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LT1246CS8#PBF

P1-P3P4-P6P7-P9P10-P12
1
LT1246/LT1247
1MHz Off-Line
Current Mode PWM
and DC/DC Converter
+
–
+
–
1
2
FEEDBACK
COMPENSATION
2.5V
2R
R
1V
1.5V
–
+
3
I
SENSE
BLANKING
1mA
5.6V
4
R
T
/C
T
OSCILLATOR
R
S
18V
7V
CC
UV
LOCKOUT
5 GND
6 OUTPUT
8
V
REF
5V REF
MAIN BIAS
REFERENCE PULLDOWN
OUTPUT
PULLDOWN
REFERENCE ENABLE
LT1246 • BD01
D
U
ESCRIPTIO
S
F
EA
T
U
RE
U
S
A
O
PP
L
IC
AT
I
■
Current Mode Operation to 1MHz
■
30ns Current Sense Delay
■
< 250µA 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
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 V
OUT
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.
W
IDAGRA
B
L
O
C
K
Minimum
Start-Up Operating Maximum
Device Threshold Voltage Duty Cycle Replaces
LT1246 16V 10V 100% UC1842
LT1247 8.4V 7.6V 100% UC1843
LT1246/LT1247
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 ● 320 mV
Load Regulation 1mA < I
REF
< 20mA ● –6 –25 mV
Temperature Stability 0.1 mV/°C
Total Output Variation Line, Load, Temperature ● 4.87 5.13 V
Output Noise Voltage 10Hz < F < 10kHz, T
J
= 25°C50µV
Long-Term Stability T
A
= 125°C, 1000 Hrs. 5 25 mV
Output Short-Circuit Current ● –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
= 6.2k, C
T
= 500pF, T
J
= 25°C 465 500 535 kHz
Voltage Stability 12V < V
CC
< 25V, T
J
= 25°C1%
Temperature Stability T
MIN
< T
J
< T
MAX
–0.05 %/°C
Amplitude 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
PIN
1
= 2.5V ● 2.42 2.50 2.58 V
Input Bias Current V
FB
= 2.5V ● –2 µA
Open-Loop Voltage Gain 2 < V
O
< 4V ● 65 90 dB
Unity-Gain Bandwidth T
J
= 25°C 1 2 MHz
Power Supply Rejection Ratio 12V < V
CC
< 25V ● 60 dB
Output Sink Current V
PIN
2
= 2.7V, V
PIN
1
= 1.1V ● 26 mA
Output Source Current V
PIN
2
= 2.3V, V
PIN
1
= 5V ● –0.5 –0.75 mA
(Notes 1, 2)
E
LECTR
IC
AL C CHARA TERIST
ICS
WU
U
PACKAGE
/
O
RDER I FOR ATIO
A
U
G
W
A
W
U
W
ARB
S
O
LU
T
EXI T
I
S
Supply Voltage ....................................................... 25V
Output Current...................................................... ±1A*
Output Energy (Capacitive Load per Cycle)............. 5µJ
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
LT1246C/LT1247C ............................. 0°C to 100°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.
S8 PART MARKING
LT1246CN8
LT1246CS8
LT1247CN8
LT1247CS8
ORDER PART
NUMBER
1246
1247
Consult factory for Industrial and Military grade parts.
1
2
3
4
8
7
6
5
TOP VIEW
COMP
FB
I
SENSE
R
T
/C
T
V
REF
V
CC
OUTPUT
GND
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 100°C, θ
JA
= 130°C/W (N8)
T
JMAX
= 100°C, θ
JA
= 150°C/W (S8)
3
LT1246/LT1247
E
LECTR
IC
AL C CHARA TERIST
ICS
(Notes 1, 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Error Amplifier Section
Output Voltage High Level V
PIN
2
= 2.3V, R
L
= 15k to GND ● 5 5.6 V
Output Voltage Low Level V
PIN
2
= 2.7V, R
L
= 15k to Pin 8 ● 0.2 1.1 V
Current Sense Section
Gain ● 2.85 3.00 3.15 V/V
Maximum Current Sense Input Threshold V
PIN 3
< 1.1V ● 0.90 1.00 1.10 V
Power Supply Rejection Ratio 70 dB
Input Bias Current ● –1 –10 µA
Delay to Output 30 ns
Blanking Time 60 ns
Blanking Override Voltage 1.5 V
Output Section
Output Low Level I
OUT
= 20mA ● 0.25 0.4 V
I
OUT
= 200mA ● 0.75 2.2 V
Output High Level I
OUT
= 20mA ● 12.0 V
I
OUT
= 200mA ● 11.75 V
Rise Time C
L
= 1nF, T
J
= 25°C3070ns
Fall Time C
L
= 1nF, T
J
= 25°C2060ns
Output Clamp Voltage I
O
= 1mA ● 18 19 V
Undervoltage Lockout
Start-Up Threshold LT1246 ● 15 16 17 V
LT1247
● 7.8 8.4 9.0 V
Minimum Operating Voltage LT1246 ● 9.0 10 11 V
LT1247
● 7.0 7.6 8.2 V
Hysteresis LT1246 ● 5.5 6.0 V
LT1247
● 0.4 0.8 V
PWM
Maximum Duty Cycle T
J
= 25°C 94 100 %
Minimum Duty Cycle T
J
= 25°C0%
Total Device
Start-Up Current ● 170 250 µA
Operating Current ● 13 20 mA
The ● 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.
Note 2: Low duty cycle pulse techniques are used during test to maintain
junction temperature close to ambient.
P1-P3P4-P6P7-P9P10-P12

LT1246CS8#PBF

Mfr. #:
Buy LT1246CS8#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Controllers 1MHz Off-Line C Mode PWM & DC/DC Conv
Lifecycle:
New from this manufacturer.
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