LTC3736-2 Linear Technology, LTC3736-2 Datasheet - Page 15

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LTC3736-2

Manufacturer Part Number
LTC3736-2
Description
Synchronous Controller
Manufacturer
Linear Technology
Datasheet
APPLICATIO S I FOR ATIO
The MOSFET power dissipations at maximum output
current are:
Both MOSFETs have I
includes an additional term for transition losses, which are
largest at high input voltages. The bottom MOSFET losses
are greatest at high input voltage or during a short-circuit
when the bottom duty cycle is nearly 100%.
The LTC3736-2 utilizes a nonoverlapping, antishoot-
through gate drive control scheme to ensure that the P-
and N-channel MOSFETs are not turned on at the same
time. To function properly, the control scheme requires
that the MOSFETs used are intended for DC/DC switching
applications. Many power MOSFETs, particularly P-chan-
nel MOSFETs, are intended to be used as static switches
and therefore are slow to turn on or off.
Reasonable starting criteria for selecting the P-channel
MOSFET are that it must typically have a gate charge (Q
less than 25nC to 30nC (at 4.5V
P
P
TOP
BOT
=
=
2.0
1.5
1.0
0.5
V
V
I
0
V
IN
OUT
– 50
OUT MAX
IN
Figure 4. R
V
IN
(
V
OUT
I
JUNCTION TEMPERATURE (°C)
OUT MAX
U
0
)
(
2
DS(ON)
C
R losses and the P
I
OUT MAX
RSS
U
)
50
2
(
vs Temperature
f
r
OSC
T
GS
)
2
W
100
) and a turn-off delay
R
r
DS ON
T
(
37362 F04
R
150
DS ON
)
TOP
+
(
2
U
equation
)
V
IN
2
G
)
(t
to differences in test and specification methods of various
MOSFET manufacturers, and in the variations in Q
t
ultimately should be evaluated in the actual LTC3736-2
application circuit to ensure proper operation.
Shoot-through between the P-channel and N-channel
MOSFETs can most easily be spotted by monitoring the
input supply current. As the input supply voltage in-
creases, if the input supply current increases dramatically,
then the likely cause is shoot-through. Note that some
MOSFETs that do not work well at high input voltages (e.g.,
V
Table 1 shows a selection of P-channel MOSFETs from
different manufacturers that are known to work well in
LTC3736-2 applications.
Selecting the N-channel MOSFET is typically easier, since
for a given R
off delays are much smaller than for a P-channel MOSFET.
Table 1. Selected P-Channel MOSFETs Suitable for LTC3736-2
Applications
PART
NUMBER
Si7540DP
Si9801DY
FDW2520C
FDW2521C
Si3447BDV
Si9433BDY
FDC602P
FDC606P
FDC638P
FDW2502P
FDS6875
HAT1054R
NTMD6P02R2-D
D(OFF)
IN
D(OFF)
> 5V) may work fine at lower voltages (e.g., 3.3V).
with gate drive (V
) of less than approximately 140ns. However, due
DS(ON)
MANUFACTURER
Siliconix
Siliconix
Fairchild
Fairchild
Siliconix
Siliconix
Fairchild
Fairchild
Fairchild
Fairchild
Fairchild
On Semi
, the gate charge and turn-on and turn-
Hitachi
IN
) voltage, the P-channel MOSFET
Complementary
Complementary
Complementary
Complementary
www.DataSheet4U.com
Single P
Single P
Single P
Single P
Single P
Dual P
Dual P
Dual P
Dual P
TYPE
P/N
P/N
P/N
P/N
LTC3736-2
PowerPak
PACKAGE
TSSOP-8
TSSOP-8
TSSOP-8
TSOP-6
TSOP-6
TSOP-6
TSOP-6
SO-8
SO-8
SO-8
SO-8
SO-8
SO-8
15
G
37362fa
and

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