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參數(shù)資料
| 型號： | LTC1267-ADJ5 |
| 廠商： | Linear Technology Corporation |
| 元件分類： | 圓形連接器 |
| 英文描述： | Circular Connector; No. of Contacts:37; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:15; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:15-35 |
| 中文描述： | 雙通道高效率同步降壓型開關(guān)穩(wěn)壓器 |
| 文件頁數(shù)： | 9/16頁 |
| 文件大?。?/td> | 341K |
| 代理商： | LTC1267-ADJ5 |
9
LTC1267
LTC1267-ADJ/LTC1267-ADJ5
APPLICATIU
1400
V
OUT
= 5V
W
U
U
value, but it is very dependent on inductance selected. As
inductance increases, core losses go down but copper I
2
R
losses increase. For additional information regarding in-
ductor selection, please refer to the LTC1159 data sheet.
Power MOSFET and Diode Selection
Two external power MOSFETs must be selected for use
with each section of the LTC1267: a P-channel MOSFET
for the main switch, and an N-channel MOSFET for the
synchronous switch.
The peak-to-peak gate drive levels are set by the V
CC
voltage on the LTC1267. This voltage is typically 4.5V
during start-up and 5V to 7V during normal operation (see
EXT V
CC
Pin Connection). Consequently, logic-level hresh-
old MOSFETs must be used in most LTC1267 family
applications The only exceptions are applications in
which EXT V
CC
is powered from an external supply greater
than 8V, in which standard threshold MOSFETs (V
GS(TH)
> 4V) may be used. Pay close attention to the BV
DSS
specification for the MOSFETs as well; many of the logic-
level MOSFETs are limited to 30V.
Selection criteria for the power MOSFETs include the on-
resistance R
DS(ON)
, reverse transfer capacitance C
RSS
,
input voltage, and maximum output current. When the
LTC1267 is operating in continuous mode, the duty cycles
for the two MOSFETs are given by:
Duty Cycle =V
OUT
V
IN
N-Channel Duty Cycle =V
IN
– V
OUT
V
IN
The MOSFET dissipations at maximum output current are
given by:
P-Ch P
D
=
(I
MAX
)
2
(1 +
δ
P
) R
DS(ON)
+ k (V
IN
)
2
(I
MAX
) (C
RSS
) f
O
V
OUT
V
IN
N-Ch P
D
=
(I
MAX
)
2
(1 +
δ
N
) R
DS(ON)
V
IN
– V
OUT
V
IN
FREQUENCY (kHz)
0
1000
1200
150
200
LTC1267 F03
800
600
50
100
250
400
200
0
T
V
IN
= 24V
V
IN
= 12V
Figure 3. Timing Capacitor Value
As the operating frequency is increased the gate charge
losses will be higher, reducing efficiency (see Efficiency
Considerations). The complete expression for operating
frequency is given by:
)
where:
t
OFF
= 1.3
×
10
4
×
C
T
Once the frequency has been set by C
T
, the inductor L must
be chosen to provide no more than 0.025V/R
SENSE
of
peak-to-peak inductor ripple current. This results in a
minimum required inductor value of:
L
MIN
= 5.1
×
10
5
×
R
SENSE
×
C
T
×
V
OUT
As the inductor value is increased from the minimum
value, the ESR requirements for the output capacitor are
eased at the expense of efficiency. If too small an inductor
is used, the LTC1267 may not enter Burst Mode
operation
and efficiency will be severely degraded at low currents.
f
O
= 1
t
OFF
)
1 –V
OUT
V
IN
Inductor Core Selection
Once the minimum value for L is known, the type of
inductor must be selected. High efficiency converters
generally cannot afford the core loss found in low cost
powdered iron cores, forcing the use of more expensive
ferrite, molypermalloy (MPP), or Kool M
μ
cores. Actual
core loss is independent of core size for a fixed inductor
Kool M
μ
is a registered trademark of Magnetics, Inc.
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| LTC1267 | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| LTC1267CG-ADJ5 | Circular Connector; No. of Contacts:37; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:15; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:15-35 |
| LTC1267CG-ADJ | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
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|---|---|
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