Datasheet

STM690A/692A/703/704/802/805/817/818/819 Operation
Doc ID 10522 Rev 10 19/43
2.12 Battery freshness seal (STM817/818/819)
The battery freshness seal disconnects the backup battery from internal circuitry and V
OUT
until it is needed. This allows an OEM to ensure that the backup battery connected to V
BAT
will be fresh when the final product is put to use. To enable the freshness seal:
1. Connect a battery to V
BAT
2. Ground PFO
3. Bring V
CC
above the reset threshold and hold it there until reset is deasserted following
the reset timeout period and
4. Bring V
CC
down again (Figure 16)
Use the same procedure for the STM818, but ground E
CON
instead of PFO. Once the
battery freshness seal is enabled (disconnecting the backup battery from internal circuitry
and anything connected to V
OUT
), it remains enabled until V
CC
is brought above V
RST
.
Figure 15. Using a SuperCap™
Figure 16. Freshness seal enable waveform
AI08805
STMXXX
V
BAT
V
CC
V
OUT
5V
GND
RST
To external SRAM
To µP
AI08806
RST
PFO
(STM817/819)
V
CC
V
RST
E
CON
(STM818)
t
rec
(Externally held at 0V)
(Externally held at 0V)
E
CON
out state latched
at 1/2 t
rec
,
Freshness
Seal enabled
PFO out state latched
at 1/2 t
rec
,
Freshness
Seal Enabled