MIC2777-XXBM5 MICREL [Micrel Semiconductor], MIC2777-XXBM5 Datasheet - Page 7

• Manufacturer Part Number: MIC2777-XXBM5
• Description: Dual Micro-Power Low Voltage Supervisor
• Manufacturer: MICREL [Micrel Semiconductor]

Transient response
The MIC2777 is inherently immune to very short negative-
going “glitches.” Very brief transients may exceed the voltage
thresholds without tripping the output.
As shown in Figure 2a and 2b, in general the narrower the
transient, the deeper the threshold overdrive that will be
ignored by the MIC2777. The graph represents the typical
allowable transient duration for a given amount of threshold
overdrive that will not generate a reset.
November 2005
Figure 2a. Typical INPUT Transient Response
1.0V 5%
2.5V 5%
V
Figure 2b. Typical V
V
CORE
I/O
Figure 1. MIC2777 Example Design
RESET COMP. OVERDRIVE, V
100
RESET COMP. OVERDRIVE, V
R1
676k
1%
R2
324k
1%
80
60
40
20
40
35
30
25
20
15
10
0
5
0
0
0
Transient Response
Transient Response
VDD
IN
MIC2777-23
500
Typical V
Typical INPUT
100
/RST
GND
1000
DD
RST
Transient Response
DD
200
1500
REF
MICROPROCESSOR
REF
–V
VCORE
/RESET
VI/O
2000
–V
300
DD
IN(mV)
(mV)
GND
7
Ensuring Proper Operation at Low Supply
At levels of V
cannot turn on sufficiently to produce a valid logic-low on
/RST. In this situation, other circuits driven by /RST could
be allowed to float, causing undesired operation. (In most
cases, however, it is expected that the circuits driven by the
MIC2777 will be similarly inoperative at V
If a given application requires that /RST be valid below V
= 1.2V, this can be accomplished by adding a pull-down re-
sistor to the /RST output. A value of 100kΩ is recommended
as this is usually an acceptable compromise of quiescent
current and pull-down current. The resistor’s value is not
critical, however. See Figure 3.
The statements above also apply to the MIC2777’s RST out-
put. That is, to ensure valid RST signal levels at V
a pull-up resistor (as opposed to a pull-down) should be
added to the RST output. A value of 100kΩ is typical for this
application as well. See Figure 4.
V
CC
V
Figure 3. MIC2777 Valid /RST Below 1.2V
CC
Figure 4. MIC2777 Valid RST Below 1.2V
R1
R2
DD
R1
R2
below 1.2V, the MIC2777’s /RST output
VDD
IN
MIC2777-XX
VDD
IN
MIC2777-XX
/RST
GND
RST
/RST
GND
RST
100k
Rpull-up
100k
Rpull-down
MICROPROCESSOR
MICROPROCESSOR
VCC
/RESET
VCC
RESET
DD
≤ 1.2V.)
GND
GND
MIC2777
DD
<1.2V,
DD