–0.84
( )
kΩ
may be used to approximate the value. To the seasoned
designer, this exponential equation may seem unusual.
The equation is exponential due to non-linear current
sources that are used to temperature compensate the
output regulation.
LTM8046
9
8046fb
For more information www.linear.com/LTM8046
block DiagraM
V
IN
RUN
FB
*DO NOT ALLOW BIAS VOLTAGE TO EXCEED V
IN
GND
0.1µF
1µF
V
OUT
CURRENT
MODE
CONTROLLER
V
OUT
–
SS
BIAS*
8046 BD
•
•
operaTion
The LTM8046 is a stand-alone isolated flyback switching
DC/DC µModule converter that can deliver over 700mA of
output current. This module provides a regulated output
voltage programmable via one external resistor from 1.8V
to 12V. The input voltage range of the LTM8046 is 3.1V
to 31V. Given that the LTM8046 is a flyback converter,
the output current depends upon the input and output
voltages, so make sure that the input voltage is high
enough to support the desired output voltage and load
current. The Typical Performance Characteristics section
gives several graphs of the maximum load versus V
IN
for
several output voltages.
A simplified block diagram is given. The LTM8046 contains
a current mode controller, power switching element, power
transformer, power Schottky diode, a modest amount of
input and output capacitance.
The LTM8046 has a galvanic primary to secondary isola
-
tion rating of 2kVAC. This is verified by applying 3kVDC
between the primary to
secondary for 1 second. Note
that the 2kVAC isolation is verified by a 3kVDC test. This
is because the 2kVAC waveform has a peak voltage 1.414
times higher than 2kV, or 2.83kVDC. For the LTM8046, at
least 3kVDC is applied. For further details
please refer to
the Isolation and Working Voltage section.
An internal regulator
provides power to the control cir
-
cuitry. The bias regulator normally draws power from the
V
IN
pin, but if the BIAS pin is connected to an external
voltage higher than 3.1V, bias power will be drawn from
the external source, improving efficiency. V
BIAS
must not
exceed V
IN
. The RUN pin is used to turn on or off the
LTM8046, disconnecting the output and reducing the
input current to 1μA or less.
The LTM8046 is a variable frequency device. For a fixed
input and output voltage, the frequency decreases as
the load increases. For light loads, the current through
the internal transformer may be discontinuous, so that
frequency may appear to decrease. Note that a minimum
load is required to keep the output voltage in regulation.
Refer to the Typical Performance Characteristics section.
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LTM8046IY

Mfr. #:
Buy LTM8046IY
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 3.1VIN to 32VIN, 2kVAC Isolated DC/DC Module Converter
Lifecycle:
New from this manufacturer.
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