HT49CA1 View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT49CA1' PDF : 58 Pages View PDF
HT49RA1/HT49CA1
Oscillator
The one methods of generating the system clock are:
· External RC oscillator
More information regarding the oscillator is located in
Application Note HA0075E on the Holtek website.
External RC Oscillator
As an RC oscillator is used, an external resistor be-
tween OSC1 and VSS is required whose value should
be 12kW for a frequency of 4MHz. The RC oscillator pro-
vides a ±3% accuracy, the conditions are:
· VDD=2.0V~3.6V
· Temp.= 0°C ~ 50°C
· fSYS=4MHz
O SC1
RC Oscillator
External RTC Oscillator
When the microcontroller enters the Power Down Mode,
the system clock is switched off to stop microcontroller
activity and to conserve power. However, in many
microcontroller applications it may be necessary to keep
the internal timers operational even when the
microcontroller is in the Power Down Mode. To do this,
another clock, independent of the system clock, must be
provided. To do this a configuration option exists for a
Real Time Clock - RTC oscillator. Here the OSC3 and
C1
32768H z
O SC3
Ca
Rp
Rf
Cb
C2
O SC4
N o te : R p is n o r m a lly n o t r e q u ir e d .
T o in te r n a l
c ir c u its
OSC4 pins, should be connected to a 32768Hz crystal
to implement this internal RTC oscillator. However, for
some crystals, to ensure oscillation and accurate fre-
quency generation, it may be necessary to add two
small value external capacitors, C1 and C2. The exact
values of C1 and C2 should be selected in consultation
with the crystal or resonator manufacturer¢s specifica-
tion. The external parallel feedback resistor, Rp, is nor-
mally not required but in some cases may be needed to
assist with oscillation start up.
Internal Ca, Cb, Rf Typical Values @ 5V, 25°C
Ca
Cb
Rf
TBD
TBD
TBD
RTC Oscillator Internal Component Values
RTC Oscillator C1 and C2 Values
Crystal Frequency C1
C2
CL
32768Hz
TBD
TBD
TBD
Note: 1. C1 and C2 values are for guidance only.
2. CL is the crystal manufacturer specified
load capacitor value.
32768 Hz Crystal Recommended Capacitor Values
External RTC Oscillator
Rev. 1.10
37
March 30, 2014
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