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Электронный компонент: LT124XI

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1
LT1241 Series
The LT
1241 series devices are 8-pin, fixed frequency,
current mode, pulse width modulators. They are improved
plug compatible versions of the industry standard UC1842
series. These devices have both improved speed and
lower quiescent current. The LT1241 series is optimized
for off-line and DC/DC converter applications. They con-
tain a temperature-compensated reference, high gain er-
ror amplifier, current sensing comparator and a high
current totem pole output stage ideally suited to driving
power MOSFETs. Start-up current has been reduced to
less than 250
A. Cross-conduction current spikes in
the output stage have been eliminated, making 500kHz
operation practical. Several new features have been incor-
porated. Leading edge blanking has been added to the
current sense comparator. Trims have been added to the
oscillator circuit for both frequency and sink current, and
both of these parameters are tightly specified. The output
stage is clamped to a maximum V
OUT
of 18V in the
on state. The output and the reference output are actively
pulled low during undervoltage lockout.
High Speed Current Mode
Pulse Width Modulators
s
Low Start-Up Current: < 250
A
s
50ns Current Sense Delay
s
Current Mode Operation: To 500kHz
s
Pin Compatible with UC1842 Series
s
Undervoltage Lockout with Hysteresis
s
No Cross-Conduction Current
s
Trimmed Bandgap Reference
s
1A Totem Pole Output
s
Trimmed Oscillator Frequency and Sink Current
s
Active Pull-Down on Reference and Output During
Undervoltage Lockout
s
High Level Output Clamp: 18V
s
Current Sense Leading Edge Blanking
D
U
ESCRIPTIO
S
FEATURE
U
S
A
O
PPLICATI
s
Off-Line Converters
s
DC/DC Converters
, LTC and LT are registered trademarks of Linear Technology Corporation.
+
+
1
2
FB
COMP
2.5V
2R
R
1V
1.5V
+
3
I
SENSE
BLANKING
1mA
5.6V
4
R
T
/C
T
OSCILLATOR
R
S
18V
7
V
CC
5
GND
6
OUTPUT
8
V
REF
5V REF
MAIN BIAS
REFERENCE PULL-DOWN
OUTPUT
PULL-DOWN
REFERENCE ENABLE
1241 BD01
T
UV
LOCKOUT
W
I
D AGRA
BLOCK
LT1241 Series
2
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Reference Section
Output Voltage
I
O
= 1mA, T
J
= 25
C
4.925
5.000
5.075
V
Line Regulation
12V < V
CC
< 25V
q
3
20
mV
Load Regulation
1mA < I
VREF
< 20mA
q
6
25
mV
Temperature Stability
0.1
mV/
C
Total Output Variation
Line, Load, Temp
q
4.87
5.13
V
Output Noise Voltage
10Hz < F < 10kHz, T
J
= 25
C
50
V
Long Term Stability
T
A
= 125
C, 1000 Hrs.
5
25
mV
Output Short-Circuit Current
q
30
90
180
mA
Oscillator Section
Initial Accuracy
R
T
= 10k, C
T
= 3.3nF, T
J
= 25
C
47.5
50
52.5
kHz
R
T
= 13.0k, C
T
= 500pF, T
J
= 25
C
228
248
268
kHz
Voltage Stability
12V < V
CC
< 25V, T
J
= 25
C
1
%
Temperature Stability
T
MIN
< T
J
< T
MAX
0.05
%/
C
Amplitude
T
J
= 25
C (Pin 4)
1.7
V
Clock Ramp Reset Current
V
OSC
(Pin 4) = 2V, T
J
= 25
C
7.9
8.2
8.5
mA
Error Amplifier Section
Feedback Pin Input Voltage
V
PIN1
= 2.5V
q
2.42
2.50
2.58
V
Input Bias Current
V
FB
= 2.5V
q
2
A
Open-Loop Voltage Gain
2 < V
O
< 4V
q
65
90
dB
Unity-Gain Bandwidth
T
J
= 25
C
0.7
1.3
2
MHz
Power Supply Rejection Ratio
12V < V
CC
< 25V
q
60
dB
Output Sink Current
V
PIN2
= 2.7V, V
PIN1
= 1.1V
q
2
6
mA
Output Source Current
V
PIN2
= 2.3V, V
PIN1
= 5V
q
0.5
0.75
mA
ELECTRICAL C
C
HARA TERISTICS
(Notes 1, 2)
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
Supply Voltage ........................................................ 25V
Output Current .......................................................
1A*
Output Energy (Capacitive Load per Cycle) ...............5
J
Analog Inputs (Pins 2, 3) ............................... 0.3 to 6V
Error Amplifier Output Sink Current...................... 10mA
Power Dissipation at T
A
25
C ................................ 1W
Operating Junction Temperature Range
LT124XC ............................................. 0
C to 100
C
LT124XI......................................... 40
C to 100
C
LT124XM........................................ 55
C to 125
C
Storage Temperature Range ................. 65
C to 150
C
Lead Temperature (Soldering, 10 sec).................. 300
C
*The 1A rating for output current is based on transient switching
requirements.
ORDER PART
NUMBER
LT124XCJ8
LT124XCN8
LT124XCS8
LT124XIN8
LT124XIS8
LT124XMJ8
S8 PART MARKING
124X
124XI
W
U
U
PACKAGE/ORDER I FOR ATIO
COMP
FB
I
SENSE
R
T
/C
T
V
REF
V
CC
OUTPUT
GND
S8 PACKAGE
8-LEAD PLASTIC SO
N8 PACKAGE
8-LEAD PDIP
J8 PACKAGE
8-LEAD CERDIP
1
2
3
4
8
7
6
5
TOP VIEW
T
JMAX
= 125
C,
JA
= 100
C/W (J8)
T
JMAX
= 100
C,
JA
= 130
C/W (N8)
T
JMAX
= 100
C,
JA
= 150
C/W (S8)
3
LT1241 Series
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Error Amplifier Section
Output Voltage High Level
V
PIN2
= 2.3V, R
L
= 15k to GND
q
5
5.6
V
Output Voltage Low Level
V
PIN2
= 2.7V, R
L
= 15k to Pin 8
q
0.2
1.1
V
Current Sense Section
Gain
q
2.85
3.00
3.15
V/V
Maximum Current Sense Input Threshold
V
PIN3
< 1.1V
q
0.90
1.00
1.10
V
Power Supply Rejection Ratio
q
70
dB
Input Bias Current
q
1
10
A
Delay to Output
q
50
100
ns
Blanking Time
100
ns
Blanking Override Voltage
1.5
V
Output Section
Output Low Level
I
OUT
= 20mA
q
0.25
0.4
V
I
OUT
= 200mA
q
0.75
2.2
V
Output High Level
I
OUT
= 20mA
q
12.0
V
I
OUT
= 200mA
q
11.75
V
Rise Time
C
L
= 1nF, T
J
= 25
C
50
80
ns
Fall Time
C
L
= 1.0nF, T
J
= 25
C
30
60
ns
Output Clamp Voltage
I
O
= 1mA
q
18
19.5
V
Undervoltage Lockout
Start-Up Threshold
LT1241
q
9.0
9.6
10.2
V
LT1242/LT1244
q
15
16
17
V
LT1243/LT1245
q
7.8
8.4
9.0
V
Minimum Operating Voltage
LT1241/LT1243/LT1245
q
7.0
7.6
8.2
V
LT1242/LT1244
q
9.0
10
11
V
Hysteresis
LT1241
1.6
2.0
V
LT1242/LT1244
5.5
6.0
V
LT1243/LT1245
0.4
0.8
V
PWM
Maximum Duty Cycle
LT1241/LT1244/LT1245
T
J
= 25
C
46
48
%
LT1242/LT1243
T
J
= 25
C
94
96
%
Minimum Duty Cycle
q
0
%
Total Device
Start-Up Current
q
170
250
A
Operating Current
q
7
10
mA
The
q
denotes those specifications which apply over the full operating
temperature range.
Note 1: Unless otherwise specified, V
CC
= 15V, R
T
= 10k, C
T
= 3.3nF.
(Notes 1, 2)
ELECTRICAL C
C
HARA TERISTICS
Note 2: Low duty cycle pulse techniques are used during test to maintain
junction temperature close to ambient.
LT1241 Series
4
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Undervoltage Lockout
Undervoltage Lockout
Undervoltage Lockout LT1241
LT1242, LT1244
LT1243, LT1245
Supply Current vs
Oscillator Frequency
Oscillator Frequency
Oscillator Sink Current
TEMPERATURE (
C)
50
6
V
CC
(V)
7
8
9
10
11
25
25
75
125
LT1241 TPC01
0
50
100
MINIMUM OPERATING VOLTAGE
START-UP THRESHOLD
TEMPERATURE (
C)
50
9
V
CC
(V)
10
11
16
17
25
25
75
125
LT1241 TPC02
0
50
100
MINIMUM OPERATING VOLTAGE
START-UP THRESHOLD
15
TEMPERATURE (
C)
50
6
V
CC
(V)
7
8
9
10
11
25
25
75
125
LT1241 TPC03
0
50
100
MINIMUM OPERATING VOLTAGE
START-UP THRESHOLD
TEMPERATURE (
C)
50
5
I
CC
(mA)
6
7
8
9
10
25
25
75
125
LT1241 TPC06
0
50
100
V
CC
= 15V
R
T
= 10k
C
T
= 3300pF
TEMPERATURE (
C)
50
0
START-UP CURRENT (
A)
40
80
120
160
200
25
25
75
125
LT1241 TPC05
0
50
100
180
140
100
60
20
Start-Up Current
Start-Up Current
Supply Current
V
CC
(V)
0
0
START-UP CURRENT (
A)
50
100
150
200
2
8
12
18
LT1241 TPC04
4
10
14
6
16
LT1241
LT1242/4
LT1243/5
T
J
= 25
C
START-UP
THRESHOLD
OSCILLATOR FREQUENCY (Hz)
10k
0
SUPPLY CURRENT (mA)
2
3
5
7
8
10
100k
1M
LT1241 TPC18
9
6
4
1
LT1242, LT1243
LT1241, LT1244, LT1245
V
CC
= 15V
R
T
= 10k
C
L
= 15pF
TEMPERATURE (
C)
50
40
FREQUENCY (kHz)
44
48
52
56
60
25
25
75
125
LT1241 TPC07
0
50
100
42
46
50
54
58
V
CC
= 5V
R
T
= 10k
C
T
= 3300pF
TEMPERATURE (
C)
50
7.7
OSCILLATOR SINK CURRENT (mA)
8.7
25
25
75
125
LT1241 TPC08
0
50
100
7.8
8.0
8.2
8.4
8.6
8.5
7.9
8.1
8.3
V
PIN4
= 2V
5
LT1241 Series
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Error Amplifier Open-Loop Gain
and Phase
Current Sense Clamp Voltage
Current Sense Input Threshold
Low Level Output Saturation
High Level Output
Low Level Output
Voltage During Undervoltage
Saturation Voltage
Saturation Voltage
Lockout
TEMPERATURE (
C)
50
20
REFERENCE SHORT-CIRCUIT CURRENT (mA)
140
25
25
75
125
LT1241 TPC09
0
50
100
40
80
100
120
60
TEMPERATURE (
C)
50
4.95
REFERENCE VOLTAGE (V)
5.05
25
25
75
125
LT1241 TPC10
0
50
100
4.96
5.00
5.01
4.97
4.98
4.99
5.02
5.03
5.04
I
O
= 1mA
Reference Voltage
Reference Short-Circuit Current
Feedback Pin Input Voltage
TEMPERATURE (
C)
50
2.45
FEEDBACK PIN INPUT VOLTAGE (V)
2.55
25
25
75
125
LT1241 TPC11
0
50
100
2.46
2.50
2.51
2.47
2.48
2.49
2.52
2.53
2.54
ERROR AMP OUTPUT VOLTAGE (V)
0
0
CURRENT SENSE INPUT THRESHOLD (V)
1.2
3
6
LT1241 TPC17
0.6
0.2
0.4
0.8
1.0
1
2
4
5
T
J
= 55
C
T
J
=125
C
T
J
= 25
C
TEMPERATURE (
C)
50
0.95
CURRENT SENSE CLAMP VOLTAGE (V)
1.05
25
25
75
125
LT1241 TPC12
0
50
100
0.96
1.00
1.01
0.97
0.98
0.99
1.02
1.03
1.04
FREQUENCY (Hz)
10
20
A
VOL
OPEN-LOOP VOLTAGE GAIN (dB)
100
10k
10M
LT1241 TPC16
40
0
20
60
80
100
1k
100k
1M
PHASE
GAIN
V
CC
= 15V
V
O
= 2.0V - 4.0V
R
L
= 100k
T
A
= 25
C
PHASE (DEG)
180
45
225
90
0
45
135
OUTPUT SOURCE CURRENT (mA)
0
0
OUTPUT SATURATION VOLTAGE (V)
4.0
200
LT1241 TPC13
0.5
2.0
2.5
1.0
1.5
3.0
3.5
T
J
= 55
C
T
J
= 25
C
T
J
= 125
C
100
OUTPUT SINK CURRENT (mA)
0
0
OUTPUT SATURATION VOLTAGE (V)
1.0
100
200
LT1241 TPC14
T
J
= 55
C
T
J
= 25
C
T
J
= 125
C
0.5
OUTPUT SINK CURRENT (mA)
0
0
OUTPUT SATURATION VOLTAGE (V)
4.0
5
10
LT1241 TPC15
2.0
0.5
1.0
1.5
2.5
3.0
3.5
T
J
= 125
C
T
J
= 55
C
T
J
= 25
C