STM6502 Datasheet, PDF (11/29 Pages) STMicroelectronics – Dual push-button Smart ResetTM with user-adjustable setup delays

STM6502, STM6503, STM6504, STM6505
Description
1.2.5
Note:
1.2.6
Edge-triggered Smart Reset input (SRE pin) – STM6504 only
The SRE pin is active-high, immediate and independent reset input that includes an edge
trigger with debounce delay t_DEBOUNCE on the falling edge.
The triggering edge must be a high-to-low or low-to-high transition with a slew-rate faster
than 1 V/µs typ.
Figure 8. STM6504 timing
t < tDEBOUNCE
=> tREC timer reset
t < tSRC
=> no output response
SR0
Independent
SRE
No debounce
RST
tREC
tSRC
tDEBOUNCE
tREC
(rising edges within
tDEBOUNCE are ignored)
tREC
AM00328V2
Adjustable delay of Smart Reset input (SRC pin) – STM6502 and
STM6505 only
This pin controls the setup time before the push-button action is validated by the reset
output. It is connected to an external capacitor (C_SRC), which is tied to ground to provide the
desired value of the setup time (t_SRC).
Calculated t_SRC and C_SRC examples are given in Table 3. Refer also to Table 6.
Table 3. t_SRC programmed by an ideal external capacitor – STM6502 and STM6505
Calculated C_SRC
value [µF]
Min.
Setup delay t_SRC [s]⁽¹⁾⁽²⁾
Typ.
Max.
Closest common
C_SRC value [µF]
0.2
2
2.5
3.0
0.22
0.3
3
3.75
4.5
0.33
0.6
6
7.5
9
0.56
1
10
12.5
15
1
1. At 25 °C. Example calculations based on an ideal capacitor. During application design and component
selection it should be considered that the current flowing into the external t_SRC programming capacitor
(C_SRC) is on the order of 100 nA, therefore a low-leakage capacitor (ceramic or film capacitor) should be
used and placed as close as possible to the SRC pin. Also an adequate low-leakage PCB environment
should be ensured to prevent t_SRC accuracy from being affected. A recommended minimum value of C_SRC
is 0.01 µF.
2. In case of repeated activations of the t_SRC timer, an interval of 10 ms min. is needed between the
activations to fully discharge C_SRC, so that the next t_SRC is as specified.
Doc ID 16101 Rev 5
11/29