参数资料
型号: LT1871IMS-7#TR
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO10
封装: PLASTIC, MSOP-10
文件页数: 5/32页
文件大小: 461K
代理商: LT1871IMS-7#TR
LTC1871-7
13
18717fc
APPLICATIONS INFORMATION
Application Circuits
A basic LTC1871-7 application circuit is shown in Figure 9.
External component selection is driven by the characteris-
tics of the load and the input supply. The rst topology to
be analyzed will be the boost converter, followed by SEPIC
(single-ended primary inductance converter).
Boost Converter: Duty Cycle Considerations
For a boost converter operating in a continuous conduction
mode (CCM), the duty cycle of the main switch is:
D=
VO + VD –VIN
VO + VD
where VD is the forward voltage of the boost diode. For
converters where the input voltage is close to the output
voltage, the duty cycle is low and for converters that develop
a high output voltage from a low voltage input supply,
the duty cycle is high. The maximum output voltage for a
boost converter operating in CCM is:
VO(MAX) =
VIN(MIN)
1–DMAX
(
) –VD
The maximum duty cycle capability of the LTC1871-7 is
typically 92%. This allows the user to obtain high output
voltages from low input supply voltages.
Boost Converter: The Peak and Average Input Currents
The control circuit in the LTC1871-7 is measuring the input
current typically using a sense resistor in the MOSFET
source, so the output current needs to be reected back
to the input in order to dimension the power MOSFET
properly. Based on the fact that, ideally, the output power
is equal to the input power, the maximum average input
current is:
IIN(MAX) =
IO(MAX)
1–DMAX
The peak input current is:
IIN(PEAK) = 1+ 2
IO(MAX)
1–DMAX
The maximum duty cycle, DMAX, should be calculated at
minimum VIN.
Figure 9. A High Efciency 42V, 1.5A Automotive Boost Converter
RUN
ITH
FB
FREQ
MODE/SYNC
SENSE
VIN
INTVCC
GATE
GND
1
2
3
4
5
10
9
8
7
6
LTC1871-7
f = 250kHz
RT
100k
1%
R1
12.4k
1%
R2
412k
1%
R3
1M
CVCC
4.7μF
X5R
RSENSE
0.005Ω
1W
CIN2
10μF
50V
X5R
×2
M1
D1
L1
6.8μH
RC
24k
CC1
2.2nF
CC2
100pF
COUT1
68μF
100V
×2
VIN
8V TO 28V
VOUT
42V
1.5A
GND
18717 F09
+
CIN1*
560μF
50V
+
COUT2
10μF
50V
X5R
×2
CIN1:
SANYO 50MV560AXL (*RECOMMENDED FOR LAB EVALUATION
FOR SUPPLY LEAD LENGTHS GREATER THAN A FEW INCHES)
CIN2:
TDK C5750X5R1H106M
COUT1: SANYO 100CV68FS
COUT2: TDK C5750X5R1H106M
D1: DIODES INC B360B
L1: COOPER DR127-6R8
M1: SILICONIX/VISHAY Si7370DP
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