LT8300E Просмотр технического описания (PDF) - Analog Devices
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LT8300E Datasheet PDF : 24 Pages
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LT8300
APPLICATIONS INFORMATION
3.5
MAXIMUM
3.0
OUTPUT
POWER
N = 12:1
2.5
N = 8:1
2.0
N = 6:1
1.5
N = 4:1
1.0
0.5
0
0
20
40
60
80 100
INPUT VOLTAGE (V)
8300 F01
Figure 1. Output Power for 3.3V Output
3.5
N = 4:1
3.0
MAXIMUM
2.5 OUTPUT
POWER
2.0
N = 3:1
N = 2:1
1.5
N = 1:1
1.0
0.5
0
0
20
40
60
80 100
INPUT VOLTAGE (V)
8300 F03
Figure 3. Output Power for 12V Output
3.5
MAXIMUM
3.0
OUTPUT
POWER N = 8:1
N = 6:1
2.5
2.0
N = 4:1
1.5
N = 2:1
1.0
0.5
0
0
20
40
60
80 100
INPUT VOLTAGE (V)
8300 F02
Figure 2. Output Power for 5V Output
3.5
N = 2:1
3.0
2.5
MAXIMUM
OUTPUT
POWER
2.0
N = 3:2
N = 1:1
1.5
N = 1:2
1.0
0.5
0
0
20
40
60
80 100
INPUT VOLTAGE (V)
8300 F04
Figure 4. Output Power for 24V Output
Primary Inductance Requirement
The LT8300 obtains output voltage information from the
reflected output voltage on the SW pin. The conduction of
secondary current reflects the output voltage on the pri-
mary SW pin. The sample-and-hold error amplifier needs
a minimum 350ns to settle and sample the reflected out-
put voltage. In order to ensure proper sampling, the sec-
ondary 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)
• N PS • VOUT
I SW (MIN)
+
VF
tOFF(MIN) = Minimum switch-off time = 350ns
ISW(MIN) = Minimum switch current limit = 52mA
In addition to the primary inductance requirement for
the minimum switch-off time, the LT8300 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
blanking 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 cur-
rent 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 magnetiz-
ing inductance:
LPRI
≥
tON(MIN) • VIN(MAX)
I SW (MIN)
tON(MIN) = Minimum Switch-On Time = 160ns
Rev. A
10
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