Datasheet

STM690, STM704, STM795, STM802, STM804, STM805, STM806 Operation
Doc ID 10519 Rev 9 19/42
2.10 Using a SuperCap™ as a backup power source
SuperCaps™ are capacitors with extremely high capacitance values (e.g., order of 0.47 F)
for their size. Figure 14 shows how to use a SuperCap as a backup power source. The
SuperCap may be connected through a diode to the V
CC
supply. Since V
BAT
can exceed
V
CC
while V
CC
is above the reset threshold, there are no special precautions when using
these supervisors with a Super-Cap.
Figure 14. Using a SuperCap™
2.11 Negative-going V
CC
transients
The STM690/704/795/802/804/805/806 supervisors are relatively immune to negative-going
V
CC
transients (glitches). Figure 32 was generated using a negative pulse applied to V
CC
,
starting at V
RST
+ 0.3 V and ending below the reset threshold by the magnitude indicated
(comparator overdrive). The graph indicates the maximum pulse width a negative V
CC
transient can have without causing a reset pulse. As the magnitude of the transient
increases (further below the threshold), the maximum allowable pulse width decreases. Any
combination of duration and overdrive which lies under the curve will NOT generate a reset
signal. Typically, a V
CC
transient that goes 100 mV below the reset threshold and lasts 40 µs
or less will not cause a reset pulse. A 0.1 µF bypass capacitor mounted as close as possible
to the V
CC
pin provides additional transient immunity.
AI08805
STMXXX
V
BAT
V
CC
V
OUT
5 V
GND
RST
To external SRAM
To µP