LP87702 datasheet(17/98 Pages) TI

17 / 98 page

Some of the key parameters that can be programmed through the registers (with default values set by OTP bits):

• Output voltage

• Forced PWM operation

• Switch current limit

• Output voltage slew rate

• Enable and disable delays with ENx pin control

There are two modes of operation for the buck converters, depending on the output current required: pulse width

modulation (PWM) and pulse-frequency modulation (PFM). The converter operates in PWM mode at high load

currents of approximately 520 mA or higher. Lighter output current loads will cause the converter to automatically

switch into PFM mode for reduced current consumption when forced PWM mode is disabled. The forced PWM

mode can be selected to maintain fixed switching frequency at all load currents. When buck is disabled, buck

output is isolated from the input voltage rail. Output has an optional pulldown resistor.

Figure 7-1 shows a block diagram of a single buck converter.

POWER

GOOD

LOOP

COMP

RAMP

GENERATOR

HS FET

CURRENT

SENSE

LS FET

CURRENT

SENSE

GATE

CONTROL

IADC

VDAC

ERROR

AMP

GND

NEG

CURRENT

LIMIT

ZERO

CROSS

DETECT

POS

CURRENT

LIMIT

VIN

VOUT

CONTROL

BLOCK

PROGRAMMABLE

PARAMETERS

VOLTAGE

SETTING

SLEW RATE

CONTROL

Figure 7-1. Detailed Block Diagram Showing One Buck Converter

7.3.1.2 Transition Between PWM and PFM Modes

The LP87702 buck converter operates in PWM mode at load current of about 520 mA or higher. The device

automatically switches into PFM mode for reduced current consumption when forced PWM mode is disabled

(AUTO mode operation) at lighter load current levels. A high efficiency is achieved over a wide output-load

current range by combining the PFM and the PWM modes.

7.3.1.3 Buck Converter Load Current Measurement

Buck load current can be monitored through the I2C registers. The monitored buck converter is selected

with the LOAD_CURRENT_BUCK_SELECT bit in the SEL_I_LOAD register. A write to this selection register

starts a current measurement sequence. The converter is forced to PWM mode during the measurement. The

measurement sequence is 50 µs long at maximum. LP87702 can be configured to give out an I_MEAS_INT

interrupt in the INT_TOP_1 register after the load current measurement sequence is finished. Load current

measurement interrupt can be masked with I_MEAS_MASK bit in TOP_MASK_1 register. The measurement

result can be read from I_LOAD_1 and I_LOAD_2 registers. The buck converter load current measurement

result is 9-bit wide, with 8 LSB bits stored in I_LOAD_1 register and 1 MSB bit stored in I_LOAD_2 register. The

single bit resolution is 20 mA, with a maximum load current value of 10.22 A.

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LP87702

SNVSBU3 – MARCH 2021

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LP87702 Datasheet(PDF) 17 Page - Texas Instruments

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