LT1247CN8 Linear Technology Corporation, LT1247CN8 Datasheet

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LT1247CN8

Manufacturer Part Number
LT1247CN8
Description
Manufacturer
Linear Technology Corporation
Datasheet

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Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LT1247CN8#PBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
FEATURE
Device
LT1246
LT1247
BLOCK
A
PPLICATI
Current Mode Operation to 1MHz
30ns Current Sense Delay
< 250 A Low Start-Up Current
Current Sense Leading Edge Blanking
Pin Compatible with UC1842
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
18V High Level Output Clamp
Off-Line Converters
DC/DC Converters
COMPENSATION
FEEDBACK
I
R
SENSE
T
/C
Threshold
I D AGRA
Start-Up
T
8.4V
S
16V
4
1
2
3
O
2.5V
U
+
S
Operating
Minimum
Voltage
W
7.6V
10V
Duty Cycle
Maximum
100%
100%
1mA
5.6V
2R
Replaces
UC1842
UC1843
OSCILLATOR
R
1V
+
D
The LT
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 250 A. 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 V
on state. The output and the reference output are actively
pulled low during under-voltage lockout.
REFERENCE ENABLE
, LTC and LT are registered trademarks of Linear Technology Corporation.
ESCRIPTIO
MAIN BIAS
5V REF
®
1246/LT1247 are 8-pin, fixed frequency, current
and DC/DC Converter
REFERENCE PULLDOWN
Current Mode PWM
BLANKING
R
S
U
1.5V
+
PULLDOWN
1MHz Off-Line
OUTPUT
LT1246/LT1247
LOCKOUT
UV
18V
OUT
of 18V in the
8
7
6
5
LT1246 • BD01
V
V
OUTPUT
GND
REF
CC
1

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LT1247CN8 Summary of contents

Page 1

... V Maximum on state. The output and the reference output are actively Duty Cycle Replaces pulled low during under-voltage lockout. 100% UC1842 100% UC1843 , LTC and LT are registered trademarks of Linear Technology Corporation. REFERENCE ENABLE 5V REF MAIN BIAS OSCILLATOR 5.6V 1V 1mA 2R – ...

Page 2

... PIN 1 = 2.3V PIN 2 PIN ORDER PART NUMBER TOP VIEW REF LT1246CN8 LT1246CS8 3 6 OUTPUT LT1247CN8 4 5 GND LT1247CS8 N8 PACKAGE 8-LEAD PDIP S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO 1246 = 100 C, = 130 C/W (N8 100 C, = 150 C/W (S8) JA 1247 MIN TYP MAX 4.925 5.000 5.075 ...

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

LT1246/LT1247 W U TYPICAL PERFOR A LT1246 Undervoltage Lockout 17 START-UP THRESHOLD MINIMUM OPERATING VOLTAGE 10 9 –50 – 100 125 TEMPERATURE ( C) LT1246 • TPC01 Start-Up Current 200 START-UP THRESHOLD 150 ...

Page 5

W U TYPICAL PERFOR A 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 – 100 125 TEMPERATURE ( C) LT1246 • TPC10 Low Level Output Saturation Voltage 1.0 ...

Page 6

LT1246/LT1247 W U TYPICAL PERFOR A Output Deadtime vs Oscillator Frequency 100 OSCILLATOR FREQUENCY (kHz) Output Rise and Fall Time V = 15V TIME 50ns/DIV 1nF L 1246/7 G20 ...

Page 7

GND (Pin 5): Ground. OUTPUT (Pin 6): Current Output. This pin is the output of a high current totem pole output stage capable of driving ...

Page 8

LT1246/LT1247 PPLICATI FOR ATIO inverting input (pin 2) and the output (pin 1) are made available to the user. The output voltage in a regulator circuit is normally fed back to the inverting input ...

Page 9

PPLICATI S I FOR ATIO ing conditions (V = 2.5V). The blanking time goes to zero FB as the feedback pin is pulled to 0V. This means that the blanking time will be minimized during start-up ...

Page 10

LT1246/LT1247 TYPICAL PPLICATI EXTERNAL V REF 8 R COMP 1 C FEEDBACK 2 I SENSE 3 V REF COMP R2 100k 1 FEEDBACK – 2.5V 1.67 V ...

Page 11

... FEEDBACK + 2.5V 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. S Slope Compensation at I Pin ...

Page 12

... MAX 0.255 0.015* (6.477 0.381) 0.015 (0.380 MIN N8 0694 0.189 – 0.197* (4.801 – 5.004 0.228 – 0.244 (5.791 – 6.197 LT/GP 0395 5K REV A • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1992 0.150 – 0.157* (3.810 – 3.988) SO8 0294 ...

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