48V No-Opto Isolated Applications

48V No-Opto Isolated Applications
VOUT+
12V
2A
4:1
VIN
22V TO 75V
10µF
412k
EN/UVLO
60.8µH
VIN
RFB
15.4k
3.8µH
243k
100µF
VOUT–
RREF
6.04k
LT3748
GATE
TC
SENSE
SS
VC
56.2k
2nF
GND
10k
INTVCC
0.033Ω
4.7µF
4700pF
The Transformer is the Only Part Crossing the Isolation Barrier
The LT®3748 is a high input voltage isolated flyback DC/DC controller that does not require an opto-isolator, third winding or signal
transformer for feedback. The output voltage is sensed from the primary-side flyback signal, and is set with two external resistors
and the transformer turns ratio. The LT3748 operates over a 5V to 100V input voltage range, drives an external N-channel power
MOSFET and maintains better than ±5% overall regulation.
Output Load and Line Regulation
Features
Input Voltage Range: 5V to 100V
12.6
No Opto-Coupler Required
Primary-Side Winding VOUT Sensing
12.4
n
n
n
VOUT Set with Two External Resistors
1.9A Onboard Gate Driver
Boundary Mode Operation
Off-the-Shelf Transformers
Only One Part Crossing the Isolation Barrier
MSOP-16 with High Voltage Spacing
Programmable Soft-Start
n
n
n
n
12.2
VOUT (V)
n
12.0
11.8
n
n
VIN = 72V
VIN = 48V
VIN = 36V
11.6
11.4
0
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
0.5
1.0
1.5
LOAD CURRENT (A)
2.0
LT3748 Demo Board
LT3748 Package Outline
TOP VIEW
VIN 1
16 RFB
EN/UVLO 3
INTVCC
GATE
SENSE
GND
14 RREF
5
6
7
8
12
11
10
9
1mm
TC
VC
SS
GND
MS PACKAGE
16 (12)-LEAD PLASTIC MSOP
Primary-Side Switch
Node Waveform
ACTUAL CIRCUIT SIZE: 38mm × 19mm × 9.5mm
N-TRANSFORMER
TURNS RATIO
The LT3748 is available in an MSOP-16 package with 4 pins
removed for high voltage spacing. The high level of integration,
readily available off-the-shelf transformers and the use of
boundary mode operation results in a simple, clean application
solution.
VC
NVOUT
VIN
tSP
OUTPUT VOLTAGE SENSING AT SWITCH NODE
Examples of Off-the-Shelf Transformers (See Data Sheet for More Options)
Target Application
20V to 75V → 12V/1A
20V to 75V → 5V/2A
10V to 40V → 10V/2.5A
30V to 75V → 12V/1A
30V to 75V → 5V/3A
10V to 40V → 5V/3A
20V to 75V → 12V/2.5A
Supplier
Size (W × L × H) (mm)
Part Number
Pulse
Pulse
Pulse
Wurth
Wurth
Wurth
Wurth
18 × 14 × 13
18 × 14 × 13
29 × 22 × 11.5
18 × 14 × 13
18 × 14 × 13
18 × 14 × 13
29 × 23 × 11.5
PA2367NL
PA1260NL
PA3177NL
750311424
750311423
750311564
750311607
Other Related Flyback Converters and Controllers from Linear Technology
Part Number
LT3511
LT3512
LT3574
LT3573
LT3575
LT3758
LT3757
VIN Range (V)
4.5 to 100
4.5 to 100
3 to 40
3 to 40
3 to 40
5.5 to 100
2.9 to 40
No Opto-Coupler Required
Onboard Switch
Max Output Power
√
√
√
√
√
0.24A/150V
0.40A/150V
0.65A/60V
1.25A/60V
2.5A/60V
NA
NA
2.5W
5W
3W
7W
14W
60W
60W
www.linear.com/3748 n 1-800-4-LINEAR
1110
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