LT3991EMSE-3.3#PBF Linear Technology, LT3991EMSE-3.3#PBF Datasheet - Page 19

• Manufacturer Part Number: LT3991EMSE-3.3#PBF
• Description: IC, DC-DC CONV, 2MHz, MSOP10
• Manufacturer: Linear Technology

Specifications of LT3991EMSE-3.3#PBF

• Primary Input Voltage: 55V
• No. Of Outputs: 1
• Output Voltage: 3.3V
• Output Current: 1.2A
• No. Of Pins: 10
• Operating Temperature Range: -40°C To +125°C
• Peak Reflow Compatible (260 C): Yes
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

6.6V TO 55V
APPLICATIONS INFORMATION
loss. The die temperature is calculated by multiplying the
LT3991 power dissipation by the thermal resistance from
junction to ambient.
Also keep in mind that the leakage current of the power
Schottky diode goes up exponentially with junction tem-
perature. When the power switch is closed, the power
Schottky diode is in parallel with the power converter’s
output filter stage. As a result, an increase in a diode’s
leakage current results in an effective increase in the load,
and a corresponding increase in input power. Therefore,
the catch Schottky diode must be selected with care to
TYPICAL APPLICATIONS
4.3V TO 55V
V
V
IN
IN
OFF ON
4.7µF
4.7µF
OFF ON
118k
f = 400kHz
3.3V Step-Down Converter
118k
5V Step-Down Converter
f = 400kHz
EN
PG
SS
RT
EN
PG
SS
RT
SYNC
V
IN
LT3991
SYNC
LT3991
GND
V
IN
BOOST
GND
SW
BOOST
BD
FB
SW
BD
FB
309k
0.47µF
10pF
1M
0.47µF
1.78M
10µH
1M
47µF
10µH
3991 TA02
10pF
3991 TA09
V
5V
1.2A
OUT
V
3.3V
1.2A
47µF
OUT
4.3V TO 55V
6.6V TO 55V
avoid excessive increase in light load supply current at
high temperatures.
Other Linear Technology Publications
Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 318
shows how to generate a bipolar output supply using a
buck regulator.
LT3991/LT3991-3.3/LT3991-5
V
V
IN
IN
OFF ON
OFF ON
4.7µF
4.7µF
162k
118k
f = 300kHz
f = 400kHz
2.5V Step-Down Converter
5V Step-Down Converter
EN
PG
SS
RT
EN./UVLO
PG
SS
RT
SYNC
V
SYNC
IN
LT3991
LT3991-5
V
IN
GND
GND
BOOST
BOOST
V
SW
BD
OUT
FB
SW
BD
909k
1µF
10pF
0.47µF
10µH
15µH
1M
47µF
47µF
3991 TA10
3991 TA03
19
3991fa
V
2.5V
1.2A
V
5V
1.2A
OUT
OUT