LT8602 datasheet(21/30 Pages) LINER

21 / 30 page

LT8602

8602fb

For more information www.linear.com/LT8602

Figure 5. Burst Mode SW Waveforms with

All Channels in Burst Mode

applicaTions inForMaTion

the system can tolerate a small current (<100µA) in this

state. If the LT8602 is disabled, the SW pin current will

drop to essentially zero. However, if the VIN or PVIN pin is

grounded while the output is held high, an external diode

is required at the VIN/PVIN pin to prevent current being

pulled out of the VIN/PVIN pin. An example is shown in

Figure 3. In this case, both OUT1 and OUT3 are held high

by batteries. PVIN1 must be diode protected, as well as

PVIN3 if it is connected to an external supply.

four channels go into Burst Mode operation, the oscillator

will also shut off between bursts with a further savings in

power(Figure5).BecausethechannelsoftheLT8602may

havedifferentloads,channelscanhavedifferentswitching

frequencies when in Burst Mode operation.

Figure 3. Reverse Protection Diodes

Figure 4. Burst Mode SW Waveforms with Oscillator Running

8602 F03

OUT3

OUT1

GND

FB3

SW3

SW1

EN/UVLO

VIN

BST1

LT8602

PVIN3

RUV1

RUV2

FB1

–

PVIN1

IN3

1µs/DIV

VSW1

10V/DIV

VSW2

10V/DIV

VSW3

5V/DIV

VSW4

5V/DIV

8602 F04

100ms/DIV

VERT

5V/DIV

VSW4

VSW3

VSW2

VSW1

8602 F05

Burst Mode Operation

To improve efficiency at light loads, the LT8602 automati-

cally switches to Burst Mode operation which minimizes

the switching loss and keeps the output voltage ripple

small. In Burst Mode operation, most of the circuits are

shut down between switch-on bursts to minimize power

loss. If at least one channel remains full frequency, the

oscillator remains on and all bursts are synchronized to

the appropriate phase of the oscillator (Figure 4). If all

Mode Selection and Synchronization

To select low ripple Burst Mode operation, tie the SYNC

pin below 0.3V (this can be ground or a logic low output).

To select pulse-skipping operation, tie the SYNC pin above

1.2V. To synchronize the LT8602 oscillator to an external

frequency connect a square wave (with 20% to 80% duty

cycle) to the SYNC pin. The square wave amplitude should

have valleys that are below SYNC VIL and peaks above

SYNC VIH (up to 6V).

The LT8602 will not enter Burst Mode operation at low

output loads while synchronized to an external clock, but

instead will pulse skip to maintain regulation. The LT8602

may be synchronized over a 250kHz to 2.2MHz range. The

RT resistor should be chosen to set the LT8602 switching

frequency equal to the synchronization input. If a range of

frequencies is used, set RT to the center of the range. For

example, if the synchronization signal will be 400kHz to

600kHz, the RT should be selected for 500kHz. The SYNC

lock range is ±20% of the RT set frequency.

For some applications it is desirable for the LT8602 to

operate in pulse-skipping mode, offering two major dif-

ferences from Burst Mode operation. First is that the clock

staysawakeatalltimesandallswitchingcyclesarealigned

to the clock. Second is that full switching frequency is

LT8602 Datasheet(PDF) 21 Page - Linear Technology

LT8602 Datasheet(HTML) 21 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Datasheet Download

Link URL