LTM8021IV#PBF Linear Technology, LTM8021IV#PBF Datasheet - Page 10

• Manufacturer Part Number: LTM8021IV#PBF
• Description: IC DC/DC UMODULE 500MA 35-LGA
• Manufacturer: Linear Technology
• Series: µModuler
• Type: Point of Load (POL) Non-Isolatedr

Specifications of LTM8021IV#PBF

• Design Resources: LTM8021 Spice Model
• Output: 0.8 ~ 5 V
• Number Of Outputs: 1
• Power (watts): 2.5W
• Mounting Type: Surface Mount
• Voltage - Input: 3 ~ 36 V
• Package / Case: 35-LGA
• 1st Output: 0.8 ~ 5 VDC @ 500mA
• Size / Dimension: 0.44" L x 0.25" W x 0.11" H (11.25mm x 6.25mm x 2.82mm)
• Power (watts) - Rated: 2.5W
• Operating Temperature: -40°C ~ 125°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• 3rd Output: -
• 2nd Output: -

LTM8021
APPLICATIONS INFORMATION
Soft-Start
The RUN/SS pin can be used to soft-start the LTM8021,
reducing the maximum input current during start-up.
The RUN/SS pin is driven through an external RC fi lter
to create a voltage ramp at this pin. Figure 2 shows the
soft-start circuit. By choosing a large RC time constant,
the peak start-up current can be reduced to the current
that is required to regulate the output, with no overshoot.
Choose the value of the resistor so that it can supply 80μA
when the RUN/SS pin reaches 2V.
10
Figure 2. To Soft-Start the LTM8021, Add a
Resisitor and Capacitor to the RUN/SS Pin
0.22μF
RUN
15k
RUN/SS
GND
8021 F02
Shorted Input Protection
Care needs to be taken in systems where the output will
be held high when the input to the LTM8021 is absent.
This may occur in battery charging applications or in
battery backup systems where a battery or some other
supply is diode ORed with the LTM8021’s output. If the
V
(either by a logic signal or because it is tied to V
the LTM8021’s internal circuitry will pull its quiescent
current through its internal power switch. This is fi ne if
your system can tolerate a few milliamps in this state. If
the RUN/SS pin is grounded, the internal power switch
current will drop to essentially zero. However, if the V
is grounded while the output is held high, then parasitic
diodes inside the LTM8021 can pull large currents from
the output through the internal power switch and the V
pin. Figure 3 shows a circuit that will run only when the
input voltage is present and that protects against a shorted
or reversed input.
Figure 3. The Input Diode Prevents a Shorted Input from
Discharging a Backup Battery Tied to the Output. It Also Protects
the Circuit from a Reversed Input. The LTM8021 Runs Only When
the Input is Present
IN
pin is allowed to fl oat and the RUN/SS pin is held high
4V TO 36V
V
IN
C
IN
V
RUN/SS
IN
GND
LTM8021
RT
V
BIAS
OUT
R
ADJ
8021 F03
C
V
IN
OUT
OUT
), then
IN
8021fc
pin
IN