Datasheet
LT3976
24
3976f
For more information www.linear.com/3976
applicaTions inForMaTion
and a SYNC pin resistor to GND added, so that a PG pin
short to either SYNC or RT will form resistor dividers to
keep the voltage on the SYNC and RT pins below their
rated absolute maximum. This application is shown in
Figure 12b. The external Schottky must be connected
such that the absolute maximum of the BOOST pin is not
violated. The SYNC pin resistor can be removed if the
SYNC pin is grounded or PG is left floating both of which
also result in fault tolerant circuits.
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.
V
IN
EN
BOOST
V
IN
SYNC
EXTERNAL
INPUT
0.47µF
470pF
47µF
1210
×2
3976 F12a
10nF
10µF
f = 800kHz
34.9k
V
OUT
PGOOD
3.3µH
1M
10pF
LT3976
SS
RT
SW
OUT
FB
PG
GND
150k
2Ω
316k
V
IN
EN
BOOST
V
IN
SYNC
EXTERNAL
INPUT
0.47µF
47µF
1210
×2
3976 F12b
10nF
10µF
f = 800kHz
54.9k
V
OUT
PGOOD
3.3µH
1M
10pF
LT3976
SS
RT
SW
OUT
FB
PG
GND
249k
316k
40.2k
470pF
2Ω
Figure 12a. Fault Tolerant for V
OUT
< 6V
(Note: For V
OUT
< 3.3V External Boost Schottky Diode Is Needed)
Figure 12b. Fault Tolerant for V
OUT
< 27V
(Note: For V
OUT
< 3V External Boost Schottky Diode
Should Be Connected to the Input)
Figure 12. Tw o Example Circuits to Achieve Fault Tolerance (FMEA) with the LT3976 QFN Package