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PDF LT8303 Data sheet ( Hoja de datos )
| Número de pieza | LT8303 | |
| Descripción | Micropower Isolated Flyback Converter | |
| Fabricantes | Linear | |
| Logotipo |  |
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Features
n 5.5V to 100V Input Voltage Range
n 450mA, 150V Internal DMOS Power Switch
n Up to 5W of Output Power
n Low Quiescent Current:
70µA in Sleep Mode
280µA in Active Mode
n Boundary Mode Operation at Heavy Load
n Low-Ripple Burst Mode® Operation at Light Load
n Minimum Load <0.5% (Typ) of Full Output
n VOUT Set with a Single External Resistor
n No Transformer Third Winding or Opto-Isolator
Required for Regulation
n Accurate EN/UVLO Threshold and Hysteresis
n Internal Compensation and Soft-Start
n 5-Lead TSOT-23 Package
Applications
n Isolated Telecom, Datacom, Automotive, Industrial,
and Medical Power Supplies
n Isolated Auxiliary/Housekeeping Power Supplies
LT8303
100VIN Micropower Isolated
Flyback Converter with
150V/450mA Switch
Description
The LT®8303 is a micropower high voltage isolated flyback
converter. By sampling the isolated output voltage directly
from the primary-side flyback waveform, the part requires
no third winding or opto-isolator for regulation. The output
voltage is programmed with a single external resistor.
Internal compensation and soft-start further reduce external
component count. Boundary mode operation provides a
small magnetic solution with excellent load regulation.
Low ripple Burst Mode operation maintains high efficiency
at light load while minimizing the output voltage ripple.
A 450mA, 150V DMOS power switch is integrated along
with all high voltage circuitry and control logic into a 5-lead
ThinSOT™ package.
The LT8303 operates from an input voltages range of
5.5V to 100V and can deliver up to 5W of isolated output
power. The high level of integration and the use of boundary
and low ripple burst modes result in a simple to use, low
component count, and high efficiency application solution
for isolated power delivery.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents, including 5438499, 7463497,
and 7471522.
Typical Application
VIN
6V TO 80V
6V to 80VIN, 5VOUT Isolated Flyback Converter
4.7µF
VIN
LT8303
EN/UVLO
SW
GND
RFB
8303 TA01a
T1
6:1
•
150µH
4.2µH
•
VOUT+
5V
100µF
VOUT–
316k
2.5mA TO 0.33A (VIN = 12V)
2.5mA TO 0.52A (VIN = 24V)
2.5mA TO 0.73A (VIN = 48V)
2.5mA TO 0.84A (VIN = 72V)
For more information www.linear.com/LT8303
Efficiency vs Load Current
100
90
80
70
60
VIN = 12V
50 VIN = 24V
VIN = 48V
40 VIN = 72V
0 100 200 300 400 500 600 700 800 900
LOAD CURRENT (mA)
8303 TA01b
8303f
1
1 page  
LT8303
Typical Performance Characteristics TA = 25°C, unless otherwise noted.
EN/UVLO Enable Threshold
1.28
1.27
1.26
1.25
RISING
1.24
1.23 FALLING
1.22
1.21
1.20
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8303 G10
EN/UVLO Hysteresis Current
5
4
3
2
1
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8303 G11
RFB Regulation Current
105
104
103
102
101
100
99
98
97
96
95
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8303 G12
RDS(ON)
10
1SW = 100mA
8
6
4
2
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8303 G13
Switch Current Limit
700
600 MAXIMUM CURRENT LIMIT
500
400
300
200
MINIMUM CURRENT LIMIT
100
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8303 G14
Maximum Switching Frequency
500
400
300
200
100
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8303 G15
Minimum Switching Frequency
20
16
12
8
4
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8303 G16
Minimum Switch-On Time
400
300
200
100
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8303 G17
For more information www.linear.com/LT8303
Minimum Switch-Off Time
400
300
200
100
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8303 G18
8303f
5
5 Page 
Applications Information
6
MAXIMUM
5
OUTPUT
POWER
N = 12:1
4 N = 8:1
N = 6:1
3
N = 4:1
2
1
ASSUME 80% EFFICIENCY
0
0 20 40 60 80 100
INPUT VOLTAGE (V)
8303 F01
Figure 1. Output Power for 3.3V Output
6
MAXIMUM
OUTPUT
5 POWER
4
3
2
N =4:1
N = 3:1
N = 2:1
N = 1:1
1
ASSUME 85% EFFICIENCY
0
0 20 40 60 80 100
INPUT VOLTAGE (V)
8303 F03
Figure 3. Output Power for 12V Output
LT8303
6
MAXIMUM
5 OUTPUT
POWER
4
3
2
N = 8:1
N = 6:1
N = 4:1
N = 2:1
1
ASSUME 85% EFFICIENCY
0
0 20 40 60 80 100
INPUT VOLTAGE (V)
8303 F02
Figure 2. Output Power for 5V Output
6
MAXIMUM
5
OUTPUT
POWER
4
3
2
N = 2:1
N = 3:2
N = 1:1
N = 1:2
1
ASSUME 85% EFFICIENCY
0
0 20 40 60 80 100
INPUT VOLTAGE (V)
8303 F04
Figure 4. Output Power for 24V Output
Primary Inductance Requirement
In addition to the primary inductance requirement for
The LT8303 obtains output voltage information from the
reflected output voltage on the SW pin. The conduction
of secondary current reflects the output voltage on the
primary SW pin. The sample-and-hold error amplifier needs
a minimum 350ns to settle and sample the reflected output
voltage. In order to ensure proper sampling, the second-
ary winding needs to conduct current for a minimum of
350ns. The following equation gives the minimum value
for primary-side magnetizing inductance:
( )
LPRI
≥
tOFF(MIN)
• NPS • VOUT
ISW(MIN)
+
VF
the minimum switch-off time, the LT8303 has minimum
switch-on time that prevents the chip from turning on
the power switch shorter than approximately 160ns. This
minimum switch-on time is mainly for leading-edge blank-
ing the initial switch turn-on current spike. If the inductor
current exceeds the desired current limit during that time,
oscillation may occur at the output as the current control
loop will lose its ability to regulate. Therefore, the following
equation relating to maximum input voltage must also be
followed in selecting primary-side magnetizing inductance:
LPRI
≥
tON(MIN) • VIN(MAX)
ISW(MIN)
tOFF(MIN) = Minimum switch-off time = 350ns
tON(MIN) = Minimum Switch-On Time = 160ns
ISW(MIN) = Minimum switch current limit = 105mA
8303f
For more information www.linear.com/LT8303
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT8303.PDF ] | |
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