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DS1818 3.3V EconoReset with Pushbutton
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FEATURES
Automatically restarts a microprocessor after power failure Monitors pushbutton for external override Maintains reset for 150 ms after VCC returns to an in-tolerance condition Reduces need for discrete components Precision temperature-compensated voltage reference and voltage sensor Accurate 5%, 10% or 20% power monitoring Low-cost TO-92 or space saving surface mount SOT-23 packages available Efficient open-drain output with internal 5.5 k=pull-up resistor Operating temperature -40C to +85C
PIN ASSIGNMENT
3
1 2 SOT-23 PACKAGE
123
123 TO-92 PACKAGE See Mech. Drawings Section
PIN DESCRIPTION TO-92
1 2 3
RST
VCC GND
Active Low Reset Output Power Supply Ground
SOT-23
1 2 3
RST
VCC GND
Active Low Reset Output Power Supply Ground
DESCRIPTION
The DS1818 EconoReset uses a precision temperature-compensated reference and comparator circuit to monitor the status of the power supply (VCC). When an out-of-tolerance condition is detected, an internal power-fail signal is generated which forces reset to the active state. When VCC returns to an in-tolerance condition, the reset signal is kept in the active state for approximately 150 ms to allow the power supply and processor to stabilize. The DS1818 also monitors a pushbutton on the reset output. If the reset line is pulled low, a reset is generated upon release and the DS1818 output will be held in reset output low for typically 150 ms.
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OPERATION - POWER MONITOR
The DS1818 provides the functions of detecting out-of-tolerance power supply conditions and warning a processor-based system of impending power failures. When VCC is detected as out-of-tolerance, the RST signal is asserted. On power-up, RST is kept active for approximately 150 ms after the power supply has reached the selected tolerance. This allows the power supply and microprocessor to stabilize before RST is released.
BLOCK DIAGRAM (OPEN-DRAIN OUTPUT) Figure 1
APPLICATION EXAMPLE Figure 2
OPERATION - PUSHBUTTON RESET
The DS1818 provides a pushbutton switch for manual reset control. When the DS1818 is not in a reset cycle, a pushbutton reset can be generated by pulling the RST pin low for at least 1 s. When the pushbutton is held low, the RST is forced active low and will remain active low for about 150 ms after the pushbutton is released. See Figure 2 for an application example and Figure 3 for the timing diagram.
TIMING DIAGRAM: PUSHBUTTON RESET Figure 3
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TIMING DIAGRAM: POWER-UP Figure 4
TIMING DIAGRAM: POWER-DOWN Figure 5
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ABSOLUTE MAXIMUM RATINGS*
Voltage on VCC Pin Relative to Ground Voltage on RST Relative to Ground Operating Temperature Storage Temperature Soldering Temperature * -0.5V to +7.0V -0.5V to +5VCC +0.5V -40C to +85C -55C to +125C 260C for 10 seconds
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
PARAMETER Supply Voltage SYMBOL VCC MIN 1.0 TYP MAX 5.5
(-40C to +85C)
UNITS V NOTES 1
DC ELECTRICAL CHARACTERISTICS
PARAMETER Output Current @ 0.4 V Voltage Input Low Voltage Input High Operating Current VCC < 5.5V VCC Trip Point (DS1818-5) VCC Trip Point (DS1818-10) VCC Trip Point (DS1818-20) Internal Pull-up Resistor Output Capacitance SYMBOL IOL VIL VIH ICC VCCTP VCCTP VCCTP RP COUT
(-40C to +85C; VCC=1.2V to 5.5V)
MIN +10 0.4 0.7 *VCC 28 2.98 2.80 2.47 3.50 3.06 2.88 2.55 5.5 35 3.15 2.97 2.64 7.5 10 TYP MAX UNITS mA V V A V V V k pF NOTES 2, 3 1 1 4 1 1 1 7
AC ELECTRICAL CHARACTERISTICS
PARAMETER RESET Active Time VCC Detect to RST VCC Slew Rate (VCCTP (MAX) to VCCTP (MIN)) VCC Slew Rate (VCCTP (MIN) to VCCTP (MAX)) VCC Detect to RST Pushbutton Detect to RST Pushbutton Reset SYMBOL tRST tRPD tF tR tRPU tPB tPBRST
(-40C to +85C; VCC=1.2V to 5.5V)
MIN 100 300 0 100 1 100 150 250 150 250 TYP 150 2 MAX 250 5 UNITS ms s s ns ms s ms 5 5, 6 8 NOTES 5
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NOTES:
1. All voltages are referenced to ground. 2. Measured with VCC 2.7V. 3. A 1 k external pull-up resistor may be required in some applications for proper operation of the microprocessor reset control circuit. 4. Measured with RST output open. 5. Measured with 2.7V VCC 3.3V. 6. tR = 5 s. 7. VOH and IOH are a function of the value of RP and the associated output load conditions. 8. The tF value is for reference in defining values for tRPD and should not be considered a requirement for proper operation or use of the device.
PART MARKING CODES
"A", "B", &"C" represent the device type. 810 DS1810 811 DS1811 812 DS1812 813 DS1813 815 DS1815 816 DS1816 817 DS1817 818 DS1818
"D" represents the device tolerance. A 5% B 10% C 15% D 20%
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