SH3003 Datasheet, PDF (16/30 Pages) Semtech Corporation – MicroBuddy® Support IC for Microcontrollers

SH3003
POWER MANAGEMENT
Application Information (continued)
Not authorized for release outside of Semtech - DRAFT
Special Operating Modes
Real Time Support
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.
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%).
©2006 Semtech Corp.
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