1831-A-B.PDF

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DS1831/A/B
Multi-Supply Micromonitor
www.dalsemi.com
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 IN
5V
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 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
DS1831
IN
5V
RST
5V
TOL
5V
TD
5V
PBRST
5V
IN1
IN2
GND
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
IN
3.3V
RST
3.3V
TOL
3.3V
TD
3.3V
PBRST
3.3V
NMI1
NMI2
MPBRST
16-Pin (300 mil) DIP
&
16-Pin (150 mil) SOIC
DS1831A
IN1
ST
GND
6
7
8
11
10
9
NMI1
WDS
TD
WD
DS1831B
TD
5V
PBRST
5V
IN1
4
5
6
13
12
11
TD
3.3V
PBST
NMI1
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 reference comparator and the master pushbutton with watchdog and the DS1831B
replaces the 3.3-volt PBRST with a last reset status output.
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051100
DS1831/A/B
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
1
2
IN
5V
5V Power Supply Input
9
MPBRST
TD
WD
Master Pushbutton (DS1831)
Watchdog Time Delay Select (DS1831A)
Non Maskable Interrupt 2 (DS1831)
RST
5V
TOL
5V
TD
5V
5V Reset Open Drain Output
Selects 5V Input Tolerance
Selects 5V Reset Time Delay
5V Reset Pushbutton
Sense Input 1
Sense Input 2 (DS1831)
Watchdog Strobe Inputs
(DS1831A)
Ground
10
11
12
13
14
15
NM12
WDS
Watchdog Status Output (DS1831A)
Non Maskable Interrupt 1
3.3V Reset Pushbutton
Pushbutton Status Output (DS1831B)
Select 3.3V Reset Time Delay
Selects 3.3V Input Tolerance
3.3V Reset Open Drain Output
3
4
5
6
7
NM11
PBRST
3.3V
PBST
TD
3.3V
TOL
3.3V
RST
3.3V
IN
3.3V
PBRST
5V
IN1
IN2
ST
GND
8
16
3.3V Power Supply Input
BLOCK DIAGRAM
Figure 1
IN
5V
100k
PBRST
5V
TD
5V
TOL
5V
V
CC
TOLERANCE
BIAS
+
TIME
DELAY
RST
5V
1.25V T.C.
REFERENCE
-
MPBRS
IN
3.3V
100k
PBRST
3.3V
TD
3.3V
TOL
3.3V
100k
Level
Sense
&
V
CC
TOLERANCE
BIAS
+
TIME
DELAY
RST
3.3V
-
-
NMI
IN
+
-
NMI
IN
GROUN
+
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DS1831/A/B
OPERATION – POWER MONITOR
The DS1831 provides the functions of detecting out-of-tolerance 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 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
5V
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 supply is tied to the 5 volt 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 3.3 volt supply 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 IN
5V
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 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
TD
GND
Float
V
CC
MIN
10 ms
100 ms
1000 ms
RESET TIME-DELAY
TYP
16 ms
160 ms
1600 ms
MAX
20 ms
200 ms
2000 ms
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DS1831/A/B
PUSHBUTTON RESET SEQUENCING
Figure 2
5V Supply
3.3V Supply
IN
5V
1
2
3
16
DS1831
15
14
13
12
IN
3.3V
RST
3.3V
TOL
3.3V
TD
3.3V
PBRST
3.3V
*
RST
5V
TOL
5V
TD
5V
PBRST
5V
GND
4
5
*NOTE:
The
RST
5V
output is connected to the IN
3.3V
via a 100 kΩ 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 3.3 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 (IN
5V
, IN
3.3V
, 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 circuitry. 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 “IN
5V
” and “IN
3.3V
” 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.
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DS1831/A/B
PUSHBUTTON RESET
Figure 3
5V Supply
IN
5V
10 kΩ
RST
5V
1
2
16
DS1831
15
14
13
12
TOL
5V
3
TD
5V
4
PBRST
5V
5
GND
TIMING DIAGRAM – MASTER PUSHBUTTON RESET
Figure 4
MPBRST
t
PDLY
V
IL
t
RST
RST
5V
and RST
3.3V
V
OH
t
PB
V
IH
NMI1 and NMI2
t
NMI
V
OH
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