LT3757 datasheet(10/24 Pages) AD

10 / 24 page

LT8300

Rev. A

For more information www.analog.com

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 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) •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 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)

ISW(MIN)

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

LT3757 Datasheet(PDF) 10 Page - Analog Devices

LT3757 Datasheet(HTML) 10 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL