Data Sheet

LT8638-2

analog.com

Rev.0

19 of 35

Figure 45. SW Frequency vs. Load Information in Burst Mode Operation

To achieve higher light load efficiency, more energy must be delivered to the output during the single small pulses

in Burst Mode operation such that the LT8638-2 can stay in sleep mode longer between each pulse. This can be

achieved using a larger value inductor (that is, 4.7µH), and should be considered independent of switching frequency

when choosing an inductor. For example, while a lower inductor value is typically used for a high switching frequency

application, if high light load efficiency is desired, a higher inductor value should be chosen. See the curve in Typical

Performance Characteristics.

While in Burst Mode operation, the current limit of the top switch is approximately 2A (as shown in Figure 46),

resulting in low output voltage ripple. Increasing the output capacitance decreases output ripple proportionally. As

load ramps upward from zero, the switching frequency increases, but only up to the switching frequency

programmed by the resistor at the RT pin, as shown in Figure 45.

Figure 46. Burst Mode Operation

The output load at which the LT8638-2 reaches the programmed frequency varies based on input voltage, output

voltage, and inductor choice. To select low ripple Burst Mode operation, tie the SYNC/MODE pin below 0.7V (this can

be ground or a logic low output).

FRONT PAGE APPLICATION

VIN = 12V

VOUT = 5V

LOAD CURRENT (A)

0

0.2

0.4

0.6

0.8

1.0

0

200

400

600

800

1000

1200

FRONT PAGE APPLICATION

12VIN TO 5VOUT AT 10mA

Burst Mode OPERATION

20µs/DIV

IL

1A/DIV

VSW

5V/DIV