LT8580 Ver la hoja de datos (PDF) - Linear Technology

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Fabricante

LT8580

Boost/SEPIC/Inverting DC/DC Converter with 1A, 65V Switch, Soft-Start and Synchronization

Linear Technology 

LT8580

Applications Information

Using the circuit in Figure 4 as an example, Table 3 shows

the parameters used to generate the bode plot shown in

Figure 6.

140

0

120

–45

100

PHASE

–90

80

–135

60

–180

40

GAIN

20

55° AT

20kHz

–225

–270

0

–315

–20

10

–360

100

1k

10k 100k 1M

FREQUENCY (Hz)

8580 F06

Figure 6. Bode Plot for Example Boost Converter

Table 3. Bode Plot Parameters

PARAMETER

VALUE

RL

40

COUT

4.7

RESR

10

RO

305

CC

3300

CF

47

CPL

0

RC

6.04

R1

130

R2

14.6

VOUT

12

VIN

5

gma

230

gmp

7

L

15

fS

1.5

UNITS

W

µF

mW

kW

pF

pF

pF

kW

kW

kW

V

V

µmho

mho

µH

MHz

COMMENT

Application Specific

Application Specific

Application Specific

Not Adjustable

Adjustable

Optional/Adjustable

Optional/Adjustable

Adjustable

Adjustable

Not Adjustable

Application Specific

Application Specific

Not Adjustable

Not Adjustable

Application Specific

Adjustable

In Figure 6, the phase is –125° when the gain reaches 0dB

giving a phase margin of 55°. The crossover frequency is

20kHz, which is more than three times lower than the fre-

quency of the RHP zero to achieve adequate phase margin.

Diode Selection

Schottky diodes, with their low forward-voltage drops and

fast switching speeds, are recommended for use with the

LT8580. For applications where VR (see Tables 4, 5 and

6) < 40V, the Diodes, Inc. SBR1V40LP is a good choice.

Where VR > 40V, the Diodes Inc. DFLS1100 works well.

These diodes are rated to handle an average forward

current of 1A.

Oscillator

The operating frequency of the LT8580 can be set by the

internal free-running oscillator. When the SYNC pin is

driven low (< 0.4V), the frequency of operation is set by a

resistor from RT to ground. An internally trimmed timing

capacitor resides inside the IC. The oscillator frequency

is calculated using the following formula:

fOSC

=

85.5

(RT + 1)

where fOSC is in MHz and RT is in kΩ. Conversely, RT

(in kΩ) can be calculated from the desired frequency

(in MHz) using:

RT

=

85.5

fOSC

−1

Clock Synchronization

The operating frequency of the LT8580 can be synchro-

nized to an external clock source. To synchronize to the

external source, simply provide a digital clock signal into

the SYNC pin. The LT8580 will operate at the SYNC clock

frequency. The LT8580 will revert to the internal free-

running oscillator clock after SYNC is driven low for a few

free-running clock periods.

For more information www.linear.com/LT8580

8580f

15

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