参数资料
型号: LT1737IS#TRPBF
厂商: Linear Technology
文件页数: 24/28页
文件大小: 0K
描述: IC REG CTRLR FLYBK ISO CM 16SOIC
标准包装: 2,500
PWM 型: 电流模式
输出数: 1
频率 - 最大: 125kHz
占空比: 90%
电源电压: 4.1 V ~ 20 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: 16-SOIC(0.154",3.90mm 宽)
包装: 带卷 (TR)
LT1737
TYPICAL APPLICATIO S
(
)
? R 3 ?
V FB FLBK BE ?
?
R3  and  D2.  (Diode  D2  prevents  reverse  emitter/base
breakdown in Q1 when MOSFET M1 is in the “ON” state.)
The raw flyback voltage at the drain of MOSFET M1 minus
the V BE of Q1 is converted to a current by R2 and then back
to a voltage at R3. Or, stated mathematically:
= V – V
? R 2 ?
Resistor R13 provides an initial pre-load to the supply
output to improve light load regulation. Resistor divider
R8/R9 sets the undervoltage lockout threshold at nomi-
nally 10.4V for turn-on, with turn-off about 600mV lower.
Overall power supply efficiency and output regulation
versus input voltage and load current may be seen in
Figures 13 and 14.
R2
11.0k
5V IN APPLICATION
The LT1737 is a bipolar technology IC specified to operate
down to a minimum input supply voltage of 4.5V. Although
its GATE pin drives “low” nearly to ground, its “high”
capability is limited by a headroom requirement of roughly
2V BE s. Thus when operating at a worst case 4.5V supply,
the GATE output will only drive up to a nominal 3V or so.
Fortunately, MOSFETs are now available with specified
performance at this level of gate voltage.
The circuit shown in Figure 15 provides an isolated 5V
output from an input between 4.5V and 5.5V. Two Si9804
low gate voltage MOSFETs are paralleled to handle the
primary-side current—up to 12A peak. This circuit pro-
vides more output power than the previous examples. It
V IN
? 4 ? 5 ? 6
10V
+
2.2nF
X7R
Q1
2N3906
D2
BAS16
1%
C8
1 μ F
25V
Z5U
C1A
220 μ F
10V
D4
1N5240
D3
MBR0520
+
C1B +
220 μ F
10V
R8
10 ? 12
5%
C6 1
4.7nF
50V
X7R
?
11
2
?
T1
COILTRONICS
VP5-0083
10
3 ? 9 8 7
D1
MBRD835L
R9 + C2A
15 ? 220 μ F
5%
C7
C2B
50V 220 μ F
10V
R10
270 ?
5%
V OUT
5V
3A
9
10
15
R4
R5
R6
R7
75k
51k
51k
2.2k
5%
5%
5%
5%
R3
3.01k
1%
8
7
C3
1nF
25V
X7R
3V OUT UVLO V CC
FB
LT1737
V C
OSCAP SFST t ON ENDLY MINENAB R OCMP
6 3 14 13 12 4
C5
47pF
50V
NPO
R CMPC
5
GATE
I SENSE
SGND PGND
11 1
C4
0.1 μ F
25V
Z5U
16
2
C9
1nF
25V
X7R
M1
SI9804
R11
51 ?
5%
R1
0.02 ?
1737 F15
M2
SI9804
C1A-B, C2A-B: SANYO POSCAP (10TPB220M)
D1: MOTOROLA 35V, 8A SCHOTTKY DIODE
D2: SIGNAL DIODE
D3: MOTOROLA 20V, 0.5A SCHOTTKY DIODE
D4: 10V, 500mW ZENER DIODE
M1, M2: SILICONIX/VISHAY 25V, 0.023 ? N-CH MOSFET
R1: 5 × 0.10 ? , 1W (IRC LR2512)
T1: COILTRONICS TRANSFORMER
Figure 15. 4.5V-5.5V to Isolated 5V Converter
1737fa
24
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