LT1767 Datasheet, PDF (12/16 Pages) Linear Technology – Monolithic 1.5A, 1.25MHz Step-Down Switching Regulators

LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
D2
CMDSH-3
V_IN
12V _C3
2.2µF
CERAMIC
OPEN
OR
HIGH
= ON
C2
0.1µF
BOOST
V_IN
V_SW
LT1767-2.5
SHDN
FB
SYNC GND V_C
C_C
1.5nF
R_C
4.7k
L1
5µH
D1
UPS120
OUTPUT
2.5V
1.2A
C1
10µF
CERAMIC
1767 F06a
C3
V_IN
MINIMIZE LT1767,
C3, D1 LOOP
D2
C2
GND
PLACE FEEDTHROUGHS
AROUND GROUND PIN
AND UNDER GROUND PAD
FOR GOOD THERMAL
CONDUCTIVITY
SYNC
SHDN
KEEP FB AND V_C
COMPONENTS
AWAY FROM
HIGH INPUT
COMPONENTS
D1
C_C
L1
R_C
V_OUT
C1 _GND
CONNECT TO
GROUND PLANE
KELVIN SENSE
V_OUT
1767 F06
Figure 6. Typical Application and Suggested Layout (Topside Only Shown)
Total power dissipation is 0.34 + 0.05 + 0.01 = 0.4W.
Thermal resistance for LT1767 package is influenced by
the presence of internal or backside planes. With a full
plane under the package, thermal resistance for the
exposed pad package will be about 40°C/W. No plane will
increase resistance to about 150°C/W. To calculate die
temperature, use the appropriate thermal resistance
number and add in worst-case ambient temperature:
T_J = T_A + θ_JA (P_TOT)
When estimating ambient, remember the nearby catch
diode and inductor will also be dissipating power.
( )( )( ) ^VF ^VIN ^{− V}OUT ^ILOAD
P_DIODE =
V_IN
V_F = Forward voltage of diode (assume 0.5V at 1A)
(^0.5)(^{12 − 5})(¹)
P_DIODE =
12
= 0.29W
12
sn1767 1767fas