參數(shù)資料
型號: MIC2774
廠商: Micrel Semiconductor,Inc.
英文描述: Dual Micro-Power Low Voltage Supervisor Advance Information
中文描述: 雙路微功率低電壓監(jiān)控進展信息
文件頁數(shù): 7/8頁
文件大小: 381K
代理商: MIC2774
September 29, 2000
7
MIC2774
MIC2774
Micrel
IN
/RST
VDD
/MR
GND
MIC2774L-23
R1
676k
1%
R2
324k
1%
/RESET
VCORE
VI/O
GND
V
CORE
1.0V
5%
Manual
Reset
MICROPROCESSOR
V
I/O
2.5V
±
5%
Figure 1. MIC2774 Example Design
Interfacing to Processors With Bidirectional Reset Pins
Some microprocessors have reset signal pins that are bidi-
rectional, rather than input only. The Motorola 68HC11 family
is one example. Because the MIC2774N
s output is open-
drain, it can be connected directly to the processor
s reset pin
using only the pull-up resistor normally required. See Figure 2.
IN
/RST
VDD
/MR
GND
MIC2774N-XX
R1
R2
/RESET
VCC
GND
V
CC
MICROPROCESSOR
100k
Figure 2. Interfacing to Bidirectional Reset Pin
Transient response
The MIC2774 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 3a and 3b, in general the narrower the
transient, the deeper the threshold overdrive that will be
ignored by the MIC2774. The graphs represent the typical
allowable transient duration for a given amount of threshold
overdrive that will not generate a reset.
0
5
10
15
20
25
30
35
40
0
100
200
300
M
μ
s
RESET COMP. OVERDRIVE, V
REF
V
IN
(mV)
Figure 3a. Typical INPUT Transient Response
Typical IN
Transient Response
0
20
40
60
80
100
0
500
1000
1500
2000
M
μ
s
RESET COMP. OVERDRIVE, V
REF
V
DD
(mV)
Typical V
DD
Transient Response
Figure 3b. Typical V
DD
Transient Response
Ensuring Proper Operation at Low Supply
At levels of V
DD
below 1.2V, the MIC2774
s reset output
cannot turn on sufficiently to produce a valid logic-low on
/RST. In this situation, 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 MIC2774L
will be similarly inoperative at V
DD
1.2V.)
If a given application requires that /RST be valid below V
DD
= 1.2V, this can be accomplished by adding a pull-down
resistor to the /RST output. A value of 100k
is recom-
mended as this is usually an acceptable compromise of
quiescent current and pull-down current. The resistor
s value
is not critical, however. See Figure 4.
The statements above also apply to the MIC2774H
s RST
output. That is, to ensure valid RST signal levels at V
DD
<
1.2V, a pull-up resistor (as opposed to a pull-down) should be
added to the RST output. A value of 100k
is typical for this
application as well. See Figure 5.
IN
/RST
VDD
/MR
GND
MIC2774L-XX
R1
R2
/RESET
VCC
GND
V
CC
Manual
Reset
MICROPROCESSOR
100k
Rpull-down
Figure 4. MIC2774L Valid /RST Below 1.2V
IN
RST
VDD
/MR
GND
MIC2774H-XX
R1
R2
RESET
VCC
GND
V
CC
Manual
Reset
MICROPROCESSOR
100k
Rpull-up
Figure 5. MIC2774H Valid RST Below 1.2V
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