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060303

FEATURES

§ 5V power-on reset
§ 3.3V power-on reset
§ Two referenced comparators with separate

outputs for monitoring additional supplies

§ Internal power is drawn from higher of either

the IN

input or the IN

3.3V

input

§ Excellent for systems designed to operate

with multiple power supplies

§ Asserts resets during power transients
§ Pushbutton reset input for system override
§ Maintains reset for user configurable times

of 10ms, 100ms, or 1s

§ Watchdog timer for software monitoring

(DS1831A)

§ Precision temperature-compensated voltage

reference and voltage sensor

§ 16 pin DIP and 16 pin 150mil SO available
§ Operating Temperature of -40°C to +85°C

PIN ASSIGNMENT

DESCRIPTION

The DS1831 multisupply monitor and reset monitors up to four system voltages: 5V supply, 3.3V (or 3V)
supply, and two additional user configurable voltage monitors. DS1831 power for internal operation
comes from the higher voltage level of the 3.3V input or the 5V input. One of these inputs must be greater
than 1V for device operation. Pushbutton (manual reset) functionality is provided for the 5V reset, the

DS1831/A/B

Multisupply Micromonitor

www.maxim-ic.com

3.3V

RST

3.3V

TOL

3.3V

PBRST

3.3V

NMI1

NMI2

MPBRST

RST

TOL

PBRST

IN1

IN2

GND

DS1831

16-Pin (300mil) DIP

16-Pin (150mil) SO

3.3V

RST

3.3V

TOL

3.3V

PBRST

3.3V

NMI1

WDS

RST

TOL

PBRST

IN1

GND

DS1831A

16-Pin (300mil) DIP

16-Pin (150mil) SO

3.3V

RST

3.3V

TOL

3.3V

PBST

NMI1

NMI2

MPBRST

RST

TOL

PBRST

IN1

IN2

GND

DS1831B

16-Pin (300mil) DIP

16-Pin (150mil) SO

DS1831/A/B

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3.3V reset or for all reset outputs by the master pushbutton. The DS1831A replaces one reference
comparator and the master pushbutton with watchdog and the DS1831B replaces the 3.3V

PBRST

with a

last reset status output.

TOL and TD inputs allow user configuration of the DS1831 for multiple applications. The TOL inputs
configure the tolerance for the specified output and the TD inputs configure the reset time delays.

PIN DESCRIPTION

5V Power Supply Input

MPBRST

Master Pushbutton (DS1831)

Watchdog Time Delay Select (DS1831A)

RST

5V Reset Open Drain Output

NMI2

Non-maskable Interrupt 2 (DS1831)

WDS

Watchdog Status Output (DS1831A)

TOL

Selects 5V Input Tolerance

NMI1

Non-maskable Interrupt 1

Selects 5V Reset Time Delay

PBRST

3.3V

3.3V Reset Pushbutton

PBST

Pushbutton Status Output (DS1831B)

PBRST

5V Reset Pushbutton

3.3V

Select 3.3V Reset Time Delay

IN1

Sense Input 1

TOL

3.3V

Selects 3.3V Input Tolerance

IN2
ST

Sense Input 2 (DS1831)
Watchdog Strobe Inputs
(DS1831A)

RST

3.3V

3.3V Reset Open Drain Output

GND

Ground

3.3V

3.3V Power Supply Input

DS1831 BLOCK DIAGRAM Figure 1

RST

3.3V

TOLERANCE

BIAS

TIME

DELAY

1.25V T.C.

REFERENCE

TOL

GROUND

TOLERANCE

BIAS

3.3V

TOL

3.3V

TIME

DELAY

Level

Sense

MPBRST

100k

3.3V

100k

PBRST

3.3V

PBRST

100k

IN1

IN2

NMI1

NMI2

RST

DS1831/A/B

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OPERATION--POWER MONITOR

The DS1831 provides the functions of detecting out-of-tolerance conditions on a 3.3V (or 3V) and 5V
power supply and warning a processor-based system of impending power failure. When an input is
detected as out-of-tolerance on either voltage input the

RST

for that supply will be forced active low.

When that input returns to a valid state the associated

RST

will remain active for the time delay selected

with the associated TD input and then return to an inactive state until the next input out-of-tolerance
condition.

On power-up both resets are kept active for the selected reset time after the associated power supply input
has reached the selected tolerance. This allows the power supply and system power to stabilize before

RST

is released.

All internal operating current for the DS1831 will be supplied by either the IN

3.3V

or IN

input which

ever has the highest voltage level.

OPERATION--TOLERANCE SELECT

The DS1831 provides two TOL inputs for individual customization of the DS1831 to specific application
requirements. If the TOL for the 5V supply is tied to the 5V input a 5% tolerance is selected. If the TOL
is connected to ground a 10% tolerance is selected or if it is left unconnected a 15% tolerance is selected.
If the TOL for the 3.3V supply is tied to the 3.3V input a 5% tolerance is selected, a 10% tolerance is
selected if it is connected to ground, and a 20% tolerance is selected if the input is left unconnected.
These tolerance conditions are set at power up and can only be changed by power cycling the device.

OPERATION--RESET TIME-DELAY SELECT

The DS1831 provides two TD inputs for individual customization of reset time-delays and an additional
one for the DS1831A watchdog. TD inputs select time delays for the IN

and IN

3.3V

resets outputs and

the Watchdog on the DS1831A. The reset time delays are shown in Table 1. These allow the selection of
minimum delays of 10ms, 100ms, and 1000ms.

Wiring an individual reset output to the push-button input of the other voltage reset allows custom reset
timings or allows for the sequencing of the reset outputs. See Figure 2.

These time-delays are set at power-up and cannot be changed after the device reaches an in-tolerance
condition.

TD INPUTS/RESET AND WATCHDOG TIME-DELAYS Table 1

RESET TIME-DELAY

MIN

TYP

MAX

GND

10ms

16ms

20ms

Float

100ms

160ms

200ms

1000ms

1600ms

2000ms

DS1831/A/B

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PUSHBUTTON RESET SEQUENCING Figure 2

NOTE: The

RST

output is connected to the IN

3.3V

via a 100 k

W resistor in the push-button input and

therefore does not require a pull-up resistor (an addition pull up can be used to accelerate responses). If an
external pull up is used in this example it must be connected to the 3.3V power supply.

OPERATION--PUSHBUTTON RESET

The DS1831 provides three pushbutton inputs for manual reset of the device. Pushbutton inputs for the
3.3V reset, 5V reset, and a master pushbutton reset (DS1831 and DS1831B only) input; provide multiple
options for system control. The 3.3V pushbutton reset and 5V pushbutton resets provide a simple manual
reset for the associated reset output; while the master pushbutton reset forces all resets and NMI outputs
active low.

The 5V reset pushbutton input and the 3.3V reset pushbutton input provide manual reset control input for
each associated reset output. When the output associated with a pushbutton input is not active, a
pushbutton reset can be generated by pulling the associated

PBRST

pin low for at least 20µs. When the

pushbutton is held low the reset will be forced active and will remain active for a reset cycle after the
pushbutton is released. See Figure 2 for an application example that allows a user to sequence the reset
outputs.

A master pushbutton reset cycle can be started if at least one voltage input (IN

, IN

3.3V

, IN1, or IN2) is in

tolerance and at least one output is active. A master pushbutton reset is generated by pulling the

MPBRST

pin low for at least 20µs. When the pushbutton is held low all outputs are forced active and will remain
active for a reset or NMI time delay after the pushbutton is released. The Master Pushbutton input is
pulled high through an internal 100k

W pull up resistor and debounced via internal circuitry. See Figure 3

for an application example. Figures 4 and 5 for the timing diagram.

The 5V and 3.3V pushbutton reset inputs are pulled high through an internal 100k

W pull up resistor to the

voltage input, which is associated with that pushbutton. The master pushbutton is pulled to the greater of
the IN

and IN

3.3V

inputs.

RST

PBRST

3.3V

GND

3.3V

RST

3.3V

TOL

3.3V

PBRST

TOL

DS1831

3.3V

5V Supply

3.3V Supply

DS1831/A/B

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TIMING DIAGRAM--5V OR 3.3V PUSHBUTTON RESET Figure 5

OPERATION--PUSHBUTTON STATUS

The DS1831B provides a master pushbutton status open drain output. The

PBST

output indicates the

status of the most recent reset condition. If the last reset was generated by the master pushbutton input it
would maintain a low condition until cleared by another event (except the master pushbutton) generating
a reset. Once cleared it will remain high until the master pushbutton is pulled low generating a reset
condition. The

PBST

output is open drain and will require a pull-up resistor on the output to maintain a

valid condition. The value of the pull up resistor is not critical in most cases but must be set low enough
to pull the output to a high state. A common value used is 10k

W (see Figure 6).

DS1831B APPLICATION EXAMPLE Figure 6

PDLY

RST

PBRST

(or PBRST

3.3V

)

RST

(or RST

3.3V

)

5V Supply

PBRST

GND

NMI2

IN1

NMI1

SENSE1

IN2

MPBRST

SENSE2

10k

DS1831B

RST

TOL

PBST

3.3V

RST

3.3V

TOL

3.3V

3.3V Supply

10 k

DS1831/A/B

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OUTPUT VALID CONDITIONS

The DS1831 can maintain valid outputs as long as one input remains above 1.0V. Accurate voltage
monitoring additionally requires that either the 3.3V IN or 5V IN input be above 1.5V. If this condition is
not met and at least one of the supply inputs are at or above 1.0V all outputs are maintained in the active
condition. The DS1831 requires pull-up resistors on the outputs to maintain a valid output. The value of
the pull up resistor is not critical in most cases but must be set low enough to pull the output to a high
state. A common pull-up resistor value used is 10k

W (see Figure 7).

APPLICATION DIAGRAM--OPEN DRAIN OUTPUTS Figure 7

NOTE: If outputs are at different voltages the outputs can not be connected to form a wired AND.

OPERATION--NON-MASKABLE INTERRUPT

The DS1831 has two referenced comparator (DS1831A has only one referenced comparator) that can be
used to monitor upstream voltages or other system specific voltages. Each comparator is referenced to the
1.25V internal band gap reference and controls an open-drain output. When a voltage being monitored
decays to the voltage sense point, the DS1831 pulses the

NMI

output to the active state for a minimum

10µs. The comparator detection circuitry also has built-in hysteresis of 100µV. The supply must be below
the voltage sense point for approximately 2µs before a low

NMI

will be generated. In this way, power

supply noise is minimized in the monitoring function, reducing false interrupts. See Figure 8 for the non-
maskable timing diagram.

Versatile trip voltages can be configured by the use of an external resistor divider to divide the voltage at
a sense point to the 1.25V trip levels of the referenced comparators. See Figure 9 for an example circuit
diagram and sample equations. The equations demonstrate a design process to determine the resistor
values to use.

Connecting one or both

NMI

outputs to one of the reset specific

PBRST

s allows the non-maskable

interrupt to generate an automatic reset for the reset time period when an out-of-tolerance condition
occurs in a monitored supply. An example is shown in Figure 9.

RST

PBRST

3.3V

GND

3.3v

RST

3.3V

TOL

3.3V

PBRST

TOL

DS1831

3.3V

5V Supply

3.3V Supply

10 k

10 K

DS1831/A/B

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The output associated with the specific input will be held low if the voltage on the input pin is less than
1.25V. If the voltage is above 1.25V the output will not sink current and will be pulled up by the required
pull up resistor. The value of the resistors is not critical in most cases but must be set low enough to pull
the output to a high state. A common value used is 10k

W. If a

NMI

output is connected to a pushbutton

input an additional pull-up resistor can be used (to improve speed of transitions) but is not required.

During a power-up, any detected IN pin levels above V

by the comparator are disabled from generating

an inactive (high) interrupt until at least 1 supply on the V

inputs rises above 1.5 volts. All NMI outputs

will be held active (low) until at least one V

reaches 1.5 volts at which point the

NMI

outputs will be

based on the value of the associated IN input.

TIMING DIAGRAM--NON-MASKABLE INTERRUPT Figure 8

>1.25V

TP(min)

TP(max)

IPD

NMI

TP(min)

TP(max)

NMI

DS1831/A/B

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NON-MASKABLE INTERRUPT CIRCUIT EXAMPLE Figure 9

Example:

SENSE1

= 11.50V trip point V

SENSE1

X 1.25V

Therefore:

11.50V =

100

X 1.25V

Resulting In: R1 = 820k

Repeat the same steps to solve for R3 and R4 with V

SENSE2

OPERATION - WATCHDOG TIMER

The watchdog timer function (DS1831A only) forces the

WDS

signal active (low) when the

input

does not have a transition (high-to-low or low-to-high) within the predetermined time period. The time-
out period is determined by the condition of the TD

pin (see Table 1). If TD

is connected to ground

the minimum watchdog time-out would be 10ms, TD floating would yield a minimum time-out of 100ms,
and TD

connected to V

would provide a time-out of 1000ms minimum. Time-out of the watchdog

starts when at least one of the

RST

outputs becomes inactive (high). If a transition occurs on the ST input

pin prior to time-out, the watchdog timer is reset and begins to time-out again. If the watchdog timer is
allowed to time-out, then the

WDS

output is pulsed active for a minimum of 100µs.

The

WDS

output is an open-drain output and must be pulled up externally. In most applications this

output would be connected to one of the Pushbutton inputs and would not require an external pull-up
resistor. The value of the resistors is not critical in most cases but must be set low enough to pull the
output to a high state. A common value used is 10k

W. If a

WDS

output is connected to a pushbutton input

an additional pull-up resistor can be used (to improve speed of transitions) but is not required.

DS1831

GND

IN1

SENSE1

IN2

SENSE2

10 K

PBRST

3.3V

NMI1

NMI2

MPBRST

DS1831/A/B

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The

input can be derived from many microprocessor outputs. The most typical signals used are the

microprocessor address signals, data signals, or control signals. When the microprocessor functions
normally, these signals would, as a matter of routine, cause the watchdog to be reset prior to time-out. To
guarantee that the watchdog timer does not time-out, a transition must occur at or less than the minimum
times shown in Table 1. A typical circuit example is shown in Figure 10. The watchdog timing is shown
in Figure 11.

The DS1831A watchdog function cannot be disabled. The watchdog strobe input must be strobed to avoid
a watchdog time-out however the watchdog status output can be disconnected yielding the same result.

WATCHDOG CIRCUIT EXAMPLE Figure 10

TIMING DIAGRAM -- STROBE INPUT Figure 11

PBRST

3.3V

DS1831

GND

WDS

IN1

NMI1

SENSE1

µP

10k

INVALID

EDGES

VALID

EDGES

INDETERMINATE

EDGES

MIN

MAX

WDS

DS1831/A/B

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ABSOLUTE MAXIMUM RATINGS*

Voltage on IN

or IN

3.3V

Pins Relative to Ground

-0.5V to +6.0V

Voltage on either RST Relative to Ground

-0.5V to the greater of IN

+ 0.5V or IN

3.3V

+ 0.5V

Voltage on PBRST

3.3V

Relative to Ground

-0.5V to IN

3.3V

+ 0.5V

Voltage on PBRST

Relative to Ground

-0.5V to IN

+ 0.5V

Voltage on MPBRST, IN1, IN2

Relative to Ground

-0.5V to the greater of IN

+ 0.5V or IN

3.3V

+ 0.5V

Operating Temperature Range

-40°C to +85°C

Storage Temperature Range

-55°C to +125°C

Soldering Temperature

See IPC/JEDEC J-STD-020A specification

* This is a stress rating only and functional operation of the device at these or any other conditions

above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.

RECOMMENDED DC OPERATING CONDITIONS (-40

°C to 85°C)

PARAMETER

SYMBOL

MIN

MAX

UNITS

NOTES

(Supply Voltage)

1.0

5.5

3.3V

(Supply Voltage)

1.0

5.5

PBRST

3.3V

PBRST

MPBRST

, ST

input High Level

0.7 x V

INT

+ 0.3

PBRST

3.3V

PBRST

MPBRST

, ST

input Low Level

-0.3

0.3 x V

INT

* V

INT

is the greater voltage level of the IN

or IN

3.3V

DC ELECTRICAL CHARACTERISTICS
(-40

°C to 85°C; IN

3.3V

, IN

= 1.0V to 5.5V)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Input Leakage

-1.0

+1.0

µA

Output Current @ 2.4V

Output Current @ 0.4V

+10

Operating Current @

Ü5.5V

100

µA

Operating Current @

Ü3.6V

µA

Trip Point (TOL

= IN

)

INTP

4.50

4.63

4.75

Trip Point (TOL

= GND)

INTP

4.25

4.38

4.49

Trip Point (TOL

= Float)

INTP

4.00

4.15

4.24

3.3V

Trip Point (TOL

3.3V

= IN

3.3V

)

INTP

2.98

3.06

3.15

3.3V

Trip Point (TOL

3.3V

= GND)

INTP

2.80

2.88

2.97

3.3V

Trip Point (TOL

3.3V

= Float)

INTP

2.47

2.55

2.64

IN Input Trip Points

1.15

1.25

1.30

DS1831/A/B

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CAPACITANCE (t

= +25

°C)

PARAMETER

SYMBOL

MAX

UNITS

NOTES

Input Capacitance

OUT

AC ELECTRICAL CHARACTERISTICS
(-40

°C to 85°C; IN

3.3V

, IN

= 1.0V to 5.5V)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

RESET Active Time (TD=Low)

RST

RESET Active Time (TD=Float)

RST

100

160

200

RESET Active Time (TD=High)

RST

1000

1600

2000

Detect to

RST

RPU

See RESET Active Time

Detect to

RST

RPD

VIN Detect to

NMI

IPD

NMI Active Time

NMI

PBRST

= V

PBRST

Stable Low to Reset

Active

PDLY

Watchdog Timeout (TD

(WD)

=Low)

Watchdog Timeout (TD

=Float)

100

160

200

Watchdog Timeout (TD

=High)

1000

1600

2000

ST Pulse Width

Slew Rate (V

INTP(MAX)

to V

INTP(MIN)

)

300

Slew Rate (V

INTP(MAX)

to V

INTP(MIN)

)

NOTES:

1) All voltages are referenced to ground.
2) All Pushbutton inputs are internally pulled to the associated Supply IN input or the greatest Supply IN

input for the

MPBRST

with an internal Impedance of 100k

3) Measured with outputs open and IN

3.3V

or IN

£ 5.5V

4) Measured with outputs open and IN

3.3V

or IN

£ 3.6V.

5) Measured using t

= 5µs

6) Noise immunity - pulses <2µs at a trip level will not cause a

RST

NMI

DS1831/A/B

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ORDERING INFORMATION

Ordering Part

Number

Package Type

Description

DS1831

16-Pin DIP 300mil

5V/3.3V Multisupply Monitor

DS1831S

16-Pin SO 150mil

5V/3.3V Multisupply Monitor

DS1831A

16-Pin DIP 300mil

5V/3.3V Multisupply Monitor w/Watchdog

DS1831AS

16-Pin SO 150mil

5V/3.3V Multisupply Monitor w/Watchdog

DS1831B

16-Pin DIP 300mil

5V/3.3V Multisupply Monitor w/Pushbutton Status

DS1831BS

16-Pin SO 150mil

5V/3.3V Multisupply Monitor w/Pushbutton Status

* Add "/T&R" for tape and reeling of surface mount packages.

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