pca8802 NXP Semiconductors, pca8802 Datasheet - Page 6

• Manufacturer Part Number: pca8802
• Description: Smartcard Rtc; Ultra Low Power Oscillator With Integrated Counter For Initiating One Time Password Generation
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCA8802_1
Product data sheet
9.1.2 Low power operation
9.2 Divider
With the power-down instruction (pwd_cmd) the oscillator can be stopped and the device
can be put into a low power state where power consumption is reduced to an absolute
minimum. The chip would normally reset when the oscillator is stopped, so to prevent a
reset of the chip during this state, a special software power-down sequence must be used
(see
A prime consideration for low power consumption is the series resistance R
used. The series resistance acts as a loss element. Low R
consumption further.
The divider chain is responsible for reducing the 32.768 kHz oscillator frequency down to
1
The dividers (see
instruction. The 24 bit counter may be set when the dividers are held in reset, but this is
not a requirement. This allows for accurate setting and restarting of the counter.
The interface is asynchronous to the quartz oscillator and the state of divider_1 can not be
known when the dvs_cmd is enabled. The 8.192 kHz clock could have just occurred and
hence a delay of
the 8.192 kHz clock could be just about to occur and immediately increment the divider_2.
As a consequence, an uncertainty of between zero and one 8192 Hz clock period (i.e. a
time uncertainty of about 0 s to 122 s) will be present when restarting the counter.
Fig 6.
32
Hz.
Table
(nA)
I
DD
250
210
170
130
90
50
V
I
DD
DD
7). In power-down state, the interface is still accessible.
0
with respect to R
= 3 V.
1
Figure
8192
Rev. 01 — 19 February 2009
seconds will occur before the next increment of the divider_2, or
20
7) divider_2 and divider_3 may be reset with the dvs_cmd
s
40
60
Quartz series resistance, Rs (k )
s
will reduce current
80
PCA8802
© NXP B.V. 2009. All rights reserved.
001aaj165
Smartcard RTC
s
100
of the quartz
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