34710 datasheet(10/17 Pages) FREESCALE

10 / 17 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

34710

FUNCTIONAL DESCRIPTION

FUNCTIONAL TERMINAL DESCRIPTION

SUPERVISORY FUNCTIONS

Supervisory Circuitry

The supervisory circuitry provides control of the RST line,

an open drain signal, based on system operating conditions

monitored by the 34710. VI/O, VCORE, VB+, and thermal

shutdown (TSD) detectors in various parts of the chip are

monitored for error conditions. VI/O, VCORE, VB+, and thermal

shutdown have both positive- and negative-going thresholds

for triggering the reset function.

The supervisor circuitry also ensures that the regulator

outputs follow a predetermined power-up and power-down

sequence. Specifically, the sequencing ensures that VI/O is

never less than 0.9 V below VCORE. This means that VCORE -

VI/O will be clamped at 0.5 V, and that the VCORE regulator

operation will be suppressed during startup and shutdown to

ensure that VCORE - VI/O = 0.9 V.

VB Charge Pump

The high-side MOSFET in the switching regulator (buck

converter) requires a gate drive supply voltage that is biased

higher than the B+ voltage, and this boosted voltage is

provided by the internal charge pump and stored in a

capacitor between the VB pin and the B+ pin. The charge

pump operates directly from the B+ supply, and uses an

internal oscillator operating at 200 kHz.

Internal Oscillator

The internal oscillator provides a 200 kHz square wave

signal for charge pump operation and for the buck converter.

34710 Datasheet(PDF) 10 Page - Freescale Semiconductor, Inc