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LT8300

8300f

applicaTions inForMaTion

Figure 4. Output Power for 24V Output

Figure 1. Output Power for 3.3V Output

Figure 2. Output Power for 5V Output

Figure 3. Output Power for 12V Output

INPUT VOLTAGE (V)

3.5

2.5

1.5

3.0

2.0

1.0

0.5

8300 F01

100

N = 12:1

MAXIMUM

OUTPUT

POWER

N = 8:1

N = 6:1

N = 4:1

INPUT VOLTAGE (V)

3.5

2.5

1.5

3.0

2.0

1.0

0.5

8300 F02

100

MAXIMUM

OUTPUT

POWER

N = 2:1

N = 4:1

N = 6:1

N = 8:1

INPUT VOLTAGE (V)

3.5

2.5

1.5

3.0

2.0

1.0

0.5

8300 F03

100

N = 4:1

MAXIMUM

OUTPUT

POWER

N = 3:1

N = 2:1

N = 1:1

INPUT VOLTAGE (V)

3.5

2.5

1.5

3.0

2.0

1.0

0.5

8300 F04

100

N = 1:1

N = 3:2

N = 1:2

MAXIMUM

OUTPUT

POWER

N = 2:1

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

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:

LPRI ≥

tOFF(MIN) •NPS • VOUT + VF

(

)

ISW(MIN)

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

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:

LPRI ≥

tON(MIN) • VIN(MAX)

ISW(MIN)

tON(MIN) = Minimum Switch-On Time = 160ns

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