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PDF LT1246 Data sheet ( Hoja de datos )
| Número de pieza | LT1246 | |
| Descripción | 1MHz Off-Line Current Mode PWM and DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Current Mode Operation to 1MHz
s 30ns Current Sense Delay
s < 250µA Low Start-Up Current
s Current Sense Leading Edge Blanking
s Pin Compatible with UC1842
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 18V High Level Output Clamp
APPLICATI S
s Off-Line Converters
s DC/DC Converters
Device
LT1246
LT1247
Start-Up
Threshold
16V
8.4V
Minimum
Operating
Voltage
10V
7.6V
Maximum
Duty Cycle
100%
100%
Replaces
UC1842
UC1843
LT1246/LT1247
1MHz Off-Line
Current Mode PWM
and DC/DC Converter
DESCRIPTIO
The LT®1246/LT1247 are 8-pin, fixed frequency, current
mode, pulse width modulators. These devices are de-
signed to be improved plug compatible versions of the
industry standard UC1842 PWM circuit. The LT1246/
LT1247 are optimized for off-line and DC/DC converter
applications. They contain a temperature compensated
reference, high gain error amplifier, current sensing com-
parator, and a high current totem pole output stage ideally
suited to driving power MOSFETs. Start-up current has
been reduced to less than 250µA. Cross-conduction cur-
rent spikes in the totem pole output stage have been
eliminated, making 1MHz operation practical. Several new
features have been incorporated. Leading edge blanking
has been added to the current sense comparator. This
minimizes or eliminates the filter that is normally required.
Eliminating this filter allows the current sense loop to
operate with minimum delays. 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 VOUT of 18V in the
on state. The output and the reference output are actively
pulled low during under-voltage lockout.
, LTC and LT are registered trademarks of Linear Technology Corporation.
BLOCK DIAGRA
RT/CT 4
COMPENSATION 1
FEEDBACK 2
–
2.5V
+
ISENSE 3
REFERENCE ENABLE
5V REF
MAIN BIAS
UV
LOCKOUT
REFERENCE PULLDOWN
OUTPUT
PULLDOWN
OSCILLATOR
5.6V
1mA
2R
R
1V
–
+
S
R
BLANKING
+
1.5V
–
18V
8 VREF
7 VCC
6 OUTPUT
5 GND
LT1246 • BD01
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LT1246/LT1247
Feedback Pin Input Voltage
2.55
2.54
2.53
2.52
2.51
2.50
2.49
2.48
2.47
2.46
2.45
–50 –25
0
25 50 75 100 125
TEMPERATURE (°C)
LT1246 • TPC10
Current Sense Clamp Voltage
1.05
1.04
1.03
1.02
1.01
1.00
0.99
0.98
0.97
0.96
0.95
–50 –25
0
25 50 75 100 125
TEMPERATURE (°C)
LT1246 • TPC11
High Level Output
Saturation Voltage
4.0
3.5
3.0
2.5
2.0
1.5
1.0
TJ = – 55°C
TJ = 25°C
TJ = 125°C
0.5
0
0
100 200
OUTPUT SOURCE CURRENT (mA)
LT1246 • TPC12
Low Level Output
Saturation Voltage
1.0
TJ = 125°C
0.5
TJ = 25°C
TJ = – 55°C
0
0 100 200
OUTPUT SINK CURRENT (mA)
LT1246 • TPC13
Low Level Output Saturation Voltage
During Undervoltage Lockout
4.0
3.5
3.0
2.5 TJ = – 55°C
2.0
1.5
1.0 TJ = 125°C
TJ = 25°C
0.5
0
0 5 10
OUTPUT SINK CURRENT (mA)
LT1246 • TPC14
Supply Current vs
Oscillator Frequency
14
13
12
11
10
9
10k
100k 1M
OSCILLATOR FREQUENCY (Hz)
LT1246 • TPC15
Error Amplifier Open-Loop Gain
and Phase
100 225
80 GAIN
180
Current Sense Input Threshold
1.2
1.0
60 135 0.8
PHASE
TJ = – 55°C
40 90 0.6
TJ =125°C
20 45 0.4
00
–20
10 100
–45
1k 10k 100k 1M 10M
FREQUENCY (Hz)
LT1246 • TPC16
0.2 TJ = 25°C
0
01 2 34 5 6
ERROR AMP OUTPUT VOLTAGE (V)
LT1246 • TPC17
5
5 Page 
TYPICAL APPLICATI S
LT1246/LT1247
VREF
8
RT RT/CT
4
COMP
CT 1
FEEDBACK
2
–
+
2.5V
Slope Compensation at ISENSE Pin
5V REF
MAIN BIAS
OSCILLATOR
5.6V
1mA
2R
R
1V
–
+
REFERENCE ENABLE
REFERENCE PULLDOWN
UV
LOCKOUT
OUTPUT
PULLDOWN
S
R
BLANKING
+
1.5V
–
18V
VIN
VCC
7
OUTPUT
6
GND
5
ISENSE
3
RS
LT1246 • TA08
TO
VOUT
RSLOPE
VREF
8
RT RT/CT
4
CT COMP
1
Rf
2
FEEDBACK
–
+
2.5V
Slope Compensation at Error Amp
5V REF
MAIN BIAS
OSCILLATOR
5.6V
1mA
2R
R
1V
–
+
REFERENCE ENABLE
UV
LOCKOUT
REFERENCE PULLDOWN
OUTPUT
PULLDOWN
VCC
7
S
R
BLANKING
+
1.5V
–
OUTPUT
6
18V GND
5
ISENSE
3
LT1246 • TA09
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LT1246.PDF ] | |
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