RC

filter

BOOST

OSCILLATOR

SYNC

FB

OFF/BLANK

TIME

PULSE

GENERATOR

CURRENT

RAMP

GENERATOR

BLANK

TIME

SW

OVP

S

OCP

LIGHT

LOAD

R

R

R

R

-

+

FSET

CTRL

ADAPTIVE

VOLTAGE

CONTROL

D

CURRENT

SENSE

PGND

R1

R2

LP8862-Q1

www.ti.com

SNVSA75A – NOVEMBER 2015 – REVISED NOVEMBER 2015

Feature Description (continued)

Figure 8. Boost Block Diagram

DC-DC can be driven by an external SYNC signal between 300 kHz…2.2 MHz (Table 2). If the external

external frequency disappears and SYNC pin level is low, DC-DC continues operation without spread spectrum

immediately. If SYNC remains high, DC-DC continues switching with spread spectrum enabled after 256 µs.

The optional spread spectrum feature (±3% from central frequency, 1-kHz modulation frequency) reduces EMI

noise at the switching frequency and its harmonic frequencies. When external synchronization is used, internal

spread spectrum feature is not available.

Table 2. DC-DC Synchronization Mode

SYNC PIN INPUT

MODE

Low

Spread spectrum disabled

High

Spread spectrum enabled

300...2200 kHz frequency

Spread spectrum disabled, external synchronization mode

TYPICAL

TYPICAL INPUT

CURRENT

FREQUENCY

MINIMUM SWITCH

BLANK

CURRENT

RANGE

INDUCTANCE

AND OUTPUT

RAMP

(kHz)

TIME (ns)

RAMP (A/s)

(µH)

CAPACITORS (µF)

DELAY (ns)

2 × 10 (ceramic) +

1

300...480

33

150

95

24

550

33 (electrolytic)

10 (ceramic) +

2

480...1150

15

60

95

43

300

33 (electrolytic)

3

1150...1650

10

3 × 10 (ceramic)

40

95

79

0

4

1650...2200

4.7

3 × 10 (ceramic)

40

70

145

0

(1)

Parameters are for reference only

(2)

Due to current-sensing comparator delay the actual minimum off time is 6 ns (typical) longer than in the table.

Copyright © 2015, Texas Instruments Incorporated

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