LT8301H Просмотр технического описания (PDF) - Linear Technology
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LT8301H Datasheet PDF : 24 Pages
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LT8301
APPLICATIONS INFORMATION
7
6
MAXIMUM
OUTPUT
CURRENT
5
4
3
N = 5:1
N = 3:1
N = 2:1
2
N = 1:1
1
0
0
10
20
30
40
INPUT VOLTAGE (V)
8301 F01
Figure 1. Output Power for 3.3V Output
7
6
MAXIMUM
OUTPUT
CURRENT
5
4
3
2
N = 3:2
N = 1:1
N = 2:3
N = 1:3
1
0
0
10
20
30
40
INPUT VOLTAGE (V)
8301 F03
Figure 3. Output Power for 12V Output
7
6
MAXIMUM
OUTPUT
CURRENT
5
4
3
2
N = 4:1
N = 3:1
N = 2:1
N = 1:1
1
0
0
10
20
30
40
INPUT VOLTAGE (V)
8301 F02
Figure 2. Output Power for 5V Output
7
6
MAXIMUM
OUTPUT
CURRENT
5
4
3
2
N = 4:5
N = 1:2
N = 1:3
N = 1:5
1
0
0
10
20
30
40
INPUT VOLTAGE (V)
8301 F04
Figure 4. Output Power for 24V Output
Primary Inductance Requirement
The LT8301 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 450ns 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
450ns. The following equation gives the minimum value
for primary-side magnetizing inductance:
( ) LPRI
≥
tOFF(MIN)
•NPS • VOUT
ISW(MIN)
+
VF
In addition to the primary inductance requirement for
the minimum switch-off time, the LT8301 has minimum
switch-on time that prevents the chip from turning on
the power switch shorter than approximately 170ns. 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 = 450ns
ISW(MIN) = Minimum switch current limit = 290mA (typ)
tON(MIN) = Minimum switch-on time = 170ns
8301f
For more information www.linear.com/LT8301
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