LT1245 Linear Technology Corporation, LT1245 Datasheet

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LT1245

Manufacturer Part Number
LT1245
Description
High Speed Current Mode Pulse Width Modulators
Manufacturer
Linear Technology Corporation
Datasheet

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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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LT1245 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

... LT1242/LT1244 LT1243/LT1245 Minimum Operating Voltage LT1241/LT1243/LT1245 LT1242/LT1244 Hysteresis LT1241 LT1242/LT1244 LT1243/LT1245 PWM Maximum Duty Cycle LT1241/LT1244/LT1245 T LT1242/LT1243 T Minimum Duty Cycle Total Device Start-Up Current Operating Current The denotes those specifications which apply over the full operating temperature range. Note 1: Unless otherwise specified, V ...

Page 4

... (V) CC LT1241 • TPC04 Supply Current vs Oscillator Frequency 10 9 LT1242, LT1243 8 LT1241, LT1244, LT1245 15V 10k 15pF 10k 100k 1M OSCILLATOR FREQUENCY (Hz) LT1241 • TPC18 HARA TERISTICS C Undervoltage Lockout – ...

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

... Output Rise and Fall Time TIME 50ns/DIV V = 15V LT1241 • TPC22 1nF HARA TERISTICS C Output Deadtime vs Oscillator Frequency – LT1241, LT1243,LT1245 75 70 10nF 5nF 2nF 65 500pF 100 OSCILLATOR FREQUENCY (kHz) LT1241 • TPC20 Output Cross-Conduction Current ...

Page 7

... LT1243 8.4V 7.6V LT1244 16V 10V LT1245 8.4V 7.6V Oscillator The LT1241 series devices are fixed frequency current mode pulse width modulators. The oscillator frequency and the oscillator discharge current are both trimmed and tightly specified to minimize the variations in frequency and deadtime. The oscillator frequency is set by choosing ...

Page 8

... LT1242 and LT1243. The output switching frequency will be equal to one-half the oscillator appear in the Typical frequency for LT1241, LT1244 and LT1245. The oscillator of LT1241 series devices will run at frequencies up to 1MHz, allowing 500kHz output switching frequencies for all devices. Error Amplifier 3 46 ...

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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