MAXIM MAX6716UTYDD3-T

19-2325; Rev 2; 10/02
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
The MAX6715–MAX6729 are ultra-low-voltage microprocessor (µP) supervisory circuits designed to monitor two or three
system power-supply voltages. These devices assert a system reset if any monitored supply falls below its factorytrimmed or adjustable threshold and maintain reset for a
minimum timeout period after all supplies rise above their
thresholds. The integrated dual/triple supervisory circuits significantly improve system reliability and reduce size compared to separate ICs or discrete components.
These devices monitor primary supply voltages (VCC1) from
1.8V to 5.0V and secondary supply voltages (VCC2) from
0.9V to 3.3V with factory-trimmed reset threshold voltage
options (see Reset Voltage Threshold Suffix Guide). An
externally adjustable RSTIN input option allows customers to
monitor a third supply voltage down to 0.62V. These devices
are guaranteed to be in the correct reset output logic state
when either VCC1 or VCC2 remains greater than 0.8V.
A variety of push-pull or open-drain reset outputs along with
watchdog input, manual reset input, and power-fail input/output features are available (see Selector Guide). Select reset
timeout periods from 1.1ms to 1120ms (min) (see Reset
Timeout Period Suffix Guide). The MAX6715–MAX6729 are
available in small 5, 6, and 8-pin SOT23 packages and operate over the -40°C to +85°C temperature range.
Features
♦ VCC1 (primary supply) Reset Threshold Voltages
from 1.58V to 4.63V
♦ VCC2 (secondary supply) Reset Threshold
Voltages from 0.79V to 3.08V
♦ Externally Adjustable RSTIN Threshold for
Auxiliary/Triple-Voltage Monitoring
(0.62V internal reference)
♦ Watchdog Timer Option
35s (min) Long Startup Period
1.12s (min) Normal Timeout Period
♦ Manual Reset Input Option
♦ Power-Fail Input/Power-Fail Output Option
(Push-Pull and Open-Drain Active-Low)
♦ Guaranteed Reset Valid Down to VCC1 or
VCC2 = 0.8V
♦ Reset Output Logic Options
♦ Immune to Short VCC Transients
♦ Low Supply Current 14µA (typ) at 3.6V
♦ Small 5, 6, and 8-Pin SOT23 Packages
Ordering Information
Applications
Multivoltage Systems
Telecom/Networking Equipment
TEMP RANGE
PIN-PACKAGE
MAX6715UT_ _D_ -T
PART
-40°C to +85°C
6 SOT23-6
Computers/Servers
Portable/Battery-Operated Equipment
MAX6716UT_ _D_ -T
-40°C to +85°C
6 SOT23-6
MAX6717UK_ _D_ -T
-40°C to +85°C
5 SOT23-5
Industrial Equipment
Printer/Fax
MAX6718UK_ _D_ -T
-40°C to +85°C
5 SOT23-5
MAX6719UT_ _D_ -T
-40°C to +85°C
6 SOT23-6
MAX6720UT_ _D_ -T
-40°C to +85°C
6 SOT23-6
Set-Top Boxes
Typical Operating Circuit
UNREGULATED
DC
IN
OUT2
DC/DC
CONVERTER
OUT1
1.8V
VCC1
VCC2
0.9V
I/O
CORE
SUPPLY SUPPLY
Note: The first “_ _” are placeholders for the threshold voltage
levels of the devices. Desired threshold levels are set by the part
number suffix found in the Reset Voltage Threshold Suffix Guide.
The “_” after the D is a placeholder for the reset timeout delay
time. Desired delay time is set using the timeout period suffix
found in the Reset Timeout Period Suffix Guide. For example the
MAX6716UTLTD3-T is a dual-voltage supervisor VTH1 = 4.625V,
VTH2 = 3.075V, and 210ms (typ) timeout period.
R1
R2
PUSHBUTTON
SWITCH
RST
RESET
RSTIN/PFI
WDI
I/O
MR
PFO
NMI
MAX67_ _
µP
Ordering Information continued at end of data sheet.
Pin Configurations appear at end of data sheet.
Selector Guide appears at end of data sheet.
________________________________________________________________ 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.
1
MAX6715–MAX6729
General Description
MAX6715–MAX6729
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
VCC1, VCC2 ..........................................................-0.3V to +6V
Open-Drain RST, RST1, RST2, PFO, RST ................-0.3V to +6V
Push-Pull RST, RST1, PFO, RST...............-0.3V to (VCC1 + 0.3V)
Push-Pull RST2 .........................................-0.3V to (VCC2 + 0.3V)
RSTIN, PFI, MR, WDI ................................................-0.3V to +6V
Input Current/Output Current (all pins) ...............................20mA
Continuous Power Dissipation (TA = +70°C)
5-Pin SOT23-5 (derate 7.1mW/°C above +70°C) ........571mW
6-Pin SOT23-6 (derate 8.7mW/°C above +70°C) ........696mW
8-Pin SOT23-8 (derate 8.9mW/°C above +70°C) ........714mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature ......................................................+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
(VCC1 = VCC2 = 0.8V to 5.5V, GND = 0, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
Supply Voltage
SYMBOL
VCC
ICC1
Supply Current
ICC2
VCC1 Reset Threshold
VCC2 Reset Threshold
CONDITIONS
VTH1
VTH2
2
VHYST
TYP
0.8
MAX
UNITS
5.5
V
VCC1 < 5.5V, all I/O pins open
15
VCC1 < 3.6V, all I/O pins open
10
28
VCC2 < 3.6V, all I/O pins open
4
11
VCC2 < 2.75V, all I/O pins open
39
3
9
L (falling)
4.500
4.625
4.750
M (falling)
4.250
4.375
4.500
T (falling)
3.000
3.075
3.150
S (falling)
2.850
2.925
3.000
R (falling)
2.550
2.625
2.700
Z (falling)
2.250
2.313
2.375
Y (falling)
2.125
2.188
2.250
W (falling)
1.620
1.665
1.710
V (falling)
1.530
1.575
1.620
T (falling)
3.000
3.075
3.150
S (falling)
2.850
2.925
3.000
R (falling)
2.550
2.625
2.700
Z (falling)
2.250
2.313
2.375
Y (falling)
2.125
2.188
2.250
W (falling)
1.620
1.665
1.710
V (falling)
1.530
1.575
1.620
I (falling)
1.350
1.388
1.425
H (falling)
1.275
1.313
1.350
G (falling)
1.080
1.110
1.140
F (falling)
1.020
1.050
1.080
E (falling)
0.810
0.833
0.855
D (falling)
0.765
0.788
0.810
Reset Threshold Tempco
Reset Threshold Hysteresis
MIN
Referenced to VTH typical
µA
V
V
20
ppm/°C
0.5
%
_______________________________________________________________________________________
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
(VCC1 = VCC2 = 0.8V to 5.5V, GND = 0, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
VCC to Reset Output Delay
SYMBOL
tRD
CONDITIONS
D1
Reset Timeout Period
tRP
MIN
TYP
VCC1 = (VTH1 + 100mV) to (VTH1 - 100mV) or
VCC2 = (VTH2 + 75mV) to (VTH2 - 75mV)
MAX
20
UNITS
µs
1.1
1.65
2.2
D2
8.8
13.2
17.6
D3
140
210
280
D5
280
420
560
D6
560
840
1120
D4
1120
1680
2240
626.5
ms
ADJUSTABLE RESET COMPARATOR INPUT (MAX6719/MAX6720/MAX6723–MAX6727)
RSTIN Input Threshold
VRSTIN
611
RSTIN Input Current
IRSTIN
-25
RSTIN Hysteresis
RSTIN to Reset Output Delay
tRSTIND
VRSTIN to (VRSTIN - 30mV)
642
mV
+25
nA
3
mV
22
µs
POWER-FAIL INPUT (MAX6728/MAX6729)
PFI Input Threshold
VPFI
611
PFI Input Current
IPFI
-25
PFI Hysteresis
VPFH
PFI to PFO Delay
tDPF
626.5
(VPFI + 30mV) to (VPFI - 30mV)
642
mV
+25
nA
3
mV
2
µs
MANUAL RESET INPUT (MAX6715–MAX6722/MAX6725–MAX6729)
0.3 ✕ VCC1
VIL
MR Input Voltage
0.7 ✕ VCC1
VIH
MR Minimum Pulse Width
1
MR Glitch Rejection
MR to Reset Delay
µs
100
tMR
ns
200
MR Pullup Resistance
V
ns
25
50
80
35
54
72
1.12
1.68
2.24
kΩ
WATCHDOG INPUT (MAX6721–MAX6729)
Watchdog Timeout Period
tWD
First watchdog period after reset timeout
period
Normal mode
WDI Pulse Width
WDI Input Voltage
WDI Input Current
tWDI
(Note 2)
50
IWDI
ns
0.3 ✕ VCC1
VIL
0.7 ✕ VCC1
VIH
WDI = 0 or VCC1
-1
s
+1
V
µA
_______________________________________________________________________________________
3
MAX6715–MAX6729
ELECTRICAL CHARACTERISTICS (continued)
MAX6715–MAX6729
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
ELECTRICAL CHARACTERISTICS (continued)
(VCC1 = VCC2 = 0.8V to 5.5V, GND = 0, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
RESET/POWER-FAIL OUTPUTS
RST/RST1/RST2/PFO
Output LOW
(Push-Pull or Open-Drain)
RST/RST1/PFO
Output HIGH
(Push-Pull Only)
RST2
Output HIGH
(Push-Pull Only)
RST
Output HIGH
(Push-Pull Only)
VOL
VOH
VOH
VOH
VCC1 or VCC2 ≥ 0.8V, ISINK = 1µA,
output asserted
0.3
VCC1 or VCC2 ≥ 1.0V, ISINK = 50µA,
output asserted
0.3
VCC1 or VCC2 ≥ 1.2V, ISINK = 100µA,
output asserted
0.3
VCC1 or VCC2 ≥ 2.7V, ISINK = 1.2mA,
output asserted
0.3
VCC1 or VCC2 ≥ 4.5V, ISINK = 3.2mA,
output asserted
0.4
VCC1 ≥ 1.8V, ISOURCE = 200µA, output not
asserted
0.8 ✕ VCC1
VCC1 ≥ 2.7V, ISOURCE = 500µA, output not
asserted
0.8 ✕ VCC1
VCC1 ≥ 4.5V, ISOURCE = 800µA, output not
asserted
0.8 ✕ VCC1
VCC2 ≥ 1.8V, ISOURCE = 200µA, output not
asserted
0.8 ✕ VCC2
VCC2 ≥ 2.7V, ISOURCE = 500µA, output not
asserted
0.8 ✕ VCC2
VCC2 ≥ 4.5V, ISOURCE = 800µA, output not
asserted
0.8 ✕ VCC2
VCC1 ≥ 1.0V, ISOURCE = 1µA, reset asserted
0.8 ✕ VCC1
VCC1 ≥ 1.8V, ISOURCE = 150µA,
reset asserted
0.8 ✕ VCC1
VCC1 ≥ 2.7V, ISOURCE = 500µA,
reset asserted
0.8 ✕ VCC1
VCC1 ≥ 4.5V, ISOURCE = 800µA,
reset asserted
0.8 ✕ VCC1
V
V
V
V
VCC1 or VCC2 ≥ 1.8V, ISINK = 500µA,
reset not asserted
0.3
VCC1 or VCC2 ≥ 2.7V, ISINK = 1.2mA,
reset not asserted
0.3
VCC1 or VCC2 ≥ 4.5V, ISINK = 3.2mA,
reset not asserted
0.4
RST/RST1/RST2/PFO Output
Open-Drain Leakage Current
Output not asserted
0.5
µA
RST Output Open-Drain
Leakage Current
Output asserted
0.5
µA
RST
Output LOW
(Push-Pull or Open Drain)
VOL
Note 1: Devices tested at +25°C. Overtemperature limits are guaranteed by design and not production tested.
Note 2: Parameter guaranteed by design.
4
_______________________________________________________________________________________
V
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
ICC1
12
10
8
6
ICC2
4
10
8
ICC1
6
16
14
12
8
-15
10
35
60
85
ICC1
6
4
ICC2
ICC2
2
0
-40
TOTAL
10
2
0
0
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
SUPPLY CURRENT vs. TEMPERATURE
VCC1 = 1.8V, VCC2 = 1.2V
NORMALIZED RESET/WATCHDOG
TIMEOUT PERIOD vs. TEMPERATURE
MAXIMUM VCC TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
12
10
TOTAL
8
6
ICC1
4
2
ICC2
1.005
1.004
1.003
1.002
1.001
1.000
0.999
0
10,000
RESET OCCURS ABOVE
THIS LINE
1000
0.998
-15
10
35
60
85
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
NORMALIZED VCC RESET THRESHOLD
vs. TEMPERATURE
RESET INPUT AND POWER-FAIL INPUT
THRESHOLD vs. TEMPERATURE
1.003
630
THRESHOLD (mV)
1.002
1.001
1.000
0.999
10
100
1000
VCC TO RESET DELAY
vs. TEMPERATURE
629
628
627
0.998
54
100mV OVERDRIVE
53
52
51
50
49
48
47
46
626
0.997
1
RESET THRESHOLD OVERDRIVE (mV)
631
MAX6715-29 toc07
1.004
100
10
-40
VCC TO RESET DELAY (µs)
-40
MAX6715-29 toc06
1.006
MAXIMUM VCC TRANSIENT DURATION (µs)
14
MAX6715-29 toc05
16
1.007
RESET/WATCHDOG PERIOD
MAX6715-29 toc04
18
SUPPLY CURRENT (µA)
TOTAL
12
4
2
RESET THRESHOLD
14
18
MAX6715-29 toc03
16
MAX6715-29 toc09
14
MAX6715-29 toc02
TOTAL
18
SUPPLY CURRENT vs. TEMPERATURE
VCC1 = 2.5V, VCC2 = 1.8V
MAX6715-29 toc08
SUPPLY CURRENT (µA)
16
SUPPLY CURRENT (µA)
MAX6715-29 toc01
18
SUPPLY CURRENT vs. TEMPERATURE
VCC1 = 3.3V, VCC2 = 2.5V
SUPPLY CURRENT (µA)
SUPPLY CURRENT vs. TEMPERATURE
VCC1 = 5V, VCC2 = 3.3V
45
625
0.996
-40
-15
10
35
TEMPERATURE (°C)
60
85
44
-40
-15
10
35
TEMPERATURE (°C)
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
_______________________________________________________________________________________
5
MAX6715–MAX6729
Typical Operating Characteristics
(VCC1 = 5V, VCC2 = 3.3V, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VCC1 = 5V, VCC2 = 3.3V, TA = +25°C, unless otherwise noted.)
RESET INPUT TO RESET OUTPUT DELAY
vs. TEMPERATURE
POWER-FAIL INPUT TO POWER-FAIL
OUTPUT DELAY vs. TEMPERATURE
MR TO RESET OUTPUT DELAY
24.0
23.8
23.6
23.4
23.2
2.4
MAX6715-29 toc11
24.2
30mV OVERDRIVE
RSTIN TO RESET DELAY (µs)
30mV OVERDRIVE
MAX6715-29 toc10
MAX6715-29 toc12
24.4
RSTIN TO RESET DELAY (µs)
MAX6715–MAX6729
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
VMR
2V/div
2.3
0
2.2
VRST
2V/div
2.1
23.0
0
22.8
2.0
-40
-15
10
35
60
85
-40
TEMPERATURE (°C)
-15
10
35
60
50ns/div
85
TEMPERATURE (°C)
Pin Description
PIN
MAX6715/ MAX6717/ MAX6719/ MAX6721/ MAX6723/ MAX6725/
MAX6728/ NAME
MAX6727
MAX6716 MAX6718 MAX6720 MAX6722 MAX6724 MAX6726
MAX6729
1
6
1
1
1
1
1
1, 4
1
RST/
RST1
FUNCTION
Active-Low Reset Output,
Open-Drain or Push-Pull.
RST/RST1 changes from
high to low when VCC1 or
VCC2 drops below the
selected reset thresholds,
RSTIN is below threshold,
MR is pulled low, or the
watchdog triggers a
reset. RST/RST1 remains
low for the reset timeout
period after VCC1/
VCC2/RSTIN exceed the
device reset thresholds,
MR goes low to high, or
the watchdog triggers a
reset. Open-drain outputs
require an external pullup
resistor. Push-pull
outputs are referenced to
VCC1.
_______________________________________________________________________________________
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
PIN
MAX6715/ MAX6717/ MAX6719/ MAX6721/ MAX6723/ MAX6725/
MAX6728/ NAME
MAX6727
MAX6716 MAX6718 MAX6720 MAX6722 MAX6724 MAX6726
MAX6729
FUNCTION
5
—
—
—
—
—
—
—
RST2
Active-Low Reset Output,
Open-Drain or Push-Pull.
RST2 changes from high
to low when VCC1 or
VCC2 drops below the
selected reset thresholds
or MR is pulled low. RST2
remains low for the reset
timeout period after
VCC1/VCC2 exceed the
device reset thresholds
or MR goes low to high.
Open-drain outputs
require an external pullup
resistor. Push-pull
outputs are referenced to
VCC2.
2
2
2
2
2
2
2
2
GND
Ground
3
3
3
3
—
5
5
5
MR
4
4
4
4
4
6
6
6
VCC2
6
5
6
6
6
8
8
8
VCC1
Active-Low Manual Reset
Input. Internal 50kΩ
pullup to VCC1. Pull low
to force a reset. Reset
remains active as long as
MR is low and for the
reset timeout period after
MR goes high. Leave
unconnected or connect
to VCC1 if unused.
Secondary Supply
Voltage Input. Powers the
device when it is above
VCC1 and input for
secondary reset
threshold monitor.
Primary Supply Voltage
Input. Powers the device
when it is above VCC2
and input for primary
reset threshold monitor.
_______________________________________________________________________________________
7
MAX6715–MAX6729
Pin Description (continued)
MAX6715–MAX6729
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
Pin Description (continued)
PIN
MAX6715/ MAX6717/ MAX6719/ MAX6721/ MAX6723/ MAX6725/
MAX6728/ NAME
MAX6727
MAX6716 MAX6718 MAX6720 MAX6722 MAX6724 MAX6726
MAX6729
—
—
—
8
—
—
—
—
5
—
5
—
—
3
5
—
3
7
—
3
7
—
3
—
7
FUNCTION
WDI
Watchdog Input. If WDI
remains high or low for
longer than the watchdog
timeout period, the
internal watchdog timer
runs out and the reset
output asserts for the
reset timeout period. The
internal watchdog timer
clears whenever a reset
is asserted or WDI sees a
rising or falling edge. The
watchdog has a long
timeout period (35s min)
after each reset event
and a short timeout
period (1.12s min) after
the first valid WDI
transition. Leave WDI
floating to disable the
watchdog timer function.
RSTIN
Undervoltage Reset
Comparator Input. Highimpedance input for
adjustable reset monitor.
The reset output is
asserted when RSTIN falls
below the 0.626V internal
reference voltage. Set the
monitored voltage reset
threshold with an external
resistor-divider network.
Connect RSTIN to VCC1 or
VCC2 if not used.
PFI
Power-Fail Voltage
Monitor Input. Highimpedance input for
internal power-fail monitor
comparator. Connect PFI
to an external resistordivider network to set the
power-fail threshold
voltage (0.626V typical
internal reference
voltage). Connect to
GND, VCC1, or VCC2 if
not used.
_______________________________________________________________________________________
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
PIN
MAX6715/ MAX6717/ MAX6719/ MAX6721/ MAX6723/ MAX6725/
MAX6728/ NAME
MAX6727
MAX6729
MAX6716 MAX6718 MAX6720 MAX6722 MAX6724 MAX6726
—
—
—
—
—
—
—
—
—
—
Detailed Description
Supply Voltages
The MAX6715–MAX6729 microprocessor (µP) supervisory circuits maintain system integrity by alerting the µP
to fault conditions. These ICs are optimized for systems
that monitor two or three supply voltages. The outputreset state is guaranteed to remain valid while either
VCC1 or VCC2 is above 0.8V.
Threshold Levels
Input voltage threshold level combinations are indicated by a two-letter code in the Reset Voltage Threshold
—
4
—
—
4
—
FUNCTION
PFO
Active-Low Power-Fail
Monitor Output, OpenDrain or Push-Pull. PFO is
asserted low when PFI is
less than 0.626V. PFO
deasserts without a reset
timeout period. Opendrain outputs require an
external pullup resistor.
Push-pull outputs are
referenced to VCC1.
RST
Active-High Reset
Output, Open-Drain or
Push-Pull. RST changes
from low to high when
VCC1 or VCC2 drops
below selected reset
thresholds, RSTIN is
below threshold, MR is
pulled low, or the
watchdog triggers a
reset. RST remains HIGH
for the reset timeout
period after VCC1/
VCC 2/RSTIN exceed the
device reset thresholds,
MR goes low to high, or
the watchdog triggers a
reset. Open-drain outputs
require an external pullup
resistor. Push-pull
outputs are referenced to
VCC1.
Suffix Guide (Table 1). Contact factory for availability of
other voltage threshold combinations.
Reset Outputs
The MAX6715–MAX6729 provides an active-low reset
output (RST) and the MAX6725/MAX6726 provides
both an active-high (RST) and an active-low reset output (RST). RST, RST, RST1, and RST2 are asserted
when the voltage at either VCC1 or VCC2 falls below the
voltage threshold level, RSTIN drops below threshold,
or MR is pulled low. Once reset is asserted it stays low
for the reset timeout period (see Table 2). If V CC1,
VCC2, or RSTIN goes below the reset threshold before
the reset timeout period is completed, the internal timer
_______________________________________________________________________________________
9
MAX6715–MAX6729
Pin Description (continued)
MAX6715–MAX6729
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
restarts. The MAX6715/MAX6717/MAX6719/MAX6721/
MAX6723/MAX6725/MAX6727/MAX6728 contain opendrain reset outputs, while the MAX6716/MAX6718/
MAX6720/MAX6722/MAX6724/MAX6726/MAX6729
contain push-pull reset outputs. The MAX6727 provides
two separate open-drain RST outputs driven by the
same internal logic.
R1
RSTIN
Manual Reset Input
Many microprocessor-based products require manual
reset capability, allowing the operator, a test technician, or external logic circuitry to initiate a reset. A logic
low on MR asserts the reset output. Reset remains
asserted while MR is low and for the reset timeout period (tRP) after MR returns high. This input has an internal
50kΩ pullup resistor to VCC1 and can be left unconnected if not used. MR can be driven with TTL or
CMOS logic levels, or with open-drain/collector outputs.
Connect a normally open momentary switch from MR to
GND to create a manual reset function; external
debounce circuitry is not required. If MR is driven from
long cables or if the device is used in a noisy environment, connect a 0.1µF capacitor from MR to GND to
provide additional noise immunity.
Adjustable Input Voltage
The MAX6719/MAX6720 and MAX6723–MAX6727 provide
an additional input to monitor a third system voltage. The
threshold voltage at RSTIN is typically 626mV. Connect a
resistor-divider network to the circuit as shown in Figure 1
to establish an externally controlled threshold voltage,
VEXT_TH.
MAX6719/
MAX6720/
MAX6723–
MAX6727
VEXT_TH
R2
GND
Figure 1. Monitoring a Third Voltage
when processor activity fails. After each reset event
(VCC power-up/brownout, manual reset, or watchdog
reset), there is a long initial watchdog period of 35s
minimum. The long watchdog period mode provides an
extended time for the system to power-up and fully initialize all µP and system components before assuming
responsibility for routine watchdog updates.
The normal watchdog timeout period (1.12s min)
begins after the first transition on WDI before the conclusion of the long initial watchdog period (Figure 2).
During the normal operating mode, the supervisor will
issue a reset pulse for the reset timeout period if the µP
does not update the WDI with a valid transition (high-tolow or low-to-high) within the standard timeout period
(1.12s min).
VEXT_TH = 626mV((R1 + R2)/R2)
Low leakage current at RSTIN allows the use of largevalued resistors resulting in reduced power consumption of the system.
Power-Fail Comparator
PFI is the noninverting input to a comparator. If PFI is
less than VPFI (626.5mV), PFO goes low. Common uses
for the power-fail comparator include monitoring preregulated input of the power supply (such as a battery) or
Watchdog Input
The watchdog monitors µP activity through the watchdog input (WDI). To use the watchdog function, connect WDI to a bus line or µP I/O line. When WDI
remains high or low for longer than the watchdog timeout period, the reset output asserts. Leave WDI floating
to disable the watchdog function.
The MAX6721–MAX6729 include a dual-mode watchdog timer to monitor µP activity. The flexible timeout
architecture provides a long period initial watchdog
mode, allowing complicated systems to complete
lengthy boots, and a short period normal watchdog
mode, allowing the supervisor to provide quick alerts
10
VTH
VCC
tWDI-NORMAL
1.12s MAX
tWDI-STARTUP
35s MAX
WDI
1.12s MAX
RESET
tRP
Figure 2. Normal Watchdog Startup Sequence
______________________________________________________________________________________
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
RESET TO OTHER SYSTEM COMPONENTS
VCC1 VCC2
VIN
MAX6728/
MAX6729
R1
VTRIP = VPFI
PFI
( R1R2+ R2 )
MAX6715–
MAX6729
PFO
µP
4.7kΩ
VCC2
R2
RST
RESET
VCC1
GND
GND
GND
B
VCC
MAX6728/
MAX6729
R1
PFI
Figure 4. Interfacing to µPs with Bidirectional Reset I/O
PFO
[ (R11 + R21 ) - VR1 ]
VTRIP = R2 (VPFI)
CC
VPFI = 626.5mV
R2
VIN
GND
Figure 3. Using Power-Fail Input to Monitor an Additional
Power-Supply a) VIN is Positive b) VIN is Negative
providing an early power-fail warning so software can
conduct an orderly system shutdown. It can also be
used to monitor supplies other than VCC1 or VCC2 by
setting the power-fail threshold with a resistor-divider, as
shown in Figure 3. PFI is the input to the power-fail comparator. The typical comparator delay is 2µs from PFI to
PFO. Connect PFI to ground of VCC1 if unused.
Ensuring a Valid Reset Output
Down to VCC = 0
The MAX6715–MAX6729 are guaranteed to operate
properly down to V CC = 0.8V. In applications that
require valid reset levels down to VCC = 0 use a pulldown resistor at RST to ground. The resistor value used
is not critical, but it must be large enough not to load
the reset output when VCC is above the reset threshold.
For most applications, 100kΩ is adequate. This configuration does not work for the open-drain outputs of the
MAX6715/MAX6717/MAX6719/MAX6721/MAX6723/
MAX6725/MAX6727/MAX6728. For push-pull, activehigh RST output connect the external resistor as a
pullup from RST to VCC1.
Applications Information
Interfacing to µPs with Bidirectional
Reset Pins
Most microprocessors with bidirectional reset pins can
interface directly to open-drain RST output options.
Systems simultaneously requiring a push-pull RST output and a bidirectional reset interface can be in logic
contention. To prevent contention, connect a 4.7kΩ
resistor between RST and the µP’s reset I/O port as
shown in Figure 4.
Adding Hysteresis to the Power-Fail
Comparator
The power-fail comparator has a typical input hysteresis
of 3mV. This is sufficient for most applications where a
power-supply line is being monitored through an external
voltage-divider (see the Power-Fail Comparator section).
If additional noise margin is desired, connect a resistor
between PFO and PFI as shown in Figure 5. Select the
values of R1, R2, and R3 so PFI sees VPFI (626mV) when
VEXT falls to its power-fail trip point (VFAIL) and when VIN
rises to its power-good trip point (VGOOD). The hysteresis
window extends between the specified VFAIL and VGOOD
thresholds. R3 adds the additional hysteresis by sinking
current from the R1/R2 divider network when PFO is logic
low and sourcing current into the network when PFO is
logic high. R3 is typically an order of magnitude greater
than R1 or R2.
The current through R2 should be at least 2.5µA to
ensure that the 25nA (max) PFI input current does not
significantly shift the trip points. Therefore, R2 <
VPFI/2.5µA < 248kΩ for most applications. R3 will provide
additional hysteresis for PFO push-pull (VOH = VCC1) or
open-drain (VOH = VPULLUP) applications.
______________________________________________________________________________________
11
MAX6715–MAX6729
A
MAX6715–MAX6729
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
R3
START
A
VIN
VEXT
VGOOD
VFAIL
PFO
MAX6728/
MAX6729
SET WDI
HIGH
R1
PFI
PROGRAM
CODE
PFO
R2
GND
VGOOD = DESIRED VEXT GOOD VOLTAGE THRESHOLD
VFAIL = DESIRED VEXT FAIL VOLTAGE THRESHOLD
VOH = VCC1 (FOR PUSH-PULL PFO)
R2 = 200kΩ (FOR > 2.5µA R2 CURRENT)
R1 = R2 ((VGOOD - VPFI) - (VPFI)(VGOOD - VFAIL) / VOH) / VPFI
R3 = (R1 x VOH) / (VGOOD - VFAIL)
Figure 5. Adding Hysteresis to Power-Fail for Push-Pull PFO
Monitoring an Additional Power Supply
These µP supervisors can monitor either positive or
negative supplies using a resistor voltage-divider to
PFI. PFO can be used to generate an interrupt to the µP
or cause reset to assert (Figure 3).
Monitoring a Negative Voltage
The power-fail comparator can be used to monitor a
negative supply voltage using the circuit shown in
Figure 3. When the negative supply is valid, PFO is low.
When the negative supply voltage drops, PFO goes
high. The circuit’s accuracy is affected by the PFI
threshold tolerance, VCC, R1, and R2.
Negative-Going VCC Transients
The MAX6715–MAX6729 supervisors are relatively
immune to short-duration negative-going VCC transients
(glitches). It is usually undesirable to reset the µP when
V CC experiences only small glitches. The Typical
Operating Characteristics show Maximum Transient
Duration vs. Reset Threshold Overdrive, for which reset
pulses are not generated. The graph was produced
using negative-going VCC pulses, starting above VTH
and ending below the reset threshold by the magnitude
indicated (reset threshold overdrive). The graph shows
the maximum pulse width that a negative-going VCC
transient may typically have without causing a reset
pulse to be issued. As the amplitude of the transient
increases (i.e., goes farther below the reset threshold),
the maximum allowable pulse width decreases. A 0.1µF
bypass capacitor mounted close to the VCC pin provides additional transient immunity.
SUBROUTINE OR
PROGRAM LOOP
SET WDI LOW
HANG IN
SUBROUTINE
SUBROUTINE
COMPLETED
RETURN
Figure 6. Watchdog Flow Diagram
watchdog timer to closely monitor software execution.
This technique avoids a “stuck” loop where the watchdog timer continues to be reset within the loop, keeping
the watchdog from timing out. Figure 6 shows an example flow diagram where the I/O driving the watchdog
input is set high at the beginning of the program, set low
at the beginning of every subroutine or loop, then set
high again when the program returns to the beginning. If
the program should “hang” in any subroutine, the I/O is
continually set low and the watchdog timer is allowed to
time out, causing a reset or interrupt to be issued.
Chip Information
TRANSISTOR COUNT: 1072
PROCESS: BiCMOS
Watchdog Software Considerations
Setting and resetting the watchdog input at different
points in the program, rather than “pulsing” the watchdog input high-low-high or low-high-low, helps the
12
______________________________________________________________________________________
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
VCC1
VCC1
MR
MR
PULLUP
VCC1
VCC1
VCC2
VREF
RESET
TIMEOUT
PERIOD
VCC2
RST
RESET
OUTPUT
DRIVER
RST
RSTIN/PFI
PFO
VCC1
VREF
VCC1
WATCHDOG
TIMER WITH
FLOAT DISABLE
WDI
VREF/2
______________________________________________________________________________________
13
MAX6715–MAX6729
Functional Diagram
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
MAX6715–MAX6729
Selector Guide
PART
NUMBER
NUMBER OF
VOLTAGE
MONITORS
OPENDRAIN
RESET
OPENDRAIN
RESET
PUSHPULL
RESET
PUSHPULL
RESET
MANUAL
RESET
WATCHDOG
INPUT
POWERFAIL
INPUT/
OUTPUT
MAX6715
2
2
—
—
—
√
—
—
MAX6716
2
—
—
2
—
√
—
—
MAX6717
2
1
—
—
—
√
—
—
MAX6718
2
—
—
1
—
√
—
—
MAX6719
3
1
—
—
—
√
—
—
MAX6720
3
—
—
1
—
√
—
—
MAX6721
2
1
—
—
—
√
√
—
MAX6722
2
—
—
1
—
√
√
—
MAX6723
3
1
—
—
—
—
√
—
MAX6724
3
—
—
1
—
—
√
—
MAX6725
3
1
1
—
—
√
√
—
MAX6726
3
—
—
1
1
√
√
—
MAX6727
3
2
—
—
—
√
√
—
MAX6728
2
1
—
—
—
√
√
√ (open drain)
MAX6729
2
—
—
1
—
√
√
√ (push-pull)
Ordering Information (continued)
TEMP RANGE
PIN-PACKAGE
MAX6721UT_ _D_ -T
PART
-40°C to +85°C
6 SOT23-6
MAX6722UT_ _D_ -T
-40°C to +85°C
6 SOT23-6
MAX6723UT_ _D_ -T
-40°C to +85°C
6 SOT23-6
MAX6724UT_ _D_ -T
-40°C to +85°C
6 SOT23-6
MAX6725KA_ _D_ -T
-40°C to +85°C
8 SOT23-8
MAX6726KA_ _D_ -T
-40°C to +85°C
8 SOT23-8
MAX6727KA_ _D_ -T
-40°C to +85°C
8 SOT23-8
MAX6728KA_ _D_ -T
-40°C to +85°C
8 SOT23-8
MAX6729KA_ _D_ -T
-40°C to +85°C
8 SOT23-8
Note: The first “_ _” are placeholders for the threshold voltage
levels of the devices. Desired threshold levels are set by the part
number suffix found in the Reset Voltage Threshold Suffix Guide.
The “_” after the D is a placeholder for the reset timeout delay
time. Desired delay time is set using the timeout period suffix
found in the Reset Timeout Period Suffix Guide. For example the
MAX6716UTLTD3-T is a dual-voltage supervisor VTH1 = 4.625V,
VTH2 = 3.075V, and 210ms (typ) timeout period.
14
______________________________________________________________________________________
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
Table 2. Reset Timeout Period Suffix
Guide
ACTIVE TIMEOUT PERIOD
PART NUMBER
SUFFIX
(_ _)
VCC1 NOMINAL
VOLTAGE
THRESHOLD (V)
VCC2 NOMINAL
VOLTAGE
THRESHOLD (V)
TIMEOUT
PERIOD SUFFIX
MIN [ms]
MAX [ms]
D1
1.1
2.2
LT
4.625
3.075
D2
8.8
17.6
MS
4.375
2.925
D3
140
280
MR
4.375
2.625
D5
280
560
TZ
3.075
2.313
D6
560
1120
SY
2.925
2.188
D4
1120
2240
RY
2.625
2.188
TW
3.075
1.665
SV
2.925
1.575
RV
2.625
1.575
TI
3.075
1.388
SH
2.925
1.313
RH
2.625
1.313
TG
3.075
1.110
SF
2.925
1.050
RF
2.625
1.050
TE
3.075
0.833
SD
2.925
0.788
RD
2.625
0.788
ZW
2.313
1.665
YV
2.188
1.575
ZI
2.313
1.388
YH
2.188
1.313
ZG
2.313
1.110
YF
2.188
1.050
ZE
2.313
0.833
YD
2.188
0.788
WI
1.665
1.388
VH
1.575
1.313
WG
1.665
1.110
1.050
VF
1.575
WE
1.665
0.833
VD
1.575
0.788
MAX6715–MAX6729
Table 1. Reset Voltage Threshold Suffix
Guide**
**Standard versions are shown in bold and are available in a D3
timeout option only. Standard versions require 2,500 piece order
increments and are typically held in sample stock. There is a
10,000 order increment on nonstandard versions. Other threshold voltages may be available, contact factory for availability.
______________________________________________________________________________________
15
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
MAX6715–MAX6729
Pin Configurations
TOP VIEW
RST1 1
GND 2
MAX6715/
MAX6716
MR 3
6
VCC1
RST 1
5
RST2
GND 2
4
VCC2
MR 3
SOT23-6
VCC1
MAX6717/
MAX6718
MAX6721/
MAX6722
MR 3
6
VCC1
RST 1
5
WDI
GND 2
4
VCC2
WDI 3
SOT23-6
MAX6719/
MAX6720
GND 2
VCC2
4
MR 3
GND 2
6
VCC1
5
RSTIN
4
VCC2
5
RSTIN
4
VCC2
RST 1
WDI
MAX6725/
MAX6726
3
RST 4
SOT23-8
8
VCC1
RST 1
7
RSTIN
GND 2
3
6
VCC2
WDI
RST 4
5
MR
PFO 4
SOT23-8
VCC1
GND 2
MAX6723/
MAX6724
MAX6727
WDI
6
SOT23-6
SOT23-6
RST 1
16
RST 1
SOT23-5
RST 1
GND 2
5
3
MAX6728/
MAX6729
8
VCC1
7
PFI
6
VCC2
5
MR
SOT23-8
______________________________________________________________________________________
8
VCC1
7
RSTIN
6
VCC2
5
MR
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
SOT5L.EPS
______________________________________________________________________________________
17
MAX6715–MAX6729
Package Information
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
6LSOT.EPS
MAX6715–MAX6729
Package Information (continued)
18
______________________________________________________________________________________
Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits
SOT23, 8L.EPS
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 19
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX6715–MAX6729
Package Information (continued)