LTC3609IWKG-TRPBF(RevB) Просмотр технического описания (PDF) - Linear Technology

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LTC3609IWKG-TRPBF
(Rev.:RevB)

32V, 6A Monolithic Synchronous Step-Down DC/DC Converter

Linear Technology 

LTC3609

Applications Information

with changes in VIN. Tying the FCB pin below the 0.6V

threshold forces continuous synchronous operation, al-

lowing current to reverse at light loads and maintaining

high frequency operation.

In addition to providing a logic input to force continuous

operation, the FCB pin provides a means to maintain a

flyback winding output when the primary is operating

in discontinuous mode. The secondary output VOUT2 is

normally set as shown in Figure 4 by the turns ratio N

of the transformer. However, if the controller goes into

discontinuous mode and halts switching due to a light

primary load current, then VOUT2 will droop. An external

resistor divider from VOUT2 to the FCB pin sets a minimum

voltage VOUT2(MIN) below which continuous operation is

forced until VOUT2 has risen above its minimum:

VOUT2(MIN)

=

0.6V

1+



R4

R3







Fault Conditions: Current Limit and Foldback

The LTC3609 has a current mode controller which inher-

ently limits the cycle-by-cycle inductor current not only

in steady-state operation but also in transient. To further

limit current in the event of a short circuit to ground, the

LTC3609 includes foldback current limiting. If the output

falls by more than 25%, then the maximum sense voltage is

progressively lowered to about one sixth of its full value.

INTVCC Regulator and EXTVCC Connection

An internal P-channel low dropout regulator produces the

5V supply that powers the drivers and internal circuitry

within the LTC3609. The INTVCC pin can supply up to 50mA

RMS and must be bypassed to ground with a minimum of

4.7µF tantalum or ceramic capacitor. Good bypassing is

necessary to supply the high transient currents required

by the MOSFET gate drivers.

VOUT2

CSEC +

1µF

VOUT1

+

COUT

IN4148

SW

GND

40 39 38 37 36 35 34 33 32 31 30 29 28 27

T1

1:N

VIN

+

CIN

41 SW

42 SW

43 SW

44 SW

45 SW

46 SW

47 SW

48 PVIN

49 PVIN

50 PVIN

51 PVIN

52 PVIN

LTC3609

SGND 26

NC 25

NC 24

VFB 23

ION 22

NC 21

SGND 20

FCB 19

ITH 18

VRNG 17

PGOOD 16

SGND 15

R4

OPTIONAL EXTVCC

CONNECTION

5V < VOUT2 < 7V

R3

1 2 3 4 5 6 7 8 9 10 11 12 13 14

SGND

SW

3609 F04

Figure 4. Secondary Output Loop and EXTVCC Connection

3609fb

15

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