LTC3411EMS#TRPBF Linear Technology, LTC3411EMS#TRPBF Datasheet - Page 16

• Manufacturer Part Number: LTC3411EMS#TRPBF
• Description: IC CONV DC/DC SYNC STPDWN 10MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3411EMS#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 5 V
• Current - Output: 1.25A
• Frequency - Switching: 1MHz
• Voltage - Input: 2.63 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
LTC3411
To avoid the LTC3411 from exceeding the maximum junc-
tion temperature, the user will need to do some thermal
analysis. The goal of the thermal analysis is to determine
whether the power dissipated exceeds the maximum
junction temperature of the part. The temperature rise is
given by:
where P
is the thermal resistance from the junction of the die to
the ambient temperature.
The junction temperature, T
As an example, consider the case when the LTC3411 is
in dropout at an input voltage of 3.3V with a load current
of 1A. From the Typical Performance Characteristics
graph of Switch Resistance, the R
P-channel switch is 0.11Ω. Therefore, power dissipated
by the part is:
The MS10 package junction-to-ambient thermal resistance,
θ
the junction temperature of the regulator operating in a
70°C ambient temperature is approximately:
Remembering that the above junction temperature is
obtained from an R
the junction temperature based on a higher R
it increases with temperature. However, we can safely as-
sume that the actual junction temperature will not exceed
the absolute maximum junction temperature of 125°C.
16
JA
P
T
, will be in the range of 100°C/W to 120°C/W. Therefore,
J
D
= 0.11 • 120 + 70 = 83.2°C
= I
T
D
T
2
RISE
J
is the power dissipated by the regulator and θ
• R
= T
DS(ON)
= P
RISE
D
+ T
• θ
DS(ON)
= 110mW
AMBIENT
JA
at 25°C, we might recalculate
J
, is given by:
DS(ON)
resistance of the
DS(ON)
since
JA
Design Example
As a design example, consider using the LTC3411 in a por-
table application with a Li-Ion battery. The battery provides
a V
in active mode and 10mA in standby mode. The output
voltage is V
standby, Burst Mode operation is selected for good low
load effi ciency.
First, calculate the timing resistor:
Use a standard value of 324k. Next, calculate the inductor
value with 40% ripple current which is 500mA :
Choosing the closest inductor from a vendor of 2.2μH,
results in a maximum ripple current of:
For cost reasons, a ceramic capacitor will be used. C
selection is then based on load step droop instead of ESR
requirements. For a 5% output droop:
The closest standard value is 22μF . Since the output
impedance of a Li-Ion battery is very low, C
10μF . In noisy environments, decoupling SV
with an R6/C8 fi lter of 1Ω/0.1μF may help, but is typically
not needed.
R
L
C
IN
Δ =
T
=
OUT
I
L
= 2.5V to 4.2V. The load requires a maximum of 1A
=
1
MHz
9 78 10 1
≈
1
.
MHz
OUT
2 5
2 5
.
•
.
2 5
•
500
.
1
V
= 2.5V. Since the load still needs power in
• .
MHz
V
2 2
11
mA
(
μ
• ( %• . )
MHz
•
•
1
5
⎛
⎝ ⎜
⎛
⎜
⎝
A
1
1
−
)
−
−
2 5
4 2
2 5
1 08
2 5
4 2
.
.
.
.
.
V
V
V
V
V
=
⎞
⎠ ⎟
⎞
⎟ =
⎠
=
323 8
= μ
20
2
460
.
μ
H
F
k
mA
IN
IN
is typically
from PV
3411fb
OUT
IN