lt1941 Linear Technology Corporation, lt1941 Datasheet - Page 20

• Manufacturer Part Number: lt1941
• Description: Triple Monolithic Switching Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT1941
temperature. The output current capability of the third
channel can be calculated from the output currents and
voltages of the other channels, the switching regulator
efficiency (η), the ambient temperature (T
mum junction temperature (T
resistance from junction to ambient (θ
Example: LT1941 at V1 = 2.5V, I
V3 = 12V, η = 80%, T
25°C/W:
20
P
P
I
3
P
P
I
3
DISS
3
DISS
3
=
=
=
=
Power Output Capability for P
1 7
P
12
V
1 0 8
.
P
=
1
=
3
3
– .
2
Figure 9. Power Output Capability of an Individual Channel Depends on the Output Power of the Other Channels
DISS
–
W
V
125
W
6
5
1
0
4
3
2
T
η
0
JMAX
=
25
–
°
CHANNEL 1 OUTPUT POWER (WATTS)
θ
– .
0 141
C
P3 = 6W
°
JA
V I
.
1
2 5
C W
–
1
–
U
/
75
• –
T
V
P3 = 4W
A
A
1
2
°
•
A
CHANNEL 3
OUTPUT POWER (P3)
P3 = 2W
C
2
= 75°C, T
U
V
=
A
2
3
2
– .
•
W
3 3
I
2
1
JMAX
4
DISS
= 2A, V2 = 3.3V, I
V
W
JMAX
•
= 2W, η = 0.75
1
) and the thermal
5
A
1941 F09a
JA
=
= 125°C, θ
) as follows:
1 7
6
.
A
), the maxi-
W
U
2
= 1A,
JA
=
Note that decreasing θ
capability. The power output capability of the individual
channels can be calculated from the following:
Channel 1 Output Power (P1) = V1 • I
Channel 2 Output Power (P2) = V2 • I
Channel 3 Output Power (P3) = V3 • I
Total Output Power (P123) = P
Figure 9 shows power output capability if overall system
efficiency (η) is 75% and maximum allowable power
dissipation (P
allowable power dissipation is 2W, Channel 3 output
power is 2W and Channel 2 output power is 1W, then
Channel 1 output power can be up to 5W.
RELATED LINEAR TECHNOLOGY PUBLICATIONS
Application notes 19, 35, 44, 76 and 88 contain more
detailed descriptions and design information for buck
regulators and other switching regulators. The LT1375
data sheet has a more extensive discussion of output
ripple, loop compensation, and stability testing. Design
Notes 100 and 318 show how to generate a dual polarity
output supply using a buck regulator.
Power Output Capability for P
3.0
2.5
2.0
1.5
1.0
0.5
0
0
DISS
CHANNEL 1 OUTPUT POWER (WATTS)
P3 = 3W
) is either 1W or 2W. For example, if
P3 = 2W
1
CHANNEL 3
OUTPUT POWER (P3)
P3 = 1W
JA
increases the power output
DISS
DISS
2
/η = P1 + P2 + P3
= 1W, η = 0.75
1
2
3
1941 F09b
3
1941fa