DS1831AST - Maxim Integrated Products, Inc.

1 of 14 051100

FEATURES

 5V power-on reset

 3.3 (or 3V) power-on reset

 2 referenced comparators with separate

outputs for monitoring additional supplies

 Internal power is drawn from higher of either

the IN5V input or the IN3.3V 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 10 ms, 100 ms, or 1 sec

 Watchdog timer for software monitoring

(DS1831A)

 Precision temperature-compensated voltage

reference and voltage sensor

 16 pin DIP & 16 pin 150-mil SOIC available

 Operating Temperature of -40°C to +85°C

PIN ASSIGNMENT

DESCRIPTION

The DS1831 Multi-Supply Monitor & Reset monitors up to 4 system voltages: 5 volt supply, 3.3

(or 3) volt supply, and 2 additional user configurable voltage monitors. DS1831 power for internal

operation comes from the higher voltage level of the 3.3 volt input or the 5 volt input. One of these

inputs must be greater than 1 volt for device operation. Pushbutton (manual reset) functionality is

provided for the 5 volt reset, the 3.3 volt reset or for all reset outputs by the master pushbutton. The

DS1831A replaces one referen ce comparator and the master pushbutton with watchdog and the DS1831B

replaces the 3.3-volt PBRST with a last reset status output.

DS1831/A/B

Multi-Supply Micromonito

www.dalsemi.com

IN3.3V

RST3.3V

TOL3.3V

TD3.3V

PBRST3.3V

MI1

MI2

MPBRST

IN5V

RST5V

TOL5V

TD5V

PBRST5V

IN1

IN2

GND

DS1831

16-Pin (300 mil) DIP

16-Pin

(

150 mil

)

SOIC

MI1

WDS

IN1

GND

DS1831

3.3V

PBST

MI1

PBRST

IN1

DS1831B

DS1831/A/B

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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 CONFIGURATION

1IN

5V 5V Power Supply Input 9 MPBRST Master Pushbutton (DS1831)

TDWD Watchdog Time Delay Select (DS1831A)

2RST 5V 5V Reset Open Drain Output 10 NM12 Non Maskable Interrupt 2 (DS1831)

WDS Watchdog Status Output (DS1831A)

3TOL

5V Selects 5V Input Tolerance 11 NM11 Non Maskable Interrupt 1

4TD

5V Selects 5V Reset Time Delay 12 PBRST3.3V 3.3V Reset Pushbutton

PBST Pushbutton Status Output (DS1831B)

5PBRST5V 5V Reset Pushbutton 13 TD3.3V Select 3.3V Reset Time Delay

6 IN1 Sense Input 1 14 TOL3.3V Selects 3.3V Input Tolerance

7IN2

ST Sense Input 2 (DS1831)

Watchdog Strobe Inputs

(DS1831A)

15 RST 3.3V 3.3V Reset Open Drain Output

8 GND Ground 16 IN3.3V 3.3V Power Supply Input

BLOCK DIAGR AM Figure 1

RST3.3V

VCC

TOLERANCE

BIAS

TIME

DELAY

1.25V T.C.

REFERENCE

TOL5V

GROUN

VCC

TOLERANCE

BIAS

3.3V

TOL3.3V TIME

DELAY

Level

Sense

MPBRS

100k

TD5V

TD3.3V

100k

PBRST3.3V

PBRST 5V

100k

NMI

RST5V

DS1831/A/B

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OPERATION – POWER MONITOR

The DS1831 provides the functions of detecting out-of-toleran ce conditions on a 3.3 (or 3) volt and 5 volt

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 sele cted r eset time after the associat ed powe r suppl y 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 IN3.3V or IN5V input which

ever has the highest voltage level.

OPERATION - TOLERANCE SELECT

The DS1831 provides 2 TOL inputs for individual customization of the DS1831 to specific application

requirements. If the TOL for the 5 volt suppl y is tied to the 5 volt input a 5% toler ance is sele cted. 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 3.3 volt suppl y is tied to the 3.3 volt 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 2 TD inputs for individual customization of reset time-delays and an additional one

for the DS1831A watchdog. TD inputs select time delays for the IN5V and IN3.3V 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 10 ms, 100 ms, and 1000 ms.

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

TD MIN TYP MAX

GND 10 ms 16 ms 20 ms

Float 100 ms 160 ms 200 ms

VCC 1000 ms 1600 ms 2000 ms

DS1831/A/B

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PUSHBUTTON RESET SEQUENCING Figure 2

*NOTE:

The RST 5V output is connected to the IN3.3V via a 100 k Ω resistor in the push-button input and therefore

does not require a pull-up resistor (an addition pull up can be used to acc elera te r esponses.) If an ex ternal

pull up is used in this example it must be connected to the 3.3 volt power supply.

OPERATION - PUSHBUTTON RESET

The DS1831 provides 3 pushbutton inputs for manual reset of the device. Pushbutton inputs for the

3.3 volt reset, 5 volt reset, and a master pushbutton reset (DS1831 & DS1831B only) input; provide

multiple options for system control. The 3.3 volt pushbutton reset and 5 volt 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 5 volt reset pushbutton input and the 3.3 volt 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 20 µs. 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 (IN5V, IN3.3V, IN1, or IN2) is in

tolerance and at least 1 output is active. A master pushbutton reset is generated by pulling the MPBRST

pin low for at least 20 µs. 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 100 kΩ pull up resistor and debounced via internal cir cuitry. See figure 3

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

The 5 volt and 3.3 volt pushbutton reset inputs are pulled high through an internal 100 kΩ pull up resistor

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

greater of the “IN5V” and “IN3.3V” inputs.

*Caution should be exercised to avoid pulling the pushbutton inputs above associated supply inputs.

Generally all pushbutton inputs should be driven low with open drain inputs.

RST5V

PBRST3.3V

GND

TD5V

IN3.3V

IN5V

RST3.3V

TOL3.3V

PBRST 5V

TOL5V DS1831

TD3.3V

5V Supply 3.3V Supply

DS1831/A/B

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PUSHBUTTON RESET Figure 3

TIMING DIAGRAM – MASTER PUSHBUTTON RESET Figure 4

RST5V

GND

TD5V

IN5V

PBRST5V

TOL5V

5V Supply

DS1831

10 kΩ

VIH

VIL

tPDLY

tPB

tRST

MPBRST

RST5V and RST3.3V

VOH

tNMI

NMI1 and NMI2

VOH

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 ev ent (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 10 kΩs (See Figure 6).

DS1831B APPLICATION EXAMPLE Figure 6

VIH

VIL

tPDLY

tPB

tRST

PBRST5V

(or PBRST3.3V)

RST5V (or RST3.3V)

VOH

VIL

5V Supply

PBRST5V

GND

NMI2

IN1 NMI1

VSENSE1

IN2

MPBRST

VSENSE2

VCC

10k

DS1831B

RST5V

TD5V

IN5V

TOL5V

PBST

IN3.3V

RST3.3V

TOL3.3V

TD3.3V

3.3V Supply

VCC

Ω

DS1831/A/B

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OUTPUT VALID CONDITIONS

The DS1831 can maintain valid outputs as long as one input remains above 1.0 volt. Accurate voltage

monitoring additionally requires that either the 3.3 volt IN or 5 volt IN input be above 1.5 volts. If this

condition is not met and at least one of the supply inputs are at or above 1.0 volt 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 10 kΩs (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 2 referenced compar ator (DS1831A has only 1 referenced c omparator) that can be used

to monitor upstream voltages or other system specific voltages. Each comparator is referenced to the

1.25 volt internal band gap reference and controls an open drain output. When a voltage bein g monitored

decays to the voltage sense point, the DS1831 pulses the NMI output to the active state for a minimum 10

µs. The comparator detection circuitry also has built-in hysteresis of 100 µV. The suppl y must be below

the voltage sense point for approximately 2 µs 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 1.25 volt 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.

RST5V

PBRST3.3V

GND

TD5V

IN3.3v

IN5V

RST3.3V

TOL3.3V

PBRST5V

TOL5V

DS1831

TD3.3V

5V Supply 3.3V Supply

10 kΩ

Ω

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

1.25 volts. If the voltage is above 1.25 volts the output will not sink current and will be pulled up b y 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 10 kΩs. 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, an y detected IN pin levels above VTP b y the comparat or are di sabled from generatin g

an inactive (high) interrupt until at least 1 supply on the VIN inputs rises above 1.5 volts. All NMI outputs

will be held active (low) until at least one VIN reaches 1.5 volts at which point the NMI outputs will be

based on the value of the associated IN input.

TIMING DI AGRAM - NON MASKABLE INTERRUPT Figure 8

VIN >1.25 V

VTP VTP(min)

VTP(max)

tIPD

NMI

VOL

VTP

VTP(min)

VTP(max)

VOH

tNMI

DS1831/A/B

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NON MASKABLE INTERRUPT CIRCUIT EXAMPLE Figure 9

Example: VSENSE1 = 11.50 volts trip point VSENSE1 = R2R2R1+X 1.25V

Therefore: 11.50V = k 100

k 100R1+X 1.25V

Resulting In: R1 = 820 kΩ

Repeat the same steps to solve for R3 and R4 with VSENSE2.

OPERATION - WATCHDOG TIMER

The watchdog timer function (DS1831A only) forces the WDS signal active (low) when the ST 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 TDWD pin. If TDWD is co nnect ed to ground the minimum

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

connected to VCC would provide a time-out of 1000 ms minimum. Time-out of the watchdo g 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 100 µs.

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 10 kΩs. 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

VSENSE1

IN2

VSENSE2

VCC

10 KΩ

PBRST5V PBRST3.3V

NMI1

NMI2

MPBRST

Ω

DS1831/A/B

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The ST 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 w atchdo g 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 EX AMPLE Figure 10

TIMING DI AGRAM-STROBE INPUT Figure 11

R1 PBRST5V PBRST3.3V

DS1831

GND

WDS

IN1 NMI1

VSENSE1

R2 ST

TDWD

µP

VCC

10 kΩ

INVALID

EDGES VALID

EDGES INDETERMINATE

EDGES

MIN.

MAX.

WDS tST tTD

DS1831/A/B

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RESET TIMING DIAG RAM - POWER UP Figure 12

RESET TIMING DIAG RAM - POWER DOWN Figure 13

tRPU

VOH

VINTP

VINTP (MIN)

VINTP (MAX)

IN5V (or IN3.3V)

RST5V (or RST3.3V)

IN5V (or IN3.3V)

tRPD

VOL

VINTP VINTP (MIN)

VINTP (MAX)

RST5V (or RST3.3V)

DS1831/A/B

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ABSOLUTE MAXIMUM RA TINGS*

Voltage on IN5V or IN3.3V

Pins Relative to Ground -0.5V to +7.0V

Voltage on either RST Relative to Ground -0.5V to the greater of IN5V + 0.5V or IN3.3V + 0.5V

Voltage on PBRST 3.3V Relative to Ground -0.5V to IN3.3V + 0.5V

Voltage on PBRST 5V Relative to Ground -0.5V to IN5V + 0.5V

Voltage on MPBRST Relative to Ground -0.5V to the greater of IN5V + 0.5V or IN3.3V + 0.5V

Operating Temperature -40°C to +85°C

Storage Temperature -55°C to +125°C

Soldering Temperature See 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.

** The voltage input on IN and ST inputs can be exceeded if the input current is less than 10 mA.

RECOMMENDED DC OPERATING CONDITIONS (-40° to 85°C)

PARAMETER SYMBOL MIN MAX UNITS NOTES

IN5V (Supply Voltage) V IN 1.0 5.5 V 1

IN3.3V (Supply Voltage) V IN 1.0 5.5 V 1

2 V 1,2*

ST and MPBRST input

High Level VIH VINT-0.4 VINT + 0.3 V 1,3*

PBRST 3.3V input High Level VIH 2IN

3.3V + 0.3 V 1

PBRST 5V input High Level VIH 2IN

5V +0.3 V 1

ST, PBRST 3.3V, PBRST 5V and

MPBRST input Low Level VIL -0.3 .5 V 1

* VINT is the greater voltage level of the IN5V or IN3.3V.

DC ELECTRICAL CHARACTERISTICS (-40° to 85°C, VCC = 1.0V TO 5.5V)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Input Leakage IIL -1.0 +1.0 µA4

Output Current @ 2.4V IOH 5

Output Current @ 0.4V IOL +10 mA 6

Operating Current @ ⇐5.5V ICC 80 100 µA7

Operating Current @ ⇐3.6V ICC 60 80 µA 8

IN5V Trip Point (TOL5V = IN5V)V

INTP 4.50 4.63 4.75 V 1

IN5V Trip Point (TOL5V = GND) VINTP 4.25 4.38 4.49 V 1

IN5V Trip Point (TOL5V = Float) VINTP 4.00 4.15 4.24 V 1

IN3.3V Trip Point (TOL3.3V = IN3.3V)V

INTP 2.98 3.06 3.15 V 1

IN3.3V Trip Point (TOL3.3V = GND) VINTP 2.80 2.88 2.97 V 1

IN3.3V Trip Point (TOL3.3V = Float) VINTP 2.47 2.55 2.64 V 1

IN Input Trip Points VTP 1.20 1.25 1.30 V 1

DS1831/A/B

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CAPACITANCE (tA = 25 °C)

PARAMETER SYMBOL MAX UNITS NOTES

Input Capacitance CIN 5pF

Input Capacitance COUT 7pF

AC ELECTRICAL CHARACTERISTIC S (-40° to 85°C, VCC = 1.0V TO 5.5V)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

RESET Active Time (TD=Low) tRST 10 16 20 ms 8

RESET Active Time (TD=Float) tRST 100 160 200 ms 8

RESET Active Time (TD=High) tRST 1000 1600 2000 ms 8

VCC Detect to RST tRPU See RESET Active Time ms 8

VCC Detect to RST tRPD 210

µs9

VIN Detect to NMI tIPD 210

µs9

NMI Active Time tNMI 20 µs

PBRST = VIL tPB 20 µs

PBRST Stable Low to Reset

Active tPDLY 50 µs

Watchdog Timeout (TD(WD)=Low) tTD 10 16 20 ms

Watchdog Timeout (TDWD=Float) tTD 100 160 200 ms

Watchdog Timeout (TDWD=High) tTD 1000 1600 2000 ms

ST Pulse Width tST 10 ns

Vin Slew Rate (V INTP(MAX) to V

INTP(MIN))tF300 µs

Vin Slew Rate (V INTP(MAX) to V

INTP(MIN))tR0ns

NOTES:

1. All voltages are referenced to ground.

2. Measured with both IN3.3V & IN5V ≥ 2.7V.

3. Measured with both IN3.3V & IN5V ≤ 2.7V.

4. 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 100 kΩ.

5. All outputs are Open Drain and output IOH would be determined by the external pull-up resistor.

6. Measured with outputs open and IN3.3V or IN5V ≤ 5.5V

7. Measured with outputs open and IN3.3V or IN5V ≤ 3.6V.

8. Measured using tR = 5 µs

9. Noise immunity - pulses <2 µs at a trip level will not cause a RST or NMI .

DS1831/A/B

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Ordering I nformation

Ordering Part

Number Package Type Description

DS1831 16 Pin DIP 300 mil 5V/3.3V MultiSupply Monitor

DS1831S 16 Pin SO 150 mil 5V/3.3V MultiSupply Monitor

DS1831A 16 Pin DIP 300 mil 5V/3.3V MultiSupply Monitor w/Watchdog

DS1831AS 16 Pin SO 150 mil 5V/3.3V MultiSupply Monitor w/Watchdog

DS1831B 16 Pin DIP 300 mil 5V/3.3V MultiSupply Monitor w/Pushbutton Status

DS1831BS 16 Pin SO 150 mil 5V/3.3V MultiSupply Monitor w/Pushbutton Status

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