MC34710 Datasheet, PDF (10/18 Pages) Motorola, Inc – Adjustable Dual Output Switching Power Supply

FUNCTIONAL DESCRIPTION
FUNCTIONAL PIN 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. V_I/O, V_CORE, V_B+, and thermal
shutdown (TSD) detectors in various parts of the chip are
monitored for error conditions. V_I/O, V_CORE, V_B+, 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 V_I/O is
never less than 0.9V below V_CORE. This means that V_CORE -
V_I/O will be clamped at 0.5V, and that the V_CORE regulator
operation will be suppressed during startup and shutdown to
ensure that V_CORE - V_I/O = 0.9V.
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 200kHz.
Internal Oscillator
The internal oscillator provides a 200kHz square wave
signal for charge pump operation and for the buck converter.
34710
10
Analog Integrated Circuit Device Data
Freescale Semiconductor