SH3003 datasheet(16/30 Pages) SEMTECH

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SH3003

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POWER MANAGEMENT

Application Information (continued)

The SH3003 has two support modules that are speciﬁ-

cally designed for various real time support functions.

They are the Real-Time Clock and the Periodic Interrupt /

Wakeup Timer. Both of these units as well as other func-

tions of the SH3003 depend on the internal 32.768kHz

clock for accuracy.

The SH3003 allows a trade-off between the cost of a sys-

tem and its accuracy. For some devices, a single SH3003

without any support components provides sufﬁcient ac-

curacy.

These units can operate with processor clock accuracy of

±0.5% and the accuracy of the real-time system of ±3%.

At the other end of the spectrum, with one external com-

ponent (a 32.768kHz crystal), the SH3003 can provide a

processor clock accuracy of ±256ppm (±0.0256%) and

the accuracy of the real-time system of ±4ppm

(± 0.0004%).

Real Time Support

Special Operating Modes

The SH3003 can operate stand-alone, without connec-

tions to the In and Out terminals of the host’s oscillator.

For example, a bank of SH3003 chips can generate sev-

eral different frequencies for simultaneous use in the sys-

tem, all controlled by a single micro (and possibly sharing

one 32.768kHz crystal by chaining the CLK32 pin to XIN

pin on the next device). In this case the CLKIN pin should

be connected to VSS. The clock output on the CLKOUT pin is

continuous; the correct operating mode is automatically

recognized by the SH3003.

A microcontroller may not have a STOP command. With

the SH3003, this controller can do a “simulated” STOP by

issuing an instruction to the SH3003 to stop the clock.

This command is accepted only if the Periodic Interrupt

/ Wakeup Timer has started (otherwise, once the system

is put to sleep, it would never wake up again). This mode

of operations is only possible if the host processor is ca-

pable of correct operations with clock frequency down

to zero, and keeps all of the internal RAM alive while the

clock is stopped.

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