LP87702 datasheet(18/98 Pages) TI

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7.3.2 Boost Converter

The LP87702 device integrates a boost converter with programmable output voltage from 4.9 V to 5.2 V in 0.1

V steps, and input voltage range from 2.8 V to 4 V. The boost converter has flexibility to support wide range of

application conditions:

• Forced PWM operation

• Optional external clock input to minimize crosstalk

• Optional spread spectrum technique to reduce EMI

• Synchronous rectification

• Current mode loop with PI compensator

• Soft start

• Programmable output voltage monitoring with maskable interrupt and selectable connection to PG0 and PG1

or both

The following parameters can be programmed through the registers, with default values set by the OTP bits

(unless otherwise noted):

• Output voltage level (BOOST_VSET)

• Switch current limit (BOOST_ILIM)

• Enable and disable delays when ENx pin control is used (BOOST_DELAY register)

• Output pulldown resistor enable or disable when boost is disabled (BOOST_RDIS_EN bit, discharge is

enabled by default)

• Output voltage monitoring enable or disable and monitoring window thresholds

The boost converter operates in forced PWM mode with fixed switching frequency across all load currents.

When boost is disabled, boost output is isolated from the input voltage rail.

Boost converter supports an alternative operating mode as a bypass or load switch, with input voltage range

from 4.5 V to 5.5 V. Operating mode is selected in OTP and is fixed; changing the mode on-the-fly is not

supported.

7.3.3 Spread-Spectrum Mode

Systems with periodic switching signals may generate a large amount of switching noise in a set of narrowband

frequencies (the switching frequency and its harmonics). The usual solution to reduce noise coupling is to add

EMI-filters and shields to the boards. The LP87702 device supports the spread-spectrum switching frequency

modulation mode that is register controlled. This mode minimizes the need for output filters, ferrite beads, or

chokes. The switching frequency varies between 0.85 × fSW and fSW in spread spectrum mode, where fSW is

switching the frequency selected in the OTP. Figure 7-2 shows how the spread spectrum modulation reduces

conducted and radiated emissions by the converter and associated passive components and PCB traces. This

feature is available only when internal RC oscillator is used (EN_PLL is 0 in PLL_CTRL register) and it is

enabled with the EN_SPREAD_SPEC bit in CONFIG register, and it affects both buck converters and the boost

converter.

LP87702

SNVSBU3 – MARCH 2021

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