DS32kHz
6 of 8
The DS32kHz is packaged in a 36-pin ball grid array (BGA). It also is available in a 16-pin 0.300” SO and a 14-pin
encapsulated DIP (EDIP) module.
The additional PC board space required to add the DS32kHz as an option for driving a RTC is negligible in many
applications (see
Figure 6
) Therefore, adding the DS32kHz to new designs and future board revisions allows the
use of the DS32kHz where applications require improved timekeeping accuracy.
Figure 3. Block Diagram
OPERATION
The DS32kHz module contains a quartz tuning-fork crystal and an IC. When power is first applied, and when the
device switches between supplies, the DS32kHz measures the temperature and adjusts the crystal load to
compensate the frequency. The power supply must remain at a valid level whenever a temperature measurement
is made, including when V
CC
is first applied. While powered, the DS32kHz measures the temperature once every
64 seconds and adjusts the crystal load.
The DS32kHz is designed to operate in two modes. In the dual-supply mode, a comparator circuit, powered by V
CC
,
monitors the relationship between the V
CC
and V
BAT
input levels. When V
CC
drops below a certain level compared to
V
BAT
, the device switches over to V
BAT
(Figure 4A). This mode uses V
CC
to conserve the battery connected to V
BAT
while V
CC
is applied.
In the single-supply mode, V
CC
is grounded and the unit is powered by V
BAT
. Current consumption is less than V
CC
,
because the comparator circuit is unpowered (Figure 4B
).
Figure 4A
shows how the DS32kHz should be connected when using two power supplies. V
CC
should be between
4.5V and 5.5V, and V
BAT
should be between 2.7V and 3.5V. Figure 4B shows how the DS32kHz can be used when
only a single-supply system is available. V
CC
should be grounded and V
BAT
should then be held between 2.7V and
5.5V. The V
BAT
pin should be connected directly to a battery. Figure 4C shows a single-supply mode where V
CC
is
held at +5V. See the frequency stability vs. operating voltage for information about frequency error vs. supply
voltage.
Temperature
Measurement
V
BAT
32.768kHz
V
CC
Power
Switching
Circuit
GND
P
N
Power Control
Dallas
Semiconductor
DS32kHz
