參數(shù)資料
型號(hào)： LTC1439
廠商： Linear Technology Corporation
元件分類： 基準(zhǔn)電壓源/電流源
英文描述： Dual High Efficiency, Low Noise, Synchronous Step-Down Switching Regulators
中文描述： 雙通道高效率，低噪聲，同步降壓型開關(guān)穩(wěn)壓器
文件頁(yè)數(shù)： 16/32頁(yè)
文件大?。?/td> 596K
代理商： LTC1439
16
LTC1438/LTC1439
APPLICATIO
S I
FOR
ATIO
U
in an efficiency penalty of up to 10% at high input
voltages.
2. EXTV
CC
connected directly to V
OUT
. This is the normal
connection for a 5V regulator and provides the highest
efficiency.
3. EXTV
CC
connected to an output-derived boost network.
For 3.3V and other low voltage regulators, efficiency
gains can still be realized by connecting EXTV
CC
to an
output-derived voltage which has been boosted to
greater than 4.8V. This can be done with either the
inductive boost winding as shown in Figure 4a or the
capacitive charge pump shown in Figure 4b. The charge
pump has the advantage of simple magnetics.
4. EXTV
CC
connected to an external supply. If an external
supply is available in the 5V to 10V range (EXTV
CC
≤
V
IN
) it may be used to power EXTV
CC
providing it is
W
U
U
compatible with the MOSFET gate drive requirements.
When driving standard threshold MOSFETs, the exter-
nal supply must be always present during operation to
prevent MOSFET failure due to insufficient gate drive.
Topside MOSFET Driver Supply (C
B
, D
B
)
External bootstrap capacitors C
B
connected to the BOOST
1 and BOOST 2 pins supply the gate drive voltages for the
topside MOSFETs. Capacitor C
B
in the Functional Dia-
gram is charged through diode D
B
from INTV
CC
when the
SW1(SW2) pin is low. When one of the topside MOSFETs
is to be turned on, the driver places the C
B
voltage across
the gate source of the desired MOSFET. This enhances
the MOSFET and turns on the topside switch. The switch
node voltage SW1(SW2) rises to V
IN
and the BOOST
1(BOOST 2) pin follows. With the topside MOSFET on,
the boost voltage is above the input supply: V
BOOST
= V
IN
+ V
INTVCC
. The value of the boost capacitor C
B
needs to
be 100 times that of the total input capacitance of the
topside MOSFET(s). The reverse breakdown on D
B
must
be greater than V
IN(MAX)
.
Output Voltage Programming
The LTC1438/LTC1439 have pin selectable output voltage
programming. Controller 1 on the LTC1438-ADJ is a
dedicated adjustable controller. The output voltage is
selected by the V
PROG1
(V
PROG2
) pin as follows on all of the
other parts:
V
PROG1,2
= 0V
V
PROG1,2
= INTV
CC
V
PROG2
= Open (DC)
V
OUT1,2
= 3.3V
V
OUT1,2
= 5V
V
OUT2
= Adjustable
Except for the LTC1438-ADJ, the top of an internal resis-
tive divider is connected to SENSE
–
1 pin in Controller 1.
For fixed output voltage applications the SENSE
–
1 pin is
connected to the output voltage as shown in Figure 5a.
When using an external resistive divider for an adjustable
regulator, the V
PROG2
pin is left open (V
PROG1
is internally
left open on the LTC1438-ADJ) and the V
OSENSE2
pin is
connected to the feedback resistors as shown in Figure 5b.
The adjustable controller will force the externally attenu-
ated output voltage to 1.19V.
Figure 4a. Secondary Output Loop and EXTV
CC
Connection
+
+
+
V
IN
V
IN
V
SEC
V
OUT
C
OUT
1438 F04a
1
μ
F
R
SENSE
C
IN
TGL1
N-CH
OPTIONAL EXTV
CC
CONNECTION
5V
≤
V
SEC
≤
9V
N-CH
R5
N-CH
1N4148
LTC1438
LTC1439*
L1
1:1
TGS1*
SW1
BG1
PGND
SGND
SFB1
EXTV
CC
R6
*TGS1 ONLY AVAILABLE ON THE LTC1439
+
+
V
IN
V
IN
V
OUT
+
C
OUT
1438 F04b
1
μ
F
0.22
μ
F
R
SENSE
C
IN
TGL1
N-CH
N-CH
N-CH
VN2222LL
LTC1438
LTC1439*
L1
BAT85
BAT85
BAT85
TGS1*
SW1
BG1
PGND
EXTV
CC
*TGS1 ONLY AVAILABLE ON THE LTC1439
Figure 4b. Capacitive Charge Pump for EXTV
CC
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參數(shù)描述
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