LTC3413 LINER [Linear Technology], LTC3413 Datasheet - Page 10

• Manufacturer Part Number: LTC3413
• Description: 3A, 2MHz Monolithic Synchronous Regulator for DDR/QDR Memory Termination
• Manufacturer: LINER [Linear Technology]

LTC3413
APPLICATIO S I FOR ATIO
high to low to high again, a packet of charge dQ moves
from V
of V
continuous mode, I
are the gate charges of the internal top and bottom
switches. Both the DC bias and gate charge losses are
proportional to V
pronounced at higher supply voltages.
2. I
internal switches, R
tinuous mode the average output current flowing through
inductor L is “chopped” between the main switch and the
synchronous switch. Thus, the series resistance looking
into the SW pin is a function of both top and bottom
MOSFET R
The R
obtained from the Typical Performance Characteristics
curves. Thus, to obtain I
and multiply the result by the square of the average output
current.
Other losses including C
losses and inductor core losses generally account for less
than 2% of the total loss.
Thermal Considerations
In most applications, the LTC3413 does not dissipate
much heat due to its high efficiency.
But, in applications where the LTC3413 is running at high
ambient temperature with low supply voltage and high
duty cycles, such as in dropout, the heat dissipated may
10
R
2
IN
SW
R losses are calculated from the resistances of the
DS(ON)
that is typically larger than the DC bias current. In
IN
= (R
to ground. The resulting dQ/dt is the current out
DS(ON)
DS(ON)TOP
for both the top and bottom MOSFETs can be
IN
and the duty cycle (DC) as follows:
GATECHG
U
SW
and thus their effects will be more
)(DC) + (R
, and external inductor R
2
R losses, simply add R
U
IN
= f(Q
and C
DS(ON)BOT
T
+ Q
W
OUT
B
) where Q
ESR dissipative
)(1 – DC)
U
L
SW
T
. In con-
and Q
to R
B
L
exceed the maximum junction temperature of the part. If
the junction temperature reaches approximately 150 C,
both power switches will be turned off and the SW node
will become high impedance.
To avoid the LTC3413 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.
The junction temperature, T
where T
As an example, consider the LTC3413 in dropout at an
input voltage of 3.3V, a load current of 3A and an ambient
temperature of 70 C. From the Typical Performance graph
of switch resistance, the R
at 70 C is approximately 97m . Therefore, power dissi-
pated by the part is:
For the TSSOP package, the
junction temperature of the regulator is:
which is below the maximum junction temperature of
T
T
P
T
R
J
J
D
= T
= 70 C + (0.87W)(38 C/W) = 103 C
= (P
= (I
D
A
A
LOAD
is the power dissipated by the regulator and
is the ambient temperature.
D
+ T
)(
R
2
JA
)(R
)
DS(ON)
) = (3A)
DS(ON)
J
, is given by:
JA
2
of the P-channel switch
(97m ) = 0.87W
is 38 C/W. Thus the
sn3413 3413fs
JA