LP87702 datasheet(28/98 Pages) TI

28 / 98 page

Table 7-4. Watchdog Window Periods

CONTROL BIT

DEFAULT

VALUES

WD_LONG_OPEN_TIME

OTP

00 – 200 ms

01 – 600 ms

10 – 2000 ms

11 – 5000 ms

WD_CLOSE_TIME

OTP

00 – 10 ms

01 – 20 ms

10 – 50 ms

11 – 100 ms

7.3.9 Device Reset Scenarios

There are four reset methods implemented on the LP87702:

• Software reset with the SW_RESET bit in the RESET register

• NRST input signal low

• Undervoltage lockout (UVLO) reset from VANA supply

• Watchdog expiration (depending on the watchdog settings)

A SW reset occurs when the SW_RESET bit is set to 1. The bit is automatically cleared after writing. Figure

7-14shows how this event disables all the converters immediately, drives GPO signals low, resets all the register

bits to the default values and the OTP bits are loaded. I2C interface is not reset during a software reset. The host

must wait at least 1.2 ms after writing SW reset until making a new I2C read or write to the device.

If VANA supply voltage falls below the UVLO threshold level or the NRST signal is set low, then all the

converters are disabled immediately, the GPOx signals are driven low, and all the register bits are reset to the

default values. When the VANA supply voltage rises above the UVLO threshold level and the NRST signal rises

above the threshold level, the OTP bits are loaded to the registers and a start-up is initiated according to the

Depending on the watchdog settings, the watchdog expiration can reset the device to the OTP default values.

7.3.10 Diagnostics and Protection Features

The LP87702 provides four levels of protection features:

• Input and output voltage information. Non-valid voltage sets interrupt or PGx signal:

– Validity of the output voltage of BUCK or BOOST converters

– Validity of VANA, VMON1, and VMON2 input voltages

• Warnings causing interrupt:

– Peak current limit detection in BUCK or BOOST converters

– Thermal warning

• Protection events which are disabling the converters:

– Short-circuit and overload protection for BUCK and BOOST converters

– Input overvoltage protection (VANAOVP)

– Watchdog expiration (optional, depends on the watchdog settings)

– Thermal shutdown

• Protection events which are causing the device to shutdown:

– Undervoltage lockout (VANAUVLO)

• Protections not causing interrupt or converter disable:

– Negative current limit detection in the BUCK or BOOST converters

7.3.10.1 Voltage Monitorings

The LP87702 device has programmable voltage monitoring for the BUCKx and BOOST converter output

voltages and for VANA, VMON1, and VMON2 inputs. Monitoring of each signal is independently enabled in

the PGOOD_CTRL register. Voltage monitoring can be under-voltage monitoring only (PGOOD_WINDOW =

0) or overvoltage and undervoltage monitoring (PGOOD_WINDOW = 1). This selection is common for all

LP87702

SNVSBU3 – MARCH 2021

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