lt3991 Linear Technology Corporation, lt3991 Datasheet - Page 19

• Manufacturer Part Number: lt3991
• Description: 55v, 1.2a Step-down Regulator With 2.8?a Quiescent Current
• Manufacturer: Linear Technology Corporation

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 fi lter 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
6.6V TO 55V
4.3V TO 55V
V
V
IN
IN
OFF ON
OFF ON
4.7μF
4.7μF
118k
162k
f = 400kHz
f = 300kHz
5V Step-Down Converter
2.5V Step-Down Converter
EN
EN
PG
SS
RT
PG
SS
RT
SYNC
V
SYNC
V
IN
IN
LT3991
LT3991
GND
GND
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.
BOOST
BOOST
SW
SW
BD
BD
FB
FB
309k
909k
1μF
0.47μF
10pF
10pF
10μH
10μH
1M
1M
47μF
47μF
3991 TA03
3991 TA02
V
2.5V
1.2A
V
5V
1.2A
OUT
OUT
LT3991
19
3991f