19-2210; Rev 1; 10/02
Dual-Voltage µP Supervisory Circuits
with Sequenced Reset Outputs
General Description
The MAX6391/MAX6392 microprocessor (µP) supervisory
circuits provide sequenced logic reset outputs for multi-
component or dual-voltage systems. Each device can
monitor two supply voltages and time-sequence two reset
outputs to control the order in which system components
are turned on and off. The MAX6391/MAX6392 increase
system reliability and reduce circuit complexity and cost
compared to separate ICs or discrete components.
The MAX6391/MAX6392 monitor V
CC
as the master
reset supply. Both
RESET1
and
RESET2
are asserted
whenever V
CC
drops below the selected factory-fixed
reset threshold voltage.
RESET1
remains asserted as
long as V
CC
is below the threshold and deasserts
140ms (min) after V
CC
exceeds the thresholds.
RESET IN2 is monitored as the secondary reset supply
and is adjustable with an external resistive-divider net-
work.
RESET2
is asserted whenever either V
CC
or
RESET IN2 is below the selected thresholds.
RESET2
remains asserted 140ms (min) or a capacitor-
adjustable time period after V
CC
and RESET IN2
exceed their thresholds.
RESET2
is always deasserted
after
RESET1
during system power-up and is always
asserted before
RESET1
during power-down.
The MAX6391 includes two internal pullup resistors for
RESET1
and
RESET2
(the open-drain outputs can be
externally connected to the desired pullup voltages).
The MAX6392 includes an active-low manual reset
input (MR) that asserts both
RESET1
(push-pull) and
RESET2
(open drain).
The MAX6391/MAX6392 are available in small 8-pin
SOT23 packages and are specified over the -40°C to
+85°C extended temperature range.
Features
o
Preset VCC Reset Threshold Voltages from 1.58V
to 4.63V (master supply)
o
Customer-Adjustable RESET IN2 to Monitor
Voltages Down to 625mV (secondary supply)
o
Fixed (140ms min)
RESET1
Timeout
o
Fixed (140ms min) or Customer-Adjustable
RESET2
Timeout Period
o
Guaranteed Reset Valid to V
CC
= 1V
o
Active-Low Open-Drain Outputs or Push-
Pull/Open-Drain Combination
o
Internal Open-Drain Pullup Resistors (for external
V
OH
voltage connections)
o
Manual Reset Input (MAX6392 only)
o
Immune to Short Negative V
CC
Transients
o
15µA Typical Supply Current
o
Few External Components
o
Small 8-Pin SOT23 Package
MAX6391/MAX6392
Ordering Information
PART*
MAX6391KA_
_-T
MAX6392KA_
_-T
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
SOT23-8
SOT23-8
Applications
Computers
Controllers
Critical µP Power Monitoring
Set-Top Boxes
Printers
Servers/Workstations
Industrial Equipment
Multivoltage Monitoring
*Insert
the desired suffix (see Selector Guide) into the blanks to
complete the part number. The MAX6391/MAX6392 require a
2.5k minimum order increment and are available in tape-and-
reel only. Samples are typically available for standard versions
(see Selector Guide for standard versions). Contact factory for
availability.
Pin Configurations
TOP VIEW
RESET IN2
1
V
CC
2
CSRT
3
8
7
R1
RESET1
R2
RESET2
MAX6391
6
5
GND
4
SOT23-8
Typical Operating Circuit appears at end of data sheet.
Pin Configurations continued at end of data sheet.
1
________________________________________________________________
Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Dual-Voltage µP Supervisory Circuits
with Sequenced Reset Outputs
MAX6391/MAX6392
ABSOLUTE MAXIMUM RATINGS
V
CC
to GND ...........................................................-0.3V to +6.0V
RESET1
(MAX6392), RESET IN2, CSRT,
MR
to GND ..............................................-0.3V to (V
CC
+ 0.3V)
RESET1
(MAX6391),
RESET2,
R1, R2 to GND......-0.3V to +6.0V
Input Current (V
CC
, GND, CSRT, R1, R2,
MR)
.................±20mA
Output Current (RESET1,
RESET2)
..................................±20mA
Continuous Power Dissipation (T
A
= +70°C)
8-Pin SOT23 (derate 5.26mW/°C above +70°C)...........421mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= 1.2V to 5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise specified. Typical values are at V
CC
= +5V and T
A
= +25°C.) (Note 1)
PARAMETER
V
CC
Range
Supply Current
I
CC
SYMBOL
CONDITIONS
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
No load
MAX639_UA46
MAX639_UA44
MAX639_UA31
MAX639_UA29
V
CC
Reset Threshold
V
TH1
MAX639_UA26
MAX639_UA23
MAX639_UA22
MAX639_UA17
MAX639_UA16
RESET IN2 Threshold
RESET IN2 Input Current
V
CC
to
RESET1
Delay
V
CC
or RESET IN2 to
RESET2
Delay
t
RD1
t
RD2
V
CC
falling at 1mV/µs (Note 2)
20
10
µs
V
TH2
V
CC
= 5V
4.50
4.25
3.00
2.85
2.55
2.25
2.12
1.62
1.54
610
MIN
1.0
1.2
15
4.63
4.38
3.08
2.93
2.63
2.32
2.19
1.67
1.58
625
TYP
MAX
5.5
5.5
25
4.75
4.50
3.15
3.00
2.70
2.38
2.25
1.71
1.61
640
50
mV
nA
V
UNITS
V
µA
2
_______________________________________________________________________________________
Dual-Voltage µP Supervisory Circuits
with Sequenced Reset Outputs
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 1.2V to 5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise specified. Typical values are at V
CC
= +5V and T
A
= +25°C.) (Note 1)
PARAMETER
RESET1
Timeout Period
RESET2
Timeout Period (Note 3)
SYMBOL
t
RP1
t
RP2
C
CSRT
= 1500pF
C
CSRT
= V
CC
I
SINK
= 50µA,
reset asserted
V
OL
V
CC
≥
1.0V,
T
A
= 0°C to +85°C
V
CC
≥
1.2V,
T
A
= -40°C to +85°C
CONDITIONS
MIN
140
2.2
140
TYP
200
3.1
200
MAX
280
4.0
280
0.3
0.3
0.3
0.4
1.0
µA
V
UNITS
ms
ms
MAX6391/MAX6392
RESET_
Output Voltage Low
I
SINK
= 1.2mA, reset asserted, V
CC
≥
2.5V
I
SINK
= 3.2mA, reset asserted, V
CC
≥
4.25V
Open-Drain
RESET
Output
Leakage Current
Push-Pull
RESET1
Output
Voltage High (MAX6392 only)
I
LKG
V
CC
≥
V
TH1
, V
RESET IN2
≥
V
TH2
,
reset not asserted
V
CC
≥
2.25V, I
SOURCE
= 500µA,
reset not asserted
V
OH
V
CC
≥
4.5V, I
SOURCE
= 800µA, reset not
asserted
V
CC
> 4.0V
2.4
0.8
✿
V
CC
0.8
0.3
✿
V
CC
0.7
✿
V
CC
50
100
V
V
IL
V
IH
MR
Input
V
IL
V
V
CC
< 4.0V
V
IH
MR
Minimum Pulse Width
MR
Glitch Rejection
MR
to
RESET1
Delay
MR
to
RESET2
Delay
t
MR
Skew
MR
Pullup Resistance
Reset Pullup Resistance
t
MR1
t
MR2
t
MR1
- t
MR2
Pullup to V
CC
RESET1
to R1 or
RESET2
to R2
µs
ns
µs
ns
µs
60
60
kΩ
kΩ
10
100
10
35
35
47
47
Note 1:
Overtemperature limits are guaranteed by design and not production tested. Devices tested at +25°C only.
Note 2:
RESET2
asserts before
RESET1
when V
CC
goes below the threshold for all supply voltage and temperature ranges.
Note 3:
CSRT must be connected to either V
CC
(for fixed
RESET2
timeout period) or an external capacitor (for user-
adjustable
RESET2
timeout period).
_______________________________________________________________________________________
3
Dual-Voltage µP Supervisory Circuits
with Sequenced Reset Outputs
MAX6391/MAX6392
Typical Operating Characteristics
(V
CC
= +5V, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX6391 toc01
V
CC
FALLING TO RESET1 DELAY
VS.
TEMPERATURE
MAX6391 toc02
V
CC
FALLING TO RESET2 DELAY
vs. TEMPERATURE
16
15
DELAY (µs)
14
13
12
11
10
9
MAX6391 toc03
17
28
27
26
DELAY (µs)
25
24
23
17
SUPPLY CURRENT (µA)
16
15
14
22
21
13
-40
-15
10
35
60
85
TEMPERATURE (°C)
20
-40
-15
10
35
60
85
TEMPERATURE (°C)
-40
-15
10
35
60
85
TEMPERATURE (°C)
RESET2 TO RESET1 DELAY
vs. TEMPERATURE
MAX6391 toc04
RESET1 TIMEOUT PERIOD
vs. TEMPERATURE
MAX6391 toc05
RESET1 TO RESET2 TIMEOUT PERIOD
vs. TEMPERATURE (CSRT = 1500pF)
MAX6391 toc06
11.8
300
3.50
11.6
DELAY (µs)
TIMEOUT DELAY (ms)
11.4
250
TIMEOUT DELAY (ms)
-40
-15
10
35
60
85
275
3.25
3.00
11.2
11.0
225
2.75
10.8
-40
-15
10
35
60
85
TEMPERATURE (°C)
200
TEMPERATURE (°C)
2.50
-40
-15
10
35
60
85
TEMPERATURE (°C)
RESET1 TO RESET2 TIMEOUT PERIOD
vs. TEMPERATURE (CSRT TIED TO V
CC
)
MAX6391 toc07
MAXIMUM TRANSIENT DURATION
vs. RESET COMPARATOR OVERDRIVE
MAXIMUM TRANSIENT DURATION (µs)
MAX6391 toc08
300
60
50
TIMEOUT DELAY (ms)
275
40
RESET ASSERTS ABOVE
THIS LINE
30
250
225
20
200
-40
-15
10
35
60
85
TEMPERATURE (°C)
10
1
10
100
1000
OVERDRIVE (mV)
4
_______________________________________________________________________________________
Dual-Voltage µP Supervisory Circuits
with Sequenced Reset Outputs
Pin Description
PIN
MAX6391
1
2
3
4
MAX6392
1
2
3
4
NAME
FUNCTION
Input Voltage for
RESET2
Monitor. High-impedance input for internal reset
comparator. Connect this pin to an external resistive-divider network to set the reset
threshold voltage.
Supply Voltage and Input Voltage for Primary Supply Monitor
RESET2
Delay Set Capacitor. Connect to V
CC
for a fixed 140ms (min) timeout period
or to an external capacitor for a user-adjustable timeout period after V
CC
exceeds its
minimum threshold.
Ground
Secondary Reset Output, Open-Drain, Active-Low.
RESET2
changes from high to low
when either V
CC
or RESET IN2 drop below their thresholds.
RESET2
remains low for a
user-adjustable timeout period (see CSRT) or a fixed 140ms (min) after V
CC
and
RESET IN2 meet their minimum thresholds.
47kΩ Internal Pullup Resistor for
RESET2.
Connect to external voltage for
RESET2
high pullup.
Primary Reset Output, Open-Drain (MAX6391) or Push-Pull (MAX6392), Active-Low.
RESET1
changes from HIGH to LOW when the V
CC
input drops below the selected
reset threshold.
RESET1
remains LOW for the reset timeout period after V
CC
exceeds
the minimum threshold.
47kΩ Internal Pullup Resistor for
RESET1.
Connect to external voltage for
RESET1
high pullup.
Manual Reset, Active-Low, Internal 47kΩ Pullup to V
CC
. Pull LOW to force a reset.
RESET1
and
RESET2
remain asserted as long as
MR
is LOW and for the
RESET1
and
RESET2
timeout periods after
MR
goes HIGH. Leave unconnected or connect to V
CC
if unused.
MAX6391/MAX6392
RESET IN2
V
CC
CSRT
GND
5
5
RESET2
6
6
R2
7
7
RESET1
8
—
R1
—
8
MR
Detailed Description
Each device includes a pair of voltage monitors with
sequenced reset outputs. The first block monitors V
CC
only (RESET1 output is independent of the RESET IN2
monitor). It asserts a reset signal (LOW) whenever V
CC
is below the preset voltage threshold.
RESET1
remains
asserted for at least 140ms after V
CC
rises above the
reset threshold.
RESET1
timing is internally set in each
device. V
CC
voltage thresholds are available from
1.57V to 4.63V. In all cases V
CC
acts as the master
supply (all resets are asserted when V
CC
goes below
its selected threshold). The V
CC
input also acts as the
device power supply.
The second block monitors both RESET IN2 and V
CC
. It
asserts a reset signal (LOW) whenever RESET IN2 is
below the 625mV threshold or V
CC
is below its reset
threshold.
RESET2
remains asserted for a fixed 140ms
(min) or a user-adjustable time period after RESET IN2
rises above the 625mV reset threshold and
RESET1
is
deasserted. Resets are guaranteed valid for V
CC
down
to 1V.
The timing diagram in Figure 2 shows the reset timing
characteristics of the MAX6391/MAX6392. As shown in
Figure 2,
RESET1
deasserts 140ms (min) (t
RP1
) after
V
CC
exceeds the reset threshold.
RESET2
deasserts
t
RP2
(140ms minimum or a user-adjustable timeout peri-
od) after RESET IN2 exceeds 625mV and
RESET1
is
deasserted. When RESET IN2 drops below 625mV
while V
CC
is above the reset threshold,
RESET2
asserts
within 10µs typ.
RESET1
is unaffected when this hap-
pens. When V
CC
falls below V
TH1
,
RESET2
always
asserts before
RESET1
(t
RD2
< t
RD1
).
_______________________________________________________________________________________
5
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