LTM8027IV#PBF Linear Technology, LTM8027IV#PBF Datasheet - Page 12

• Manufacturer Part Number: LTM8027IV#PBF
• Description: IC BUCK SYNC ADJ 4A 113LGA
• Manufacturer: Linear Technology
• Series: µModuler
• Type: Point of Load (POL) Non-Isolatedr

Specifications of LTM8027IV#PBF

• Design Resources: LTM8027 Spice Model
• Output: 2.5 ~ 24 V
• Number Of Outputs: 1
• Power (watts): 96W
• Mounting Type: Surface Mount
• Voltage - Input: 4.5 ~ 60 V
• Package / Case: 113-LGA
• 1st Output: 2.5 ~ 24 VDC @ 4A
• Size / Dimension: 0.59" L x 0.59" W x 0.17" H (15mm x 15mm x 4.32mm)
• Power (watts) - Rated: 96W
• Operating Temperature: -40°C ~ 125°C
• Efficiency: 95%
• Primary Input Voltage: 60V
• No. Of Outputs: 1
• Output Voltage: 24V
• Output Current: 4A
• No. Of Pins: 113
• Operating Temperature Range: -40°C To +125°C
• Voltage Regulator Type: Buck DC/DC Converter
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• 3rd Output: -
• 2nd Output: -

LTM8027
APPLICATIONS INFORMATION
For example, suppose the LTM8027 needs to provide 5V
from an input voltage source that is nominally 12V. From
Table 2, the recommended R
responds to an operating frequency of 210kHz. From the
graphs in the Typical Performance Characteristics, the
typical internal regulator (INTV
210kHz is 15mA. The power dissipated by the internal
linear regulator at 12V
or only 60mW. This has a small but probably acceptable
effect on the operating temperature of the LTM8027.
If the input rises to 60V, however, the power dissipation is
a lot higher, over 780mW. This can cause unnecessarily
high junction temperatures if the INTV
dissipate this amount of power for very long.
Soft-Start
The soft-start function controls the slew rate of the power
supply output voltage during start-up. A controlled output
voltage ramp minimizes output voltage overshoot, reduces
inrush current from the V
sequencing. A capacitor connected from the SS pin to GND
programs the slew rate. The capacitor is charged from an
internal 2µA current source producing a ramped voltage
that overrides the command reference to the controller,
resulting in a smooth output voltage ramp. The soft-start
circuit is disabled once the SS pin voltage has been charged
to 200mV above the internal reference of 1.231V.
During a V
bias, the SS pin voltage is discharged with a 50µA current.
Therefore, the value of the SS capacitor determines how
long one of these events must be in order to completely
discharge the soft-start capacitor. In the case of an output
overload or short circuit, the SS pin voltage is clamped to
a diode drop above the ADJ pin. Once the short has been
removed the V
start circuit takes control of the output voltage slew rate
once the V
12
P
INTVCC
IN
ADJ
= (V
UVLO, RUN event, or undervoltage on internal
pin voltage has exceeded the slowly ramp-
ADJ
IN
– 8) • I
pin voltage starts to recover. The soft-
IN
INTVCC
is given by the equation:
IN
supply, and facilitates supply
T
value is 162k, which cor-
CC
) current at 12V
CC
regulator must
IN
and
ing SS pin voltage, reducing the output voltage overshoot
during a short-circuit recovery.
The desired soft-start time (t
C
The amount of time in which the power supply must be
under a V
fault condition (t
its active region is approximated by the following formula:
Operating Frequency Tradeoffs
The LTM8027 uses a constant frequency architecture that
can be programmed over a 100kHz to 500kHz range with
a single resistor from the RT pin to ground. The nominal
voltage on the RT pin is 1V and the current that flows from
this pin is used to charge an internal oscillator capacitor.
The value of R
chosen from Figure 1 or Table 1.
SS
C
t
FAULT
capacitor as follows:
SS
=
IN
2µA • t
600
500
400
300
200
100
=
1.231V
, internal regulator (INTV
0
Figure 1. Timing Resistor (R
C
0
SS
T
50µA
for a given operating frequency can be
FAULT
SS
• 0.65V
50
) before the SS pin voltage enters
R
T
100
(k )
SS
) is programmed via the
150
CC
T
) Value
) or V
8027 F01
200
SHDN
UVLO
8027fa