LT3980EDE#TRPBF Linear Technology, LT3980EDE#TRPBF Datasheet - Page 9

• Manufacturer Part Number: LT3980EDE#TRPBF
• Description: IC SWITCHING REG STP-DN 2A 14DFN
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT3980EDE#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.79 ~ 52.2 V
• Current - Output: 2A
• Frequency - Switching: 100kHz ~ 2.4MHz
• Voltage - Input: 3.6 ~ 58 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 14-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis-
tors according to:
Reference designators refer to the Block Diagram.
Setting the Switching Frequency
The LT3980 uses a constant frequency PWM architecture
that can be programmed to switch from 100kHz to 2.4MHz
by using a resistor tied from the RT pin to ground. A table
showing the necessary RT value for a desired switching
frequency is in Figure 1.
Operating Frequency Trade-Offs
Selection of the operating frequency is a trade-off between
effi ciency, component size, minimum dropout voltage, and
maximum input voltage. The advantage of high frequency
operation is that smaller inductor and capacitor values may
be used. The disadvantages are lower effi ciency, lower
maximum input voltage, and higher dropout voltage. The
highest acceptable switching frequency (f
given application can be calculated as follows:
R
f
SW MAX
SWITCHING FREQUENCY (MHz)
1
=
(
R
2
Figure 1. Switching Frequency vs R
⎛
⎜
⎝
)
0 79
=
V
.
OUT
t
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.2
1.4
1.6
1.8
2.0
ON MIN
V
(
–
1
)
⎞
⎟
⎠
V
(
D
V
+
D
+
V
OUT
V
IN
–
V
SW
R
)
T
T
VALUE (kΩ)
Value
SW(MAX)
97.6
76.8
60.4
51.1
43.2
35.7
32.4
24.9
16.2
432
215
137
20
14
11
) for a
where V
voltage, V
internal switch drop (~0.5V at max load). This equation
shows that slower switching frequency is necessary to
safely accommodate high V
in the next section, lower frequency allows a lower dropout
voltage. The reason input voltage range depends on the
switching frequency is because the LT3980 switch has
fi nite minimum on and off times. The switch can turn on
for a minimum of ~200ns and turn off for a minimum of
~200ns. This means that the minimum and maximum
duty cycles are:
where f
minimum switch on time (~200ns), and the t
the minimum switch off time (~200ns). These equations
show that duty cycle range increases when switching
frequency is decreased.
A good choice of switching frequency should allow ad-
equate input voltage range (see next section) and keep
the inductor and capacitor values small.
Input Voltage Range
The maximum input voltage for LT3980 applications de-
pends on switching frequency, Absolute Maximum Ratings
of the V
The LT3980 can operate from input voltages of up to 58V,
and withstand voltages up to 80V. Note that while V
above 61V typical (58V minimum and 64V maximum)
the part will keep the switch off and the output will not
be in regulation.
The switching frequency should be chosen according to
the following equation:
where V
voltage, V
drop (~0.5V), V
DC
DC
V
IN MAX
MIN
MAX
(
SW
IN
IN
IN(MAX)
D
=
OUT
and BOOST pins, and the operating mode.
=
is the typical input voltage, V
is the switching frequency, the t
)
is the catch diode drop (~0.5V) and V
f
=
1–
SW ON MIN
is the output voltage, V
f
SW ON MIN
V
f
t
SW
SW OFF MIN
is the maximum typical operating input
OUT
t
(
t
is the internal switch drop (~0.5V at
+
(
V
)
(
D
)
–
IN
)
V
/ V
D
+
OUT
V
SW
ratio. Also, as shown
D
is the catch diode
OUT
LT3980
ON(MIN)
is the output
OFF(MIN)
SW
is the
is the
IN
9
3980f
is
is