LT1245IN8 Linear Technology Corporation, LT1245IN8 Datasheet

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LT1245IN8

Manufacturer Part Number
LT1245IN8
Description
Manufacturer
Linear Technology Corporation
Datasheet

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Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LT1245IN8#PBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
BLOCK
FEATURE
A
, LTC and LT are registered trademarks of Linear Technology Corporation.
PPLICATI
Low Start-Up Current: < 250 A
50ns Current Sense Delay
Current Mode Operation: To 500kHz
Pin Compatible with UC1842 Series
Undervoltage Lockout with Hysteresis
No Cross-Conduction Current
Trimmed Bandgap Reference
1A Totem Pole Output
Trimmed Oscillator Frequency and Sink Current
Active Pull-Down on Reference and Output During
Undervoltage Lockout
High Level Output Clamp: 18V
Current Sense Leading Edge Blanking
Off-Line Converters
DC/DC Converters
I
COMP
SENSE
R
T
/C
FB
T
4
1
2
3
I D AGRA
2.5V
S
O
+
U
S
W
1mA
5.6V
2R
OSCILLATOR
R
1V
+
MAIN BIAS
D
The LT
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
on state. The output and the reference output are actively
pulled low during undervoltage lockout.
5V REF
ESCRIPTIO
High Speed Current Mode
®
1241 series devices are 8-pin, fixed frequency,
REFERENCE PULL-DOWN
REFERENCE ENABLE
T
Pulse Width Modulators
BLANKING
R
S
1.5V
U
+
PULL-DOWN
OUTPUT
LOCKOUT
UV
18V
LT1241 Series
OUT
8
7
6
5
of 18V in the
V
V
OUTPUT
GND
REF
CC
1241 BD01
1

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LT1245IN8 Summary of contents

Page 1

... Trimmed Oscillator Frequency and Sink Current Active Pull-Down on Reference and Output During Undervoltage Lockout High Level Output Clamp: 18V Current Sense Leading Edge Blanking U O PPLICATI A S Off-Line Converters DC/DC Converters , LTC and LT are registered trademarks of Linear Technology Corporation. W BLOCK I D AGRA COMP 1 – ...

Page 2

LT1241 Series BSOLUTE Supply Voltage ........................................................ 25V Output Current ....................................................... 1A* Output Energy (Capacitive Load per Cycle) ...............5 J Analog Inputs (Pins 2, 3) ............................... – 0 Error Amplifier Output Sink ...

Page 3

ELECTRICAL C HARA TERISTICS C PARAMETER CONDITIONS Error Amplifier Section Output Voltage High Level V Output Voltage Low Level V Current Sense Section Gain Maximum Current Sense Input Threshold V Power Supply Rejection Ratio Input Bias Current Delay to Output ...

Page 4

LT1241 Series W U TYPICAL PERFOR A Undervoltage Lockout – LT1241 11 10 START-UP THRESHOLD 9 8 MINIMUM OPERATING VOLTAGE 7 6 –50 – 100 125 TEMPERATURE ( C) LT1241 • TPC01 Start-Up Current 200 START-UP ...

Page 5

W U TYPICAL PERFOR A Reference Voltage 5. 1mA O 5.04 5.03 5.02 5.01 5.00 4.99 4.98 4.97 4.96 4.95 –50 – 100 125 TEMPERATURE ( C) LT1241 • TPC10 Error Amplifier Open-Loop Gain ...

Page 6

LT1241 Series W U TYPICAL PERFOR A Output Deadtime vs Oscillator Frequency – LT1242, LT1244 60 50 5nF 2nF 1nF 40 30 500pF 20 10 100pF 0 0 100 1000 OSCILLATOR FREQUENCY (kHz) LT1241 • TPC19 Output Rise and Fall ...

Page 7

COMP (Pin 1): Compensation Pin. This pin is the output of the Error Amplifier and is made available for loop compen- sation. It can also be used to adjust the maximum ...

Page 8

LT1241 Series PPLICATI S I FOR ATIO for various values of R and Performance Characteristics section. Frequency and deadtime can also be calculated using the following formulas: Oscillator Rise Time 0.583 ...

Page 9

PPLICATI S I FOR ATIO Current Sense Comparator and PWM Latch LT1241 series devices are current mode controllers. Under normal operating conditions the output (Pin 6) is turned on at the start of every oscillator cycle, ...

Page 10

LT1241 Series PPLICATI S I FOR ATIO Undervoltage Lockout The LT1241 series devices incorporate an undervoltage lockout comparator which prevents the internal reference circuitry and the output from starting up until the supply voltage reaches the ...

Page 11

O U TYPICAL A PPLICATI External Clock Synchronization V REF 8 5V REF OSCILLATOR EXTERNAL C SYNC T 0.01 F INPUT + REQUIRED IF THE SYNC AMPLITUDE IS LARGE ...

Page 12

LT1241 Series U O TYPICAL A PPLICATI HOT 90VAC R5 0 250V BALEN 240VAC 1/2W MP3- NEU 1212-R6103 COILTRONICS AC GND R T1 MCID404 2KBPOO5M + C14 100 F 400V D6 ...

Page 13

O U TYPICAL A PPLICATI V REF COMP – 2.5V PACKAGE DESCRIPTIO CORNER LEADS OPTION (4 PLCS) 0.045 – 0.068 (1.143 – 1.727) FULL LEAD OPTION ...

Page 14

LT1241 Series PACKAGE DESCRIPTIO 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) +0.025 0.325 –0.015 +0.635 8.255 –0.381 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH ...

Page 15

... FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 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. ...

Page 16

... Boost Regulator Steps Down from Up to 25V Using 4.7 H Inductors Complete Solution for Universal Off-Line Switching Power Supplies UV LOCKOUT V CC OUTPUT 7 PULL-DOWN OUTPUT 18V GND 5 + 1.5V – I SENSE 3 LT1241 • TA05 1241fa LT/TP 0297 5K REV A • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1992 ...

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