Data Sheet

LT8349

analog.com

Rev B

18 of 29

1.0

127

2.9

33.2

1.1

113

3.0

30.9

1.2

102

3.1

29.4

1.3

93.1

3.2

28.0

1.4

84.5

3.3

26.7

1.5

78.7

3.4

25.5

1.6

73.2

3.5

24.3

1.7

68.1

3.6

23.2

1.8

61.9

3.7

22.1

1.9

59.0

3.8

21.0

2.0

54.9

3.9

20.0

2.1

51.1

4.0

18.7

The operating frequency of the LT8349 can be synchronized to an external clock source with 100ns minimum pulse

width. Figure 26 shows the external clock threshold (typ) required at the SYNC pin for synchronization.

Figure 26. Sync/Mode Pin Logic Level (typ) vs Input Voltage

By providing a digital clock signal to the SYNC/MODE pin, the IC operates at the half of the SYNC clock frequency and

automatically enters FCM operation at light load. While in FCM the oscillator operates continuously, and the falling

SW1 and SW2 transitions are aligned to the rising edges of the clock alternatively (180° out-of-phase), with a delay

time of 80ns (typical). Figure 27 shows the synchronization between the SYNC/MODE pin input clock and the SW1

and SW2 transitions. If this feature is used, an RT resistor should be chosen to program switching frequency as close

as possible to the SYNC pulse frequency.

Figure 27. The synchronization between the SYNC/MODE pin input clock and the SW1 and SW2 transitions

SYNC LOGIC HIGH

SYNC LOGIC LOW

INPUT VOLTAGE (V)

2.5

3.0

3.5

4.0

4.5

5.0

5.5

0

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

tDELAY

tDELAY

SYNC

INPUT

SW1

SW2

tDELAY

tDELAY