FM1233 Precision Reset Generator Circuit
August 2000
FM1233
Precision Reset Generator Circuit
General Description
The FM1233 features comprehensive reset generation for
microcontroller/microprocessor based systems. If the system V
CC
voltage level is determined to be in an out-of-tolerance state, the
device automatically generates a low-going reset signal. The
reset signal is held in the active state (low) for a specified duration
(minimum 140 ms) after the V
CC
returns to an in-tolerance state.
The FM1233 also allows an external reset to be connected to the
reset pin without adding aditional debounce logic or extra pins.
This device is fabricated using CMOS technology. This device is
available in the SOT-23 package.
Features
I
Automatic reset generation on power-up
I
Minimum 140 ms reset pulse — compatible with other similar
1233 class devices
I
Other reset pulse choices available: 32 - 256 ms
I
Choice of commercial and extended temperature ranges
I
Choice of Reset Thresholds: 4.63V, 4.38V, 4.00V, 3.08V,
2.93V, 2.63V
I
Package available: SOT-23
Block Diagram
V
CC
V
CC
Tolerance Detect
& Reset Monitor
Output
Stage
Reset_out
(active low)
Temp. Compensated
Reference
External Reset
Detection
Connection Diagram
1
1 = GND
2 = RESET'
3 = V
CC
2
FM1233
3
© 2000 Fairchild Semiconductor International
FM1233 Rev. A
1
www.fairchildsemi.com
FM1233 Precision Reset Generator Circuit
Each FM1233 device has the following Identifier (FM1233yz) (Top Mark on devices will be 10yz)
Reset Characteristics
RESET THRESHOLD (V)
4.63
4.38
4.00
3.08
2.93
2.63
Identifier(y)
L
M
J
T
S
R
Fairchild Part Number
FM1233Lz
FM1233Mz
FM1233Jz
FM1233Tz
FM1233Sz
FM1233Rz
RESET PULSE DURATION (mS)
32
64
128
256
Identifier(z)
E
F
H
Blank
Fairchild Part Number
FM1233yE*
FM1233yF*
FM1233yH*
FM1233y
Note*:
These choices are available upon special request only. Please work with Fairchild Marketing to determine availability.
2
FM1233 Rev. A
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FM1233 Precision Reset Generator Circuit
Product Specifications
Absolute Maximum Ratings
Ambient Storage Temperature
All Input or Output Voltages
with Respect to Ground
Lead Temperature (Soldering, 10 seconds)
ESD Rating
–65°C to +150°C
-0.3V to 6.5V
+300°C
2000V min.
Operating Conditions
Ambient Operating Temperature
Commercial
Industrial
0°C to +70°C
-40°C to +85°C
Electrical Characteristics
Parameter
V
CC
Range
Symbol
Temp
Com
Ind
Conditions
Min
1.0
1.2
Typ
Max
5.5V
5.5
50
100
Units
V
V
µA
µA
V
V
V
V
V
V
V
V
V
V
V
V
V
V
Supply Current
I
CC
Com
Reset Threshold
V
TH
Com
Ind
Com
Ind
Com
Ind
Com
Ind
Com
Ind
Com
Ind
‘L’ Identifier
4.50
4.40
4.63
4.63
4.38
4.38
4.00
4.00
3.08
3.08
2.93
2.93
2.63
2.63
4.75
4.85
4.50
4.56
4.10
4.20
3.15
3.23
3.00
3.08
2.70
2.75
‘M’ Identifier
4.25
4.16
‘J’ Identifier
3.89
3.80
‘T’ Identifier
3.00
2.92
‘S’ Identifier
2.85
2.78
‘R’ Identifier
2.55
2.50
nRESET Output Voltage High
nRESET Output Voltage Low
Reset Timeout Period
V
OH
V
OL
T
RST
All
All
All
Isource = 150 mA
Isink = 1.2mA
0.8V
CC
0.4
175
240
375
ms
Note:
Production testing done at TA = +25°C, over temperature limits guaranteed by design only.
3
FM1233 Rev. A
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FM1233 Precision Reset Generator Circuit
General Description
The FM1233 features a highly accurate voltage reference against
which the Vcc is compared. Once the Vcc is below the specified
threshold, it will drive the RESET line and continue to hold it low
until the V
CC
returns above the threshold and the time for the
RESET pulse duration has expired. The FM1233 is immune to short
negative going transients on the V
CC
line. The placement of a
0.1µF bypass capacitor as close as possible to the V
CC
pin
provides additional transient immunity.
For a V
CC
value below 1.0V-1.3V, the FM1233 does not sink current
on the RESET pin. This is not a problem in most systems since
most common devices are not functional in this range. If it is desired
for the FM1233 reset to be functional below the range above, it is
suggested to use a 100KΩ pull-down resistor between RESET and
V
SS
.
Connecting an External Reset to the FM1233
FM1233
Reset
Interfacing to Bidirectional reset pins
FM1233 can be used with microprocessors with bidirectional reset
pins. The microprocessors can still drive the reset line but when the
microprocessor has released the reset line the FM1233 will
continue to hold it for a duration no longer that 300 ms.
Bi-Directional Reset
The FM1233 allows for the connection of an external reset switch
to be wired to the reset pin. The FM1233 has the feature of allowing
an external reset pin to be connected without having to add
debounce logic or an extra pin to the package. The FM1233 detects
when an external source is pulling the reset line low. Once this
occurs the FM1233 will pull the reset line low as well. When the
external source stops driving the reset line the FM1233 will continue
to hold the reset line low so as to prevent debounce. After a certain
length of time the FM1233 will stop driving the reset line and it will
return to its non-active (high) state.
4
FM1233 Rev. A
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FM1233 Precision Reset Generator Circuit
Typical Operating Characteristics
Supply Current Vs. Temperature (FM1233R/S/T)
8
7
6
I
CC
(µA)
V
CC
= 5V
5
4
3
2
1
0
-60
-40
-20
0
20
Temperature (C)
V
CC
= 3.3V
40
60
80
100
Power up Reset Timeout Vs. Temperature FM1233(R/S/T)
Power Up Reset Timeout (ms)
300
280
260
240
220
200
-60
-40
-20
0
20
40
60
80
100
Temperature (C)
Normalized Reset Threshold Vs. Temperature FM1233(R/S/T)
1.050
Normalized Threshold
1.025
1.000
0.975
0.950
-60
-40
-20
0
-20
-40
60
80
100
Temperature (C)
5
FM1233 Rev. A
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