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LT1737IGN#TRPBF

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1
LT1737
1737fa
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
U
FEATURES
DESCRIPTIO
U
High Power
Isolated Flyback Controller
The LT
®
1737 is a monolithic switching regulator control-
ler specifically designed for the isolated flyback topology.
It drives the gate of an external MOSFET and is generally
powered from a DC supply voltage. Output voltage feed-
back information may be supplied by a variety of methods
including a third transformer winding, the primary wind-
ing or even direct DC feedback (see Applications Informa-
tion). Its gate drive capability, coupled with a suitable
external MOSFET and other power path components, can
deliver load power up to tens of Watts.
The LT1737 has a number of features not found on other
isolated flyback controller ICs. By utilizing current mode
switching techniques, it provides excellent AC and DC line
regulation. Its unique control circuitry can maintain regu-
lation well into discontinuous mode in most applications.
Optional load compensation circuitry allows for improved
load regulation. An optional undervoltage lockout pin
halts operation when the application input voltage is too
low. An optional external capacitor implements a soft-
start function.
■
Drives External Power MOSFET
■
Supply Voltage Range: 4.5V to 20V
■
Flyback Voltage Limited Only by
External Components
■
Senses Output Voltage Directly from Primary Side
Winding—No Optoisolator Required
■
Switching Frequency from 50kHz to 250kHz
with External Capacitor
■
Moderate Accuracy Regulation Without User Trims
■
Regulation Maintained Well into Discontinuous Mode
■
External I
SENSE
Resistor
■
Optional Load Compensation
■
Optional Undervoltage Lockout
■
Shutdown Feature Reduces I
Q
to 50µA Typ
■
Available in 16-Pin GN and SO Packages
■
Isolated Flyback Switching Regulators
■
Medical Instruments
■
Instrumentation Power Supplies
12V-18V to Isolated 15V Converter
PGND
I
SENSE
GATE
V
C
FB
R1
0.27Ω
M1
IRFL014
T1
COILTRONICS
CTX150-4
V
IN
V
CC
UVLO
SGND
1737 TA01
R
CMPC
R
OCMP
MINENAB
LT1737
ENDLYOSCAP t
ON
R3
3.01k
1%
C3
0.1µF
•
•
D1
MBRS1100
C2
33µF
+
R4
7.5k
V
OUT
= 15V
I
OUT
= 300mA
D2
BAS16
Q1
2N3906
R2
35.7k
1%
C1
22µF
150µH 150µH
+
240k
33k
1nF
47pF
75k 150k 100k 4.7k 0.1µF
NOTE: SEE APPLICATIONS
INFORMATION FOR ADDITIONAL
COMPONENT SPECIFICATIONS
TYPICAL APPLICATIO
U
2
LT1737
1737fa
(Note 1)
V
CC
Supply Voltage................................................. 22V
UVLO Pin Voltage .................................................... V
CC
I
SENSE
Pin Voltage .................................................... 2V
FB Pin Current ..................................................... ±2mA
Operating Junction
Temperature Range
LT1737C ............................................... 0°C to 100°C
LT1737I ............................................ –40°C to 125°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
ORDER PART
NUMBER
LT1737CGN
LT1737CS
LT1737IGN
LT1737IS
T
JMAX
= 125°C, θ
JA
= 110°C/W (GN)
T
JMAX
= 125°C, θ
JA
= 110°C/W (SO)
PACKAGE/ORDER I FOR ATIO
UU
W
ABSOLUTE AXI U RATI GS
WWWU
TOP VIEW
S PACKAGE
16-LEAD PLASTIC SO
GN PACKAGE
16-LEAD PLASTIC SSOP
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
PGND
I
SENSE
SFST
R
OCMP
R
CMPC
OSCAP
V
C
FB
GATE
V
CC
t
ON
ENDLY
MINENAB
SGND
UVLO
3V
OUT
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 14V, GATE open, V
C
= 1.4V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Power Supply
V
CC(MIN)
Minimum Input Voltage ● 4.1 4.5 V
I
CC
Supply Current V
C
= Open ● 10 15 mA
Shutdown Current V
UVLO
= 0V, V
C
= Open ● 50 150 µA
Feedback Amplifier
V
FB
Feedback Voltage 1.230 1.245 1.260 V
● 1.220 1.270 V
I
FB
Feedback Pin Input Current 500 nA
g
m
Feedback Amplifier Transconductance ∆l
C
= ±10µA ● 400 1000 1800 µmho
I
SRC
, I
SNK
Feedback Amplifier Source or Sink Current ● 30 50 80 µA
V
CL
Feedback Amplifier Clamp Voltage 2.5 V
Reference Voltage/Current Line Regulation 4.75V ≤ V
IN
≤ 18V ● 0.01 0.05 %/V
Voltage Gain V
C
= 1V to 2V 2000 V/V
Soft-Start Charging Current V
SFST
= 0V 25 40 50 µA
Soft-Start Discharge Current V
SFST
= 1.5V, V
UVLO
= 0V 0.8 1.5 mA
Gate Output
V
GATE
Output High Level I
GATE
= 100mA ● 11.5 12.1 V
I
GATE
= 500mA ● 11.0 11.8 V
Output Low Level I
GATE
= 100mA ● 0.3 0.45 V
I
GATE
= 500mA ● 0.6 1.0 V
I
GATE
Output Sink Current in Shutdown, V
UVLO
= 0V V
GATE
= 2V ● 1.2 2.5 mA
t
r
Rise Time C
L
= 1000pF 30 ns
t
f
Fall Time C
L
= 1000pF 30 ns
GN PART MARKING
1737
1737I
Consult LTC Marketing for parts specified with wider operating temperature ranges.
3
LT1737
1737fa
Note 1: Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2: Component value range guaranteed by design.
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 14V, GATE open, V
C
= 1.4V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Current Amplifier
V
C
Control Pin Threshold Duty Cycle = Min 0.90 1.12 1.25 V
● 0.80 1.35 V
V
ISENSE
Switch Current Limit Duty Cycle ≤ 30% 220 250 270 mV
Duty Cycle ≤ 30%
● 200 280 mV
Duty Cycle = 80% 220 mV
∆V
ISENSE
/∆V
C
0.30 mV
Timing
f Switching Frequency C
OSCAP
= 100pF 90 100 115 kHz
● 80 125 kHz
C
OSCAP
Oscillator Capacitor Value (Note 2) 33 200 pF
t
ON
Minimum Switch On Time R
tON
= 50k 200 ns
t
ED
Flyback Enable Delay Time R
ENDLY
= 50k 200 ns
t
EN
Minimum Flyback Enable Time R
MENAB
= 50k 200 ns
R
t
Timing Resistor Value (Note 2) 24 240 kΩ
Maximum Switch Duty Cycle ● 85 90 %
Load Compensation
Sense Offset Voltage 25mV
Current Gain Factor 0.80 0.95 1.05 mV
UVLO Function
V
UVLO
UVLO Pin Lockout Threshold ● 1.21 1.25 1.29 V
UVLO Pin Shutdown Threshold 0.75 V
● 0.4 0.95 V
I
UVLO
UVLO Pin Bias Current V
UVLO
= 1.2V –0.25 +0.1 + 0.25 µA
V
UVLO
= 1.3V –4.50 –3.5 – 2.50 µA
3V Output Function
V
REF
Reference Output Voltage I
LOAD
= 1mA ● 2.8 3.0 3.2 V
Output Impedance 10 Ω
Current Limit ● 815 mA
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LT1737IGN#TRPBF

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Buy LT1737IGN#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators Hi Pwr Iso Fly Cntr
Lifecycle:
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