Datasheet MAX6717UKSVD3-T, MAX6726KARHD3-T Datasheet (Maxim)

General Description

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.

Applications

Multivoltage Systems

Telecom/Networking Equipment

Computers/Servers

Portable/Battery-Operated Equipment

Industrial Equipment

Printer/Fax

Set-Top Boxes

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 VCCTransients

♦ Low Supply Current 14µA (typ) at 3.6V

♦ Small 5, 6, and 8-Pin SOT23 Packages

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP

Supervisory Circuits

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

IN

OUT2

OUT1

DC/DC

CONVERTER

UNREGULATED

DC

R1

R2

VCC1VCC2

RSTIN/PFI

MR

RST

WDI

PFO

MAX67_ _

PUSHBUTTON

SWITCH

I/O

SUPPLY

CORE

SUPPLY

RESET

I/O

NMI

µP

1.8V 0.9V

Typical Operating Circuit

19-2325; Rev 3; 6/03

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.

Pin Configurations appear at end of data sheet.

Selector Guide appears at end of data sheet.

PART TEMP RANGE PIN-PACKAGE

MAX6715UT_ _D_ -T -40°C to +85°C 6 SOT23-6
MAX6716UT_ _D_ -T -40°C to +85°C 6 SOT23-6
MAX6717UK_ _D_ -T -40°C to +85°C 5 SOT23-5
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

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 V

TH

1 = 4.625V,

V

TH

2 = 3.075V, and 210ms (typ) timeout period.

Ordering Information continued at end of data sheet.

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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)

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.

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 (V

CC

1 + 0.3V)

Push-Pull RST2 .........................................-0.3V to (V

CC

2 + 0.3V)

RSTIN, PFI, MR, WDI ................................................-0.3V to +6V

Input Current/Output Current (all pins) ...............................20mA

Continuous Power Dissipation (T

A

= +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

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage V

CC

0.8 5.5 V

VCC1 < 5.5V, all I/O pins open 15 39

I

CC1

VCC1 < 3.6V, all I/O pins open 10 28

VCC2 < 3.6V, all I/O pins open 4 11

Supply Current

I

CC2

VCC2 < 2.75V, all I/O pins open 3 9

µA

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

VCC1 Reset Threshold V

TH1

V (falling) 1.530 1.575 1.620

V

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

VCC2 Reset Threshold V

TH2

D (falling) 0.765 0.788 0.810

V

Reset Threshold Tempco 20 ppm/°C

Reset Threshold Hysteresis V

HYST

Referenced to VTH typical 0.5 %

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP

Supervisory Circuits

_______________________________________________________________________________________ 3

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

VCC to Reset Output Delay t

RD

V

C C

1 = ( V

TH

1 + 100m V ) to ( V

TH

1 - 100m V ) or

V

C C

2 = ( V

TH

2 + 75m V ) to ( V

TH

2 - 75m V )

20 µs

D1 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

Reset Timeout Period t

RP

D4 1120 1680 2240

ms

ADJUSTABLE RESET COMPARATOR INPUT (MAX6719/MAX6720/MAX6723–MAX6727)

RSTIN Input Threshold V

RSTIN

611 626.5 642 mV

RSTIN Input Current I

RSTIN

-25 +25 nA

RSTIN Hysteresis 3mV

RSTIN to Reset Output Delay t

RSTINDVRSTIN

to (V

RSTIN

- 30mV) 22 µs

POWER-FAIL INPUT (MAX6728/MAX6729)

PFI Input Threshold V

PFI

611 626.5 642 mV

PFI Input Current I

PFI

-25 +25 nA

PFI Hysteresis V

PFH

3mV

PFI to PFO Delay t

DPF

(V

PFI

+ 30mV) to (V

PFI

- 30mV) 2 µs

MANUAL RESET INPUT (MAX6715–MAX6722/MAX6725–MAX6729)

V

IL

0.3 ✕ VCC1

MR Input Voltage

V

IH

0.7 ✕ VCC1

V

MR Minimum Pulse Width 1µs
MR Glitch Rejection 100 ns
MR to Reset Delay t

MR

200 ns

MR Pullup Resistance 25 50 80 kΩ

WATCHDOG INPUT (MAX6721–MAX6729)

First watchdog period after reset timeout
period

35 54 72

Watchdog Timeout Period t

WD

Normal mode 1.12 1.68 2.24

s

WDI Pulse Width t

WDI

(Note 2) 50 ns

V

IL

0.3 ✕ VCC1

WDI Input Voltage

V

IH

0.7 ✕ VCC1

V

WDI Input Current I

WDI

WDI = 0 or VCC1-1+1µA

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits

4 _______________________________________________________________________________________

Note 1: Devices tested at +25°C. Overtemperature limits are guaranteed by design and not production tested.
Note 2: Parameter guaranteed by design.

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

VCC1 or VCC2 ≥ 0.8V, I

SINK

= 1µA,

output asserted

0.3

VCC1 or VCC2 ≥ 1.0V, I

SINK

= 50µA,

output asserted

0.3

VCC1 or VCC2 ≥ 1.2V, I

SINK

= 100µA,

output asserted

0.3

VCC1 or VCC2 ≥ 2.7V, I

SINK

= 1.2mA,

output asserted

0.3

RST/RST1/RST2/PFO
Output LOW
(Push-Pull or Open-Drain)

V

OL

VCC1 or VCC2 ≥ 4.5V, I

SINK

= 3.2mA,

output asserted

0.4

V

VCC1 ≥ 1.8V, I

SOURCE

= 200µA, output not

asserted

0.8

✕ V

CC

1

VCC1 ≥ 2.7V, I

SOURCE

= 500µA, output not

asserted

0.8

✕ V

CC

1

RST/RST1/PFO
Output HIGH
(Push-Pull Only)

V

OH

VCC1 ≥ 4.5V, I

SOURCE

= 800µA, output not

asserted

0.8

✕ V

CC

1

V

VCC2 ≥ 1.8V, I

SOURCE

= 200µA, output not

asserted

0.8

✕ V

CC

2

VCC2 ≥ 2.7V, I

SOURCE

= 500µA, output not

asserted

0.8

✕ V

CC

2

RST2

Output HIGH
(Push-Pull Only)

V

OH

VCC2 ≥ 4.5V, I

SOURCE

= 800µA, output not

asserted

0.8

✕ V

CC

2

V

VCC1 ≥ 1.0V, I

SOURCE

= 1µA, reset asserted 0.8 ✕ VCC1

VCC1 ≥ 1.8V, I

SOURCE

= 150µA,

reset asserted

0.8

✕ V

CC

1

VCC1 ≥ 2.7V, I

SOURCE

= 500µA,

reset asserted

0.8

✕ V

CC

1

RST
Output HIGH
(Push-Pull Only)

V

OH

VCC1 ≥ 4.5V, I

SOURCE

= 800µA,

reset asserted

0.8

✕ V

CC

1

V

VCC1 or VCC2 ≥ 1.8V, I

SINK

= 500µA,

reset not asserted

0.3

VCC1 or VCC2 ≥ 2.7V, I

SINK

= 1.2mA,

reset not asserted

0.3

RST
Output LOW
(Push-Pull or Open Drain)

V

OL

VCC1 or VCC2 ≥ 4.5V, I

SINK

= 3.2mA,

reset not asserted

0.4

V

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

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP

Supervisory Circuits

_______________________________________________________________________________________ 5

0

4

2

10

8

6

16

14

12

18

-40 10-15 356085

SUPPLY CURRENT vs. TEMPERATURE

V

CC

1 = 5V, VCC2 = 3.3V

MAX6715-29 toc01

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

TOTAL

ICC1

ICC2

0

4

2

10

8

6

16

14

12

18

-40 10-15 356085

SUPPLY CURRENT vs. TEMPERATURE

V

CC

1 = 3.3V, VCC2 = 2.5V

MAX6715-29 toc02

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

TOTAL

ICC1

ICC2

0

4

2

10

8

6

16

14

12

18

-40 10-15 356085

SUPPLY CURRENT vs. TEMPERATURE

V

CC

1 = 2.5V, VCC2 = 1.8V

MAX6715-29 toc03

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

TOTAL

ICC1

ICC2

0

4

2

10

8

6

16

14

12

18

-40 10-15 356085

SUPPLY CURRENT vs. TEMPERATURE

V

CC

1 = 1.8V, VCC2 = 1.2V

MAX6715-29 toc04

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

TOTAL

ICC1

ICC2

0.998

1.000

0.999

1.003

1.002

1.001

1.006

1.005

1.004

1.007

-40 10-15 356085

NORMALIZED RESET/WATCHDOG

TIMEOUT PERIOD vs. TEMPERATURE

MAX6715-29 toc05

TEMPERATURE (°C)

RESET/WATCHDOG PERIOD

10,000

1000

100

10

110010 1000

MAXIMUM VCC TRANSIENT DURATION

vs. RESET THRESHOLD OVERDRIVE

MAX6715-29 toc06

RESET THRESHOLD OVERDRIVE (mV)

MAXIMUM V

CC

TRANSIENT DURATION (µs)

RESET OCCURS ABOVE

THIS LINE

0.996

0.997

0.998

0.999

1.000

1.001

1.002

1.003

1.004

-40 -15 10 35 60 85

NORMALIZED VCC RESET THRESHOLD

vs. TEMPERATURE

MAX6715-29 toc07

TEMPERATURE (°C)

RESET THRESHOLD

625

627

626

629

628

630

631

-40 85

RESET INPUT AND POWER-FAIL INPUT

THRESHOLD vs. TEMPERATURE

MAX6715-29 toc08

TEMPERATURE (°C)

THRESHOLD (mV)

10-15 35 60

44

47

46

45

48

49

50

51

52

53

54

-40 10-15 35 60 85

VCC TO RESET DELAY

vs. TEMPERATURE

MAX6715-29 toc09

TEMPERATURE (°C)

V

CC

TO RESET DELAY (µs)

100mV OVERDRIVE

Typical Operating Characteristics

(VCC1 = 5V, VCC2 = 3.3V, TA= +25°C, unless otherwise noted.)

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits

6 _______________________________________________________________________________________

Pin Description

22.8

23.0

23.2

23.4

23.6

23.8

24.0

24.2

24.4

-40 -15 10 35 60 85

RESET INPUT TO RESET OUTPUT DELAY

vs. TEMPERATURE

MAX6715-29 toc10

TEMPERATURE (°C)

RSTIN TO RESET DELAY (µs)

30mV OVERDRIVE

2.0

2.1

2.2

2.4

2.3

-40 10-15 35 60 85

POWER-FAIL INPUT TO POWER-FAIL

OUTPUT DELAY vs. TEMPERATURE

MAX6715-29 toc11

TEMPERATURE (°C)

RSTIN TO RESET DELAY (µs)

30mV OVERDRIVE

0

0

V

RST

2V/div

MAX6715-29 toc12

50ns/div

MR TO RESET OUTPUT DELAY

V

MR

2V/div

Typical Operating Characteristics (continued)

(VCC1 = 5V, VCC2 = 3.3V, TA= +25°C, unless otherwise noted.)

PIN

MAX6715/

MAX6716

MAX6717/

MAX6718

MAX6719/

MAX6720

MAX6721/

MAX6722

MAX6723/

MAX6724

MAX6725/

MAX6726

MAX6727

MAX6728/

MAX6729

NAME FUNCTION

1111111, 41

RST/
RST1

Active-Low Reset Output,
Open-Drain or Push-Pull.
RST/RST1 changes from
high to low when V

CC

1 or

V

CC

2 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 V

CC

1/

V

CC

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
V

CC

1.

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP

Supervisory Circuits

_______________________________________________________________________________________ 7

Pin Description (continued)

PIN

MAX6715/

MAX6716

MAX6717/

MAX6718

MAX6719/

MAX6720

MAX6721/

MAX6722

MAX6723/

MAX6724

MAX6725/

MAX6726

MAX6727

MAX6728/

MAX6729

NAME FUNCTION

5 ———————RST2

Active-Low Reset Output,
Open-Drain or Push-Pull.
RST2 changes from high
to low when V

CC

1 or

V

CC

2 drops below the
selected reset thresholds
or MR is pulled low. RST2
remains low for the reset
timeout period after
V

CC

1/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
V

CC

2.

22222222GNDGround

3333— 555MR

Active-Low Manual Reset
Input. Internal 50kΩ
pullup to V

CC

1. 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 V

CC

1 if unused.

44444666V

CC

2

Secondary Supply
Voltage Input. Powers the
device when it is above
V

CC

1 and input for
secondary reset
threshold monitor.

65666888V

CC

1

Primary Supply Voltage
Input. Powers the device
when it is above VCC2
and input for primary
reset threshold monitor.

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits

8 _______________________________________________________________________________________

Pin Description (continued)

PIN

MAX6715/

MAX6716

MAX6717/

MAX6718

MAX6719/

MAX6720

MAX6721/

MAX6722

MAX6723/
MAX6724

MAX6725/

MAX6726

MAX6727

MAX6728/

MAX6729

NAME FUNCTION

——— 53333WDI

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.

—— 5 — 577— 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 V

CC

1 or

V

CC

2 if not used.

——————— 7 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, V

CC

1, or VCC2 if

not used.

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

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 VCC1,
V

CC

2, or RSTIN goes below the reset threshold before

the reset timeout period is completed, the internal timer

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP

Supervisory Circuits

_______________________________________________________________________________________ 9

Pin Description (continued)

PIN

MAX6715/

MAX6716

MAX6717/

MAX6718

MAX6719/

MAX6720

MAX6721/

MAX6722

MAX6723/

MAX6724

MAX6725/

MAX6726

MAX6727

MAX6728/

MAX6729

NAME FUNCTION

——————— 4 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 V

CC

1.

————— 4 ——RST

Active-High Reset
Output, Open-Drain or
Push-Pull. RST changes
from low to high when
V

CC

1 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 V

CC

1/

V

CC

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
V

CC

1.

MAX6715–MAX6729

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.

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,
V

EXT_TH

.

V

EXT_TH

= 626mV((R1 + R2)/R2)

Low leakage current at RSTIN allows the use of large­valued resistors resulting in reduced power consump­tion of the system.

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

when processor activity fails. After each reset event
(V

CC

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).

Power-Fail Comparator

PFI is the noninverting input to a comparator. If PFI is
less than V

PFI

(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

Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits

10 ______________________________________________________________________________________

MAX6719/
MAX6720/

MAX6723–

MAX6727

V

EXT_TH

R1

R2

RSTIN

GND

Figure 1. Monitoring a Third Voltage

1.12s MAX

t

WDI-NORMAL

1.12s MAX

t

WDI-STARTUP

35s MAX

V

TH

V

CC

WDI

RESET

t

RP

Figure 2. Normal Watchdog Startup Sequence

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 V

CC

= 0

The MAX6715–MAX6729 are guaranteed to operate
properly down to VCC= 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 VCCis 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 V

CC

1.

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 out-
put 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 V

PFI

(626mV) when

V

EXT

falls to its power-fail trip point (V

FAIL

) and when VIN

rises to its power-good trip point (V

GOOD

). The hysteresis

window extends between the specified V

FAIL

and V

GOOD

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 <
V

PFI

/2.5µA < 248kΩ for most applications. R3 will provide

additional hysteresis for PFO push-pull (VOH= VCC1) or
open-drain (VOH= V

PULLUP

) applications.

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP

Supervisory Circuits

______________________________________________________________________________________ 11

MAX6728/

MAX6729

R1

R2

PFI

GND

V

IN

PFO

V

TRIP

= V

PFI

R1 + R2

R2

()

MAX6728/

MAX6729

R1

R2

PFI

GND

V

CC

V

IN

PFO

V

TRIP

= R2

(V

PFI

)

1R11

R2

+-

V

CC

R1

[]

()

V

PFI

= 626.5mV

A

B

Figure 3. Using Power-Fail Input to Monitor an Additional
Power-Supply a) V

IN

is Positive b) VINis Negative

MAX6715–

MAX6729

GND GND

V

CC1VCC

2

V

CC

2

V

CC

1

RST

RESET TO OTHER SYSTEM COMPONENTS

RESET

µP

4.7kΩ

Figure 4. Interfacing to µPs with Bidirectional Reset I/O

MAX6715–MAX6729

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 VCCTransients

The MAX6715–MAX6729 supervisors are relatively
immune to short-duration negative-going VCCtransients
(glitches). It is usually undesirable to reset the µP when
VCCexperiences 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 VCCpulses, starting above V

TH

and ending below the reset threshold by the magnitude
indicated (reset threshold overdrive). The graph shows
the maximum pulse width that a negative-going V

CC

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 V

CC

pin pro-

vides additional transient immunity.

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

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

Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits

12 ______________________________________________________________________________________

MAX6728/

MAX6729

V

EXT

R1

R3

R2

PFI

GND

PFO

A

V

GOOD

= DESIRED V

EXT

GOOD VOLTAGE THRESHOLD

V

FAIL

= DESIRED V

EXT

FAIL VOLTAGE THRESHOLD

V

OH

= VCC1 (FOR PUSH-PULL PFO)

R2 = 200kΩ (FOR > 2.5µA R2 CURRENT)
R1 = R2 ((V

GOOD

- V

PFI

) - (V

PFI

)(V

GOOD

- V

FAIL

) / VOH) / V

PFI

R3 = (R1 x VOH) / (V

GOOD

- V

FAIL

)

V

GOOD

V

FAIL

V

IN

PFO

Figure 5. Adding Hysteresis to Power-Fail for Push-Pull PFO

START

SET WDI

HIGH

PROGRAM

CODE

SUBROUTINE OR
PROGRAM LOOP

SET WDI LOW

RETURN

SUBROUTINE
COMPLETED

HANG IN

SUBROUTINE

Figure 6. Watchdog Flow Diagram

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP

Supervisory Circuits

______________________________________________________________________________________ 13

Functional Diagram

VCC1

V

REF

VCC2

RSTIN/PFI

V

REFVCC

1

MR

VCC1

V

CC

1

V

CC

1

RESET

TIMEOUT

PERIOD

VCC2

RST

RST

PFO

WATCHDOG
TIMER WITH

FLOAT DISABLE

WDI

VCC1

MR

PULLUP

RESET

OUTPUT

DRIVER

V

REF/2

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits

14 ______________________________________________________________________________________

Selector Guide

PART

NUMBER

NUMBER OF

VOLTAGE

MONITORS

OPEN­DRAIN

RESET

OPEN­DRAIN
RESET

PUSH-

PULL

RESET

PUSH-

PULL

RESET

MANUAL

RESET

WATCH-

DOG

INPUT

POWER-

FAIL

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 —— 11√√—
MAX6727 3 2 ——— √√—
MAX6728 3 1 ——— √√√ (open drain)
MAX6729 3 —— 1 — √√√ (push-pull)

Ordering Information (continued)

PART TEMP RANGE PIN-PACKAGE

MAX6721UT_ _D_ -T -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 V

TH

1 = 4.625V,

V

TH

2 = 3.075V, and 210ms (typ) timeout period.

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP

Supervisory Circuits

______________________________________________________________________________________ 15

Table 1. Reset Voltage Threshold Suffix
Guide**

PART NUMBER

SUFFIX

(_ _)

V

CC

1 NOMINAL

VOLTAGE

THRESHOLD (V)

V

CC

2 NOMINAL

VOLTAGE

THRESHOLD (V)

LT 4.625 3.075
MS 4.375 2.925

MR 4.375 2.625

TZ 3.075 2.313

SY 2.925 2.188

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

VF 1.575 1.050
WE 1.665 0.833
VD 1.575 0.788

Table 2. Reset Timeout Period Suffix
Guide

ACTIVE TIMEOUT PERIOD

TIMEOUT

PERIOD SUFFIX

MIN [ms] MAX [ms]

D1 1.1 2.2

D2 8.8 17.6

D3 140 280

D5 280 560

D6 560 1120

D4 1120 2240

**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 thresh-

old voltages may be available, contact factory for availability.

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits

16 ______________________________________________________________________________________

Pin Configurations

GND

V

CC

2

16VCC1

5

MAX6715/

MAX6716

SOT23-6

TOP VIEW

2

34

RST1

MR

RST2

GND

V

CC

2

16VCC1

5

MAX6721/

MAX6722

SOT23-6

2

34

RST

MR

WDI GND

V

CC

2

16VCC1

5

MAX6723/

MAX6724

SOT23-6

2

34

RST

WDI

RSTIN

5 RSTINGND

V

CC

2

15VCC1

MAX6717/

MAX6718

SOT23-5

2

34

RST

MR

GND

V

CC

2

16VCC1

MAX6719/

MAX6720

SOT23-6

2

34

RST

MR

VCC2

MRRST

1

2

87VCC1

RSTINGND

WDI

RST

SOT23-8

3

4

6

5

MAX6725/

MAX6726

VCC2

MR

1

2

87VCC1

RSTINGND

WDI

RST

SOT23-8

3

4

6

5

MAX6727

RST

VCC2

MR

1

2

87VCC1

PFIGND

WDI

RST

SOT23-8

3

4

6

5

MAX6728/

MAX6729

PFO

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP

Supervisory Circuits

______________________________________________________________________________________ 17

SOT-23 5L .EPS

E

1

1

21-0057

PACKAGE OUTLINE, SOT-23, 5L

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages

.)

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP
Supervisory Circuits

18 ______________________________________________________________________________________

6LSOT.EPS

F

1

1

21-0058

PACKAGE OUTLINE, SOT-23, 6L

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages

.)

MAX6715–MAX6729

Dual/Triple Ultra-Low-Voltage SOT23 µP

Supervisory Circuits

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

© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

SOT23, 8L .EPS

REV.DOCUMENT CONTROL NO.APPROVAL

PROPRIETARY INFORMATION

TITLE:

3.002.60E

C

E1

E

BETWEEN 0.08mm AND 0.15mm FROM LEAD TIP.

8. MEETS JEDEC MO178.

8

0.60

1.75

0.30

L2

0

e1

e

L

1.50E1

0.65 BSC.

1.95 REF.

0.25 BSC.

GAUGE PLANE

SEATING PLANE C

C

L

PIN 1

I.D. DOT

(SEE NOTE 6)

L

C

L

C

A2

e1

D

DETAIL "A"

5. COPLANARITY 4 MILS. MAX.

NOTE:

7. SOLDER THICKNESS MEASURED AT FLAT SECTION OF LEAD

6. PIN 1 I.D. DOT IS 0.3 MM MIN. LOCATED ABOVE PIN 1.

4. PACKAGE OUTLINE INCLUSIVE OF SOLDER PLATING.

3. PACKAGE OUTLINE EXCLUSIVE OF MOLD FLASH & METAL BURR.

HEEL OF THE LEAD PARALLEL TO SEATING PLANE C.

2. FOOT LENGTH MEASURED FROM LEAD TIP TO UPPER RADIUS OF

1. ALL DIMENSIONS ARE IN MILLIMETERS.

L2

L

A1

A

0.45

1.30

0.15

1.45

MAX

0.28b

0.90A2

0.00A1

0.90

A

MIN

SYMBOL

3.00

0.20

2.80D

0.09

C

SEE DETAIL "A"

L

C

b

e

D

1

21-0078

1

PACKAGE OUTLINE, SOT-23, 8L BODY

0

0

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages

.)