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LTM8025IV#PBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22
LTM8025
10
8025fc
For more information www.linear.com/LTM8025
applicaTions inForMaTion
For most applications, the design process is straight
forward, summarized as follows:
1. Look at Table 1 and find the row that has the desired
input range and output voltage.
2. Apply the recommended C
IN
, C
OUT
, R
ADJ
and R
T
values.
3. Connect BIAS as indicated.
While these component combinations have been tested
for proper operation, it is incumbent upon the user to
verify proper operation over the intended system’s line,
load and environmental conditions. Bear in mind that the
maximum output current is limited by junction tempera
-
turetemperature, the relationship between the input and
output voltage magnitude and polarity and other factors.
Please refer
to the graphs in the Typical Performance
Characteristics section for guidance.
The maximum frequency (and attendant R
T
value) at
which the LTM8025 should be allowed to switch is given
in Table 1 in the f
MAX
column, while the recommended
frequency (and R
T
value) for optimal efficiency over the
given input condition is given in the f
OPTIMAL
column.
There are additional conditions that must be satisfied if
the synchronization function is used. Please refer to the
Synchronization section for details.
Capacitor Selection Considerations
The C
IN
and C
OUT
capacitor values in Table 1 are the
minimum recommended values for the associated oper-
ating conditions. Applying capacitor values below those
indicated in T
able 1 is not recommended, and may result
in undesirable operation. Using larger values is generally
acceptable, and can yield improved dynamic response, if
it is necessar
y. Again, it is incumbent upon the user to
verify proper operation over the intended system’s line,
load and environmental conditions.
Ceramic capacitors are small, robust and have very low
ESR. However, not all ceramic capacitors are suitable.
X5R and X7R types are stable over temperature and ap
-
plied voltage and give dependable service. Other types,
including Y5V and Z5U have very large temperature and
voltage coefficients of capacitance. In an application cir
-
cuit they may have only a small fraction of their nominal
capacitance resulting in much higher output voltage ripple
than expected.
Ceramic capacitors are also piezoelectric.
In Burst Mode
operation, the LTM8025’s switching frequency depends
on the load current, and can excite a ceramic capacitor
at audio frequencies, generating audible noise. Since the
LTM8025 operates at a lower current limit during Burst
Mode operation, the noise is typically very quiet to a
casual ear.
If this audible noise is unacceptable, use a high perfor
-
mance electrolytic capacitor at the output. It may also be
a parallel combination of a ceramic capacitor and a low
cost electrolytic capacitor
.
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the L
TM8025. A
ceramic input capacitor combined with trace or cable
inductance forms a high Q (under damped) tank circuit.
If the LTM8025 circuit is plugged into a live supply, the
input voltage can ring to twice its nominal value, possi
-
bly exceeding the device’s rating. This situation is easily
avoided; see the Hot-Plugging Safely section.
Frequency Selection
The LTM8025 uses a constant frequency PWM architecture
that can be programmed to switch from 200kHz to 2.4MHz
by using a resistor tied from the RT pin to ground. Table 2
provides a list of R
T
resistor values and their resultant
frequencies.
LTM8025
11
8025fc
For more information www.linear.com/LTM8025
applicaTions inForMaTion
Table 1: Recommended Component Values and Configuration (T
A
= 25°C)
V
IN
V
OUT
C
IN
C
OUT
R
ADJ
BIAS f
OPTIMAL
R
T(OPTIMAL)
f
MAX
R
T(MIN)
3.6V to 36V 0.8V 10µF, 50V, 1210
4× 100µF, 6.3V, 1210
Open 2.8V to 25V 230kHz 182k 250kHz 169k
3.6V to 36V 1V 10µF, 50V, 1210
4× 100µF, 6.3V, 1210
1.87M 2.8V to 25V 240kHz 174k 285kHz 147k
3.6V to 36V 1.2V 10µF, 50V, 1210
4× 100µF, 6.3V, 1210
953k 2.8V to 25V 255kHz 162k 315kHz 130k
3.6V to 36V 1.5V 10µF, 50V, 1210
4× 100µF, 6.3V, 1210
549k 2.8V to 25V 270kHz 154k 360kHz 113k
3.6V to 36V 1.8V 10µF, 50V, 1210
3× 100µF, 6.3V, 1210
383k 2.8V to 25V 285kHz 147k 420kHz 95.3k
4.1V to 36V 2.5V 4.7µF, 50V, 1206
2× 100µF, 6.3V, 1210
226k 2.8V to 25V 300kHz 137k 540kHz 71.5k
5.3V to 36V 3.3V 4.7µF, 50V, 1206 100µF, 6.3V, 1210 154k AUX 345kHz 118k 675kHz 54.9k
7.5V to 36V 5V 4.7µF, 50V, 1206 100µF, 6.3V, 1206 93.1k AUX 425kHz 93.1k 950kHz 36.5k
10.5V to 36V 8V 4.7µF, 50V, 1206 47µF, 16V, 1210 54.9k AUX 550kHz 69.8k 1.45MHz 20.5k
16V to 36V 12V 2.2µF, 50V, 1206 22µF, 16V, 1210 34.8k AUX 760kHz 47.5k 2.3MHz 9.09k
23V to 36V 18V 2.2µF, 50V, 1206 22µF, 25V, 1812 22.6k AUX 800kHz 44.2k 2.4MHz 8.25k
31V to 36V 24V 1µF, 50V, 1206 22µF, 25V, 1812 16.5k 2.8V to 25V 1MHz 34k 2.4MHz 8.25k
3.6V to 15V 0.8V 10µF, 25V, 1210
4× 100µF, 6.3V, 1210
Open V
IN
230kHz 182k 575kHz 66.5k
3.6V to 15V 1V 10µF, 25V, 1210
4× 100µF, 6.3V, 1210
1.87M V
IN
240kHz 174k 660kHz 56.2k
3.6V to 15V 1.2V 10µF, 25V, 1210
4× 100µF, 6.3V, 1210
953k V
IN
255kHz 162k 760kHz 47.5k
3.6V to 15V 1.5V 10µF, 25V, 1210
4× 100µF, 6.3V, 1210
549k V
IN
270kHz 154k 840kHz 42.2k
3.6V to 15V 1.8V 10µF, 25V, 1210
4× 100µF, 6.3V, 1210
383k V
IN
285kHz 147k 1.0MHz 34k
4.1V to 15V 2.5V 4.7µF, 16V, 1206
2× 100µF, 6.3V, 1210
226k V
IN
300kHz 137k 1.3MHz 23.7k
5.3V to 15V 3.3V 4.7µF, 16V, 1206 100µF, 6.3V, 1206 154k AUX 345kHz 118k 1.6MHz 17.8k
7.5V to 15V 5V 4.7µF, 16V, 1206 100µF, 6.3V, 1206 93.1k AUX 425kHz 93.1k 2.4MHz 8.25k
10.5V to 15V 8V 2.2µV, 25V, 1206 47µF, 16V, 1210 54.9k AUX 550kHz 69.8k 2.4MHz 8.25k
9V to 24V 0.8V 4.7µF, 25V, 1206
4× 100µF, 6.3V, 1210
Open V
IN
270kHz 154k 360kHz 113k
9V to 24V 1V 4.7µF, 25V, 1206
4× 100µF, 6.3V, 1210
1.87M V
IN
285kHz 147k 410kHz 97.6k
9V to 24V 1.2V 4.7µF, 25V, 1206
4× 100µF, 6.3V, 1210
953k V
IN
295kHz 140k 475kHz 82.5k
9V to 24V 1.5V 4.7µF, 25V, 1206
4× 100µF, 6.3V, 1210
549k V
IN
310kHz 133k 550kHz 69.8k
9V to 24V 1.8V 4.7µF, 25V, 1206
3× 100µF, 6.3V, 1210
383k V
IN
330kHz 124k 620kHz 60.4k
9V to 24V 2.5V 4.7µF, 25V, 1206 100µF, 6.3V, 1206 226k V
IN
345kHz 118k 800kHz 44.2k
9V to 24V 3.3V 4.7µF, 25V, 1206 100µF, 6.3V, 1206 154k AUX 425kHz 93.1k 1MHz 34k
9V to 24V 5V 4.7µF, 25V, 1206 47µF, 16V, 1210 93.1k AUX 500kHz 76.8k 1.4MHz 21.5k
10.5V to 24V 8V 2.2µF, 25V, 1206 22µF, 16V, 1210 54.9k AUX 590kHz 64.9k 2.2MHz 9.76k
16V to 24V 12V 2.2µF, 50V, 1206 22µF, 16V, 1210 34.8k AUX 760kHz 47.5k 2.3MHz 9.09k
23V to 24V 18V 2.2µF, 50V, 1206 22µF, 25V, 1812 22.6k AUX 800kHz 44.2k 2.4MHz 8.25k
18V to 36V 0.8V 1µF, 50V, 1206
4× 100µF, 6.3V, 1210
Open 2.8V to 25V 230kHz 182k 250kHz 169k
18V to 36V 1V 1µF
, 50V, 1206
4× 100µF, 6.3V, 1210
1.87M 2.8V to 25V 240kHz 174k 285kHz 147k
18V to 36V 1.2V 1µF, 50V, 1206
4× 100µF, 6.3V, 1210
953k 2.8V to 25V 255kHz 162k 315kHz 130k
18V to 36V 1.5V 1µF, 50V, 1206
4× 100µF, 6.3V, 1210
549k 2.8V to 25V 270kHz 154k 360kHz 113k
18V to 36V 1.8V 1µF, 50V, 1206
3× 100µF, 6.3V, 1210
383k 2.8V to 25V 300kHz 137k 420kHz 95.3k
18V to 36V 2.5V 1µF, 50V, 1206 100µF, 6.3V, 1206 226k 2.8V to 25V 345kHz 118k 540kHz 71.5k
18V to 36V 3.3V 1µF, 50V, 1206 100µF, 6.3V, 1206 154k AUX 385kHz 105k 675kHz 54.9k
18V to 36V 5V 1µF, 50V, 1206 47µF, 16V, 1210 93.1k AUX 500kHz 76.8k 950kHz 36.5k
18V to 36V 8V 2.2µF, 50V, 1206 22µF, 16V, 1210 54.9k AUX 550kHz 69.8k 1.45MHz 20.5k
18V to 36V 12V 2.2µF, 50V, 1206 22µF, 16V, 1210 34.8k AUX 760kHz 47.5k 2.3MHz 9.09k
4.75V to 32V –3.3V 4.7µF, 50V, 1206 100µF, 6.3V, 1210 154k AUX 345kHz 118k 675kHz 54.9k
7V to 31V –5V 4.7µF, 50V, 1206 100µF, 6.3V, 1210 93.1k AUX 425kHz 93.1k 950kHz 36.5k
15V to 28V –8V 4.7µF, 50V, 1206 47µF, 16V, 1210 54.9k AUX 550kHz 69.8k 1.45MHz 20.5k
20V to 24V –12V 4.7µF, 50V, 1206 22µF, 16V, 1210 34.8k AUX 760kHz 47.5k 2.3MHz 9.09k
Note: An input bulk capacitance is required. Do not allow V
IN
+ BIAS to exceed 56V. Refer to the Typical Performance Characteristics section for load conditions.
LTM8025
12
8025fc
For more information www.linear.com/LTM8025
applicaTions inForMaTion
Table 2. Switching Frequency vs R
T
Value
SWITCHING FREQUENCY R
T
VALUE
0.2MHz 215kΩ
0.3MHz 137kΩ
0.4MHz 100kΩ
0.5MHz 76.8kΩ
0.6MHz 63.4kΩ
0.7MHz 52.3kΩ
0.8MHz 44.2kΩ
0.9MHz 38.3kΩ
1MHz 34.0kΩ
1.2MHz 26.7kΩ
1.4MHz 21.5kΩ
1.6MHz 17.8kΩ
1.8MHz 14.7kΩ
2MHz 12.1kΩ
2.2MHz 9.76kΩ
2.4MHz 8.25kΩ
Operating Frequency Tradeoffs
It is recommended that the user apply the optimal R
T
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
LTM8025 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
LTM8025 if the output is overloaded or short circuited. 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.
BIAS Pin Considerations
The BIAS pin is used to provide drive power for the in
-
ternal power switching stage and operate other internal
cir
cuitr
y. For proper operation, it must be powered by at
least 2.8V. If the output voltage is programmed to 2.8V
or higher, BIAS may be simply tied to AUX. If V
OUT
is less
than 2.8V, BIAS can be tied to V
IN
or some other voltage
source. If the BIAS pin voltage is too high, the efficiency
of the LTM8025 may suffer. The optimum BIAS voltage is
dependent upon many factors, such as load current, input
voltage, output voltage and switching frequency, but 4V to
5V works well in many applications. In all cases, ensure
that the maximum voltage at the BIAS pin is less than 25V
and that the sum of V
IN
and BIAS is less than 56V. If BIAS
power is applied from a remote or noisy voltage source, it
may be necessary to apply a decoupling capacitor locally
to the pin.
Load Sharing
Two or more LTM8025’s may be paralleled to produce higher
currents. To do this, tie the V
IN
, ADJ, V
OUT
and SHARE
pins of all the paralleled LTM8025’s together. To ensure
that paralleled modules start up together, the RUN/SS pins
may be tied together, as well. If the RUN/SS pins are not
tied together, make sure that the same valued soft-start
capacitors are used for each module. Current sharing can
be improved by synchronizing the LTM8025s. An example
of two LTM8025s configured for load sharing is given in
the Typical Applications section.
Burst Mode Operation
To enhance efficiency at light loads, the LTM8025 auto
-
matically switches to Burst Mode operation which keeps
the output capacitor charged to the proper voltage while
minimizing the input quiescent current. During Burst Mode
operation, the L
TM8025 delivers single cycle bursts of
current to the output capacitor followed by sleep periods
where the output power is delivered to the load by the output
capacitor. In addition, V
IN
and BIAS quiescent currents are
each reduced to microamps during the sleep time. As the
load current decreases towards a no load condition, the
percentage of time that the LTM8025 operates in sleep
mode increases and the average input current is greatly
reduced, resulting in higher efficiency.
Burst Mode operation is enabled by tying SYNC to GND.
To disable Burst Mode operation, tie SYNC to a stable
voltage above 0.7V. Do not leave the SYNC pin floating.
Minimum Input Voltage
The LTM8025 is a step-down converter, so a minimum
amount of headroom is required to keep the output in
regulation. In addition, the input voltage required to turn
on is higher than that required to run, and depends upon
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22

LTM8025IV#PBF

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Description:
Switching Voltage Regulators 36V, 3A Buck Module Conv
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