參數(shù)資料
型號: LT1172
廠商: Linear Technology Corporation
元件分類: 基準(zhǔn)電壓源/電流源
英文描述: 500kHz and 1MHz High Efficiency 1.5A Switching Regulators; Package: SO; No of Pins: 8; Temperature Range: -40?°C to 85?°C
中文描述: 射頻放大器
文件頁數(shù): 4/20頁
文件大?。?/td> 275K
代理商: LT1172
4
LT1170/LT1171/LT1172
SYMBOL
I
IN
I
SW
f
PARAMETER
Supply Current Increase
During Switch On-Time
Switching Frequency
CONDITIONS
MIN
TYP
25
MAX
35
UNITS
mA/A
88
85
85
100
112
115
97
250
kHz
kHz
%
μ
A
G
DC
MAX
Maximum Switch Duty Cycle
Shutdown Mode
Supply Current
Shutdown Mode
Threshold Voltage
Flyback Sense Delay Time (Note 5)
G
92
100
3V
V
IN
V
MAX
V
C
= 0.05V
3V
V
IN
V
MAX
100
50
150
250
300
mV
mV
μ
s
G
1.5
Transformer designs will tolerate much higher input voltages because
leakage inductance limits rate of rise of current in the switch. These
designs must be evaluated individually to assure that current limit is well
controlled up to maximum input voltage.
Boost mode designs are never protected against output shorts because
the external catch diode and inductor connect input to output.
Note 3:
Measured with V
C
in hi clamp, V
FB
= 0.8V. I
SW
= 4A for LT1170,
2A for LT1171, and 1A for LT1172.
Note 4:
For duty cycles (DC) between 50% and 80%, minimum
guaranteed switch current is given by I
LIM
= 3.33 (2 – DC) for the LT1170,
I
LIM
= 1.67 (2 – DC) for the LT1171, and I
LIM
= 0.833 (2 – DC) for the
LT1172.
Note 5:
Minimum input voltage for isolated flyback mode is 7V. V
MAX
=
55V for HV grade in fully isolated mode to avoid switch breakdown.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
Minimum effective switch “on” time for the LT1170/71/72 (in current
limit only) is
0.6
μ
s. This limits the maximum safe input voltage during an
output shorted condition. Buck mode and inverting mode input voltage during
an output shorted condition is limited to:
(R)(I
L
) + Vf
V
IN
(max, output shorted) = 15V +
buck and inverting mode
R = Inductor DC resistance
I
L
= 10A for LT1170, 5A for LT1171, and 2.5A for LT1172
Vf = Output catch diode forward voltage at I
L
t = 0.6
μ
s, f = 100kHz switching frequency
Maximum input voltage can be increased by increasing R or Vf.
External current limiting such as that shown in AN19, Figure 39, will
provide protection up to the full supply voltage rating. C1 in Figure 39
should be reduced to 200pF.
Switch Current Limit vs Duty Cycle*
TEMPERATURE (
°
C)
–75
M
–25
25
50
150
1170/1/2 G02
–50
0
75 100 125
2.9
2.8
2.7
2.6
2.5
2.4
2.3
SWITCH CURRENT = 0A
SWITCH CURRENT = I
MAX
Minimum Input Voltage
Switch Saturation Voltage
DUTY CYCLE (%)
0
S
16
12
8
4
0
40
1170/1/2 G01
20 30
50
60 70 80
90 100
25
°
C
125
°
C
–55
°
C
10
* DIVIDE VERTICAL SCALE BY TWO FOR
LT1171, BY FOUR FOR LT1172.
SWITCH CURRENT (A)*
0
S
8
1170/1/2 G03
1
2
3
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
4
5
6
7
25
°
C
150
°
C
–55
°
C
100
°
C
* DIVIDE CURRENT BY TWO FOR
LT1171, BY FOUR FOR LT1172.
(t)(f)
The
G
denotes the specifications which apply over the full operating tem-
perature range, otherwise specifications are at T
A
= 25
°
C. V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF
, output pin open, unless otherwise noted.
TYPICAL PERFOR U
ELECTRICAL CHARACTERISTICS
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