LT8300
applicaTions inForMaTion
3.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
MAXIMUM
OUTPUT
POWER
MAXIMUM
OUTPUT
POWER
3.0
2.5
2.0
1.5
1.0
0.5
0
N = 12:1
N = 8:1
N = 6:1
N = 4:1
N = 8:1
N = 6:1
N = 4:1
N = 2:1
0
20
40
60
80
100
0
20
40
60
80
100
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
8300 F01
8300 F02
Figure 1. Output Power for 3.3V Output
Figure 2. Output Power for 5V Output
3.5
3.5
N = 4:1
MAXIMUM
OUTPUT
POWER
N = 2:1
3.0
2.5
2.0
1.5
1.0
0.5
0
3.0
2.5
2.0
1.5
1.0
0.5
0
N = 3:1
N = 3:2
N = 1:1
MAXIMUM
OUTPUT
POWER
N = 2:1
N = 1:1
N = 1:2
0
20
40
60
80
100
0
20
40
60
80
100
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
8300 F03
8300 F04
Figure 3. Output Power for 12V Output
Figure 4. Output Power for 24V Output
Primary Inductance Requirement
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
minimumswitch-ontimeismainlyforleading-edgeblank-
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
loopwillloseitsabilitytoregulate.Therefore,thefollowing
equation relating to maximum input voltage must also be
followedinselectingprimary-sidemagnetizinginductance:
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
primarySWpin.Thesample-and-holderroramplifierneeds
aminimum350nstosettleandsamplethereflectedoutput
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:
tOFF(MIN) •NPS • V
+ VF
(
)
OUT
tON(MIN) • VIN(MAX)
LPRI
≥
LPRI
≥
ISW(MIN)
ISW(MIN)
t
= Minimum switch-off time = 350ns
OFF(MIN)
t
= Minimum Switch-On Time = 160ns
ON(MIN)
I
= Minimum switch current limit = 52mA
SW(MIN)
8300f
11
Linear [ Linear ]
