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DS1834/A/D
Dual EconoReset with Pushbutton
www.dalsemi.com
FEATURES
5V power-on reset
3.3V power-on reset
Internal power is drawn from higher of either
the 5V
IN
input or the 3.3V
IN
input
Excellent for systems designed to operate
with dual power supplies
Asserts resets during power transients
Pushbutton reset input for system override
Maintains reset for 350 ms after V
CC
returns
to an in-tolerance condition
Reduces need for discrete components
Precision temperature-compensated voltage
reference and voltage sensor
8-pin DIP, 8-pin SOIC, and 8-pin
µ-SOP
available
CMOS output for low current operation on
the DS1834 and DS1834D
Operating temperature of -40°C to +85°C
PIN ASSIGNMENT
5V
IN
5V RST
5V TOL
GND
1
2
3
4
8
7
6
5
3.3V
IN
3.3V RST
3.3V TOL
PBRST
DS1834 8-Pin DIP (300-mil)
5V
IN
5V RST
5V TOL
GND
1
2
3
4
8
7
6
5
3.3V
IN
3.3V RST
3.3V TOL
PBRST
DS1834 8-Pin SOIC (150-mil)
5V
IN
5V RST (*RST)
5V TOL
GND
1
2
3
4
8
7
6
5
3.3V
IN
3.3V RST (*RST)
3.3V TOL
PBRST
DS1834 8-Pin
µ-SOP
(118-mil)
PIN DESCRIPTION
5V
IN
5V
RST
(*RST)
5V TOL
GND
- 5V Power Supply Input
- 5V Reset Output
- Selects 5V Input Tolerance
- Ground
PBRST
- Pushbutton Reset
3.3V TOL
- Selects 3.3V Input Tolerance
3.3V
RST
(*RST) - 3.3V Reset Output
3.3V
IN
- 3.3V Power Supply Input
*DS1834D Active High Reset
DESCRIPTION
The DS1834 Dual EconoResets monitors three vital system conditions: 5-volt supply, 3.3-volt supply,
and an external override. First a precision temperature reference and comparator circuit monitor the status
of the 5-volt supply and the 3.3-volt supply. When an out-of-tolerance condition is detected, an internal
power-fail signal is generated which forces the reset of the affected supply to an active state.
Lastly, the DS1834 supports an external reset via an internally debounced pushbutton input. When the
pushbutton is pulled low both resets will be asserted for approximately 350 ms after the pushbutton is
released.
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071700
DS1834/A/D
OPERATION
Power Monitor
The DS1834 provides the functions of detecting out-of-tolerance conditions on a 3.3-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. When
that input returns to a valid state the RST will remain active for about 350 ms and then return to an
inactive state until the next input out-of-tolerance condition.
On power-up both resets are kept active for approximately 350 ms after the power supply inputs have
reached the selected tolerance. This allows the power supply and system power to stabilize before RST is
released.
All internal operating current for the DS1834 will be drawn from the input with the highest voltage level.
The outputs will draw current only from the controlling input (5V IN or 3.3V IN).
DS1834 BLOCK DIAGRAM
Figure 1
DS1834A BLOCK DIAGRAM OUTPUT
Figure 2
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DS1834/A/D
Tolerance Select
The DS1834 provides two TOL inputs for individual customization of the DS1834 to specific application
requirements. If the TOL for the 5-volt supply is tied to the 5-volt input a 10% tolerance is selected for
the 5 volt supply. If the TOL for the 3.3-volt supply is tied to the 3.3-volt input, a 20% tolerance is
selected for the 3.3-volt supply. If TOL inputs are tied to ground, the 5-volt input will be set at a 5%
tolerance and the 3.3-volt input would be set to a 10% tolerance.
Pushbutton Reset
The DS1834 provides a pushbutton switch for manual reset control. When at least one of the DS1834
resets are not in a reset cycle, a pushbutton reset can be generated by pulling the
PBRST
pin low for at
least 2 ms. When the pushbutton is held low, both resets are forced active and will remain active for about
350 ms after the pushbutton is released. The pushbutton input is pulled high through an internal
40 kΩ=pull-up resistor and debounced via internal circuitry. See Figure 3 for an application example and
Figure 4 for the timing diagram.
PUSHBUTTON RESET
Figure 3
TIMING DIAGRAM: PUSHBUTTON RESET
Figure 4
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DS1834/A/D
OUTPUT VALID CONDITIONS
All versions of the DS1834 can maintain valid outputs as long as one input remains above 1.2 volts.
However, the
RST
outputs on the DS1834 use a push-pull output structure which can maintain a valid
output below 1.2 volts. To sink current below 1.2 volts a resistor can be connected from
RST
to GND
(see Figure 5). This arrangement will maintain a valid value on the
RST
outputs even if all inputs are at 0
volts. During both power-up and power-down this arrangement will draw current when
RST
is in the high
state. A value of about 100 kΩ=should be adequate to maintain a valid condition.
The DS1834A requires pull-up resistors on the outputs to maintain a valid output. 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 (see Figure 6 and Figure 7).
APPLICATION DIAGRAM:
RST
VALID TO 0 VOLTS V
CC
ON THE DS1834
Figure 5
APPLICATION DIAGRAM: DS1834A NMOS OUTPUTS
Figure 6
Note: If outputs are pulled-up to different voltages the outputs can not be connected to form a wired
"AND".
APPLICATION DIAGRAM: DS1834A WIRED "AND" OUTPUT
Figure 7
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