STM690_10 datasheet(19/42 Pages) STMICROELECTRONICS

19 / 42 page

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 VCC supply. Since VBAT can exceed

VCC while VCC 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 VCC transients

The STM690/704/795/802/804/805/806 supervisors are relatively immune to negative-going

VCC transients (glitches). Figure 32 was generated using a negative pulse applied to VCC,

starting at VRST + 0.3 V and ending below the reset threshold by the magnitude indicated

(comparator overdrive). The graph indicates the maximum pulse width a negative VCC

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 VCC 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 VCC pin provides additional transient immunity.

AI08805

STMXXX

VBAT

VCC

VOUT

5 V

GND

RST

To external SRAM

To µP

STM690 Datasheet(PDF) 19 Page - STMicroelectronics