9202 datasheet(50/175 Pages) STMICROELECTRONICS

50 / 175 page

UPSD3254A, UPSD3254BV, UPSD3253B, UPSD3253BV

50/175

OSCILLATOR

The oscillator circuit of the uPSD325X devices is a

single stage inverting amplifier in a Pierce oscilla-

tor configuration. The circuitry between XTAL1

and XTAL2 is basically an inverter biased to the

transfer point. Either a crystal or ceramic resonator

can be used as the feedback element to complete

the oscillator circuit. Both are operated in parallel

resonance.

XTAL1 is the high gain amplifier input, and XTAL2

is the output. To drive the uPSD325X devices ex-

ternally, XTAL1 is driven from an external source

and XTAL2 left open-circuit.

Figure 19. Oscillator

SUPERVISORY

There are four ways to invoke a reset and initialize

the uPSD325X devices.

Via the external RESET pin

Via the internal LVR Block.

Via USB bus reset signaling.

Via Watch Dog timer

The RESET mechanism is illustrated in Figure 20.

Figure 20. RESET Configuration

AI06620

XTAL1

XTAL2

8 to 40 MHz

XTAL1

XTAL2

External Clock

AI06621

Reset

CPU

PERI.

Noise

Cancel

LVR

CPU

Clock

Sync

10ms

Timer

USB Reset

RSTE

WDT

PSD_RST

“Active Low

10ms at 40Mhz

50ms at

8Mhz

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