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參數(shù)資料
| 型號： | LTC3776EUF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual 2-Phase, No RSENSE Synchronous Controller for DDR/QDR Memory Termination |
| 中文描述： | 1 A DUAL SWITCHING CONTROLLER, 825 kHz SWITCHING FREQ-MAX, PQCC24 |
| 封裝： | 4 X 4 MM, PLASTIC, MO-220-WGGD, QFN-24 |
| 文件頁數(shù)： | 15/28頁 |
| 文件大?。?/td> | 429K |
| 代理商： | LTC3776EUF |
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15
LTC3776
3776f
Reasonable starting criteria for selecting the P-channel
MOSFET are that it must typically have a gate charge (Q
G
)
less than 25nC to 30nC (at 4.5V
GS
) and a turn-off delay
(t
D(OFF)
) of less than approximately 140ns. However, due
to differences in test and specification methods of various
MOSFET manufacturers, and in the variations in Q
G
and
t
D(OFF)
with gate drive (V
IN
) voltage, the P-channel MOSFET
ultimately should be evaluated in the actual LTC3776
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
IN
> 5V) may work fine at lower voltages (e.g., 3.3V).
Table 1 shows a selection of P-channel MOSFETs from
different manufacturers that are known to work well in
LTC3776 applications.
Selecting the N-channel MOSFET is typically easier, since
for a given R
DS(ON)
, the gate charge and turn-on and turn-
off delays are much smaller than for a P-channel MOSFET.
Table 1. Selected P-Channel MOSFETs Suitable for LTC3776
Applications
PART
NUMBER
MANUFACTURER
Si7540DP
Siliconix
TYPE
PACKAGE
PowerPak
SO-8
SO-8
Complementary
P/N
Complementary
P/N
Complementary
P/N
Complementary
P/N
Single P
Single P
Single P
Single P
Single P
Dual P
Dual P
Dual P
Dual P
Si9801DY
Siliconix
FDW2520C
Fairchild
TSSOP-8
FDW2521C
Fairchild
TSSOP-8
Si3447BDV
Si9803DY
FDC602P
FDC606P
FDC638P
FDW2502P
FDS6875
HAT1054R
NTMD6P02R2-D
Siliconix
Siliconix
Fairchild
Fairchild
Fairchild
Fairchild
Fairchild
Hitachi
On Semi
TSOP-6
SO-8
TSOP-6
TSOP-6
TSOP-6
TSSOP-8
SO-8
SO-8
SO-8
APPLICATIU
W
U
U
JUNCTION TEMPERATURE (
°
C)
–50
ρ
T
1.0
1.5
150
3776 F07
0.5
0
0
50
100
2.0
Figure 5. R
DS(ON)
vs Temperature
The power dissipated in the top and bottom MOSFETs
strongly depends on their respective duty cycles and load
current. When the LTC3776 is operating in continuous
mode, the duty cycles for the MOSFETs are:
Top P-Channel Duty Cycle =V
Bottom N-Channel Duty Cycle =V
OUT
V
IN
IN
V
V
OUT
IN
–
The MOSFET power dissipations at maximum output
current are:
P
V
V
I
V
IN
I
R
V
C
f
P
V
V
I
R
TOP
OUT
IN
OUT MAX
(
T
DS ON
(
IN
OUT MAX
–
RSS
OSC
BOT
OUT
IN
OUT MAX
(
T
DS ON
(
=
+
=
)
)
(
)
)
)
2
2
2
2
ρ
ρ
Both MOSFETs have I
2
R losses and the P
TOP
equation
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 LTC3776 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.
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| LTC3776EUF#TR | 制造商:Linear Technology 功能描述:DC DC Cntrlr Dual-OUT Sync Step Down 2.75V to 9.8V Input 24-Pin QFN EP T/R |
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