LT8331 datasheet(19/30 Pages) AD

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LT8331

19

Rev. C

For more information www.analog.com

APPLICATIONS INFORMATION

In a SEPIC converter, no DC path exists between the input

and output. This is an advantage over the boost converter

for applications requiring the output to be disconnected

from the input source when the circuit is in shutdown.

SEPIC Converter: Switch Duty Cycle and Frequency

For a SEPIC converter operating in CCM, the duty cycle

of the main switch can be calculated based on the output

voltage (VOUT), the input voltage (VIN) and the diode for-

ward voltage (VD).

The maximum duty cycle (DMAX) occurs when the con-

verter operates at the minimum input voltage:

DMAX =

VOUT + VD

VIN(MIN) + VOUT + VD

Conversely, the minimum duty cycle (DMIN) occurs when

the converter operates at the maximum input voltage:

DMIN =

VOUT + VD

VIN(MAX) + VOUT + VD

Be sure to check that DMAX and DMIN obey:

DMAX < 1 – Minimum Off-Time(MAX) • fOSC(MAX)

and

DMIN > Minimum On-Time(MAX) • fOSC(MAX)

where Minimum Off-Time, Minimum On-Time and fOSC

are specified in the Electrical Characteristics table.

SEPIC Converter: The Maximum Output Current

Capability and Inductor Selection

As shown in Figure 8, the SEPIC converter contains two

inductors: L1 and L2. L1 and L2 can be independent,

but can also be wound on the same core, since iden-

tical voltages are applied to L1 and L2 throughout the

switching cycle.

For the SEPIC topology, the current through L1 is the

converter input current. Based on the fact that, ideally, the

output power is equal to the input power, the maximum

average inductor currents of L1 and L2 are:

IL1(MAX)(AVE) =IIN(MAX)(AVE)=IO(MAX) •

DMAX

1 − DMAX

IL2(MAX)(AVE)= IO(MAX)

In a SEPIC converter, the switch current is equal to IL1 +

IL2 when the power switch is on, therefore, the maximum

average switch current is defined as:

ISW(MAX)(AVE) = IL1(MAX)(AVE)+ IL2(MAX)(AVE)

=IO(MAX) •

1

1 − DMAX

and the peak switch current is:

ISW(PEAK) = 1 +

c

2

⎛

⎝

⎜

⎞

⎠

⎟ • IO(MAX) •

1

1 − DMAX

The constant c in the preceding equations represents

the percentage peak-to-peak ripple current in the switch,

relative to ISW(MAX)(AVE), as shown in Figure 9. Then, the

switch ripple current ∆ISW can be calculated by:

∆ISW = c • ISW(MAX)(AVE)

The inductor ripple currents ∆IL1 and ∆IL2 are identical:

∆IL1 = ∆IL2 = 0.5 • ∆ISW

Figure 9. The Switch Current Waveform of the SEPIC Converter

8331 F09

∆ISW = χ•ISW(MAX)(AVE)

ISW

t

DTS

ISW(MAX)(AVE)

TS

Số phần tương tự - LT8331

nhà sản xuất	tên linh kiện	bảng dữ liệu	Giải thích chi tiết về linh kiện
Linear Technology	LT8331	1Mb / 30P	Low IQ Boost/SEPIC/ Flyback/Inverting Converter with 0.5A, 140V Switch
Analog Devices	LT8331	1Mb / 24P	28V, 5A Low IQ Synchronous Step-Up Silent Switcher with PassThru
	LT8331	1Mb / 24P	Low IQ Boost/SEPIC/Inverting Converter with 5A, 40V Switch
	LT8331	2Mb / 34P	60V 2MHz Low-IQ Boost, SEPIC and Flyback Controller Rev. 0
	LT8331	2Mb / 30P	Low IQ Boost/SEPIC/Inverting Converter with 1.5A, 150V Switch Rev. A

More results

Mô tả tương tự - LT8331

nhà sản xuất	tên linh kiện	bảng dữ liệu	Giải thích chi tiết về linh kiện
Linear Technology	LT8331	1Mb / 30P	Low IQ Boost/SEPIC/ Flyback/Inverting Converter with 0.5A, 140V Switch
	LT8362	2Mb / 32P	Low IQ Boost/SEPIC/ Inverting Converter with 2A, 60V Switch
	LT8335	1Mb / 20P	Low IQ Boost/SEPIC/ Inverting Converter with 2A, 28V Switch
	LT8361	1Mb / 28P	Low IQ Boost/SEPIC/ Inverting Converter with 2A, 100V Switch
Analog Devices	LT8365	2Mb / 30P	Low IQ Boost/SEPIC/Inverting Converter with 1.5A, 150V Switch Rev. A
Analog Devices	LT8334	1Mb / 24P	Low IQ Boost/SEPIC/Inverting Converter with 5A, 40V Switch
Linear Technology	LT8330	1Mb / 24P	Low IQ Boost/SEPIC/ Inverting Converter with 1A, 60V Switch
	LT3957	365Kb / 28P	Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch
	LT3957	369Kb / 28P	Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch
	LT3957A	559Kb / 28P	Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch

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