ltc3736euf-trpbf Linear Technology Corporation, ltc3736euf-trpbf Datasheet - Page 15

• Manufacturer Part Number: ltc3736euf-trpbf
• Description: Dual 2-phase, No Rsense, Synchronous Controller With Output Tracking
• Manufacturer: Linear Technology Corporation

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 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 applica-
tions. Many power MOSFETs, particularly P-channel
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
(t
to differences in test and specification methods of various
D(OFF)
P
P
BOT
TOP
) of less than approximately 140ns. However, due
=
=
•
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
I
R losses and the P
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
(
•
3736 F04
R
150
)
DS ON
TOP
+
(
2
U
•
equation
)
V
IN
2
G
)
MOSFET manufacturers, and in the variations in Q
t
ultimately should be evaluated in the actual LTC3736
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 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
Applications
PART
NUMBER
Si7540DP
Si9801DY
FDW2520C
FDW2521C
Si3447BDV
Si9803DY
FDC602P
FDC606P
FDC638P
FDW2502P
FDS6875
HAT1054R
NTMD6P02R2-D
Operating Frequency and Synchronization
The choice of operating frequency, f
between efficiency and component size. Low frequency
D(OFF)
IN
> 5V) may work fine at lower voltages (e.g., 3.3V).
with gate drive (V
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
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
OSC
LTC3736
, is a trade-off
PACKAGE
PowerPak
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
3736fa
and