LTC3416 Linear Technology, LTC3416 Datasheet - Page 12

• Manufacturer Part Number: LTC3416
• Description: 4A/ 4MHz/ Monolithic Synchronous Step-Down Regulator
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC3416
in dropout, the heat dissipated may exceed the maximum
junction temperature of the part. If the junction tempera-
ture reaches approximately 150 C, both power switches
will be turned off and the SW node will become high
impedance.
To avoid the LTC3416 from exceeding the maximum
junction 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 tempera-
ture rise is given by:
where P
is the thermal resistance from the junction of the die to the
ambient temperature. For the 20-lead exposed TSSOP
package, the
The junction temperature, T
where T
Note that at higher supply voltages, the junction tempera-
ture is lower due to reduced switch resistance (R
To maximize the thermal performance of the LTC3416, the
Exposed Pad should be soldered to a ground plane.
Checking Transient Response
The regulator loop response can be checked by looking at
the load transient response. Switching regulators take
several cycles to respond to a step in load current.
When a load step occurs, V
amount equal to I
series resistance of C
discharge C
the regulator to return V
During this recovery time, V
overshoot or ringing that would indicate a stability prob-
lem. The I
tor shown in figure 1a will provide adequate compensation
for most applications.
12
T
T
R
J
= T
= (P
D
A
A
is the power dissipated by the regulator and
is the ambient temperature.
TH
D
+ T
)(
OUT
pin external components and output capaci-
R
JA
JA
generating a feedback error signal used by
)
is 38 C/W.
LOAD
U
OUT
(ESR), where ESR is the effective
. I
U
OUT
OUT
J
LOAD
, is given by:
OUT
to its steady-state value.
immediately shifts by an
also begins to charge or
can be monitored for
W
U
DS(ON)
JA
).
Design Example
As a design example, consider using the LTC3416 in an
application with the following specifications: V
V
f = 1MHz. V
and powering down.
First, calculate the timing resistor:
Use a standard value of 294k . Next, calculate the induc-
tor values for about 40% ripple current:
Using a 0.47 H inductor for both results in maximum
ripple currents of:
C
required to satisfy the output voltage ripple requirement
and the bulk capacitance needed for loop stability. For this
design, two 100 F ceramic capacitors will be used at each
output.
C
rating of:
OUT1
OUT1
IN1
I
I
R
L
L
RMS
RMS
1
2
OSC
I
I
and C
L
L
= 1.8V, V
1
2
and C
1
2
1
1
MHz
MHz
3 08 10
IN2
4
OUT1
1
4
1
OUT2
MHz
.
A
MHz
A
1 8
1 10
2 5
.
.
•
should be sized for a maximum current
OUT2
• .
1 8
3 3
• .
2 5
3 3
and V
•
V
1 6
1 8
V
will be selected based on the ESR that is
.
.
1 6
2 5
.
.
• .
.
• .
.
6
0 47
V
V
0 47
V
V
A
V
= 2.5V, I
11
V
A
OUT2
–
1 8
3 3
1
3 3
2 5
1
10
H
.
H
.
.
.
–
–
must track when powering up
V
V
k
1 8
V
V
3 3
2 5
3 3
OUT1(MAX)
.
.
1
.
.
1
–
–
–
V
V
–
298
1 1 99
V
V
1 1 71
w w w . D a t a S h e e t 4 U . c o m
1 8
3 3
2 5
3 3
.
.
.
.
k
V
V
V
V
.
0 51
.
0 38
.
= I
.
A
A
OUT2(MAX)
RMS
RMS
1 74
1 29
H
.
H
.
IN
A
A
= 3.3V,
= 4A,
3416f