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LTM8001IY#PBF

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LTM8001
13
8001fd
For more information www.linear.com/LTM8001
applicaTions inForMaTion
LTM8001 Table 1: Recommended Component Values and Configuration for V
OUT0
(T
A
= 25°C)
V
IN0
V
OUT0
C
IN0
C
OUT0
(CERAMIC) C
OUT0
(ELECTROLYTIC) R
FB0
f
OPTIMAL
R
T(OPTIMAL)
f
MAX
R
T(MIN)
6V to 36V 1.2V 10µF, 50V, 1210 100µF, 6.3V, 1210 470µF, 6.3V, 9mΩ, Chemi-Con,
APXF6R3ARA471MH80G
Open 200kHz 200k 250kHz 169k
6V to 36V 1.5V 10µF, 50V, 1210 100µF, 6.3V, 1210 470µF, 6.3V, 9mΩ, Chemi-Con,
APXF6R3ARA471MH80G
38.3k 300kHz 140k 350kHz 118k
6V to 36V 1.8V 10µF, 50V, 1210 100µF, 6.3V, 1210 470µF, 6.3V, 9mΩ, Chemi-Con,
APXF6R3ARA471MH80G
19.6k 350kHz 118k 400kHz 102k
6V to 36V 2.5V 10µF, 50V, 1210 100µF, 6.3V, 1210 330µF, 4V, 27mΩ, OS-CON, 4SVPC330M 9.09k 450kHz 90.9k 525kHz 78.7k
6V to 36V 3.3V 10µF, 50V, 1210 100µF, 6.3V, 1210 330µF, 4V, 27mΩ, OS-CON, 4SVPC330M 5.62k 550kHz 75.0k 625kHz 64.9k
7V to 36V 5V 10µF, 50V, 1210 100µF, 6.3V, 1210 120µF, 16V, 27mΩ, OS-CON,
16SVPC120M
3.09k 600kHz 68.1k 700kHz 57.6k
10V to 36V 8V 10µF, 50V, 1210 100µF
, 10V, 1210 120µF, 16V, 27mΩ, OS-CON,
16SVPC120M
1.74k
625kHz 64.9k 750kHz 53.6k
15V to 36V 12V 10µF, 50V, 1210 47µF, 16V, 1210 120µF, 16V, 27mΩ, OS-CON,
16SVPC120M
1.10k 650kHz 61.9k 800kHz 49.9k
22V to 36V 18V 10µF, 50V, 1210 22µF, 25V, 1210 47µF, 20V, 45mΩ, OS-CON, 20SVPS47M 715Ω 675kHz 59.0k 900kHz 44.2k
28V to 36V 24V 4.7µF, 50V,
1210
10µF, 50V, 1206 47µF, 35V, 30mΩ, OS-CON, 35SVPC47M 523Ω 700kHz 57.6k 1MHz 39.2k
9V to 15V 1.2V 10µF, 50V, 1210 100µF, 6.3V, 1210 470µF, 6.3V, 9mΩ, Chemi-Con,
APXF6R3ARA471MH80G
Open 200kHz 200k 525kHz 78.7k
9V to 15V 1.5V 10µF, 50V, 1210 100µF, 6.3V, 1210 470µF, 6.3V, 9mΩ, Chemi-Con,
APXF6R3ARA471MH80G
38.3k 300kHz 140k 650kHz 61.9k
9V to 15V 1.8V 10µF, 50V, 1210 100µF, 6.3V, 1210 470µF, 6.3V, 9mΩ, Chemi-Con,
APXF6R3ARA471MH80G
19.6k 350kHz 118k 800kHz 49.9k
9V to 15V 2.5V 10µF, 50V, 1210 100µF, 6.3V, 1210 330µF, 4V, 27mΩ, OS-CON, 4SVPC330
M 9.09k 450kHz 90.9k 1MHz 39.2k
9V to 15V
3.3V 10µF, 50V, 1210 100µF, 6.3V, 1210 330µF, 4V, 27mΩ, OS-CON, 4SVPC330M 5.62k 550kHz 75.0k 1MHz 39.2k
9V to 15V 5V 10µF, 50V, 1210 100µF, 6.3V, 1210 120µF, 16V, 27mΩ, OS-CON,
16SVPC120M
3.09k 600kHz 68.1k 1MHz 39.2k
10V to 15V 8V 10µF, 50V, 1210 100µF, 10V, 1210 120µF, 16V, 27mΩ, OS-CON,
16SVPC120M
1.74k 625kHz 64.9k 1MHz 39.2k
18V to 36V 1.2V 10µF, 50V, 1210 100µF, 6.3V, 1210 470µF, 6.3V, 9mΩ, Chemi-Con,
APXF6R3ARA471MH80G
Open 200kHz 200k 250kHz 169k
18V to 36V 1.5V 10µF, 50V, 1210 100µF, 6.3V, 1210 470µF, 6.3V, 9mΩ, Chemi-Con,
APXF6R3ARA471MH80G
38.3k 300kHz 140k 350kHz 118k
18V to 36V 1.8V 10µF, 50V, 1210 100µF, 6.3V, 1210 470µF, 6.3V, 9mΩ, Chemi-Con,
APXF6R3ARA471MH80G
19.6k 350kHz 118k 400kHz 102k
18V to 36V 2.5V 10µF, 50V, 1210 100µF, 6.3V, 1210 330µF, 4V, 27mΩ, OS-CON, 4SVPC330M 9.09k 450kHz 90.9k 525kHz 78.7k
18V to 36V 3.3 10µF, 50V
, 1210 100µF, 6.3V, 1210
330µF, 4V, 27mΩ, OS-CON, 4SVPC330M 5.62k 550kHz 75.0k 625kHz 64.9k
18V to 36V 5V 10µF, 50V, 1210 100µF, 6.3V, 1210 120µF, 16V, 27mΩ, OS-CON,
16SVPC120M
3.09k 600kHz 68.1k 700kHz 57.6k
18V to 36V 8V 10µF, 50V, 1210 100µF, 10V, 1210 120µF, 16V, 27mΩ, OS-CON,
16SVPC120M
1.74k 625kHz 64.9k 750kHz 53.6k
18V to 36V 12V 10µF, 50V, 1210 47µF, 16V, 1210 120µF, 16V, 27mΩ, OS-CON,
16SVPC120M
1.10k 650kHz 61.9k 800kHz 49.9k
Note: An input bulk capacitor is required.
LTM8001
14
8001fd
For more information www.linear.com/LTM8001
applicaTions inForMaTion
Programming Switching Frequency
The LTM8001 has an operational switching frequency
range between 200kHz and 1MHz. This frequency is
programmed with an external resistor from the RT pin to
ground. Do not leave this pin open under any condition.
See Table 2 for resistor values and the corresponding
switching frequencies.
Table 2. R
T
Resistor Values and Their Resultant Switching
Frequencies
SWITCHING FREQUENCY (MHz) R
T
(kΩ)
1 39.2
0.75 53.6
0.5 82.5
0.3 140
0.2 200
Switching Frequency Trade-Offs
It is recommended that the user apply the optimal R
T
resis-
tor value given in Table 1 for the input and output operating
condition.
System level or other considerations, however,
may necessitate another operating frequency. While the
LTM8001 is flexible enough to accommodate a wide range
of operating frequencies, a haphazardly chosen one may
result in undesirable operation under certain operating or
fault conditions. A frequency that is too high can reduce
efficiency, generate excessive heat or even damage the
LTM8001 in some fault conditions. A frequency that is too
low can result in a final design that has too much output
ripple or too large of an output capacitor.
Switching Frequency Synchronization
The nominal switching frequency of the LTM8001 is
determined by the resistor from the RT pin to GND and
may be set from 200kHz to 1MHz. The internal oscillator
may also be synchronized to an external clock through
the SYNC pin. The external clock applied to the SYNC pin
must have a logic low below 0.8V and a logic high greater
than 1.2V. The input frequency must be 20% higher than
the frequency determined by the resistor at the RT pin.
The SYNC pin must be tied to GND if the synchroniza
-
tion to an external clock is not required. When SYNC is
grounded, the switching frequency is determined by the
resistor at the RT pin.
Soft-Start
The soft-start function controls the slew rate of the power
supply output V
OUT0
voltage during start-up. A controlled
output voltage ramp minimizes output voltage overshoot,
reduces inrush current from the V
IN0
supply, and facili-
tates supply sequencing. A capacitor connected from the
SS pin to GND programs the slew rate.
The capacitor is
charged from an internal 11μA current source to produce
a ramped output voltage.
Maximum Output Current Adjust
The LTM8001 features an adjustable accurate current
limit. To adjust the load current limit, an analog voltage
is applied to the ILIM pin. Varying the voltage between
0V and 1.5V adjusts the maximum current between the
minimum and the maximum current, 5.6A typical. Above
1.5V, the control voltage has no effect on the regulated
inductor current. Graphs of the output current vs ILIM volt
-
ages are given in the Typical Performance Characteristics
section. The LTM8001 provides a 2V reference voltage for
conveniently applying resistive dividers to set the current
limit. The current limit can be set as shown in Figure 1
with the following equation:
I
MAX
=7.47
R2
R1+R2
A convenient value of R1 may be 10k. In that case,
R2=
10 •I
MAX
7.47 –I
MAX
kΩ
LTM8001
V
REF
R1
2V
R2
8001 F01
ILIM
Figure 1. Setting the Output Current Limit, I
MAX
LTM8001
15
8001fd
For more information www.linear.com/LTM8001
Load Current Derating Using the ILIM Pin
In high current applications, derating the maximum cur-
rent based on operating temperature may prevent damage
to the load
.
In addition, many applications have thermal
limitations that will require the regulated current to be
reduced based on the load and/or board temperature. To
achieve this, the LTM8001 uses the ILIM pin to reduce
the effective regulated current in the load. While ILIM
programs the regulated current in the load, it may also
be configured to reduce the regulated current. The load/
board temperature derating is programmed using a resistor
divider with a temperature dependant resistance, as shown
in Figure 2. When the board/load temperature rises, the
ILIM voltage will decrease.
Thermal Shutdown
If the part is too hot, the LTM8001 engages its thermal
shutdown, terminates switching and discharges the soft-
start capacitor. When the part has cooled, the part automati
-
cally restarts. This thermal shutdown is set to engage at
temperatures above the 125°
C absolute maximum internal
operating rating to ensure that it does not interfere with
functionality in the specified operating range. This means
that internal temperatures will exceed the 125°C absolute
maximum rating when the overtemperature protection is
active, possibly impairing the device’s reliability.
UVLO and Shutdown
The LTM8001 V
OUT0
step-down regulator has an internal
UVLO that terminates switching, resets all logic, and dis-
charges the soft-start capacitor for input voltages below
4.2
V.
The LTM8001 also has a precision RUN function
that enables switching when the voltage at the RUN pin
rises to 1.68V and shuts down the LTM8001 when the
RUN pin voltage falls to 1.55V. There is also an internal
current source that provides 5.5μA of pull-down current to
program additional UVLO hysteresis. For RUN rising, the
current source is sinking 5.5µA until RUN = 1.68V, after
which it turns off. For RUN falling, the current source is
off until the RUN = 1.55V, after which it sinks 5.5µA. The
following equations determine the voltage divider resis
-
tors for programming the falling UVLO voltage and rising
enable voltage
(V
ENA
) as configured in Figure 4.
R2=
V
ENA
–1.084 UVLO
5.5µA
R1=
1.55 R2
UVLO–1.55
applicaTions inForMaTion
LTM8001
V
REF
R
NTC
R
X
R
V
R
V
R2
R1
(OPTION A TO D)
8001 F02
ILIM
B
R
NTC
A
R
NTC
R
X
D
R
NTC
C
Figure 2. Load Current Derating vs
Temperature Using an NTC Resistor
V
OUT0
Output Overvoltage Protection
The LTM8001 switching regulator uses the FB0 pin to both
regulate the output voltage and to provide a high speed
overvoltage lockout to avoid high voltage output condi
-
tions. If the output voltage exceeds 125% of the regulated
voltage level (1.5
V at the FB0 pin), the LTM8001 terminates
switching and shuts down switching for a brief period. The
output voltage at which output overvoltage protection en
-
gages must be greater than 1.5V and is set by the equation:
V
OUT
=1.5V 1+
10k
R
FB0
⎛
⎝
⎜
⎞
⎠
⎟
where R
FB0
is shown in Figure 3.
If the output overvoltage protection engages, the LTM8001
will stop switching. If this is due to some external power
source connected to V
OUT0
, this source will be free to pull
up V
OUT0
. If the V
OUT0
voltage exceeds the V
IN0
input, an
internal power diode will clamp the output to a diode drop
above the input.
LTM8001
V
OUT
V
OUT
R
FB0
8001 F03
FB0
Figure 3. Voltage Regulation and Overvoltage
Protection Feedback Connections
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LTM8001IY#PBF

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Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 36VIN, 5A Module Regulator with 5-Output Configurable LDO Array
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